Journal of Colloid And Interface Science (v.355, #1)
Interaction of cationic liposomes with cell membrane models
by Maria Grazia Bonicelli; Luisa Giansanti; Marco Ierino; Giovanna Mancini (pp. 1-8).
The interaction of cell models with cationic liposome was studied by DSC and flourescence measurements.Display Omitted► Phosphatidylcholine vesicles used as cell models were treated with cationic vesicles. ► The interaction was evaluated by DSC and fluorescence on MLVs and LUVs, respectively. ► Subtle changes in vesicles composition influenced their interaction with cell models.The interaction of phosphatidylcholine liposomes used as cell models, with cationic liposomes formulated with 1,2-dimyristoyl- sn-glycero-3-phosphatidylcholine and amphiphiles based on a pyrrolidinium headgroup was investigated by differential scanning calorimetry and fluorescence resonance energy transfer experiments. The results obtained showed that subtle variations in the formulation can influence lipid interactions and were correlated to a previous biological evaluation.
Keywords: Cationic liposomes; Differential scanning calorimetry; Fluorescence resonance energy transfer; Fusion
Bovine serum albumin-directed synthesis of biocompatible CdSe quantum dots and bacteria labeling
by Qisui Wang; Fangyun Ye; Tingting Fang; Wenhan Niu; Peng Liu; Xinmin Min; Xi Li (pp. 9-14).
Preparation of BSA-Conjugated CdSe QDs through (a) our simple, one-pot, and “green” synthetic route and (b) the conventional and complex step method.Display Omitted► CdSe QDs were prepared by using a common protein (bovine serum albumin). ► An interesting mechanism was discussed for the formation of the BSA-CdSe QDs. ► There might be conjugated bonds between QDs and -OH, -NH and -SH groups in BSA. ► FL imaging suggests that the QDs we designed can successfully label E. coli cells.A simple method was developed for preparing CdSe quantum dots (QDs) using a common protein (bovine serum albumin (BSA)) to sequester QD precursors (Cd2+) in situ. Fluorescence (FL) and absorption spectra showed that the chelating time between BSA and Cd2+, the molar ratio of BSA/Cd2+, temperature, and pH are the crucial factors for the quality of QDs. The average QD particle size was estimated to be about 5nm, determined by high-resolution transmission electron microscopy. With FL spectra, Fourier transform infrared spectra, and thermogravimetric analysis, an interesting mechanism was discussed for the formation of the BSA–CdSe QDs. The results indicate that there might be conjugated bonds between CdSe QDs and –OH, –NH, and –SH groups in BSA. In addition, fluorescence imaging suggests that the QDs we designed can successfully label Escherichia coli cells, which gives us a great opportunity to develop biocompatible tools to label bacteria cells.
Keywords: Protein; CdSe; Quantum dots; Fluorescence; Bacteria labeling
Fine tuning of the morphology of copper oxide nanostructures and their application in ambient degradation of methylene blue
by Mingqing Yang; Junhui He (pp. 15-22).
Flower-like, boat-like, plate-like and ellipsoid-like CuO nanostructures were fabricated by simple modulation of reaction conditions. The as-prepared CuO nanostructures all show good catalytic activity by catalytic oxidation of MB.Display Omitted► Flower-like, boat-like, plate-like and ellipsoid-like CuO nanostructures were obtained by simple modulation of reactants and the time and temperature of hydrothermal treatment. ► The simple synthetic methods reported in this work allow large scale fabrication of CuO nanostructures with flexibility in morphological and dimensional control. ► The catalytic performance of as-prepared CuO products in the oxidation of MB was studied in presence of H2O2. All the obtained CuO nanostructures showed good catalytic activity in the degradation of aqueous MB.In this work, flower-like, boat-like, plate-like and ellipsoid-like copper oxide (CuO) nanostructures were fabricated by simple modulation of reaction conditions. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, nitrogen adsorption–desorption measurements and UV–visible diffuse reflectance spectra were employed to characterize the obtained CuO nanostructures. Reactants, hydrothermal temperature and time were found to largely affect the morphology and structure of CuO nanostructures. Flower-like and boat-like CuO nanostructures were successively fabricated by increasing hydrothermal time. Plate-like and ellipsoid-like CuO nanostructures were produced by modulating the use of polyethylene glycol (PEG) and NH3·H2O. The formation mechanisms were proposed based on the experimental results, which show that both PEG and NH3·H2O play an important role in the formation of the morphology and structure of CuO. The catalytic activity of the as-prepared CuO nanostructures was demonstrated by catalytic oxidation of methylene blue (MB) in presence of hydrogen peroxide (H2O2). The as-prepared CuO nanostructures all show good catalytic activity.
Keywords: Copper oxide; Nanostructure; Polyethylene glycol; Hydrothermal treatment; Catalytic activity
Thioether-functionalized mesoporous fiber membranes: Sol–gel combined electrospun fabrication and their applications for Hg2+ removal
by Minmin Teng; Hongtao Wang; Fengting Li; Bingru Zhang (pp. 23-28).
Mesoporous PVP/SiO2 composite nanofiber membranes functionalized with thioether groups have been fabricated. The membranes exhibited excellent performance in removing Hg2+ ions in aqueous solutions..Display Omitted► Thioether-functionalized fiber membranes were fabricated, which have large surface area due to the mesostructure. ► The nanofibrous membranes exhibited highly selective and capacious adsorption of Hg2+ attributed to the presence of thioether groups. ► The membranes showed good recycling properties.Mesoporous polyvinylpyrrolidone (PVP)/SiO2 composite nanofiber membranes functionalized with thioether groups have been fabricated by a combination method of sol–gel process and electrospinning. The precursor sol was synthesized by one-step co-condensation of tetraethyl orthosilicate (TEOS) and 1,4-bis(triethoxysilyl)propane tetrasulfide (BTESPTS, (CH3CH2O)3Si(CH2)3S–S–S–S(CH2)3Si–(OCH2CH3)3), with the triblock copolymer poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (P123, EO20PO70EO20) as template. After the addition of PVP, nanofiber membranes were prepared by electrospinning. The membranes were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) images, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N2 adsorption–desorption isotherms, and an Elementar Vario EL analyzer. The composites were used as highly selective adsorbents for Hg2+ due to the modification with thioether groups (–S–), and were conveniently separated from the waste water. The composite could be regenerated through acidification.
Keywords: Electrospinning; Sol–gel; Mesoporous; Membrane; Heavy metal removal
Preparation of polydiacetylene immobilized optically encoded beads
by Bong-Hyun Jun; Jongho Baek; Homan Kang; Young June Park; Dae Hong Jeong; Yoon-Sik Lee (pp. 29-34).
PDA immobilized encoded beads (PDA–SERS beads, PDA–FL beads) which have their encoding capacity and PDA properties, which cause their optical properties to be changed, are prepared.Display Omitted► A novel PDA immobilization method for optically encoded micro beads which have their encoding capacity and PDA properties was developed. ► Their optical properties of PDA immobilized encoded beads, which can be changed their property by external stress, was studied. ► The immobilization methods was successfully applied to SERS-encoded beads and proven to also be useful in fluorescence encoding systems.Polydiacetylene (PDA), which can change the chromic and fluorescence properties by inducing environmental perturbations, is immobilized on planar solid supports for many biological applications. In this work, we immobilize PDA onto optically encoded spherical beads (PDA–SERS beads). The prepared PDA immobilized beads (36μm) exhibit a blue color without fluorescence. By inducing stress, their color and fluorescence properties are changed to red with fluorescence. The SERS spectra of the PDA–SERS beads can be recognized over the PDA background. Moreover, our PDA immobilization methods are successfully applied to silica-surface SERS-encoded beads (5μm) and proven to also be useful in fluorescence encoding systems.
