Journal of Colloid And Interface Science (v.356, #1)
Development of various PS- b-P4VP micellar morphologies: Fabrication of inorganic nanostructures from micellar templates
by Heesook Cho; Hyungmin Park; Soojin Park; Heungyeal Choi; Haiying Huang; Taihyun Chang (pp. 1-7).
We describe the fabrication of various PS- b-P4VP micellar nanostructures, like spheres, cylinders, vesicles, and reverse spheres, by controlling solvent selectivity in polymer solutions. From micellar templates, metal nanodots or nanowires can be prepared..Display Omitted► Various micellar structures were prepared from block copolymer solution by a simple casting. ► Solvent quality for block copolymer plays a key role in determining the micellar morphologies. ► Micellar thin films can be used as templates for fabricating arrays of inorganic nano-objects.We demonstrate a simple route for preparing various micellar nanostructures, like spheres, cylinders, and vesicles, by spin-coating or drop-casting process of polystyrene- block-poly(4-vinylpyridine) (PS- b-P4VP) copolymer solutions in pure tetrahydrofuran (THF), THF/water, and THF/ethanol mixture. Upon drying, a solvent selectivity plays an important role in determining micellar nanostructures in thin films. In solution, micellar sizes and shapes of these PS- b-P4VP copolymers were investigated by dynamic and static light scattering. Immediately after spin-coating the polymer solutions, surface and internal morphologies of the films were observed by atomic force microscopy and transmission electron microscopy. As the polymer concentration in THF or the amounts of water or ethanol added in THF solutions was varied, a remarkable difference in the PS- b-P4VP micellar morphologies was observed, from which spherical or cylindrical or vesicular micelles were developed. These micellar films were used as scaffolds or templates for fabricating metal nanodots or nanowires arrays.
Keywords: PS-; b; -P4VP; Block copolymer micelles; Inorganic nanostructures
Preparation of perfluoro-1,3-propanedisulfonic acid/silica nanocomposites-encapsulated low molecular weight aromatic compounds possessing a nonflammable characteristic
by Hideo Sawada; Xinlai Liu; Yuki Goto; Mieko Kikuchi; Tsukasa Tashima; Masakazu Nishida (pp. 8-15).
PFPS/SiO2/ Ar-H nanocomposites after calcination can exhibit an extremely red-shifted and enhanced fluorescent.Display Omitted► Fluorinated disulfonic acid/silica nanocomposites. ► Encapsulation of low molecular weight aromatic compounds. ► Nonflammable characteristic toward aromatic compounds. ► No weight loss behavior after calcination at 800°.Perfluoro-1,3-propanedisulfonic acid/silica [PFPS/SiO2] nanocomposites were prepared by the sol–gel reactions of the corresponding disulfonic acid [PFPS] with tetraethoxysilane and silica nanoparticles under alkaline conditions. These fluorinated nanocomposites thus obtained can exhibit no weight loss behavior corresponding to the contents of PFPS in the composites after calcination at 800°C, although the parent PFPS can decompose completely around 270°C. In addition, we succeeded in encapsulation of a variety of low molecular weight aromatic compounds such as bisphenol-A, bisphenol-AF, bisphenol-F, 4,4′-biphenol and 1,1′-bi-2-naphthol into PFPS/SiO2 nanocomposite cores.1H MAS NMR spectra, UV–vis spectra, fluorescence spectra and HPLC measurements of PFPS/SiO2 nanocomposites-encapsulated bisphenol-A showed the presence of encapsulated bisphenol-A in the composites before and even after calcination at 800°C. Interestingly, it was verified that fluorescence spectra of PFPS/SiO2 nanocomposites-encapsulated bisphenol-A after calcination at 800°C can exhibit an extremely red-shifted and enhanced fluorescence peak, compared to that before calcination or parent bisphenol-A.
Keywords: Fluorinated silica nanocomposites; Perfluoro-1,3-propanedisulfonic acid; Low molecular aromatic compounds; Encapsulation; Nonflammable characteristic
Biotinylated thermoresponsive core cross-linked nanoparticles via RAFT polymerization and “click” chemistry
by Wenhui Lv; Li Liu; Yan Luo; Xiaojuan Wang; Yuwei Liu (pp. 16-23).
Biotinylated thermoresponsive nanoparticles were synthesized via the combination of RAFT polymerization and “click” chemistry.Display Omitted► “Clickable” thermoresponsive core cross-linked (CCL) nanoparticles were prepared by one-pot RAFT polymerization. ► Biotinylated CCL nanoparticles were synthesized by facile “click” chemistry. ► Biotin-conjugated nanoparticles effectively interact with protein avidin.A straightforward approach to the synthesis of “clickable” thermoresponsive core cross-linked (CCL) nanoparticles was developed. This approach was based on reversible addition-fragmentation chain transfer (RAFT) radical cross-linking polymerization of styrene and divinylbenzene with azide-functionalized poly(N-isopropylacrylamide) (PNIPAM-N3) as macro chain transfer agent in a selective solvent. Spherical nanoparticles with a diameter of 12nm were obtained after 24h polymerization. When the lyophilized CCL nanoparticles were dispersed in THF, spherical nanoparticles were observed, confirming the stability of CCL nanoparticles. The transmission electron microscopy (TEM) studies demonstrated that spherical nanoparticles and wormlike structure coexisted in the aqueous solution. The CCL nanoparticles have a lower critical solution temperature (LCST) at about 29.6°C, a little lower than that of PNIPAM homopolymer. Biotin molecules were conjugated to the surface of CCL nanoparticles via “click” chemistry in aqueous media. After bioconjugation, the LCST shifted to 28.3°C. The bioavailability of biotin to protein avidin was evaluated by a 4′-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay and TEM.
Keywords: RAFT polymerization; “Click” chemistry; Molecular recognition; Nanoparticles; Thermoresponsive
Synthesis of zwitterionic shell cross-linked micelles with pH-dependent hydrophilicity
by Xiaohui Zhang; Changjun Ai; Jinghong Ma; Jian Xu; Shuguang Yang (pp. 24-30).
Zwitterionic shell cross-linked micelles in which core and shell have different pH-dependent behaviors were studied. The hydrophilicity of the micelles can be accurately adjusted by pH.Display Omitted► Zwitterionic shell cross-linked micelles have been synthesized via a novel way. ► The hydrophilicity, size, and softness of the micelles could be tuned independently by adjusting the pH. ► A double-layer nanocage-like nanostructure with pH-dependent hydrophilic core was observed.Shell cross-linked (SCL) micelles were constructed based on the diblock copolymer poly( t-butyl acrylate)- b-poly(2-dimethylamino)ethyl methacrylate (P tBA- b-PDMAEMA) which was synthesized by sequential atom transfer radical polymerization (ATRP). Using trifluoroacetic acid (TFA) to hydrolyze the SCL micelles, zwitterionic SCL micelles were prepared. The hydrophilicity, size, and softness of the core and the shell of the micelles can be tuned independently by adjusting the pH. At low pH (3.4), the micelles turned into nanoparticles with compact cores and swollen shells; at neutral medium (6.8), the SCL micelles were entirely hydrophilic; at pH 11.6, a double-layer cage-like nanostructure was observed. Moreover, the inner and outer layers of the nanocage had opposite behaviors to the pH stimulus. The existence of tunable nanostructures of these zwitterionic SCL micelles could be proved by the ratio of gyration radius ( Rg) to hydrodynamic radius ( Rh) and SEM micrographs.
Keywords: Atom transfer radical polymerization (ATRP); Micelle; Self-assembly; Zwitterionic; pH-dependent
Surface functionalized silica as a toolkit for studying aqueous phase palladium adsorption and mineralization on thiol moiety in the absence of external reducing agents
by Jung-Sun Lim; Seung-Min Kim; Sang-Yup Lee; Eric A. Stach; James N. Culver; Michael T. Harris (pp. 31-36).
This study reports a new metallization strategy that uses palladium growth on thiol moieties without external reducing agents.Display Omitted► A model system is established to compare the sorption affinity of palladium precursor ions on hydroxyl, amine, and thiol functionalities. ► A crystallized palladium layer was coated on the thiol-terminated silica through palladium ion hydrolysis in DI-water at 50°C without externally supplied reducing agents. ► The by-product of external reducer free palladium mineralization was separated from the colloidal suspension and analyzed.Biological templates such as virions or protein assemblies have several surface functional groups that can complicate the elucidation of the fundamental mechanism(s) governing the sorption and mineralization of metals on the surface of the template. Surface functionalized silica nanoclusters with hydroxyl, amine, or thiol groups serve as surrogates for understanding the interaction between individual amino acid functionalities and inorganic precursors. Analysis of palladium ion uptake on the functionalized silica enabled the investigation of a new palladium mineralization strategy using thiol surface moieties in the absence of external reducing agents. This study reveals the nature of the palladium–thiol interaction and the resulting self-reduction mechanism that produces the metal palladium nanolayer on the thiol-terminated silica. This surface functionalized silica approach is thus an effective toolkit for exploring the fundamentals of metal precursor sorption on surface functional groups, and for developing new metal deposition methodologies.
Keywords: Palladium; Thiol; Mineralization
Concentration- and pH-dependence of highly alkaline sodium silicate solutions
by Jonas Nordström; Erik Nilsson; Patrik Jarvol; Moheb Nayeri; Anders Palmqvist; Johan Bergenholtz; Aleksandar Matic (pp. 37-45).
Gel-like materials have been prepared from commercial sodium silicate solutions, by two different routes. The resulting microstructures are found to be very different in the two cases giving the opportunity to tailor the microstructure of gels prepared from sodium silicate solutions by combining the two routes.Display Omitted► The structure and speciation of water glass can be controlled by concentration and pH. ► With increasing concentrations the equilibrium particle size shifts to smaller sizes. ► With decreasing pH condensation of the low molecular weight species occurs.In this study two routes for the gelation of water glass have been investigated; the destabilization by a change in pH and by an increase in concentration through evaporation. Both methods produce optically transparent, highly viscous, homogeneous solutions. The structure and dynamics of the solutions along the two routes have been investigated with dynamic light scattering,29Si-Nuclear Magnetic Resonance spectroscopy, viscosity measurements and infrared spectroscopy. We find that the two routes are fundamentally different. Increasing the concentration of the sodium silicate system leaves the silica speciation apparently unchanged. Lowering the pH leads to condensation reactions, thus a change in the silica speciation.
Keywords: Water glass; Gelation; Colloidal silica; Dynamic light scattering; 29; Si NMR
Influence of lipid composition on the thermotropic behavior and size distribution of mixed cationic liposomes
by Yechezkel Barenholz; Cecilia Bombelli; Maria Grazia Bonicelli; Pietro di Profio; Luisa Giansanti; Giovanna Mancini; Fabrizio Pascale (pp. 46-53).