Keywords: Polydiacetylene; Silver nanoparticles; Surface-enhanced Raman scattering; Optically encoded bead
Solvothermal synthesis of InP quantum dots and their enhanced luminescent efficiency by post-synthetic treatments
by Ho-June Byun; Ju Chul Lee; Heesun Yang (pp. 35-41).
InP QDs grown solvothermally with a safer, cheaper P source of P(N(CH3)2)3 were overcoated with a ZnS shell, exhibiting a wide spectral widow and high QYs.Display Omitted► InP QDs were solvothermally synthesized by using a greener P source of P(N(CH3)2)3. ► As-grown InP QDs were finely size-sorted. ► Highly efficient InP QDs with a wide spectral window were obtained.InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH3)2)3 instead of highly toxic P(TMS)3 widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)3. Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure.
Keywords: InP quantum dots; Greener phosphorus source; Solvothermal; Photo-etching; Photo-radiation; Core/shell
Effect of repulsive interactions on the rate of doublet formation of colloidal nanoparticles in the presence of convective transport
by Marco Lattuada; Massimo Morbidelli (pp. 42-53).
Normalized doublet formation rate of colloidal nanoparticles as a function of Pe number in the presence of an extensional flow field, for different surface potential values..Display Omitted► Repulsive interactions effect colloidal doublet formation rate with convection. ► Sharp transition between interaction and convection-controlled regimes. ► Sedimentation and extensional flow show qualitatively similar behaviors. ► A simplified model can quantitatively predict the rigorous calculations results.In this work, we have performed a systematic investigation of the effect of electrostatic repulsive interactions on the aggregation rate of colloidal nanoparticles to from doublets in the presence of a convective transport mechanism. The aggregation rate has been computed by solving numerically the Fuchs–Smoluchowski diffusion–convection equation. Two convective transport mechanisms have been considered: extensional flow field and gravity-induced relative sedimentation. A broad range of conditions commonly encountered in the applications of colloidal dispersions has been analyzed. The relative importance of convective to diffusive contributions has been quantified by using the Peclet number Pe. The simulation results indicate that, in the presence of repulsive interactions, the evolution of the aggregation rate as a function of Pe can always be divided into three distinct regimes, no matter which convective mechanism is considered. At low Pe values the rate of aggregation is independent of convection and is dominated by repulsive interactions. At high Pe values, the rate of aggregation is dominated by convection, and independent of repulsive interactions. At intermediate Pe values, a sharp transition between these two regimes occurs. During this transition, which occurs usually over a 10–100-fold increase in Pe values, the aggregation rate can change by several orders of magnitude. The interval of Pe values where this transition occurs depends upon the nature of the convective transport mechanism, as well as on the height and characteristic lengthscale of the repulsive barrier. A simplified model has been proposed that is capable of quantitatively accounting for the simulations results. The obtained results reveal unexpected features of the effect of ionic strength and particle size on the stability of colloidal suspensions under shear or sedimentation, which have relevant consequences in industrial applications.
Keywords: Doublet formation rate; Shear-induced aggregation; Extensional flow; Sedimentation; Kernel; DLVO interactions; Fuchs stability ratio; Collision efficiency
Morphological control of CaCO3 films with large area: Effect of additives and self-organization under atmospheric conditions
by Kyu-Bock Lee; Seung-Bin Park; Young-Nam Jang; Seung-Woo Lee (pp. 54-60).
This figure shows schematic illustration for the formation of hierarchically organized CaCO3 film. The morphology control of CaCO3 film depends on a kind of additives.Display Omitted► Hierarchically structured CaCO3 films are synthesized at atmospheric conditions (room temperature and 1atm). ► The building blocks of the CaCO3 film are assembled with alignment and built into higher levels of structures. ► The soluble additives play a key role on the morphological control of CaCO3 film.Hierarchically structured CaCO3 films were synthesized at atmospheric conditions (room temperature and 1atm) without the use of templates or amphiphilic molecules in this process. The resulting CaCO3 film was formed by self-organization between Ca(OH)2 and aqueous CO2. The building blocks of the CaCO3 film were thought to be CaCO3 primary nanoparticles that aligned to build higher level structures with greater size, called mesocrystals, depending on the additives. The soluble additives played a key role in the control of the morphology, crystallinity, and polymorphism of the CaCO3 film, and the effects strongly depended on the type of additive and their concentrations. The additives used in this study decreased the crystallinity of CaCO3 (calcite) film in the order of glucose>aspartic acid>serine in a manner inversely proportional to the concentration of the additives. In addition, Mg2+, K+, and Na+ ion additives led to the formation of an aragonite phase, the proportion of which increased with the concentration of ions. The threshold concentrations of these ions for the formation of the aragonite phase in CaCO3 film were found to be in the order of Na+>K+>Mg2+.
Keywords: Morphology control; Self-organization; Hierarchical structure; CaCO; 3; Thin film; Additive effect
Hydrogen-bonded layer-by-layer films of block copolymer micelles with pH-responsive cores
by Irem Erel; Zhichen Zhu; Aliaksandr Zhuk; Svetlana A. Sukhishvili (pp. 61-69).
Polymer micelles with pH-responsive cores are incorporated into hydrogen-bonded films. Dissolution of a monolayer of polymer micelles occured at moderately acidic pH, while coating monolayers with polyacids inhibited the pH-triggered dissolution of micellar cores.Display Omitted► Polymer micelles with pH-responsive cores are incorporated into hydrogen-bonded films. ► Dissolution of a monolayer of polymer micelles occured at moderately acidic pH. ► Coating the micellar monolayers with polyacids inhibited the pH-triggered dissolution of micellar cores.We report on construction of hydrogen-bonded monolayers and multilayers of micelles of the poly(2-(diethylamino)ethyl methacrylate)- block-poly(N-isopropyl acrylamide) (PDEA- b-PNIPAM) with PNIPAM-corona and polybasic PDEA cores. Films were constructed at pH 7.5 and 25°C to assure the deposition of PDEA- b-PNIPAM in the micellar form. When monolayers of block copolymer micelles (BCMs) were exposed to moderately acidic pH values, micellar cores dissolved, while PDEA- b-PNIPAM remained adsorbed at the surface as unimers. In contrast to reversible micellization of PDEA- b-PNIPAM in solution, micelle-to-unimer transition was irreversible at the surface. Adsorption of a layer of tannic acid (TA) or polyethacrylic acid (PEAA) on top of BCM monolayers inhibited pH-triggered morphological changes within adsorbed BCMs. By taking advantage of the high p Ka values of TA and PEAA, we were also able to construct multilayers of PDEA- b-PNIPAM micelles through hydrogen bonding interactions between micellar PNIPAM coronas and TA or PEAA. Similar to BCM monolayers coated with TA or PEAA, dissolution of BCMs was also inhibited when incorporated within hydrogen-bonded multilayers. Such inhibition of dissolution is due to enhanced hydrogen bonding interactions between coronal PNIPAM chains and protonated TA molecules or PEAA chains at decreasing pH values restricting the pH-induced conformational changes of the micellar core chains within the adsorbed layer. Films of responsive BCMs are attractive coatings for controlled delivery of functional molecules from surfaces due to a combination of stimuli-response properties with the relatively high loading capacity for functional molecules.
Keywords: Self-assembly; Block copolymer micelles; Layer-by-layer; Multilayers; Hydrogen bonding; pH-responsive
The synthesis of silica and silica–ceria, core–shell nanoparticles in a water-in-oil (W/O) microemulsion composed of heptane and water with the binary surfactants AOT and NP-5
by Sang-Ho Chung; Dae-Won Lee; Min-Sung Kim; Kwan-Young Lee (pp. 70-75).