Phase behavior and size distribution of mixed cationic liposomes formulated with one of four different cationic amphiphiles featuring a pyrrolidinium headgroup were investigated by turbidity, DSC and DLS measurementsDisplay Omitted► Liposomes were formulated at different DMPC/cationic amphiphile mole ratios. ► The size distribution of LUV was evaluated by DLS measurements. ► The thermotropic behavior of LUV was evaluated by turbidity measurements. ► The thermotropic behavior of MLV was evaluated by DSC measurements. ► Subtle changes in vesicle composition strongly influence lipid organization.Cationic liposomes are studied mainly as nonviral nucleic acid delivery systems and to a lesser extent as carriers/adjuvants of vaccines and as low-molecular-weight drug carriers. It is well established that the performance and the biological activity of liposomes in general are strongly related to their physicochemical properties. We investigated the thermotropic behavior and the size distribution of mixed cationic liposomes formulated with different percentages of 1,2 dimyristoyl- sn-glycero-3-phosphatidylcholine and one of four cationic amphiphiles characterized by a pyrrolidinium headgroup with the aim of achieving a better understanding of how the molecular structure of the cationic amphiphile and its mole percentage affect the physicochemical properties of the liposomes. Multilamellar vesicles and large unilamellar vesicles were studied by differential scanning calorimetry and turbidity, respectively, to characterize the thermotropic behavior and lipid phase, whereas dynamic light scattering was used to determine size distribution. This study shows that subtle modifications in the cationic amphiphile’s molecular structure and in liposome composition may have dramatic effects on the organization of the liposome bilayer and hence on the morphological and physicochemical features of the liposomes, thus being highly relevant to the biological features investigated previously.
Keywords: Cationic liposomes; Differential scanning calorimetry; Cooperative unit; Turbidity measurements; Phase separation; Exotherm
Synthesis and gas-sensing characteristics of WO3 nanofibers via electrospinning
by Ji-yan Leng; Xiu-juan Xu; Ning Lv; Hui-tao Fan; Tong Zhang (pp. 54-57).
The WO3 nanofibers prepared by an electrospinning method have fast response and recovery characteristics to different concentrations of NH3.Display Omitted► In this paper, we prepared WO3 nanofibers by an electrospinning method. ► We systemically studied the gas-sensing properties of this material. ► The result indicates that the gas sensors based on WO3 nanofibers express high and fast response and recovery characteristics to NH3. ► The WO3 nanofibers are promising sensitive materials for NH3 detecting.WO3 nanofibers were synthesized using an electrospinning method and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The obtained WO3 nanofibers were used as sensitive materials for the detection of NH3. Indirect-heating sensors based on WO3 nanofibers were prepared. When the WO3 nanofiber-based sensors were exposed to 100ppm NH3 at 500°C, the response is 5.5, and the response and recovery times are 1 and 5s, respectively. These results indicate that the gas sensors based on WO3 nanofibers express high and fast response and recovery characteristics to NH3, and the WO3 nanofibers are promising sensitive materials for NH3 detecting.
Keywords: WO; 3; Nanofibers; Electrospinning; Gas sensor; NH; 3
Structure of nanofibrillated cellulose layers at the o/w interface
by Klodian Xhanari; Kristin Syverud; Gary Chinga-Carrasco; Kristofer Paso; Per Stenius (pp. 58-62).
Sufficiently surface modified (hydrophobized) nanofibrillated cellulose stabilize water-in-toluene emulsions against coalescence by network formation at the o/w interface.Display Omitted► At o/w interface cellulose nanofibrils can occur as single dispersed or form networks. ► Network formation by cellulose nanofibrils at o/w interface prevents coalescence. ► Network formation by nanofibrillated cellulose depends on degree of substitution.The nature of layers formed by cellulose nanofibrils that had been surface modified (hydrophobized) at the oil/water (o/w) interface was investigated. The aim of the study was to clarify the mechanism underlying the excellent ability of these nanoparticles to stabilize emulsions. Layers of hydrophobized nanofibrillated cellulose spread at the o/w interface were deposited on glass slides by the Langmuir–Blodgett deposition technique. Overall evaluation of layer structures was performed by image analysis based on a Quadtree decomposition of images obtained from a flatbed scanner. A more detailed characterization of the layer structures was performed by Atomic Force Microscopy (AFM), and Field-Emission Scanning Electron Microscopy (FE-SEM). The results show that nanofibrils that were able to stabilize emulsions occur as single, dispersed fibrils or form large, network-like aggregates at the o/w interface. Fibrils that were insufficiently hydrophobized and therefore did not stabilize emulsions were only partially deposited and formed small, compact aggregates. We conclude that it is likely that the network formation is the main mechanism by which the fibrils prevent coalescence of emulsion droplets.
Keywords: Nanofibrillated cellulose; Oil/water interface; Microfibrillated cellulose (MFC); Langmuir–Blodgett technique; Emulsion stabilization mechanism; Microscopy; Image
Fluorescence enhancement by heterostructure colloidal photonic crystals with dual stopbands
by Heng Li; Jingxia Wang; Feng Liu; Yanlin Song; Rongming Wang (pp. 63-68).
A remarkable enhancement of fluorescence signal based on heterostructure photonic crystals with dual stopbands is demonstrated in comparison to that on the control sample.Display Omitted► A facile approach on the fluorescent enhancement by heterostructure PCs is presented. ► Dual stopbands of heterostructure PCs overlap the excitation and emission wavelength. ► The parameters of heterostructure PCs have important effects on fluorescence signals. ► The approach provides a promising strategy for the sensitive fluorescence-based detection.In this work, we present a facile approach on the remarkable enhancement of fluorescent signal by heterostructure colloidal photonic crystals (PCs) with dual stopbands. The intensity of fluorescent medium on heterostructure PCs with dual stopbands overlapping the excitation wavelength and the emission wavelength of fluorescent medium can be up to 162-fold enhancement in comparison to that on the control sample. Otherwise, parameters of heterostructure PC films such as film thickness or stacking order have important effects on fluorescent signals. The method will be of great significance for developing the highly sensitive fluorescence-based detection.
Keywords: Colloidal photonic crystals; Dual stopbands; Fluorescence enhancement
Growth and fire resistance of colloidal silica-polyelectrolyte thin film assemblies
by Galina Laufer; Federico Carosio; Rico Martinez; Giovanni Camino; Jaime C. Grunlan (pp. 69-77).
Cotton fabric coated with protective thin film of colloidal silica retains its weave structure after being exposed to a vertical flame test.Display Omitted► Silica-based assemblies grow linearly as a function of bilayers deposited. ► Coated fabrics retain the weave structure following burning. ► Coatings with small silica particles result in better flame retardant properties. ► Coated fabric results in reduced peak heat release rate by as much as 20%.Thin films of colloidal silica were deposited on cotton fibers via layer-by-layer (LbL) assembly in an effort to reduce the flammability of cotton fabric. Negatively charged silica nanoparticles of two different sizes (8 and 27nm) were paired with either positively charged silica (12nm) or cationic polyethylenimine (PEI). PEI/silica films were thicker due to better (more uniform) deposition of silica particles that contributed to more than 90% of the film weight. Each coating was evaluated at 10 and 20 bilayers (BL). All coated fabrics retained their weave structure after being exposed to a vertical flame test, while uncoated cotton was completely destroyed. Micro combustion calorimetry confirmed that coated fabrics exhibited a reduced peak heat release rate, by as much as 20% relative to the uncoated control. The 10 BL PEI-8nm silica recipe was the most effective because the coating is relatively thick and uniform relative to the other systems. Soaking cotton in basic water (pH 10) prior to deposition resulted in better assembly adhesion and flame-retardant behavior. These results demonstrate that LbL assembly is a useful technique for imparting flame retardant properties through conformal coating of complex substrates like cotton fabric.
Keywords: Layer-by-layer assembly; Colloidal silica; Polyethylenimine; Flame retardant; Cotton fabric
Continuous synthesis of CdSe xTe1− x nanocrystals: Chemical composition gradient and single-step capping
by Zhen Wan; Weiling Luan; Shan-tung Tu (pp. 78-85).
CdSe xTe1− x nanocrystals with composition gradient structure and tunable emission (634–783nm) were synthesized via microreaction. For improving the photostability, a single-step process was developed to realize the CdS capping.Display Omitted► CdSeTe nanocrystals were prepared via capillary microreactor in a controllable way. ► The emission wavelength can be tuned from 634 to 783nm. ► The quantum yields was up to 81%. ► The chemical composition gradient structure (Te-rich in core) was validated. ► A single-step CdS capping process was developed to improve the photostability.A capillary microreactor was firstly utilized to continuously synthesize near-infrared emitting CdSe xTe1− x nanocrystals (NCs). By using trioctylphosphine oxide and trioctylphosphine as the solvents for anion precursor as well as oleic acid and oleylamine as the solvents for cation precursor, high quantum yield zinc-blend CdSe xTe1− x NCs with a chemical composition gradient internal structure and tunable emission from 634 to 783nm were synthesized. Thus, the nonlinear relationship between the composition and the emission energies were verified. Moreover, a facile single-step capping approach was developed by using the dissolution of cadmium oxide and free element sulfur in oleic acid, and a very thin CdS shell was successfully epitaxial grown around the as-prepared CdSe xTe1− x NCs to enhance the photostability. After the capping process, the core/shell structured CdSe xTe1− x/CdS NCs remained 15–40% of their initial PL intensity after 3h of illumination.
Keywords: Microreactor; CdSeTe; Composition gradient; Core/shell; Luminescence
Organic crystallizable solvent served as template for constructing well-ordered PPE films
by Zicheng Zuo; Xiaodong Yin; Chunjie Zhou; Nan Chen; Huibiao Liu; Yongjun Li; Yuliang Li (pp. 86-91).
The naphthalene crystals served as templates to prepare PPE films with structures of 0D nanodots, 1D parallel lamellas and 2D cross-oriented textures.Display Omitted► Crystallizable naphthalene was used to dissolve PPE when it melted. ► Naphthalene solution was solidified along different orientation to prepare PPE films. ► PPE films with well-defined structures were fabricated controllably by these methods. ► The well-defined films may have many applications in electronic and photonic devices.Tuning the solidification of the crystallizable solvent naphthalene, well-patterned conjugated polymer poly(phenyleneethynylene) (PPE) films with well-defined nanostructures of 0D nanodots, 1D lamellas, and 2D texture nanostructures have been prepared by several strategies. The nanostructures have been characterized and the formation mechanisms for the morphologies have been discussed.
Keywords: Crystallizable solvent; Patterned nanostructure; Conjugated polymer film; Parallel lamella; Textured structure
Preparation of electrospun luminescent polyimide/europium nanofibers by simultaneous in situ sol–gel and imidization processes
by Si Cheng; Xiaofei Li; Sibai Xie; Yun Chen; Li-Juan Fan (pp. 92-99).
Schematic diagram for the PAA/europium mixture with chemical coupling sites between them and SEM, TEM, and laser scanning confocal microscope images of PI/europium nanofibers.Display Omitted► Simultaneous sol–gel and imidization introduced chemical coupling sites between PI and europium. ► The morphology of the europium phase was affected by the composition and calcination temperature. ► PI/europium nanofibers were demonstrated to have strong fluorescence.Luminescent polyimide (PI)/europium nanofibers have been successfully prepared by electrospinning combined with an in situ sol–gel technique. The possible reaction mechanism of the simultaneous imidization of polyamide acid and gelation of europium phase was analyzed by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The results showed that chemical coupling and noncovalent interaction existed between the polymer and the europium which formed during the preparative process. Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electronic spectroscopy (SEM) studies also indicated the successful incorporation of europium into PI matrix and various morphologies could be achieved by controlling the calcination temperature and the europium content. Nanofibers with necklace-like structures were obtained after calcination under high temperatures. These PI/europium nanofibers were further demonstrated to have strong fluorescence emission. The intensity ratio for the PI/europium nanofibers, labeled as (5D0→7F2)/(5D0→7F1), which is well known as the asymmetry parameter, was lower than that in pure Eu2O3 powder, indicating that there were highly symmetric coordination spheres around europium in the nanofibers.
Keywords: Polyimide; Europium; Electrospinning; Luminescent; In situ sol–gel
pH sensitive swelling and releasing behavior of nano-gels based on polyaspartamide graft copolymers
by Sunmi Kim; Ji-Heung Kim; Dukjoon Kim (pp. 100-106).
Synthesis of nano-gel by crosslinking of inner cores via UV radiation and its reversible pH sensitive swelling/deswelling behavior in aqueous medium.Display Omitted► pH sensitive nano-gels are prepared from C18/MPEG/API/MA-g-PASPAM synthesized. ► The nano-gels prepared are biocompatible, biodegradable, and highly pH sensitive. ► Nano-gels has a buffering effect within a pH 5–7 range by ionization of API. ► Nano-gels shows reversible and fast swelling and deswelling behavior around pH 6.7 ► Nano-gels shows sustained drug release pattern.pH sensitive nano-gels based on polyaspartamide graft copolymers are prepared by UV crosslinking the self-assembled nano-aggregates in the presence of a series of hydrophobic and hydrophilic grafting segments. While the physical nano-aggregates dissociate via ionization of the pH sensitive moiety, the nano-gels synthesized in this study swell instead. The chemical structure and morphology of the resulting nano-gels were analyzed using FTIR,1H FTNMR, and TEM. The pH dependence of the particle size, 120–250nm, was investigated using a light scattering analyzer. The swelling behavior of the nano-cores under acidic conditions triggered abrupt release of the drug; this pH dependence occurs reversibly and quickly. The nano-gels prepared may have endosomal rupturing characteristics, as their buffering capacity is as strong as that of uncrosslinked nano-aggregates. The nano-gels synthesized as such possess potential application as sustained releasing drug carriers for intracellular delivery.
Keywords: Nano-gel; Graft copolymer; pH sensitive; Swelling; Polyaspartamide; Drug release
Photoluminescent Fe3O4/carbon nanocomposite with magnetic property
by Xiaodie He; Yang Liu; Haitao Li; Hui Huang; Jinglin Liu; Zhenhui Kang; Shuit-Tong Lee (pp. 107-110).
The Fe3O4/carbon nanocomposite posses both magnetic (saturation magnetization of 44.2emu/g) and photoluminescent (emission ranging from 425 to 550nm) properties.Display Omitted► Fe3O4 nanoparticles were successfully embedded in the carbon nanoparticles. ► Fe3O4/carbon nanocomposites possess both photoluminescent and magnetic properties. ► The composites have potential applications in nanocatalysis and bio-imaging.Fe3O4/carbon nanocomposite has been prepared by a facile chemical method, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, fourier transform infrared spectroscopy and scanning electron microscopy. The fluorescent and magnetic properties of the sample were investigated by fluorescence spectroscopy and vibrating-sample magnetometer, respectively. The results indicate that the Fe3O4/carbon nanocomposite exhibit good photoluminescent (emission ranging from 425 to 550nm) and strong magnetic (saturation magnetization of 44.2emu/g) properties.
Keywords: Composites; Magnetic materials; Luminescence; Magnetic properties
Growth of gold nanorods in gelled surfactant solutions
by Yoshiko Takenaka; Hiroyuki Kitahata; Norifumi L. Yamada; Hideki Seto; Masahiko Hara (pp. 111-117).
Relation between self-assembly of surfactant growth solution and thickness of gold nanorods.Display Omitted► The growth of gold nanorods in gelled surfactant solutions was studied. ► SANS experiments revealed the gelled surfactant solutions self-assembled as lamellae. ► The lamellar structure affected the short-axis length of the gold nanorods. ► A curvature of surfactant layers around nanorods is important for the nanorod growth.Gold nanorods have been actively studied for new nanotechnological materials and industrial applications. It is well known that gold nanorods grow spontaneously in surfactant solutions, and a number of procedures for their preparation have been reported; however, the factors that determine the morphology have not been well understood. In this study, we observed the time series of the growth process of gold nanorods in gelled surfactant solutions by completely stopping the growth reaction. This growth process was compared to that in solution without gelation. The comparison indicates that the self-assembly of surfactant molecules affected the resulting shape, especially the short-axis length, of the nanorods. Small-angle neutron scattering (SANS) experiments revealed that the gelled solutions form lamellar structures, whereas nongelled systems form spherical micelles. On the bases of these results, we present a model showing that the short-axis length of gold nanorods is affected by a decrease in the spontaneous curvature of the outer surfactant layer and/or an increase in the bending modulus of the surfactant membrane neighboring the gold surface.
Keywords: Growth process; Gold nanorod; Surfactant; Gel; Small-angle neutron scattering (sans)
Influence of interfacial rheology on the viscosity of concentrated emulsions
by Rajinder Pal (pp. 118-122).
The plot shows relative viscosity as a function of the interfacial mobility parameter, predicted by the proposed models at a fixed volume fraction of dispersed phase ( ϕ=0.50).Display Omitted► Influence of interfacial rheology and Marangoni phenomenon on the relative viscosity of concentrated emulsions is considered. ► New models are developed for emulsion viscosity taking into consideration the effects of interfacial rheology and Marangoni phenomenon. ► Experimental viscosity data for emulsions are interpreted in terms of the proposed models.New models are developed for the viscosity of concentrated emulsions taking into consideration the effects of interfacial rheology and Marangoni phenomenon. The interface is assumed to be viscous with non-zero surface–shear and surface-dilational viscosities. The Marangoni effect is accounted for through non-zero Gibbs elasticity of the interface. The experimental viscosity data for a number of emulsion systems are interpreted in terms of the proposed models.
Keywords: Emulsions; Rheology; Viscosity; Interfacial rheology; Marangoni effect
Microspectroscopic analysis of green fluorescent proteins infiltrated into mesoporous silica nanochannels
by Yujie Ma; Prayanka Rajendran; Christian Blum; Yanina Cesa; Nando Gartmann; Dominik Brühwiler; Vinod Subramaniam (pp. 123-130).
EGFP is infiltrated into the nanochannels of mesoporous silica whose channel diameter approaches the dimension of the protein. The encapsulated proteins are functional and demonstrate a shortened fluorescence lifetime.Display Omitted► EGFP is successfully infiltrated into the nanochannels of mesoporous silica. ► The spectral properties of EGFP have been preserved ► The fluorescence lifetime of EGFP decreases upon encapsulation. ► The spatial distribution of EGFP is determined by fluorescence microspectroscopy. ► The EGFP-silica nanobiophotonic system may lead to a novel hybrid optical material.The infiltration of enhanced green fluorescent protein (EGFP) into nanochannels of different diameters in mesoporous silica particles was studied in detail by fluorescence microspectroscopy at room temperature. Silica particles from the MCM-41, ASNCs and SBA-15 families possessing nanometer-sized (3–8nm in diameter) channels, comparable to the dimensions of the infiltrated guest protein EGFP (barrel structure with dimensions of 2.4nm×4.2nm), were used as hosts. We found that it is necessary to first functionalize the surfaces of the silica particles with an amino-silane for effective encapsulation of EGFP. We demonstrated successful infiltration of the protein into the nanochannels based on fluorescence microspectroscopy and loading capacity calculations, even for nanochannel diameters approaching the protein dimensions. We studied the spatial distributions of the EGFPs within the silica particles by confocal laser scanning microscopy (CLSM) and multimode microscopy. Upon infiltration, the fluorescence lifetime drops as expected for an emitter embedded in a high refractive index medium. Further, the spectral properties of EGFP are preserved, confirming the structural integrity of the infiltrated protein. This inorganic-protein host–guest system is an example of a nanobiophotonic hybrid system that may lead to composite materials with novel optical properties.
Keywords: Host-guest; EGFP; Mesoporous silica; Fluorescence lifetime; Refractive index
Electrostatic effects on nanofiber formation of self-assembling peptide amphiphiles
by Sila Toksoz; Rashad Mammadov; Ayse B. Tekinay; Mustafa O. Guler (pp. 131-137).
Peptide amphiphile molecules can form in situ gels through pH change or ionic interactions with biological macromolecules or electrolytes.Display Omitted► Neutralization of charges on the peptide amphiphiles results in self-assembly. ► Ionic interactions between biological macromolecules peptide amphiphiles produce hydrogels. ► Self-assembling peptide amphiphile molecules form hydrocolloid systems for cell culturing.Self-assembling peptide amphiphile molecules have been of interest to various tissue engineering studies. These molecules self-assemble into nanofibers which organize into three-dimensional networks to form hydrocolloid systems mimicking the extracellular matrix. The formation of nanofibers is affected by the electrostatic interactions among the peptides. In this work, we studied the effect of charged groups on the peptides on nanofiber formation. The self-assembly process was studied by pH and zeta potential measurements, FT-IR, circular dichroism, rheology, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The aggregation of the peptides was triggered upon neutralization of the charged residues by pH change or addition of electrolyte or biomacromolecules. Understanding the controlled formation of the hydrocolloid gels composed of peptide amphiphile nanofibers can lead us to develop in situ gel forming bioactive collagen mimetic nanofibers for various tissue engineering studies including bioactive surface coatings.
Keywords: Self-assembly; Nanofiber; Peptide; Gel; Peptide amphiphile; Electrostatic interactions
Synthesis of hierarchical rose bridal bouquet- and humming-top-like TiO2 nanostructures and their shape-dependent degradation efficiency of dye
by Thuy-Duong Nguyen-Phan; Eui Jung Kim; Sung Hong Hahn; Woo-Jae Kim; Eun Woo Shin (pp. 138-144).
Novel carnation-, rose bridal bouquet- and humming-top-like TiO2 were controlled by varying hydrothermal temperature and the flower superstructures exhibited high UV-photoactivity.Display Omitted► Hierarchical TiO2 nanostructures were simply synthesized by hydrothermal process. ► Increasing hydrothermally treating temperature resulted in the carnation-, rose bridal bouquet-, and humming-top-shaped TiO2 nanostructures. ► Flower-like TiO2 performed the higher adsorbability and UV-photodegradation activity of dye than the other.Novel hierarchical rose bridal bouquet- and humming-top-like nanostructured TiO2 were successfully prepared by the simple process with the hydrothermal temperature as the morphology-controlling factor. The gradual transformation from layered titanate to brookite phase was well consistent with the formation mechanism of the hierarchical morphologies. The three-dimensional flower bouquets built from the bunches of roses with surrounding fern fronds displayed the best adsorptivity and completely degraded methylene blue within 60min under UV irradiation, whereas the humming-top geometry composed of anisotropically elongated spindle-like crystallites was detrimental to the dye photodegradation.
Keywords: TiO; 2; Nanostructure; Hierarchical; Photocatalyst; Dye
Concomitant synthesis of polyaniline and highly branched gold nanoparticles in the presence of DNA
by Pratap Mukherjee; Arun K. Nandi (pp. 145-150).