The silica–ceria, core–shell nanoparticles were synthesized in a water-in-oil microemulsion using the binary surfactants (AOT and NP-5). Two strategies were considered: (1) amine modification of the core silica surface and (2) deposition of the ceria through semi-batch precipitation.Display Omitted► The core-shell SiO2-CeO2 nanoparticles were prepared with microemulsion method. ► The surface precipitation of ceria was promoted by following strategies: ► (1) Chemically modification of the silica surface with organoamine group; ► (2) Controlled precipitation of ceria under semi-batch operation.In this study, a strategy was developed for the synthesis of nano-sized, silica–ceria, core–shell composites in a water–oil (W/O) microemulsion consisting of water, heptane and the binary surfactants AOT (sulfosuccinic acid bis (2-ethylhexyl) ester sodium salt) and NP-5 (polyoxyethylene (5) nonylphenyl ether). The core–shell, silica–ceria particles were prepared in a stepwise procedure: (1) the precipitation of the core-silica particles in a W/O microemulsion and (2) the surface precipitation of ceria on the core silica dispersed over the microemulsion. The composition of the binary surfactant greatly influenced the growth rate of the core-silica particles. The virial coefficient of diffusion was utilized to estimate the effect of the surfactant composition on the degree of intermicellar interaction that is important for the growth rate of the silica along with the flexibility of the micellar interface and the structure of the water domain. The deposition of the ceria on the core silica was not straightforward because the bulk and surface precipitation competed with each other. The promotion of surface precipitation was attempted by: (1) chemically modifying the silica surface with an organoamine group and (2) slowing down the precipitation rate of the ceria in a semi-batch operation. These attempts successfully produced the nano-sized silica–ceria, core–shell particles, which were evidenced through the TEM, XPS and zeta potential analysis.
Keywords: Microemulsion; Core–shell structure; Nanoparticles; Silica; Silica–ceria
Novel antifouling oligo(ethylene glycol) methacrylate particles via surfactant-free emulsion polymerization
by Fatih Buyukserin; Sevket Tolga Camli; Mustafa Selman Yavuz; Gurer Guven Budak (pp. 76-80).
Cross-linked PEGEEM colloids that display novel antifouling surface properties are introduced. A simple surfactant-free emulsion polymerization is used to prepare monodisperse cross-linked particles which were characterized by DLS and TEM.Display Omitted► PEGEEM colloids with novel antifouling surface properties is reported for the first time. ► Surfactant-free emulsion polymerization was used to prepare monodisperse crosslinked particles. ► A prominent blockage of BSA adsorption was obtained for the PEG-based sub-micron colloids.The use of particle formulations with antifouling surface properties attracts increasing interest in several biotechnological applications. Majority of these studies utilize a poly(ethylene glycol) coating to render the corresponding surface nonrecognizable to biological macromolecules. Herein, we report a simple way to prepare novel antifouling colloids composed of oligo(ethylene glycol) backbones via surfactant-free emulsion polymerization. Monodisperse cross-linked poly(ethylene glycol) ethyl ether methacrylate particles were characterized by dynamic light scattering and transmission electron microscopy. The effects of monomer, cross-linker and initiator on particle characteristics were investigated. More importantly, a prominent blockage of bovine serum albumin adsorption was obtained for the poly(ethylene glycol)-based sub-micron (∼200nm) particles when compared with similar-sized poly(methyl methacrylate) counterparts.
Keywords: Poly(ethylene glycol) ethyl ether methacrylate; Cross-linked; Surfactant-free emulsion polymerization; Antifouling; Albumin adsorption
Comparison between measurements of elasticity and free amino group content of ovalbumin microcapsule membranes: Discrimination of the cross-linking degree
by T.X. Chu; A.-V. Salsac; E. Leclerc; D. Barthès-Biesel; H. Wurtz; F. Edwards-Lévy (pp. 81-88).
The inverse correlation found between the shear modulus ( G s) and free amino group (NH2) content proves that the mechanical properties of ovalbumin microcapsules are governed by the reticulation process.Display Omitted► Comparison of mechanical and chemical characterization of ovalbumin capsules. ► Mechanical properties independent of pH for small reticulation times (pH⩽7.4). ► The shear modulus increases with the time of reticulation. ► Inverse method for mechanical characterization discriminates degrees of reticulation.An inverse method is used to characterize the membrane mechanical behavior of liquid filled microcapsules. Cross-linked ovalbumin microcapsules are flowed and deformed into a cylindrical microchannel of comparable size. The deformed shape is compared to predictions obtained numerically when modeling a capsule under the same flow conditions. The unknown shear modulus value corresponds to the best fit. The degree of reticulation is estimated in parallel by determining the free amino groups remaining on the microcapsules after the cross-linking reaction. We characterize microcapsule populations fabricated at different reaction pH (5–8) and times (5–30min) to study different cross-linking degrees. The capsule shear modulus and the amino groups are nearly constant with the reaction pH for the capsules fabricated after 5min of reticulation. The shear modulus increases with the reaction time, while the NH2 content decreases with it. A global increase in shear modulus with pH is also observed, together with an unexpected increase in NH2 content. The study shows that the inverse method is capable of discriminating between various cross-linking degrees of microcapsules. Moreover, for this type of microcapsules, the mechanical method appears more reliable than the chemical one to obtain an estimation of their cross-linking degree.
Keywords: Mechanical properties; Inverse analysis; Microcapsule population; Microfluidic technique; Cross-linking degree
The fabrication of one-dimensional Ca4Y6(SiO4)6O: Ln3+ (Ln=Eu, Tb) phosphors by electrospinning method and their luminescence properties
by Chong Peng; Guogang Li; Xiaojiao Kang; Chunxia Li; Jun Lin (pp. 89-95).
Under ultraviolet excitation, one-dimensional Ca4Y6(SiO4)6O: Ln3+ (Ln=Eu, Tb) microfibers fabricated by electrospinning method show the red and green emission, respectively.Display Omitted► One-dimensional Ca4Y6(SiO4)6O: Ln3+ (Ln=Eu, Tb) microfibers were fabricated by a simple and cost-effective electrospinning method. ► Under ultraviolet and low-voltage electron beams (3–5kV) excitation, the Ca4Y6(SiO4)6O: Ln3+ (Ln=Eu, Tb) samples show the red and green emission, corresponding to5D0→7F2 transition of Eu3+ and5D4→7F5 transition of Tb3+, respectively. ► The intensity of the cathodoluminescence emissions of Ca4Y6(SiO4)6O: Tb3+ microfibers from5D3→7F J ( J=4 and 5) of Tb3+ increases compared with the photoluminescence emissions.One-dimensional Ca4Y6(SiO4)6O: Ln3+ (Ln=Eu, Tb) microfibers were fabricated by a simple and cost-effective electrospinning method. X-ray diffraction (XRD) pattern and high-resolution transmission electron microscopy (HRTEM) confirmed that the fibers were composed of hexagonal Ca4Y6(SiO4)6O phase. Thermogravimetric and differential scanning calorimetry (TG–DSC) results showed that the Ca4Y6(SiO4)6O phase began to crystallize at 740°C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results indicated that the diameter of as-prepared microfibers ranged from 390 to 900nm and the diameter of the microfibers annealed at 1000°C ranged from to 120 to 260nm. Under ultraviolet and low-voltage electron beams (3–5kV) excitation, the Ca4Y6(SiO4)6O: Ln3+ (Ln=Eu, Tb) samples showed the red and green emission, corresponding to5D0→7F2 transition of Eu3+ and5D4→7F5 transition of Tb3+, respectively.
Keywords: Luminescence; Electrospinning; Europium; Terbium; Ca; 4; Y; 6; (SiO; 4; ); 6; O
Flocculation kinetics and aggregate structure of kaolinite mixtures in laminar tube flow
by Farid Vaezi G.; R. Sean Sanders; Jacob H. Masliyah (pp. 96-105).