Highly branched gold nanoparticles by reduction of chloroauric acid using aniline with concomitant formation of polyaniline (PANI) in the presence of DNA exhibit interesting PL properties.Display Omitted► Dendritic gold nanoparticles using aniline and ds-DNA with PANI–DNA fibrillar network. ► Without DNA, both PANI and gold nanoparticles exhibit a spherical morphology. ► Intensity ratios of emission and FRET peak are higher in dendritic Au than spherical Au–PANI. ► Dc conductivity of dendritic Au system is two orders higher than that of the spherical system.The reduction of chloroauric acid using aniline adsorbed on DNA produces highly branched dendritic gold nanoparticles with concomitant formation of polyaniline (PANI) in contrast to the formation of spherical Au nanoparticles in the absence of DNA. The conformation of DNA remains intact in the process as evident from circular dichroism (CD) spectra. The UV–Vis spectrum exhibits a broad absorption peak at 520–900nm, for a combined effect of the gold surface plasmon and π band to localized polaron band transition of DNA-doped PANI. Both the dendritic Au–PANI–DNA and the spherical Au–PANI systems emit two peaks for excitation with radiation of 300nm and the intensity ratio of the emission and FRET peak is higher in the dendritic Au–PANI than that in the spherical Au–PANI system. The dc-conductivity values of spherical Au–PANI and dendritic Au–PANI–DNA systems are 1.2×10−10 and 1.7×10−8S/cm at 30°C, respectively.
Keywords: Dendritic Au nanoparticle; Polyaniline; DNA; Photoluminescence; Conductivity
Preparation and optical properties of silver nanowires and silver-nanowire thin films
by Quocanh N. Luu; Joshua M. Doorn; Mary T. Berry; Chaoyang Jiang; Cuikun Lin; P. Stanley May (pp. 151-158).
Thickness and absorbance properties of the silver-nanowire films fabricated by Spin-Assisted Layer-by-Layer (SA-LbL) method can be controlled by the number of layers deposited.Display Omitted► Controllable fabrication of silver nanowire thin films via SA-LbL assembly. ► Observation of transverse and longitudinal surface plasmon modes of the films. ► The thickness and optical properties of the films can be controlled. ► The observed absorbance spectra are well explained by 2D FDTD simulations.Silver nanowires and silver-nanowire thin films have attracted much attention due to their extensive applications in Surface-Enhanced Raman Scattering (SERS) and Surface-Enhanced Fluorescence (SEF). Thin films of silver nanowires within polyelectrolyte layers of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were fabricated by the Spin-Assisted Layer-by-Layer (SA-LbL) method. The surface coverage, thickness, and absorbance properties of the silver-nanowire films were controlled by the number of layers deposited. Both transverse and longitudinal surface plasmon (SP) modes of the silver-nanowires were observed in the absorbance spectra, as was evidence for nanowire interaction. Two-dimensional finite difference time-domain (2D FDTD) simulations predict that the maximum field enhancement occurs at the ends and cross-sectional edges of the wires for the longitudinal and transverse modes, respectively. Silver nanowires were synthesized by a facile, high-yield solvothermal approach, which can be easily manipulated to control the aspect ratio of the nanowires. The effects of polyvinylpyrrolidone (PVP) concentration and molecular weight on the growth of the silver nanowires, which are not documented in the original procedure, are discussed. It is shown that the growth mechanism for silver nanowires in the solvothermal synthesis is similar to that reported for the polyol synthesis.
Keywords: Silver nanowires; Thin films; Optical properties
Prolonging the lifetime and activity of silica immobilised Cyanidium caldarium
by Joanna C. Rooke; Bertrand Vandoorne; Alexandre Léonard; Christophe F. Meunier; Pierre Cambier; Hugo Sarmento; Jean-Pierre Descy; Bao-Lian Su (pp. 159-164).
The photosynthetic activity of an acidophilic thermotolerant algal cell, Cyanidium caldarium, has been preserved within silica gel, yielding living hybrid materials capable of CO2 bioconversion to carbohydrates.Display Omitted► Preservation of living cells within sol–gel derived silica monoliths. ► Carbon dioxide assimilation from living hybrid materials. ► Photosynthetic oxygen production detected over 75days post immobilisation. ► Autofluorescence from chlorophyll a detected after 75days post immobilisation.Over the past few years the idea of living photosynthetic materials has advanced from concept to reality. This work outlines the improvements made in the immobilisation of the thermotolerant acidophile Cyanidium caldarium (Tilden) Geitler SAG 16.91 within porous and transparent silica gels with the view to targeting photochemical materials that can be used to mitigate rising CO2 emissions. Our results suggest that the immobilised cells are autofluorescent for at least 75days post encapsulation and can maintain a steady oxygen production rate over a similar timeframe corroborating the viability and physiological activity of silica immobilised C. caldarium.
Keywords: Cyanidium caldarium; CO; 2; mitigation; Cell immobilisation; Photosynthesis; Living materials
Diffusion of sodium dodecyl sulfate micelles in agarose gels
by Wyatt J. Musnicki; Nathan W. Lloyd; Ronald J. Phillips; Stephanie R. Dungan (pp. 165-175).
Holographic interferometry interferometry is used to measure the effect of concentration on diffusion of charged micelles in agarose. A strong effect is found, particularly at low ionic strengths. The data are in good agreement with a theory for concentration effects on the thermodynamic driving force and hydrodynamic resistance to micellar flux.▪► Solute interactions affect diffusion rate. ► Electrostatic charge enhances interactions. ► Gel fibers crowd solute by excluding volume. ► Charged micelle diffusion in gels strongly dependent on concentration.The gradient diffusion of ionic sodium dodecyl sulfate micelles in agarose gel was investigated at moderate concentrations above the CMC. Of particular interest were the effects of micelle, gel, and sodium chloride concentration on the micelle diffusivity. Holographic interferometry was used to measure the gradient diffusion coefficient at three sodium chloride concentrations (0, 0.03, 0.10M), three gel concentrations (0, 1, 2wt%), and several surfactant concentrations. Time-resolved fluorescence quenching was used to measure aggregation numbers both in solution and gel. The micelle diffusivity increased linearly with surfactant concentration at the two larger sodium chloride concentrations and all gel concentrations. In general, the strength of this effect increased with decreasing sodium chloride concentration and increased with gel concentration. This behavior is evidence of decreasing micelle–micelle electrostatic interactions with increasing sodium chloride concentrations, and increasing excluded volume effects and hydrodynamic screening with increasing gel concentration, respectively. The only exception was at 0.1M sodium chloride and 2wt% agarose, which showed a slight reduction in the slope compared to 1wt% agarose. It was found that the concentration effect is quite strong for charged solutes: at a NaCl concentration of 0.03M in a 2% agarose gel, in a solution with 3% SDS micelles by volume, the micelle diffusion coefficient is doubled relative to its value in the same gel at infinite dilution. The extrapolated, infinite-dilution diffusion coefficients and the rate at which the micelle diffusivity increased with surfactant concentration were compared with predictions of previously published theories in which the micelles are treated as charged, colloidal spheres and the gel as a Brinkman medium. The experimental data and theoretical predictions were in good agreement.
Keywords: Micelles; Electrostatic charge; Diffusion; Agarose gel
Wormlike micelles formed by mixed cationic and anionic gemini surfactants in aqueous solution
by Xiaomei Pei; Jianxi Zhao; Xilian Wei (pp. 176-181).
On the addition of a small amount of C12ϕC12, the hydrogen-bonding interaction between 12-3(OH)-12 molecules is greatly enhanced, resulting in longer micelles and a viscous solution.Display Omitted► Wormlike micelle formed in aqueous solutions of mixed gemini surfactants. ► Intermolecular hydrogen-bonding interaction promotes growth of the wormlike micelles. ► Electrostatic attraction reinforces hydrogen-bonding interactions.The formation and the properties of wormlike micelles in aqueous solutions of mixed cationic and anionic gemini surfactants, 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-3(OH)-12) and O, O′-bis(sodium 2-dodecylcarboxylate)- p-benzenediol (C12ϕC12), have been studied by steady-state and dynamic rheological measurements at 25°C. With the addition of a small amount of C12ϕC12 into the solution of 12-3(OH)-12, the total surfactant concentration of which was always kept at 80mmolL−1, the solution viscosity was strongly enhanced and its maximum was much larger than that of the mixed system of propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-3-12) and C12ϕC12. The results of dynamic rheology measurements showed that 12-3(OH)-12/C12ϕC12 formed longer wormlike micelles in comparison with 12-3-12/C12ϕC12. This was attributed to the effect of hydrogen bonding occurring between 12-3(OH)-12 molecules, which was an effective driving force promoting micellar growth. As few C12ϕC12 participated in the micelles, the electrostatic attraction between the oppositely charged head groups of 12-3(OH)-12 and C12ϕC12 made the molecules in the aggregates pack more tightly. This reinforced the hydrogen-bonding interactions and greatly promoted the micellar growth.
Keywords: Wormlike micelles; Cationic and anionic gemini surfactant mixture; Intermolecular hydrogen bonding
Selective attachment of F-actin with controlled length for developing an intelligent nanodevice
by Ming-Yuan Wei; Lenin J. Leon; Yongkuk Lee; Denzel Parks; Lloyd Carroll; Parviz Famouri (pp. 182-189).
A selective attachment of F-actin with controlled length on a patterned surface by employing biotinylated capped protein gelsolin as intermediate anchoring bridge was reported, which may open an avenue for the long-distant movement of myosin-coated beads in future work.Display Omitted► A selective attachment of F-actin with controlled length on a patterned surface. ► Biotinylated capped protein gelsolin as intermediate anchoring bridge. ► Non-specific binding of F-actin via electrostatic adsorption can be resisted. ► Open a possibility for the long-distant movement of myosin-coated beads.Development of the nanodevice that myosin-coated beads “walk” on actin filaments (F-actin) tracks for in vitro nanotransportation was hindered due to the difficulty of assembling large-area well-orientated F-actin tracks on the surface. In this work, we present a selective attachment of F-actin with controlled length on a patterned surface by employing biotinylated capped protein gelsolin as intermediate anchoring bridge. A patterned streptavidin layer was formed via coupling with a biotin layer that photo-actively attached to an amine-functionalized glass surface. The patterned film was found stable and homogenous compared to that obtained by microcontact printing method, according to the profiling with fluorescence microscopy. By a secondary blocking process, non-specific binding of F-actin to the patterned surface through electrostatic adsorption can be resisted. The length variation of F-actin as a function of gelsolin concentration was also investigated, implying that F-actin is appropriately of 2.5μm in average length once F-actin/gelsolin molar ratio is 4:1. Finally, the selective attachment of F-actin was well characterized with quantifying the number of attached F-actin per unit area in the patterned areas over that in blocked areas. The density of F-actin was estimated at c.a. 2μm2 per actin filament molecule so that the distance between one another actin filament is estimated as c.a. 1.41–1.97μm. The unique properties of F-actin, e.g. well flexibility or electrical conductivity, make it feasible to lay them down and form unidirectional aligned tracks by fluidic flow or electrical field. This may open a possibility for the long-distant movement of myosin-coated beads, offering a novel discipline for the development of micro-biochip in vitro.
Keywords: Bio-molecular motors; Atomic force microscopy; Surface modification; Photobiotin; Fluorescence microscopy
Dispersion of carbon nanotubes by carbazole-tailed amphiphilic imidazolium ionic liquids in aqueous solutions
by Bin Dong; Yijin Su; Yonghui Liu; Jie Yuan; Jingkun Xu; Liqiang Zheng (pp. 190-195).
CNTs were dispersed in water using a surface-active ionic liquid with a polycyclic aromatic moiety and a long hydrophobic chain.Display Omitted► Surfactants enhanced the solubilization of CNTs in water. ► Polycyclic compounds enhanced the solubilization of CNTs in water. ► [CzC nMIm]Br contains a polycyclic aromatic moiety and a long hydrophobic chain. ► [CzC nMIm]Br shows a strong ability to disperse CNTs in water.Surfactants with a polycyclic aromatic moiety and a long hydrocarbon chain, carbazole-tailed amphiphilic imidazolium ionic liquids 1-[ n-( N-carbazole)alkyl]-3-methylimidazolium bromide [CzC nMIm]Br ( n=10 and 12), were designed to disperse carbon nanotubes (CNTs) in aqueous solutions. UV–vis–NIR spectra were performed to determine the dispersion of CNTs and the optimal concentration ( Copt) of [CzC nMIm]Br. Compared with [C nMIm]Br, [CzC nMIm]Br was more effective with the smaller Copt and more individual CNTs, reflecting the effect of the carbazole moiety. The adsorption of [CzC nMIm]Br molecules on CNTs was investigated by zeta-potential, surface tension, fluorescence, and1H NMR. Having zeta-potentials higher than 15mV contributed to the long-term stability of aqueous CNT dispersions. The significant fluorescence quenching and the upfield shift of carbazole protons support the π– π stacking interaction between carbazole moieties and the π-networks of CNTs. Meanwhile, the upfield shift of imidazolium protons indicates the cation– π interaction between the imidazolium ions and the π-networks of CNTs.
Keywords: Carbon nanotubes; Dispersion; Surfactant; Carbazole moiety; Imidazolium ionic liquids
Simple statistical thermodynamic model of the heteroaggregation and gelation of dispersions and emulsions
by Eric Dickinson (pp. 196-202).
A model is presented to describe heteroaggregation and gelation of mixtures of equal-sized hard-sphere particles exhibiting short-ranged unlike attractive interactions.Display Omitted► Heteroaggregation is modelled as binary mixture of sticky hard-spheres. ► Average cluster size depends on volume fraction, composition and stickiness. ► Divergence of average cluster size implies gelation. ► Model describes heteroaggregation of protein-stabilized emulsions and dispersions.The heteroaggregation behaviour of mixtures of equal-sized particles (type A+type B) exhibiting short-ranged attractive interactions is investigated using the sticky hard-sphere model. The average cluster size is calculated as a function of the total particle volume fraction, the binary mixture composition, and the A–B stickiness interaction parameterτAB-1. We show that a value ofτAB-1=102, equivalent to an attractive well depth of ∼5 kT in a realistic continuous pair potential, leads to a state of heteroaggregation just below the gelation threshold of the equimolar mixture of volume fraction 0.1. We discuss the conditions under which the assumptions of this statistical thermodynamic model are satisfied experimentally, with particular reference to recent data on the heteroaggregation behaviour of protein-stabilized emulsions and latex particle dispersions.
Keywords: Sticky hard-sphere model; Heteroaggregation; Gel point; Particle interactions; Protein-based emulsions; Yukawa potential
Removal of copper by oxygenated pyrolytic tire char: Kinetics and mechanistic insights
by Augustine Quek; Rajashekhar Balasubramanian (pp. 203-210).
Change in pH with copper sorption at 297K, initial concentration 25ppm. The percentage of Cu removal onto oxygenated pyrolytic char (P550250) is much higher than that onto unoxygenated char (NoPPO).Display Omitted► The kinetics of copper ion (Cu(II)) removal by pyrolytic tire char was studied. ► Mechanistic insights into adsorption are provided. ► A reversible first-order reaction rate provided the best fit to the experimental data. ► Oxygenated tire chars were found to be able to precipitate copper from solution. ► Surface chemistry plays an important role in sorption processes.The kinetics of copper ion (Cu(II)) removal from aqueous solution by pyrolytic tire char was modeled using five different conventional models. A modification to these models was also developed through a modified equation that accounts for precipitation. Conventional first- and second-order reaction models did not fit the copper sorption kinetics well, indicating a lack of simple rate-order dependency on solute concentration. Instead, a reversible first-order rate reaction showed the best fit to the data, indicating a dependence on surface functional groups. Due to the varying solution pH during the sorption process, modified external and internal mass transfer models were employed. Results showed that the sorption of copper onto oxygenated chars was limited by external mass transfer and internal resistance with and without the modification. However, the modification of the sorption process produced very different results for unoxygenated chars, which showed neither internal nor external limitation to sorption. Instead, its slow sorption rate indicates a lack of surface functional groups. The sorption of Cu(II) by oxygenated and unoxygenated chars was also found to occur via three and two distinct stages, respectively.
Keywords: Tires; Pyrolysis; Oxygenation; Kinetic model; Film diffusion
Heterogeneous photocatalysis of methylene blue over titanate nanotubes: Effect of adsorption
by Lin Xiong; Weiling Sun; Ye Yang; Cheng Chen; Jinren Ni (pp. 211-216).
Titanate nanotubes (TNTs) exhibited a better photocatalytic degradation of methylene blue in a simultaneous adsorption and photodegradation system (A+P) than that in equilibrium adsorption followed by photodegradation system (A/P)..Display Omitted► We study the effect of adsorption on photocatalysis of methylene blue over titanate nanotubes. ► Titanate nanotubes show higher photodegradation of methylene blue with lower adsorption. ► Too high adsorption may inhibit the photocatalytic activity of titanate nanotubes. ► Titanate nanotubes exhibit better sedimentation properties than TiO2.Titanate nanotubes were synthesized with hydrothermal reaction using TiO2 and NaOH as the precursors and subsequent calcination at 400°C for 2h. The products were characterized with SEM and XRD. Adsorption and photocatalysis of methylene blue over titanate nanotubes and TiO2 were investigated. The results indicated that titanate nanotubes exhibited a better photocatalytic degradation of methylene blue in a simultaneous adsorption and photodegradation system than that in equilibrium adsorption followed by a photodegradation system, whereas TiO2 showed no significant differences in photocatalytic activity in the two systems. The methylene blue overall removal efficiency over TNTs in the first system even exceeded that over TiO2. The different catalytic performances of titanate nanotubes in the two systems were tentatively attributed to different effects of adsorption of methylene blue, i.e., the promoting effect in the former and the inhibition effect in the latter. Decantation experiments showed that the titanate nanotube photocatalyst could be easily separated from the reaction medium by sedimentation. Thus titanate nanotubes with high sedimentation rates and concurrent adsorption represent a new catalyst system with a strong potential for commercial applications.
Keywords: Titanate nanotubes; Methylene blue; Adsorption; Photodegradation; Sedimentation
Investigation of the sorption properties of β-cyclodextrin-based polyurethanes with phenolic dyes and naphthenates
by Mohamed H. Mohamed; Lee D. Wilson; John V. Headley; Kerry M. Peru (pp. 217-226).
Generalized Sorption Scheme: The heterogeneous sorption of adsorbates in the framework of a β-cyclodextrin polyurethane-based sorbent, where both inclusion and non-inclusion binding are observed in aqueous solution.Display Omitted► β-cyclodextrin (β-CD) based polyurethane sorbents exhibit tunable sorption properties according to the co-monomer composition. ► Inclusion and non-inclusion binding observed for p-nitrophenol (PNP), phenolphthalein (phth) and naphthenates (NAs). ► Tunable sorption capacity and binding affinity are observed according to the nature of the adsorbate, copolymer sorbent, and experimental (i.e. concentration and pH) conditions.The sorption of p-nitrophenol (PNP), phenolphthalein (phth) and naphthenates (NAs) with β-cyclodextrin (β-CD) based polyurethane sorbents from aqueous solutions are reported. The copolymer sorbents were synthesized at various β-CD/diisocyanate monomer mole ratios (e.g., 1:1, 1:2, and 1:3) with diisocyanates of variable molecular size and hydrogen deficiency. The copolymer sorbents were characterized in the solid state using13C CP-MAS NMR spectroscopy, IR spectroscopy and elemental (C,H,N) analysis. The equilibrium sorption properties of the copolymer sorbents in aqueous solution were characterized using isotherm models at pH 4.6 and 9.0 for PNP, pH 9.0 for naphthenates and pH 10.5 for phth. UV–Vis spectroscopy was used to monitor the unbound fraction of the phenolic dyes in the aqueous phase, whereas, electrospray ionization mass spectrometry was used to monitor the unbound fraction of naphthenates. The sorption results of the copolymer sorbents were compared with a commercially available carbonaceous standard; granular activated carbon (GAC). The sorption properties and capacities of the copolymer sorbents (Q m) were estimated using the Sips isotherm. The sorption capacity for GAC was 2.15mmol PNP/g, 0.0698mmol phth/g, and 142mg NAs/g, respectively, whereas the polymeric materials ranged from 0.471 to 1.60mmol/g (PNP), 0.114 to 0.937mmol/g (phth), and 0 to 75.5mg/g (naphthenates), respectively, for the experimental conditions investigated. The observed differences in the sorption properties were attributed to the accessible surface areas and pore structure characteristics of the copolymer sorbents. The binding constant,K eq, for copolymer materials for each sorbate is of similar magnitude to the binding affinity observed for native β-CD. PNP showed significant binding onto the copolymer framework containing diisocyanate domains, whereas, negligible sorption to the sites was observed for phth and naphthenates. The β-CD inclusion sites in the copolymer framework are concluded to be the main sorption site for phth and naphthenates through the formation of well-defined inclusion complexes.
Keywords: Copolymers; Adsorption; Cyclodextrin; Naphthenates; Phenolphthalein; p-Nitrophenol
Kinetics of adsorption of oxalic acid on different titanium dioxide samples
by Federico Roncaroli; Miguel A. Blesa (pp. 227-233).
FTIR-ATR studies for the adsorption of oxalic acid on different TiO2 samples were performed to evaluate the effect of film thickness, surface area, and particle size on kinetics and equilibrium.Display Omitted► FTIR-ATR spectroscopy studies on the equilibrium and kinetics of adsorption of oxalic acid on different TiO2 samples were performed. ► Surface complexes detected on the different samples display analogous spectroscopic characteristics and similar affinity toward TiO2. ► Adsorption and desorption kinetics are controlled by the diffusion within the pores of the films. ► The surface area of the films, TiO2 load, particle size, pore size, and film thickness strongly determine the kinetics of both adsorption and desorption. ► An analysis of the influence of the physical parameters on the kinetics is offered.FTIR-ATR kinetic studies on the adsorption of oxalic acid on different TiO2 films were performed. The particulate films were obtained through the evaporation of TiO2 suspensions. The evolution of the IR bands followed a pseudo-first-order behavior, as previously observed. Systematic studies as a function of the oxalic acid concentration afforded the specific rate constant for adsorption (k a) and desorption (k d). The influence of physical parameters of the samples, i.e., specific BET area, crystalline domain size, TiO2 load, film area, and pore size, on the kinetic parametersk a andk d was analyzed. A mechanism in which the adsorption and desorption processes are controlled by the diffusion through the pores of the films is proposed (intraparticle diffusion). It is concluded that all the samples behave in the same way. Thicker films or those with smaller particle size (higher specific surface area, smaller pores) show the slowest rates of adsorption and desorption. These results are relevant for the design of efficient heterogeneous catalysts and sensors, and for the interpretation of pollutant adsorption.