Evolution of aggregate size in two-staged flocculation process.Display Omitted► Kinetics of two-stage flocculation of kaolin. ► Laminar tube flow tube allows for realistic estimation of the shear rate. ► Direct sampling minimizes the effect of sampling on the aggregate structure. ► Aggregate structure and aggregate density evolution are monitored. ► Aggregates with statistically reproducible and well defined structure are produced.Flocculation is commonly used in various solid–liquid separation processes in chemical and mineral industries to separate desired products or to treat waste streams. This paper presents an experimental technique to study flocculation processes in laminar tube flow. This approach allows for more realistic estimation of the shear rate to which an aggregate is exposed, as compared to more complicated shear fields (e.g. stirred tanks). A direct sampling method is used to minimize the effect of sampling on the aggregate structure. A combination of aggregate settling velocity and image analysis was used to quantify the structure of the aggregate. Aggregate size, density, and fractal dimension were found to be the most important aggregate structural parameters. The two methods used to determine aggregate fractal dimension were in good agreement. The effects of advective flow through an aggregate’s porous structure and transition-regime drag coefficient on the evaluation of aggregate density were considered.The technique was applied to investigate the flocculation kinetics and the evolution of the aggregate structure of kaolin particles with an anionic flocculant under conditions similar to those of oil sands fine tailings. Aggregates were formed using a well controlled two-stage aggregation process. Detailed statistical analysis was performed to investigate the establishment of dynamic equilibrium condition in terms of aggregate size and density evolution. An equilibrium steady state condition was obtained within 90s of the start of flocculation; after which no further change in aggregate structure was observed. Although longer flocculation times inside the shear field could conceivably cause aggregate structure conformation, statistical analysis indicated that this did not occur for the studied conditions. The results show that the technique and experimental conditions employed here produce aggregates having a well-defined, reproducible structure.
Keywords: Flocculation; Laminar flow; Oil sands tailings; Aggregate structure; Density; Porous flocs
Langmuir–Blodgett films composed of amphiphilic double-decker shaped polyhedral oligomeric silsesquioxanes
by Asuman C. Kucuk; Jun Matsui; Tokuji Miyashita (pp. 106-114).
Langmuir–Blodgett films of polyhedral oligomeric silsesquioxanes (POSSs) with well-defined structures were prepared using newly synthesized amphiphilic POSSs.Display Omitted► Novel amphiphilic double-decker shape oligomeric silsesquioxane (DDSQs) were synthesized. ►The amphiphilic DDSQs formed stable monolayers at the air–water interface. ► Deposited monolayers showed different morphology depending on the surface nature of a substrate.New amphiphilic polyhedral oligomeric silsesquioxanes (POSSs) were synthesized, and their monolayer behavior on a water surface and Langmuir–Blodgett (LB) film formation were studied. Two kinds of amphiphilic POSS molecules, which have two or four di(ethylene glycol) units (2OH-DDSQ and 4OH-DDSQ, respectively), were synthesized by direct hydrosilylation of di(ethylene glycol) vinyl ether with double-decker shaped polyhedral oligomeric silsesquioxanes (DDSQs). Surface pressure ( π)–area ( A) isotherms and Brewster angle microscope (BAM) measurements indicated that both amphiphilic DDSQs form a stable monolayer at the air–water interface. In addition, 4OH-DDSQ can be deposited on a solid substrate by the LB technique. Atomic force microscope (AFM) images of a one-layer 4OH-DDSQ film showed a homogenous uniform surface on a hydrophilic silicon substrate, whereas nanometer scale dots were formed on a hydrophobic silicon substrate. Multilayer deposition on a hydrophobic substrate resulted in an increase of dot size with increasing deposition number of layers. Moreover, homogenous multilayer films with a few voids were obtained on a hydrophilic substrate. The results indicate that 4OH-DDSQ is a good candidate for preparing hybrid nanoassemblies.
Keywords: Silsesquioxane; Langmuir–Blodgett film; Hybrid film
Towards nanoscale composite particles of dual complexity
by Claudia Simone Wagner; Samuel Shehata; Katja Henzler; Jiayin Yuan; Alexander Wittemann (pp. 115-123).
Assembly of inorganic and polymer particles into nanoscale composites with full control over shape, composition, and surface roughness.Display Omitted► Complex polymer colloids as carriers for functional nanoparticles. ► Well-defined heterocomposites with high intrinsic complexity. ► Functional sites spread all over the surface of the composites. ► Charge reversal by oppositely charged nanoparticles stabilizes composites. ► Perspectives for sensing applications and as complex ferrofluids.The fabrication of heteroaggregates comprising inorganic and organic nanoparticles of different sizes is reported. Control over the assembly of nanoscale functional building units is of great significance to many practical applications. Joining together different spherical nanoparticles in a defined manner allows control over the shape of the composites. If two types of constituents are chosen that differ in size, the surfaces of the composites exhibit two specific radii of curvature, yielding aggregates of dual surface roughness. Moreover, if the constituents consist of different materials, the resulting heteroaggregates feature both compositional and interfacial anisotropy, offering unprecedented perspectives for custom-tailored colloids. This study describes a two-step approach towards such designer particles. At first, amine-modified polystyrene particles with 154nm diameter were assembled into clusters of well-defined configurations. Onto these, oppositely charged inorganic particles with diameters of only a few nanometres were deposited by direct uptake from solution, resulting in numerous functional entities all over the surface of the polymer clusters. Despite the fact that oppositely charged constituents are brought together, charge reversal by uptake of nanoparticles allows for stable suspensions of heterocomposites. Hence, the possibility to assemble particles into nanoscale heterocomposites with full control over shape, composition, and surface roughness is demonstrated.
Keywords: Nanocomposites; Hybrids; Raspberry particles; Nanoparticle adsorption; Superparamagnetic particles
Interfacial water with special electron donor properties: Effect of water–surfactant interaction in confined reversed micellar environments and its influence on the coordination chemistry of a copper complex
by Diana Blach; N. Mariano Correa; Juana J. Silber; R. Darío Falcone (pp. 124-130).
The Figure shows the initial Cu complex structure and how the electron donor ability of the entrapped water can be significantly altered depending on the kind of surfactant used to prepare the reverse micelles media.Display Omitted► The behavior of the complex [Cu(acac)(tmen)]+ was studied in benzene/AOT RMs as well as in benzene/BHDC RMs. ► At low W0, the water sequestrated by BHDC RMs is unable to act as an electron donor. ► The water electron donor ability in AOT RMs is remarkable enhanced in comparison with the BHDC RMs. ► We challenge the general idea that the properties of water entrapped in RMs depend only on confinement. ► The unique properties of RM interfaces can modify the coordination chemistry of sensitive metal complex.In this work, we have investigated the behavior of the square-planar mixed-ligand transition-metal complex N, N, N′, N′-tetramethylethylenediamine copper (II) acetylacetonate tetraphenylborate, [Cu(acac)(tmen)][B(C6H5)4], in anionic benzene/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs) as well as in cationic benzene/benzyl- n-hexadecyl dimethylammonium chloride (BHDC) RMs with and without water, using absorption spectroscopy. In the absence of water, W0=[H2O]/[surfactant]=0, our results show that the Cu complex structures are not the same in both reversed micellar media. In the BHDC RMs, due to the Cl− counterion present in the system, the Cu complex structure that exists at the interface is the neutral [Cu(acac)(tmen)(Cl)]. In contrast, in AOT RMs the surfactant sulfonate anion cannot act as a ligand and therefore the complex structure is square planar [Cu(acac)(tmen)]+. When water is added to both reversed micellar systems, different situations are observed. At low water content, the water sequestrated by BHDC RMs is unable to act as electron donor because the oxygen nonbonding electron pairs are completely involved in the cationic BHDC polar head group solvation through an ion–dipole interaction. On the contrary, in AOT RMs the results suggest that since the water molecules solvate the sulfonate group through hydrogen bonding interactions, the bulk hydrogen bond network is destroyed at the interface and therefore, the nonbonding electron pairs are more available to interact with the Cu complex. Thus, the electron donor ability of water in AOT RMs is enhanced in comparison with the BHDC RMs and bulk water, giving a remarkable electron donor character to the AOT reversed micellar interfacial water.
Keywords: Aqueous reverse micelles; Electron donor ability; AOT; BHDC; Copper complex; Coordination chemistry
Role of added counterions in the micellar growth of bisquaternary ammonium halide surfactant (14- s-14):1H NMR and viscometric studies
by Umme Salma Siddiqui; Farah Khan; Iqrar Ahmad Khan; Aijaz Ahmad Dar; Kabir-ud-Din (pp. 131-139).
Representative plots of line width at half height of the1H NMR signal corresponding to the –N+CH3 group of geminis at 25°C.Display Omitted► The interaction of salts (inorganic and organic) with cationic gemini micelles. ► Surfactant properties are improved through synergism when used in presence of additives. ► The magnitude and nature of salts as well as the mechanism involved are studied. ► The transition of different aggregate morphologies by addition of salts may be applied in the fields of natural sciences, surface chemistry, bioengineering.The change in the morphology of a series of dicationic gemini surfactants C14H29(CH3)2N+−(CH2) s−N+(CH3)2C14H29, 2Br− (14- s-14; s=4–6) on their interaction with inorganic (KBr, KNO3, KSCN) and organic salts (NaBenz, NaSal) have been thoroughly investigated by means of1H NMR spectral analysis and the results are well supported by viscosity measurements. The presence of salt counterions results in structural transition (spherical to nonspherical) of gemini micelles in aqueous solution. With an increase in salt concentration all the three gemini surfactants showed changes in their aggregate morphology. This change is dependent on the nature and size of the added counterion. The effect of inorganic counterions on the micellar growth is observed to follow the Hofmeister series (Br-− than Benz−. The results are confirmed in terms of the obtained values of chemical shift ( δ), line width at half height ( lw), and relative viscosity (η r). Also, the growth of micelles was most pronounced for the gemini surfactant with the shortest spacer ( s=4). This was attributed to the unique molecular structure of gemini surfactant micelles having flexible polymethylene spacer chain linking the twin polar headgroups.
Keywords: Gemini surfactant; Salt counterions; Relative viscosity; Line width; 1; H NMR; Viscosity
Effects of surfactant micelles on solubilization and DPPH radical scavenging activity of Rutin
by Oyais Ahmad Chat; Muzaffar Hussain Najar; Mohammad Amin Mir; Ghulam Mohammad Rather; Aijaz Ahmad Dar (pp. 140-149).
We report herein the correlation between the interaction of Rutin with different surfactant systems and its antioxidant activity against DPPH.Display Omitted► Evaluation of solubilization characteristics of Rutin and DPPH in micellar media. ► Evaluation of antioxidant activity of Rutin against DPPH in the micellar media. ► Correlation between the solubilization and antioxidant activity results. ► Cationic surfactants were efficient solubilizers for both Rutin and DPPH. ► Cationic- nonionic systems enhanced the activity over their single counterparts.The interaction of the antioxidant Rutin with the radical DPPH (2,2-diphenyl-1-picrylhydrazyl) in presence of cationic (CTAB, TTAB, DTAB), non-ionic (Brij78, Brij58, Brij35), anionic (SDS) and mixed surfactant systems (CTAB-Brij58, DTAB-Brij35, SDS-Brij35) has been followed by spectrophotometric and tensiometric methods to evaluate the DPPH radical scavenging activity (RSA) of Rutin in these model self-assembled structures. The results show that the solubilization capacity of various single surfactant systems for both DPPH as well as Rutin followed the order cationics>non-ionics>anionic. The radical scavenging activity of Rutin in the solubilized form was higher within ionic micelles than in non-ionic micelles. However, the antioxidant exhibited enhanced activity for the radical in mixed cationic–non-ionic micelles compared with any of the single component micelles. In contrast, anionic–non-ionic mixed micelles modulated the activity of Rutin in-between that seen for pure anionic and non-ionic micelles only.
Keywords: Radical scavenging activity; Rutin; Micelles; DPPH; Solubilization
Partition coefficients of nonionic surfactants in water/ n-alkane systems
by G. Catanoiu; E. Carey; S.R. Patil; S. Engelskirchen; C. Stubenrauch (pp. 150-156).
This study presents the determination of and the discussion over the water/ n-alkane partition coefficients Kp of nonionic surfactants for various n-alkanes, namely n-hexane, n-octane, n-decane and n-dodecane.Display Omitted► Partition coefficients Kp of nonionic surfactants increase with increasing alkyl chain length of the surfactant. ► Kp of nonionic surfactants increases with decreasing chain length of the n-alkane. ► Kp of nonionic surfactants in water/ n-alkane were found to increase in the order β-CnGm<nDMPO<iEj. ► For technical and pure surfactants similar trends for Kp but different equilibration times were observed..In water/oil systems, surfactants partition between the water phase and the oil phase according to their solubility in both phases. The ratio between the concentration of the surfactant in the oil phase and in the water phase at equilibrium is known as the partition or distribution coefficient ( Kp). The partition coefficient ( Kp) is an important fundamental parameter essential to understanding and controlling phenomena in water–oil-surfactant systems under both equilibrium and non-equilibrium conditions. In the present work we report on the partitioning of three different classes of nonionic surfactants in the pre-cmc regime, namely polyoxyethylene alkyl ethers (C iE j), alkyl dimethyl phosphine oxides (C nDMPO) and alkyl glycosides (β-C nG m) between water and different n-alkanes. We focus on the influence of the surfactant’s molecular structure (alkyl chain length, head group size and type), and oil chain length on Kp to derive systematic structure–property relationships. Moreover, we discuss the influence of the surfactant purity on partition coefficients of technical grade alkyl glycosides and polyoxyethylene alkyl ethers, respectively.
Keywords: Partition coefficient; Water and oil solubility; Polyoxyethylene alkyl ether; Alkyl dimethyl phosphine oxide; Alkyl glycoside; Technical grade surfactants
Effect of temperature on pseudoternary system Tween-80–butanol–hexane–water
by Partha Mukherjee; Susanta Kumar Padhan; Sukalyan Dash; Sabita Patel; Prasanta Kumar Mohapatra; Bijay Kumar Mishra (pp. 157-163).
With increase in temperature, pseudoternary mixtures of Tween-80, butanol, hexane and water are transformed into a turbid system, which separates into three different transparent phases.Display Omitted► A large Winsor IV domain consisting of micelles, reversed micelles and microemulsions. ► Addition of sodium chloride leads to formation of liquid crystalline phase.► A quantitative cloud point-composition relationship is established. ► On heating mass transfer in turbid system leads to appearance of three phases. ► Preconcentration of organic and inorganic solutes could be achieved.Phase diagrams of pseudoternary systems of Tween-80, butanol, hexane and water were constructed by a visual titration method. The cloud points (CPs) at various compositions were determined and the variations in the cloud points were analyzed on the basis of changes in the composition of the different components in the microemulsions. A quantitative model was established by using multiple regression analysis considering weight percent of emulsifier (surfactant+cosurfactant) and oil as independent variables. A lowering in the CP with increase in emulsifier content and decrease in oil content was observed. Addition of sodium chloride also depressed the CP significantly. Further, with the increase in temperature the turbid phase started separating to three different transparent zones. The upper layer was recognized as the oil-rich phase, middle layer was due to microemulsion and the lower layer was found to be a micellar system. Metal ions and colored organic substrates partitioned into these different phases, which provides scope for applications in metal ion preconcentration.