Keywords: Oxalic acid; Titanium dioxide; TiO; 2; Adsorption; Kinetics; Surface complexation; FTIR; ATR
Enhanced adsorption of arsenate onto a natural polymer-based sorbent by surface atom transfer radical polymerization
by Yu-Ting Wei; Yu-Ming Zheng; J. Paul Chen (pp. 234-239).
The adsorption of arsenate onto the N-methylglucamine-modified chitosan adsorbent was highly pH dependent, and the optimum pH for adsorption of arsenate onto the adsorbent was around 5.Display Omitted► A N-methylglucamine-modified chitosan adsorbent was successfully developed for arsenate removal. ► The adsorption of arsenate onto the adsorbent was highly pH dependent, and the optimum pH was 5. The maximum adsorption capacity was 69.28mg/g. ► The Freundlich isotherm well described the adsorption behaviour. ► The adsorption equilibrium was obtained in 16h, which was controlled by surface diffusion. ► Spectroscopic analysis showed that tertiary amine and hydroxyl groups played important roles in the adsorption.Arsenic contamination in water, especially in groundwater, has been recognized as an important issue of concern because of its high mobility and toxicity. In this study, N-methylglucamine was immobilized onto crosslinked chitosan beads via atom transfer radical polymerization for an efficient adsorption of arsenic. It was demonstrated that the immobilization significantly enhanced the adsorption capacity. The uptake onto the adsorbent was highly pH dependent, and a maximum adsorption capacity as high as 69.28mg/g was obtained at the optimum pH of 5. Most of arsenate was rapidly adsorbed in the first 5h, and the adsorption equilibrium was established in 16h, which was well described by an intraparticle diffusion model. The adsorbent exhibited a great uptake of the humic acid, which led to a decrease in the adsorption of arsenate. The effects of competitive anions on the adsorption exhibited the following descending sequence: sulfate ≫ phosphate>fluoride (negligible effect). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the arsenic adsorption resulted from the presence of tertiary amine and hydroxyl functional groups grafted on the crosslinked chitosan.
Keywords: Arsenate; Adsorption; Spectroscopic analysis; Chitosan; N-; methylglucamine
Sodium niobate adsorbents doped with tantalum (TaV) for the removal of bivalent radioactive ions in waste waters
by Blain Paul; Dongjiang Yang; Wayde N. Martens; Ray L. Frost (pp. 240-247).
Niobate solids illustrated by the SEM images of the samples: (a) 0% Ta, (b) 0.5% Ta, (c) 1% Ta, (d) 2% Ta, (e) 5% Ta, and (f) 10% Ta.Display Omitted► This study highlights new opportunities for the preparation of Nb-based adsorbents to efficiently remove the toxic radioactive ions. ► Sodium niobates doped with different amount of tantalum (TaV) were prepared via thermal reaction processes. ► For the well-crystallized fibril solids, the Na+ ions are difficult to be exchanged, and the radioactive ions such as Sr2+ and Ra2+ ions deposit on the surface of the fibers. ► The bar-like solids enable the removal of highly hazardous bivalent radioactive isotopes such as Sr2+ and Ra2+ ions.Sodium niobates doped with different amounts of tantalum (TaV) were prepared via a thermal reaction process. It was found that pure nanofibrils and bar like solids can be obtained when tantalum is introduced into the reaction system. For the well crystallized fibril solids, the Na+ ions are difficult to exchange, and the radioactive ions such as Sr2+ and Ra2+ just deposit on the surface of the fibers during the sorption process, resulting in lower sorption capacity and distribution coefficients (K d). However, the bar like solids are poorly crystallized and have many exchangeable Na+ ions. They are able to remove highly hazardous bivalent radioactive isotopes such as Sr2+ and Ra2+ ions. Even in the presence of many Na+ ions, they also have higherK d. More importantly, such sorption finally intelligently triggers considerable collapse of the structure, resulting in permanent entrapment of the toxic bivalent cations in the solids, so that they can be safely disposed of. This study highlights new opportunities for the preparation of Nb-based adsorbents to efficiently remove toxic radioactive ions from contaminated water.
Keywords: Niobates; Adsorption; Radioactive ions; Doping
Surface functionalization of SBA-15 and a nonordered mesoporous silica with a 1,4-diazabicyclo[2.2.2]octane derivative: Study of CuCl2 adsorption from ethanol solution
by Camila M. Maroneze; Herica A. Magosso; Anton V. Panteleimonov; Yuriy V. Kholin; Yoshitaka Gushikem (pp. 248-256).
Adsorption isotherms of CuCl2 (in ethanol) on mesostructured silicas and an illustrative scheme showing the porous ordering effect on the functionalization and adsorption processes..Display Omitted► The nonordered mesostructure experienced higher agglomeration of functional groups. ► Higher effective sorption capacity was observed for SBA-15. ► The equilibrium constants for CuCl2 adsorption are similar for both silicas. ► Regeneration of the adsorbents consists only in their immersion in aqueous solution. ► The studied materials are potential adsorbents for ethanol fuel purification.This work describes the preparation and characterization of postfunctionalized ordered (SBA-15) and nonordered (SMD) mesoporous silicas with n-propyl-1,4-diazoniabicycle[2.2.2]octane chloride (DbCl) moiety. The main interest is based on the fact that these materials are excellent adsorbents due to the ability of functional groups to retain copper chlorides on their surfaces as anionic complexesCuCl2+nn-. The specific surface areas ( SBET) and average pore diameters ( dpore) for SBA-15 and SMD are SBA-15, SBET=944m2g−1, dpore=9.0nm; SMD, SBET=710m2g−1, dpore=11nm. On functionalization with DbCl, reductions in the specific surface areas of the resulting materials (SBA-15/DbCl and SMD/DbCl) are observed and the following functionalization degrees ( ϕ) were determined: SBA-15/DbCl, SBET=247m2g−1, ϕ=0.95mmolg−1; SMD/DbCl, SBET=83m2g−1, ϕ=1.2mmolg−1. The adsorption equilibria of CuCl2 in ethanol were characterized, and the heterogeneous stability constants, β1 and β2, corresponding to formation ofCuCl42- andCuCl3- anionic species adsorbed on the surface were found. Also, the effective sorption capacities (t Q) were determined: SBA-15/DbCl, log β1=4.46, log β2=7.10,t Q=0.80mmolg−1; SMD/DbCl, log β1=4.95, log β2=7.52,t Q=0.75mmolg−1. Regeneration of the adsorbents requires a very simple procedure consisting of their immersion in aqueous solution followed by immediate release to the solution phase of theCu(OH2)n2+ species, followed by chloride anions as the counterions.
Keywords: SBA-15; Mesoporous silica; DABCO; Adsorbents; Ethanol purification
Photocatalytic reduction of CO2 in methanol to methyl formate over CuO–TiO2 composite catalysts
by Shiyue Qin; Feng Xin; Yuande Liu; Xiaohong Yin; Wei Ma (pp. 257-261).
The surface-phase junction of the CuO–TiO2 composite catalyst, band positions of CuO, TiO2 and the potentials of several redox couples.Display Omitted► Methanol was utilized as reductant for the photoreduction of CO2 because the reducibility of methanol is stronger than water and methanol can dissolve much more CO2 than water. ► CuO–TiO2 composite catalysts were used and the catalysts were prepared through a sol–gel method using cetyltrimethylammonium bromide (CTAB) as an auxiliary reagent. ► The surface-phase junction between CuO and TiO2 was investigated by HRTEM and it could enhance the photocatalytic activity.Photocatalytic reduction of CO2 on CuO–TiO2 composite catalysts in the presence of methanol to prepare methyl formate had been investigated. Methanol was used as sacrificial reagent to react with the photo-generated holes in the valence band, and CO2 was reduced by the electrons in the conduction band. CuO–TiO2 was optimized for CuO loading, preparation method and calcination temperature. The catalyst of 1.0CuO–TiO2, calcined at 450°C and CTAB as a dispersant showed the highest overall activity. The heterojunction between CuO and TiO2 demonstrated with HRTEM played an important role in enhancing the photocatalytic activity.
Keywords: Photocatalysis; Photocatalytic reduction of CO; 2; Composite semiconductor; Methanol; Methyl formate
Transition metal complexes on mesoporous silica nanoparticles as highly efficient catalysts for epoxidation of styrene
by Duihai Tang; Wenting Zhang; Yinling Zhang; Zhen-An Qiao; Yunling Liu; Qisheng Huo (pp. 262-266).
A series of nanocatalysts were synthesized by immobilizing metal complexes on mesoporous silica nanoparticles. All these nanocatalysts show high conversion and turnover frequency for epoxidation of styrene.Display Omitted► We synthesized a series of new nanocatalysts by the grafting method. ► All the catalysts have a spherical morphology and are monodisperse with diameters 120–150nm. ► All the catalysts are stable up to at least 200°C. ► All the catalysts show high conversion and turnover frequency for epoxidation of styrene. ► The catalysts which have been used once maintain a spherical morphology and are monodisperse.We have synthesized a series of catalysts for epoxidation of styrene by immobilizing salicylaldimine transition metal (copper, manganese, and cobalt) complexes on mesoporous silica nanoparticles (MSNs) with diameters of 120–150nm. The prepared catalysts are characterized by infrared (IR) spectra, thermal gravimetric analyses (TGA), inductively coupled plasma (ICP), CHN elemental analysis, nitrogen adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These catalysts possess excellent catalytic efficiency in epoxidation of styrene when using tert-BuOOH (TBHP) as oxidant. Styrene shows a high conversion (∼99%) as well as epoxide selectivity (∼80%) over Cu-MSN catalysts, and high conversion (∼99%) and moderate epoxide selectivity (∼65%) over Mn-MSN and Co-MSN catalysts. The recycling experiment results indicate that these catalysts maintain catalytic activity even after being used for three cycles. Our results indicate that MSNs can serve as better catalyst supports.
Keywords: Epoxidation of styrene; Salicylaldimine transition metal complexes; Mesoporous silica nanoparticles
Adsorption of oligomers on the polymer-tethered surfaces
by M. Borówko; S. Sokołowski; T. Staszewski (pp. 267-276).