Keywords: Microemulsion; Cloud point; Phase behavior; Preconcentration; Tween-80
Self-aggregation and antimicrobial activity of imidazolium and pyridinium based ionic liquids in aqueous solution
by Anna Cornellas; Lourdes Perez; Francesc Comelles; Isabel Ribosa; Angeles Manresa; M. Teresa Garcia (pp. 164-171).
Long-chain imidazolium and pyridinium ionic liquids show surfactant-like properties in aqueous solution and display antimicrobial activity which increases with the alkyl chain length.Display Omitted► Long-chain imidazolium and pyridinium ionic liquids show surfactant-like behaviour. ► Similar polarity of methylimidazolium and pyrdidinium headgroups in aqueous solution. ► Long-chain imidazolium and pyridinium ionic liquids display antimicrobial activity. ► Antimicrobial activity increases with the ionic liquid alkyl chain length.Two series of long-chain imidazolium and pyridinium based ionic liquids (1-alkyl-3-methylimidazolium and 1-alkylpyridinium bromides) were synthesised and the effect of the alkyl chain length and the nature of the cationic head group on micellization and antimicrobial activity of the ionic liquids (ILs) were investigated. Tensiometry, conductometry, spectrofluorimetry and PGSE-NMR were applied to study the self-aggregation of the amphiphilic ILs in aqueous solution. The ILs investigated displayed surface activity and the characteristic chain length dependence of the micellization process of surfactants. The antimicrobial activity was evaluated against Gram-negative and Gram-positive bacteria and fungi. ILs containing more than eight carbon atoms in the alkyl chain showed antimicrobial activity. Their efficiency as antimicrobial agents increased with the hydrophobicity of the amphiphilic cation being the C14 homologous the most active compounds.
Keywords: Long-chain ionic liquid; Surface activity; Micellization; Biological activity
Dynamics of amphiphilic diblock copolymers at the air–water interface
by Antonio Stocco; Klaus Tauer; Stergios Pispas; Reinhard Sigel (pp. 172-178).
The interfacial diffusion and the structure of two polyisoprene-polyethyleneoxide diblock copolymers at the water surface was studied in a semidilute interfacial regime.Display Omitted► Amphiphilic diblock copolymers adsorbed at the interface. ► In plane diffusion measurements by evanescent wave dynamic light scattering. ► Conformational changes in a semi dilute regimes.Two polyisoprene–polyethyleneoxide diblock copolymers with different block length ratios adsorbed to the water surface were investigated by multiple angle of incidence ellipsometry, evanescent wave light scattering, and surface tension experiments. In a semidilute interfacial regime, the transition from a two-dimensional to a “mushroom” regime, in which polymer chains form loops and tails in the subphase, was discussed. A diffusion mechanism parallel to the interface was probed by evanescent wave dynamic light scattering. At intermediate concentrations, the interfacial diffusion coefficient D∥ scales with the surface concentration Γ, as D∥∼ Γ0.77 in agreement with the scaling observed for polymer solutions in a semidilute regime. At relatively high concentrations a decreasing of D∥ is discussed in terms of increasing friction due to interactions between polyisoprene chains.
Keywords: Amphiphilic polymer; Light scattering; Ellipsometry; Diffusion; Air–water interface
Surface chemical modifications induced on high surface area graphite and carbon nanofibers using different oxidation and functionalization treatments
by A.B. Dongil; B. Bachiller-Baeza; A. Guerrero-Ruiz; I. Rodríguez-Ramos; A. Martínez-Alonso; J.M.D. Tascón (pp. 179-189).
The efficiency of the two oxidation treatments studied seems to depend on the morphology (edge to basal plane ratio) of the carbon material.Display Omitted► Two carbon materials with different edge to basal plane ratio are oxidized by nitric acid or oxygen plasma. ► Wet oxidation attacks the C atoms at the edges and oxygen plasma is able to attack both C atoms at the edges and at the basal planes. ► Plasma oxidation seems more adequate for materials with lower edge to basal plane ratio as the CNFs. ► Modification of the oxidized materials with an amine molecule gives rise to materials probably holding ammonium carboxylate salt species.Two graphitic carbon materials with different edge to basal plane ratio, high surface area graphite (HSAG) and graphitized carbon nanofibers (CNFs), were oxidized by two methods, aqueous-HNO3 wet oxidation and oxygen plasma oxidation. Characterization of the materials by temperature-programmed desorption, thermogravimetry and X-ray photoelectron and Raman spectroscopies indicated that the amount and nature of oxygen surface groups introduced depended on the oxidation method and on the structure of the original material. While surface sites within the layers were only oxidized by oxygen plasma, surface sites at the edges of graphene layers were oxidized by both treatments being the wet oxidation more effective. Modification of the oxidized materials with a diamine or a triamine molecule resulted in the formation of ammonium carboxylate salt species on the carbon surface.
Keywords: plasma oxidation; wet oxidation; high surface area graphite; carbon nanofibers
Direct synthesis of acid–base bifunctionalized hexagonal mesoporous silica and its catalytic activity in cascade reactions
by Fanpeng Shang; Jianrui Sun; Shujie Wu; Heng Liu; Jingqi Guan; Qiubin Kan (pp. 190-197).
A series of efficient acid–base bifunctionalized hexagonal mesoporous silica (HMS) catalysts have been synthesized. The novel catalysts possess high activity for cascade reactions.Display Omitted► Acid-base bifunctionalized hexagonal mesoporous silica catalysts. ► Synthesized through protection of amino group. ► Exhibit excellent acid-basic properties. ► Possess high activity for one-pot cascade reactions.A series of efficient acid–base bifunctionalized hexagonal mesoporous silica (HMS) catalysts contained aminopropyl and propanesulfonic acid have been synthesized through a simple co-condensation by protection of amino group. The results of small-angle XRD, TEM, and N2 adsorption–desorption measurements show that the resultant materials have mesoscopic structures. X-ray photoelectron spectroscopies, elemental analysis (EA), back titration,29Si NMR and13C NMR confirm that the organosiloxanes were condensed as a part of the silica framework. The resultant catalysts exhibit excellent acid-basic properties, which make them possess high activity for one-pot deacetalization–Knoevenagel and deacetalization–nitroaldol (Henry) reactions.
Keywords: HMS; Protection of amino group; Acid–base; One-pot cascade reactions
Thiocyanate removal from aqueous solution by a synthetic hydrotalcite sol
by Tao Wu; Dejun Sun; Yujiang Li; Hong Zhang; Fengjuan Lu (pp. 198-203).
The adsorption of thiocyanate on LDHC was consistent with the Langmuir equation and the saturated adsorption capacity of LDHC for thiocyanate was 98.3mg/g at 20°C. Adsorption isotherms of thiocyanate onto LDHC (LDHC dosage 2.0g/L, T=20°C, initial pH 5.5).Display Omitted► Previous research on adsorption of thiocyanate anions in aqueous solution by LDHC is limited. ► LDHC can be used as a new adsorbent for thiocyanate removal from aqueous solution because of its high adsorption capacity and fast adsorption rate. ► The adsorbed thiocyanates on LDHC can be desorbed in FeCl3 solution and the regenerated LDHC can be used repeatedly in adsorption-regeneration cycles.The use of a chloride-containing synthetic hydrotalcite sol (LDHC) as adsorbent to remove thiocyanate from aqueous solution was investigated. LDHC was prepared by coprecipitation and was characterized by HRTEM, particle size, XRD, and FTIR. The experiments showed that LDHC was particularly effective in removing thiocyanate due to its small particle size and high zeta potential. The adsorption of thiocyanate on LDHC was favored when the initial solution pH was in the range 3–10, though the most effective pH range was between 4.0 and 8.0. The adsorption reached equilibrium within 150min. The interaction between the surface sites of LDHC and thiocyanate ions may be a combination of both anion exchange and surface complexation. The pseudo-second-order model best described the adsorption kinetics of thiocyanate onto LDHC. The equilibrium isotherm showed that the adsorption of thiocyanate on LDHC was consistent with the Langmuir equation and the saturated adsorption capacity of LDHC for thiocyanate was 98.3mg/g at 20°C. The regenerated LDHC in FeCl3 solution can be used repeatedly in adsorption–regeneration cycles. The results showed that LDHC can be used as a new adsorbent for thiocyanate removal from aqueous solution because of its high adsorption capacity and rapid adsorption rate.