A density functional study of adsorption of oligomers on solid surfaces modified with grafted chains is presented. The effects of selected factors on adsorption and separation of mixtures are analyzed.Display Omitted► Adsorption on solid surfaces modified with tethered polymers. ► Structural properties of tethered polymers. ► Applications of density functional theory. ► Separation of complex mixtures.A density functional study of adsorption of oligomers on weakly attractive surfaces modified with grafted chains is presented. The chain molecules are modeled as freely jointed tangent spheres. The segments interact via Lennard–Jones (12-6) potentials. Two types of substrates are considered – a neutral surface and the Lennard–Jones (9,3) surface. The mechanism of adsorption is discussed. Depending on the system characteristics, the primary, secondary and ternary adsorption is found. The effects of selected factors on adsorption and separation of mixtures are analyzed.
Keywords: Density functional theory; Polymer brushes; Adsorption of oligomers; Separation of mixtures
Adsorption of atrazine from aqueous electrolyte solutions on humic acid and silica
by Ilias D. Kovaios; Christakis A. Paraskeva; Petros G. Koutsoukos (pp. 277-285).
Adsorption isotherms of atrazine in different mixtures of humic acid and silica at pH 5.5 and θ=25°C. Data points fit according to the Freundlich model.Display Omitted► The paper deals with the adsorption of atrazine, on main components of soils. ► The kinetics of adsorption were represented satisfactorily with the Elovich model. ► Atrazine is expected to be adsorbed on silica gel after 6h and on HA after 30days. ► Adsorption data were fitted satisfactorily to the Freundlich model. ► Experiments showed that atrazine was sorbed 28,000 times more on HA than on silica.The adsorption of, the still widely used, herbicide atrazine on model soil components, such as humic acid and humic acid–silica gel mixtures, was investigated in a series of batch experiments, under different experimental conditions (ionic strength, temperature, and pH). The investigation aimed at obtaining an estimate of the contribution of each of the soil components on the adsorption of atrazine from aqueous solutions. The kinetics of atrazine adsorption on humic acid showed two steps: a fast step, of a few hours duration, and a second slow step, which continued for weeks. The kinetics of adsorption data gave a satisfactory fit to the Elovich equation. Τhe adsorption of atrazine on the test substrates was found to be reversible in all cases. The atrazine uptake data on the test substrates were fitted best with the Freundlich adsorption isotherm. The ionic strength of the atrazine aqueous solutions did affect the amount of the atrazine adsorbed on the test substrates, suggesting that electrostatic forces between atrazine molecules and soil play a significant role in the adsorption process. An increase of temperature resulted in a decrease of atrazine adsorption on humic acid at low atrazine equilibrium concentrations. However, for higher levels of equilibrium concentrations (⩾3mg/L) the amount of atrazine adsorbed onto the test substrate increased as temperature increased. The calculated isosteric enthalpies of adsorption ranged between slightly exothermic at low atrazine uptake and slightly endothermic at high atrazine uptake, all values being in the range of physisorption.
Keywords: Atrazine; Herbicide; Sorption; Humic acid; Silica; Model soil components
Displacement of liquid droplets on a surface by a shearing air flow
by J. Fan; M.C.T. Wilson; N. Kapur (pp. 286-292).
Three types of wind-driven droplet motion are identified and a simple analytical model is formulated to enable estimates of critical air speeds to initiate motion.Display Omitted► Droplet motion initiated by shear flow. ► Motion characterised by one of three behaviors. ► Analytical model shows balance of shear and capillary forces. ► Combining experiments and analysis gives predictive tool.The motion of droplets on surfaces is crucial to the performance of a wide range of processes; this study examines the initiation of droplet motion through a shearing mechanism generated here by a controlled air flow. Systematic experiments are carried out for a range of fluids and well defined surfaces. A model is postulated that balances surface tension forces at the contact line and the drag force due to the air motion. Experiments reveal that the critical velocity at which droplet motion is initiated depends on the contact angle and the droplet size. Visualizations highlight three modes of motion: (I) the droplet retains a footprint similar to that at the point of motion; (II) a tail exists at the rear of the droplet; (III) a trail remains behind the droplet (that can shed smaller droplets). The predictions of droplet initiation velocity are good for type I motion, in accordance with the assumptions inherent within the model. This model confirms the dominant physics associated with the initiation of droplet motion and provides a useful predictive expression.
Keywords: Droplet; Shear flow; Motion; Contact line; Surface; Air flow
Spreading of fluids on solids under pressure: Slip and stick effects
by Soma Nag; Tapati Dutta; Sujata Tarafdar (pp. 293-297).
Fluids with different viscosity and hydrophilicity spread differently on substrates, when forced by an external load. To explain the curves, viscous dissipation with slip/stick is necessary.Display Omitted► We study contact area for different fluid–solid combinations under load. ► Normally low-spreading pairs spread more under loading and vice-versa. ► Viscous dissipation with slip or stick can explain the area vs. time curves.Spreading of different types of fluid on solids under an impressed force is an interesting problem. Here we study spreading of four fluids, having different hydrophilicity and viscosity on two substrates – glass and perspex, under an external force. The area of contact of fluid and solid is video-photographed and its increase with time is measured. The results for different external forces can be scaled onto a common curve. We try to explain the nature of this curve on the basis of existing theoretical treatment where either the no-slip condition is used or slip between fluid and substrate is introduced. We find that of the eight cases under study, in five cases quantitative agreement is obtained using a positive slip coefficient. The remaining three can be explained with a negative slip coefficient, equivalent to a sticking effect.
Keywords: Spreading; Squeeze film; Viscous flow; Slip; Stick
Effect of concentration of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents on surface free energy of silica aerogels
by D.B. Mahadik; A. Venkateswara Rao; A. Parvathy Rao; P.B. Wagh; S.V. Ingale; Satish C. Gupta (pp. 298-302).
This concludes that increase in hexamethyldisilazane concentration (3–2%) leads to increase in contact angle (132–153°) while decrease in surface energy (4.2319–.4871mJ/m2) of aerogels.Display Omitted► Increase in concentration of the silylating reagent affects increase in contact angle of water with surface of aerogel. ► γsl, increases from 54.45mN/m to 67.34mN/m. ► γsv, decreases from 5.5892mJ/m2 to 0.3073mJ/m2. ► Work of adhesion were decreased from 23.129mJ/m2 to 4.948mJ/m2.The surface free energy of a solid determines its surface and interfacial behavior in processes like wetting and adhesion which is crucial for silica aerogels in case of organic liquid absorption and transportation of chemicals at nano-scale for biotechnological applications. Here, we have demonstrated that the surface free energy of aerogels can be tuned in wide range from 5.5892 to 0.3073mJ/m2 by modifying their surface using TMCS and HMDZ silylating reagents. The alcogels were prepared by two step acid–base catalyzed process where the molar ratio of precursors Tetraethoxysilane (TEOS):Methanol (MeOH):Oxalic acid:NH4OH:NH4F was kept at optimal value of 1:2.7:0.18×10−4:0.02:0.22×10−3, respectively. To modify gel surfaces, TMCS and HMDZ concentration have been varied from 3% to 12% and such alcogels were dried at ambient pressure. It is observed from FTIR for aerogels that increase in concentration of silylating reagent resulted increase in hydrophobicity. This leads to increase in contact angle for water from 123° to 155° but leads to decrease in surface free energy from 5.5892 to 0.3073mJ/m2. As there is not direct method, we have used Neumann’s equation of state to estimate surface energy of aerogels.
Keywords: Silica aerogels; Sol–gel process; Silylating agent; Contact angle; Surface free energy
Influence of chemical treatments on adhesion properties of hemp fibres
by M. Le Troëdec; A. Rachini; C. Peyratout; S. Rossignol; E. Max; O. Kaftan; A. Fery; A. Smith (pp. 303-310).
Impact of chemical treatments on the surface properties of hemp fibres. Atomic Force Microscopy imaging of untreated fibres (a), and fibres chemically treated with NaOH (b), EDTA (c) and PEI (d)Display Omitted► Chemical treatments modify the structure of hemp fibres. ► Each treatment tends to lead to a morphology of interconnected web-like structure. ► Adhesion properties, measured with Colloidal Force Microscopy, change according to treatments.In addition to be an environmentally friendly material, hemp fibres are also inexpensive reinforcements in thermoplastics or concrete composites, due to their intrinsic mechanical, thermal and acoustic properties. The morphology of hemp fibres has been chemically modified in order to enhance the matrix/fibre interface and has been examined by Scanning Electron Microscopy (SEM). In this paper, Gas Chromatography (GC) and Atomic Force Microscopy (AFM) were used to investigate the influence of treatments on the composition of hemp fibres and also on the micro-adhesive interactions between a silica colloidal probe and the surface of the fibres using Chemical Force Microscopy (CFM). Microscopy studies and chemical analysis showed that each treatment tends to lead to a morphology of interconnected web-like structure of hemp fibres. It was found that on an average, the adhesion force, contribution of capillary force and Van der Waals’ forces, is higher in the case of NaOH treatment.
Keywords: Atomic Force Microscopy; Hemp fibres; Adhesion; Chemical treatments
Effects of sodium laurylsulfate on crystal structure of calcite formed from mixed solutions
by Jun-Hwan Bang; Young Nam Jang; Kyung Sun Song; Chi Wan Jeon; Wonbaek Kim; Myung Gyu Lee; So-Jin Park (pp. 311-315).
SEM-EDS images of sulfur distribution on crystallized calcite surfaces. The abnormally large particles were precipitated by macroreactors, a flocked form of microreactors consisting of micelles..Display Omitted► Carbonate source solutions containing sodium laurylsulfate (SLS) crystallize calcite. ► CMCs are suitably adjusted to 0.5 M calcium and carbonate source solutions. ► Formation of macroreactors induced by interaction of microreactors with micelles is suggested.Sodium laurylsulfate (SLS), an anionic surfactant, was used for tailoring calcite via a solution route. SLS was dissolved in calcium and carbonate source solutions at various concentrations and critical micelle concentrations (CMCs). The crystallized particles were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), laser-scattering particle size measurements, and thermogravimetric analysis (TGA). Energy dispersive spectroscopy (EDS) analysis was carried out to measure sulfur profiles on the surface of the particles. SLS tended to produce small calcite particles in the carbonate source solution, whereas this effect was not obvious in the calcium source solution. It is believed that the electrostatic repulsion force in the carbonate source solution contributes to the different particle refining effects of SLS seen in the two solutions.
Keywords: Calcite; Solution route; SLS; CMC; Microreactor; Macroreactor
Inhibition of bubble coalescence: Effects of salt concentration and speed of approach
by Lorena A. Del Castillo; Satomi Ohnishi; Roger G. Horn (pp. 316-324).
Bubble coalescence times are influenced by both the electrolyte concentration and the bubble approach speed.Display Omitted► Long-lived bubbles in pure water have been observed. ► Bubble coalescence time is influenced by the electrolyte concentration. ► Bubble coalescence time is influenced by the bubble approach speed. ► Different mechanisms that delay coalescence are operating at low and high speeds.Bubble coalescence experiments have been performed using a sliding bubble apparatus, in which mm-sized bubbles in an aqueous electrolyte solution without added surfactant rose toward an air meniscus at different speeds obtained by varying the inclination of a closed glass cylinder containing the liquid. The coalescence times of single bubbles contacting the meniscus were monitored using a high speed camera. Results clearly show that stability against coalescence of colliding air bubbles is influenced by both the salt concentration and the approach speed of the bubbles. Contrary to the widespread belief that bubbles in pure water are unstable, we demonstrate that bubbles formed in highly purified water and colliding with the meniscus at very slow approach speeds can survive for minutes or even hours. At higher speeds, bubbles in water only survive for a few seconds, and at still higher speeds they coalesce instantly. Addition of a simple electrolyte (KCl) removes the low-speed stability and shifts the transition between transient stability and instant coalescence to higher approach speeds. At high electrolyte concentration no bubbles were observed to coalesce instantly. These observations are consistent with recent results of Yaminsky et al. (Langmuir 26 (2010) 8061) and the transitions between different regions of behavior are in semi-quantitative agreement with Yaminsky’s model.