Keywords: Adsorption; Synthetic hydrotalcite sol; Thiocyanate; Kinetics
Photocatalytic degradation of phenolic syntan using TiO2 impregnated activated carbon
by Udaya Aruldoss; L. John Kennedy; J. Judith Vijaya; G. Sekaran (pp. 204-209).
The anatase phase TiO2 impregnated in activated carbon (Ti-AC) was synthesized. The higher degradation percentage of phenolic syntan was achieved by Ti-AC compared to photolysisDisplay Omitted► A bio-refractory chemical (phenolic syntan) was degraded using Ti-AC. ► The photoactive anatase phase was formed in Ti-AC on heat treatment, confirmed by surface morphological studies. ► The effect of pH, concentration and light intensity were optimized using UV light in the presence and absence of Ti-AC. ► The degradation profile shows that Ti-AC exhibits great influence on phenolic syntan.Investigations were carried out to study the photocatalytic degradation of phenolic syntan (PS), a widely used environmentally polluting chemical in the leather tanning industry. Photocatalytic inactive commercial TiO2 was used as the precursor for the preparation of TiO2 impregnated activated carbon (Ti-AC) photocatalyst. Experiments were conducted by varying the concentrations of PS solution (50–1000mg/l), pH (2.5–10) and time intervals to optimize the working parameters. A 254nm UV light was used throughout the study. The effect of PS degradation using Ti-AC was also compared with direct UV photolysis. The Ti-AC was characterized using X-ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM) and energy dispersive X-ray analysis (EDX) to determine the structural, optical, surface morphology and elemental analysis respectively. X-ray studies revealed the formation of catalytically active anatase phase in Ti-AC. Photodegradation of PS was examined by chemical oxygen demand (COD) method. PS degradation occurred at both the extreme end of acidic and alkaline pH conditions. However, the percentage degradation was comparatively higher at pH 2.5. The photodegradation followed pseudo first order kinetics. UV–Visible studies substantiated the occurrence of bathochromic and hyperchromic effects as a result of ring opening in the PS molecule.
Keywords: Phenolic syntan; Activated carbon; Titanium dioxide; Photolysis; Photocatalyst; Photodegradation
Physico-chemical mechanisms governing the adherence of starch granules on materials with different hydrophobicities
by Jean G. Detry; Marianne Sindic; Marjorie J. Servais; Yasmine Adriaensen; Sylvie Derclaye; Claude Deroanne; Paul G. Rouxhet (pp. 210-221).
Starch adherence depends on the linked effects of soiling suspension spreading, action of capillary forces on drying and dissolved macromolecules acting as adhesive joint.Display Omitted► Multitechnique approach for multifactorial process. ► Substrate hydrophobicity more important than substrate roughness. ► Link hydrophobicity – droplet spreading – aggregate morphology – adherence. ► Rate of drying acts through duration of capillary forces action. ► Dissolved macromolecules create an adhesive joint.The factors influencing the adherence of starch were examined to improve the understanding of the mechanisms affecting soiling and cleanability. Therefore an aqueous suspension of starch granules was sprayed on four model substrates (glass, stainless steel, polystyrene and PTFE) and dried, and the substrates were cleaned using a radial-flow cell. The morphology of the soiled surfaces and the substrate chemical composition were also characterized. By influencing droplet spreading and competition between granule–substrate and granule–granule interfaces regarding the action of capillary forces, substrate wettability affected the shape and compactness of the adhering aggregates, the efficiency of shear forces upon cleaning, and finally the adherence of soiling particles. The rate of drying had an influence explained by the duration left to capillary forces for acting. X-ray photoelectron spectroscopy demonstrated the presence of macromolecules, mainly polysaccharides, which were adsorbed from the liquid phase, or carried by the retracting water film and deposited at the granule–substrate interface. These macromolecules acted as an adhesive joint, the properties of which seemed to be influenced by the detailed history of drying and subsequent exposure to humidity.In summary, the substrate surface energy affects the adherence of starch aggregates by different mechanisms which are all linked together: suspension droplet spreading, action of capillary forces, direct interaction with starch particles and interfacial macromolecules.
Keywords: Radial-flow cell; Soiling; Cleaning; Wettability; Capillary forces; Macromolecules; XPS; Surface roughness
Role of interface in dispersion and surface energetics of polymer nanocomposites containing hydrophilic POSS and layered silicates
by Qi Zhou; K.P. Pramoda; Jong-Min Lee; Kean Wang; Leslie S. Loo (pp. 222-230).
Effect of different nanofillers and morphology on the hydrophilicity of the nanocomposite surfaces.Display Omitted► The degree of enhancement in hydrophilicity of polymer nanocomposite surface depends on both nanofiller type and dispersion state. ► Interfacial interactions in the form of hydrogen bonding play an important role in affecting the dispersion state of the layered silicates. ► Exfoliated layered silicates and aggregated POSS molecules cause a larger increase in surface hydrophilicity than aggregated layered silicates. ► Aggregated POSS molecules also cause significant spreading of water on the surface.Three different hydrophilic nanofillers – natural and synthetic layered silicate as well as octaammonium polyhedral oligomeric silsesquioxane (POSS) – were incorporated into polyamide-6 by a solution-mixing method. The surfaces of the resulting polymer nanocomposites were characterized by X-ray diffraction, polarized optical microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. All polymer nanocomposites displayed enhancement in surface hydrophilicity as well as increase in surface free energy due to surface enrichment of the nanofillers. The degree of enhancement was found to depend on both nanofiller type and dispersion state. Interfacial interactions in the form of hydrogen bonding played an important role in affecting the dispersion state of the layered silicates. Exfoliated layered silicates caused a larger increase in hydrophilicity than aggregated layered silicate. On the other hand, aggregated POSS molecules were able to induce a large increase in hydrophilicity. Significant spreading of water was also observed on surfaces containing POSS molecules. Surface models have been proposed to explain these phenomena.
Keywords: Polymer nanocomposites; Layered silicate; Polyhedral oligomeric silsesquioxane; Surface energy; Interfacial interactions
The effect of alkane tail length of C iE8 surfactants on transport to the silicone oil–water interface
by Nicolas J. Alvarez; Wingki Lee; Lynn M. Walker; Shelley L. Anna (pp. 231-236).
A scaling analysis is used to determine whether dynamic surface tension experiments exhibit diffusion-limited or kinetic-limited transport. If diffusion-limited, the equilibration timescale follows scaling expected for diffusion in a spherical geometry (solid line). If kinetic-limited, the timescale deviates from the diffusion scaling. Identifying when kinetics are relevant aids in correctly analyzing dynamic surface tension data to determine kinetic rate constants.Display Omitted► Scaling arguments determine relevant transport mechanisms for surface tension evolution. ► Diffusion-limited dynamics aid in fitting isotherm parameters. ► Adsorption rate constant decreases with increasing alkane tail length.Detailed surfactant transport studies have typically been restricted to the air–water interface. This is mainly due to the lack of experimental devices and techniques available to study liquid–liquid interfaces. As a result, there is a lack of relevant data and understanding of surfactant behavior in microfluidic studies and emulsion applications. Using a novel shape fitting algorithm for a pendant drop capable of handling fluids of similar densities, i.e. low Bond numbers, we measure the dynamic surface tension as a function of bulk surfactant concentration at the silicone oil–water interface for a homologous series of C iE8 nonionic surfactants. We show that the isotherms governing equilibrium at the oil–water and air–water interfaces are very different. Using a scaling analysis comparing two governing mass transport timescales, we demonstrate that there exists a transition from diffusion-limited to kinetic-limited dynamics at the silicone oil–water interface. Adsorption rate constants are determined from a one parameter nonlinear fit to dynamic surface tension data. These results demonstrate that the dynamics of interfacial transport are highly dependent on the immiscible fluids that form the interface.
Keywords: Dynamic surface tension; Oil–water interfaces; Nonionic surfactants; Adsorption; Transport; Timescales
Hydration of methane intercalated in Na-smectites with distinct layer charge: Insights from molecular simulations
by Qing Zhou; Xiancai Lu; Xiandong Liu; Lihu Zhang; Hongping He; Jianxi Zhu; Peng Yuan (pp. 237-242).
The interlayer methane molecules are solvated by nearly 12–13 water molecules and coordinated with six oxygen atoms from the smectite surface.Display Omitted► Interlayer CH4 can be solvated by 12–13 water molecules and coordinated with 5–6 oxygen atoms from the clay surface. ► Tetrahedral negative charge makes for CH4 hydration in smectite. ► Stability of the interlayer CH4 hydrate follows the order of SWy
Keywords: Methane hydrate; Molecular dynamic simulation; Na-smectite; Nontronite; Layer charge; Confining effects
Stability of a volatile liquid film spreading along a heterogeneously-heated substrate
by Naveen Tiwari; Jeffrey M. Davis (pp. 243-251).
A model is developed to investigate the dynamics of a volatile liquid film spreading over a heterogeneously-heated substrate, with emphasis on the linear stability and nonlinear rivulet evolution.Display Omitted► Stability and nonlinear evolution of volatile film spreading over heated surface. ► With significant evaporation, base profile is steady or time-periodic. ► Unstable to transverse perturbations above critical Marangoni parameter M. ► Increased evaporation generally stabilizing but can destabilize film for some M. ► 1-D time-periodic profile can evolve to steady 2-D profile after instability.The dynamics and stability of a thin, viscous film of volatile liquid flowing under the influence of gravity over a non-uniformly heated substrate are investigated using lubrication theory. Attention is focused on the regime in which evaporation balances the flow due to gravity. The film terminates above the heater at an apparent contact line, with a microscopically thin precursor film adsorbed due to the disjoining pressure. The film develops a weak thermocapillary ridge due to the Marangoni stress at the upstream edge of the heated region. As for spreading films, a more significant ridge is formed near the apparent contact line. For weak Marangoni effects, the film evolves to a steady profile. For stronger Marangoni effects, the film evolves to a time-periodic state. Results of a linear stability analysis reveal that the steady film is unstable to transverse perturbations above a critical value of the Marangoni parameter, leading to finger formation at the contact line. The streamwise extent of the fingers is limited by evaporation. The time-periodic profiles are always unstable, leading to the formation of periodically-oscillating fingers. For rectangular heaters, the film profiles after instability onset are consistent with images from published experimental studies.
Keywords: Thin liquid film; Evaporation; Fingering instability; Marangoni effect; Microfluidics; Contact line
Application of the UNIFAC model for prediction of surface tension and thickness of the surface layer in the binary mixtures
by A.A. Rafati; A. Bagheri; A.R. Khanchi; E. Ghasemian; Mojgan Najafi (pp. 252-258).
The relative Gibbs adsorption, the surface mole fraction and the thickness of liquid–vapor interfaces as a function of composition have been evaluated using the UNIFAC model.Display Omitted► The activity coefficients of surface and bulk phases have been calculated by UNIFAC methods. ► Molar surface areas are evaluated based on Paquette areas and Rasmussen areas model. ► Surface mole fraction and relative Gibbs adsorption parameters have been calculated. ► The thickness of surface layer of mixtures has been calculated by UNIFAC method.Surface properties of binary mixtures of (alkanol with acetonitrile) have been measured by surface tension method at T=298.15K and atmospheric pressure. The UNIFAC method is used for calculation activity coefficients of surface and bulk phases. Also, the surface tension has been predicted based on the Suarez method. This method combines a model for the description of surface tension of liquid mixtures with a UNIFAC group contribution method for the calculation of activity coefficient. Two techniques for calculation of molar surface areas, based on Paquette areas and Rasmussen areas are tested. On comparing the computed values of surface tension by the present approaches with experimental data, satisfactory results have been observed. In addition, the relative Gibbs adsorption and the surface mole fraction have been evaluated using this model. It is possible to calculate the thickness of liquid–vapor interfaces starting from surface tension data. A novel procedure is developed to obtain the thickness of liquid–vapor interfaces as a function of composition in binary systems.
Keywords: Surface tension; Prediction; Binary system; Adsorption; Thickness of surface layer
Kinetic theory of heterogeneous nucleation; effect of nonuniform density in the nuclei
by Gersh O. Berim; Eli Ruckenstein (pp. 259-264).
Fluid density distribution in nucleus in a cavity. The lighter areas correspond to higher fluid densities.Display Omitted► The kinetic theory of heterogeneous nucleation (Nowakowski and Ruckenstein) is revisited. ► The nonuniformity of fluid density distribution in the nucleus is taken into account. ► This nonuniformity decreases the nucleation rate I. ► In the cavity, I increases with decreasing cavity radius. ► I increases with increasing strength of solid-fluid interactions.The heterogenous nucleation of a liquid from a vapor in contact with a planar solid surface or a solid surface with cavities is examined on the basis of the kinetic theory of nucleation developed by Nowakowski and Ruckenstein [J. Phys. Chem. 96 (1992) 2313] which is extended to nonuniform fluid density distribution (FDD) in the nucleus. The latter is determined under the assumption that at each moment the FDD in the nucleus is provided by the density functional theory (DFT) for a nanodrop. As a result of this assumption, the theory does not require to consider that the contact angle which the nucleus makes with the solid surface and the density of the nucleus are independent parameters since they are provided by the DFT. For all considered cases, the nucleation rate is higher in the cavities than on a planar surface and increases with increasing strength of the fluid-solid interactions and decreasing cavity radius. The difference is small at high supersaturations (small critical nuclei), but becomes larger at low supersaturations when the critical nucleus has a size comparable with the size of the cavity. The nonuniformity of the FDD in the nucleus decreases the nucleation rate when compared to the uniform FDD.
Keywords: Heterogeneous nucleation; Kinetic theory; Rough surface; Nonuniform nucleus
Lipid membranes supported on optically transparent nanosilicas: Synthesis and application in characterization of protein-membrane interactions
by Alexander Y. Fadeev; William F. DeGrado (pp. 265-268).
Lipid bilayers supported on ∅20nm (left) and ∅100nm (right) silicas. The amount of adsorbed lipids is ∼7mg/sample in each vial.Display Omitted► We describe preparation of lipid membranes supported on optically transparent nanosilicas (∅ 20 and 30nm). ► These materials combine the properties of solid-supported membranes (easy handling and improved stability) and those of lipid vesicles (high surface area and optical transparency) providing a convenient system for characterization of membrane-protein interactions using simple techniques. ► The interactions of melittin with lipid-coated nanosilicas are investigated using conventional CD and fluorescence spectroscopy.We describe methods of preparation of lipid membranes supported on optically transparent nanosilicas (20 and 30nm diameter) and an initial application of these materials to characterize membrane-protein binding using conventional circular dichroism and fluorescence spectroscopy.
Keywords: Lipid membrane; Silica nanoparticles; Protein-membrane interactions