Keywords: Bubble coalescence; Bubble stability; Approach speed; Critical speed; Pure water; Electrolyte concentration
Electrokinetics of charged spherical colloidal particles taking into account the effect of ion size constraints
by J.J. López-García; M.J. Aranda-Rascón; C. Grosse; J. Horno (pp. 325-330).
Different minimum approach distances of ionic species to the particle surface ( h2− h1) permit explain the reversal of the electrophoretic mobility (u e).Display Omitted► Modified standard electrokinetic model taking into account the finite ion size. ► Purely physical mechanisms can lead to the reversal of the electrophoretic mobility. ► Charge reversal may occur without a change of the electrophoretic mobility sign.The electrokinetic properties of suspended spherical particles are examined using a modified standard electrokinetic model, which takes into account the finite ion size and considers that the minimum approach distance of ions to the particle surface need not be equal to their effective radius in the bulk solution. We calculate the conductivity increment and the electrophoretic mobility and present a detailed interpretation of the obtained results, based on the analysis of the equilibrium and field-induced ion concentrations, as well as the convective fluid flow in the neighborhood of the particle surface. We show that when charge reversal takes place, the sign of the concentration polarization remains unchanged while the sign of the electrophoretic mobility only changes under favorable circumstances.
Keywords: Colloids; Electrokinetic phenomena; Finite ion size; Charge reversal
Electrophoretic motion of a nanorod along the axis of a nanopore under a salt gradient
by Sang W. Joo; Shizhi Qian (pp. 331-340).
By simultaneously applying an axial electric field and salt gradient, one can use the induced diffusiophoresis to control the electrophoretic translocation of a nanorod, such as a DNA.Display Omitted► Imposed salt gradient induces a nonequilibrium electrical double layer. ► There are two mechanisms for diffusiophoresis: induced electrophoresis by the generated electric field and chemiphoresis by the induced pressure gradient. ► One can use the induced diffusiophoresis to control the electrophoretic translocation of a nanorod, such as a DNA molecule.The phoretic translation of a charged, elongated cylindrical nanoparticle, such as a DNA molecule and nanorod, along the axis of a nanopore driven by simultaneous axial electric field and salt concentration gradient, has been investigated using a continuum model, which consists of the Poisson–Nernst–Planck equations for the ionic concentrations and electric potential, and the Stokes equations for the hydrodynamic field. The induced particle motion includes both electrophoresis, driven by the imposed electric field, and diffusiophoresis, arising from the imposed salt concentration gradient. The particle’s phoretic velocity along the axis of a nanopore is computed as functions of the imposed salt concentration gradient, the ratio of the its radius to the double-layer thickness, the nanorod’s aspect ratio (length/radius), the ratio of the nanopore size to the particle size, the surface-charge density of the particle, and that of the nanopore in KCl solution. The diffusiophoresis in a nanopore mainly arises from the induced electrophoresis driven by the generated electric field, stemming from the double-layer polarization, and can be used to regulate electrophoretic translocation of a nanorod, such as a DNA molecule, through a nanopore. When both the nanorod and the nanopore wall are charged, the induced electroosmotic flow arising from the interaction of the overall electric field with the double layer adjacent to the nanopore wall has a significant effect on both electrophoresis driven by the imposed electric field and diffusiophoresis driven by the imposed salt gradient.
Keywords: Diffusiophoresis; Electrophoresis; Electrical double layer; Double layer polarization; Nanopore; Nanofluidics
Partition-induced vector chromatography in microfluidic devices
by Jorge A. Bernate; German Drazer / (pp. 341-351).
Partition Induced Vector Chromatography – PIVC – schematic view from the top of a suspended particle driven by an external force over a chemical or physical pattern of rectangular stripes that – at equilibrium – induces the spontaneous partition of particles into regions of low and high concentration. Partition leads to diffusive fluxes that causes particles exhibiting different partition ratios to migrate at a different angles when externally driven at an oblique orientation with respect to the stripes.Display Omitted► We study the biased transport of Brownian particles in a 2D periodic potential. ► Migration angles are not collinear with the driving force and are particle dependent. ► Migration angles of different species depend on partition in the periodic potential. ► Microfluidic devices are an ideal platform for partition-induced fractionation. ► Partition by gravity or Van der Waals forces in a stripe pattern show fractionation.We investigate by means of macrotransport theory the transport of Brownian particles in a slit geometry in the presence of an arbitrary two-dimensional periodic energy landscape and driven by an external force or convected by a flow field. We obtained analytical expressions for the probability distribution and the average migration angle of the particles under the Fick–Jacobs approximation. The migration angle is shown to differ from the angle of the driving field and to strongly depend on the physical properties of the suspended species, thus providing the basis for vector chromatography, in which different species move in different directions and can be continuously fractionated. The potential of microfluidic devices as a platform for partition-induced vector chromatography is demonstrated by considering the particular case of a piece-wise constant, periodic potential that, in equilibrium, induces the spontaneous partition of different species into high and low concentration stripes, and which can be easily fabricated by patterning physically or chemically one of the surfaces of a channel. We show the feasibility to fractionate a mixture of particles for systems in which partition is induced via 1-g gravity and Van der Waals interactions in physically or chemically patterned channels.
Keywords: Biased diffusion; Periodic potential; Partition; Vector separation; Fractionation; Colloidal particles; Macrotransport theory; Brownian dynamics simulations; Microfluidics
Separation profile of model water-in-oil emulsions followed by nuclear magnetic resonance (NMR) measurements: Application range and comparison with a multiple-light scattering based apparatus
by Sébastien Simon; Xavier Pierrard; Johan Sjöblom; Geir H. Sørland (pp. 352-361).
Schematic diagram of the outcome given by new NMR sequences.Display Omitted► Two NMR sequences to determine the vertical variations of the brine content of w/o emulsions. ► These sequences give consistent and meaningful. ► Limitation: the oil phase must have a viscosity higher or equal than a critical value.The application range and validity of two new NMR sequences (hereafter called sequence 1 and sequence 2) for the study of water-in-oil emulsions (w/o) has been assessed using model emulsions and comparison with results obtained by a commercial apparatus (Turbiscan). These new NMR sequences allow to determine the brine profile i.e. the vertical variations of the dispersed phase content (brine) in the NMR tube. Measuring these parameters as a function of time allows to monitor the separation (sedimentation and coalescence rate) between oil and water.The results obtained on model water-in-oil emulsions with both NMR sequences are consistent and meaningful for both stable and coalescing emulsions and are similar, even if not strictly identical, to the ones obtained with the Turbiscan. It also appears that the second NMR sequence is faster (30s to obtain a profile compared with 3min for the 1st one in the conditions used in this article) and has a broader application range. Indeed, for these two methods, the oil phase must have a viscosity higher or equal than values which is around 5mPas for the sequence 2 and 20–25mPas for the method 1.
Keywords: Water-in-oil emulsion; Oil–water separation; Sedimentation; Coalescence; Turbiscan; NMR
Dual-deposition rates in colloid filtration caused by coupled heterogeneities in a colloidal population
by Jaideep Chatterjee; Shailendra Pratap; Shajahan Abdulkareem (pp. 362-368).
The spatial variation in liquid-phase colloid concentration in an aqueous phase flowing though saturated porous media has been studied, revealing the existence of two distinct deposition rates for colloidal deposition, the causes for which are probed.Display Omitted► Deposition of colloids, suspended in an aqueous phase, during its flow through saturated porous media has been studied experimentally. ► The liquid-phase colloid concentration variation with distance of transport is reported which suggests different deposition rates in the upstream and downstream sections of the homogeneous porous medium. ► Experimental investigation reveals that the two distinct deposition rates are caused by a coupling of favorable properties in one section of the colloid population with the coupling of unfavorable properties in another section. ► Model accounting for this can significantly improve predictability in colloid filtration.Colloidal deposition from an aqueous suspension, during its flow through saturated porous media, is of significance in many natural and man-made processes which lead to water purification. Colloid filtration theory (CFT), which was used to predict removal of homogeneous colloids, in the above systems, is based on a distance-invariant deposition rate. However, many authors over the past decade have reported data which suggest that more than one deposition rate is demonstrated by colloids naturally occurring in the environment on apparently homogeneous media. The observation of two or more deposition rates has been attributed to two modes of deposition as well to the possibility of heterogeneity in the colloidal population, in the recent literature. In this paper, we first examine the variation of liquid-phase concentration C( x) with distance, and find that only two distinct deposition rates are demonstrated by the data under multiple conditions. Since heterogeneity in the colloidal population is expected to produce continuous property variations and hence multiple deposition rates, the appearance of the above dual-deposition behavior is probed further. Depth-wise zeta-potential and particle-size-distribution data reveal that there is a coupling of favorable properties (larger size with positive surface charge) in a section of the population along with a coupling of unfavorable properties in the rest. The above coupling is then confirmed by independent separation experiments. This paper experimentally demonstrates how coupling of two types of heterogeneities in a colloidal population can lead to the appearance of dual-deposition rates while recognizing that the above may be one of the many possible causes for the appearance of dual-deposition rates.
Keywords: Depth filtration; Colloid filtration; Filtration theory
Microemulsion-mediated sol–gel synthesis of mesoporous rutile TiO2 nanoneedles and its performance as anode material for Li-ion batteries
by Ramdas B. Khomane (pp. 369-372).
Mesoporous rutile TiO2 nanoneedles have been successfully synthesized using a reverse microemulsion-mediated sol–gel method at room temperature.Display Omitted► Mesoporous rutile TiO2 nanoneedles have been prepared by microemulsion technique. ► No calcination required as the rutile TiO2 phase is formed at room temperature. ► Nanoneedles sustain a capacity of 128 mAhg−1 beyond 15 cycles as anode material for Li-ion batteries. ► A possible growth mechanism for the formation of nanoneedles in microemulsion is proposed.Mesoporous rutile TiO2 nanoneedles have been successfully synthesized using a reverse microemulsion-mediated sol–gel method at room temperature. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and the Bruauner–Emmet–Teller (BET) adsorption method, and their electrochemical properties were investigated by galvanostatic charge and discharge tests. XRD observations revealed the formation of a pure rutile TiO2 phase. Furthermore, TEM observation revealed the presence of a highly porous needle-like morphology. The electrochemical measurements show that the nanoneedles deliver an initial capacity of 305mAhg−1 as anode material for Li-ion batteries and sustain a capacity value of 128mAhg−1 beyond 15cycles. The reported synthesis is simple, mild, energy efficient, and without postcalcination.
Keywords: Microemulsion; Sol–gel; Mesoporous; TiO; 2; nanoneedles; Discharge capacity
by Benjamin J. Wiley (pp. 373-373).