Journal of Colloid And Interface Science (v.341, #2)
Functional silica nanoparticles synthesized by water-in-oil microemulsion processes
by Tangi Aubert; Fabien Grasset; Stéphane Mornet; Etienne Duguet; Olivier Cador; Stéphane Cordier; Yann Molard; Valérie Demange; Michel Mortier; Hajime Haneda (pp. 201-208).
Colloid-in-water-in-oil (C/W/O) microemulsion is a well-suitable confined reacting medium for the synthesis of structured functional nanoparticles of controlled size and shape.Water-in-oil (W/O) microemulsion is a well-suitable confined reacting medium for the synthesis of structured functional nanoparticles of controlled size and shape. During the last decade, it allowed the synthesis of multi-functional silica nanoparticles with morphologies as various as core–shell, homogenous dispersion or both together. The morphology and properties of the different intermediates and final materials obtained through this route are discussed in the light of UV–Vis–NIR spectroscopy, dynamic light scattering (DLS) and X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and magnetometer SQUID analysis.
Keywords: Microemulsion; Silica nanoparticles; Ferrites; CeO; 2; Clusters; Superparamagnetism; Spinglass; Luminescence; Bio-imaging
Dry etching of colloidal crystal films
by Young-Sang Cho; Gi-Ra Yi; Jun Hyuk Moon; Dae-Chul Kim; Bong-Ju Lee; Seung-Man Yang (pp. 209-214).
We present the dry etching of colloidal crystal films made of polystyrene nanospheres. Hyperthermal neutral beam or reactive ion etching methods were adopted to change the nano-structure of colloidal crystals, and the resultant change in the photonic bandgap was studied.Two types of non-close-packed colloidal crystal films were prepared by etching the films made of polystyrene nanospheres using a hyperthermal neutral beam of oxygen gas. Etching without sintering above glass transition temperature of the polymer particles resulted in the non-close-packed structure of the nanospheres, in which polystyrene nanospheres in different lattice planes touched each other due to the reduction in the size of the nanospheres that occurred during the etching process. In contrast, a different non-close-packed structure with inter-connecting networks between etched nanospheres was generated by annealing of the colloidal crystal and a subsequent etching process. The photonic bandgap could be tuned during this dry etching of colloidal photonic crystals. This connected open structure could be used as a template for a silica inverse opal by chemical vapor deposition. An alternative dry etching process, reactive ion etching, mainly affected the morphology of particles near the top surface, and only a slight change in the stop band position of the colloidal crystal film was observed.
Keywords: Colloidal crystal; Hyperthermal neutral beam; Reactive ion etching; Photonic bandgap
Reductive dissolution of ferrihydrite by ascorbic acid and the inhibiting effect of phospholipid
by Sudeep Debnath; Douglas B. Hausner; Daniel R. Strongin; James Kubicki (pp. 215-223).
Reductive dissolution of ferrihydrite nanoparticles induced by ascorbic acid is explored in the presence and absence of adsorbed phospholipid. The presence of adsorbed phospholipid reduces the otherwise facile dissolution process.The interaction of ascorbic acid with ferrihydrite nanoparticles with and without adsorbed phospholipid has been investigated with atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), density functional theory (DFT) cluster calculations, and batch geochemical methods. Both batch geochemical rate measurements and in situ AFM showed that ferrihydrite particles dissolved in the presence of ascorbic acid over a period of hours. The area-normalized dissolution rate derived from AFM measurements of isolated ferrihydrite particles was relatively constant over the period of dissolution and was faster than the dissolution rate derived from batch reaction methods. Results from ATR-FTIR interpreted in view of theoretical calculations suggested that exposure of ferrihydrite to ascorbic acid led to an adsorbed monodentate ascorbate surface complex. Ferrihydrite dissolution was suppressed if particles were exposed to an organic lipid prior to or during exposure to ascorbic acid. AFM analysis of the lipid layer showed that its thickness was close to 7nm, the expected value for lipid assembled into a bilayer structure.
Keywords: Ferrihydrite; Ascorbic acid; Reductive dissolution; Iron oxyhydroxide; DFT; ATR-FTIR; HFO; Colloidal ferric hydroxide; Amorphous iron hydroxide
Aggregation states of rhodamine 6G in electrospun nanofibrous films
by Hengguo Wang; Qingbiao Yang; Lei Sun; Shuai Wang; Wei Wang; Chaoqun Zhang; Yanchun Li; Shufei Xu; Yaoxian Li (pp. 224-231).
Fluorescent composite nanofibers of the rhodamine 6G and polyacrylonitrile (PAN) are prepared by electrospinning.Novel fluorescent composite nanofibrous films of rhodamine 6G (Rh6G) and polyacrylonitrile (PAN) are first prepared by electrospinning. The aggregation states of Rh6G in electruspun nanofibrous films are studied as a function of concentrations and characterized by UV–vis absorption spectroscopy and emission and excitation fluorescence spectroscopy. We have also used casting films as reference material to compare the effect of incorporation of Rh6G in electrospun nanofibrous films and casting films. The large specific surface area of the nanofibers and fast evaporation of the solvents in the electrospinning process reduced the aggregation of Rh6G. The appearance of fluorescent J-type dimers, even at higher dye concentration in elctrospun films, demonstrates that the electrospun films are an ideal material for incorporation of fluorescent dyes.
Keywords: Electrospinning; Rhodamine 6G; Aggregation; J-type dimers
Surface immobilization of fibronectin-derived PHSRN peptide on functionalized polymer films – Effects on fibroblast spreading
by Cristina Satriano; Grazia M.L. Messina; Clara Marino; Ivana Aiello; Enrico Conte; Diego La Mendola; Donatella A. Distefano; Franca D’Alessandro; Giuseppe Pappalardo; Giuseppe Impellizzeri (pp. 232-239).
Spontaneous adsorption of PHSRN cell-adhesive peptide on functionalized hydrophilic (a) and unmodified hydrophobic (b) polymer surfaces result in different peptide adsorption kinetics, spatial peptide disposition at the solid interface, and cellular response to the immobilized peptide.The Pro-His-Ser-Arg-Asn (PHSRN) sequence in fibronectin is a second cell-binding site that synergistically affects Arg-Gly-Asp (RGD). The PHSRN peptide also induces cell invasion and accelerates wound healing. We report on the surface immobilization of PHSRN by spontaneous adsorption on polysiloxane thin films which have different surface free energy characteristics. Low-surface energy (hydrophobic) polysiloxane and the corresponding high-surface energy (hydrophilic) surfaces obtained by UV–ozone treatments were used as adsorbing substrates. The peptide adsorption process was investigated by quartz crystal microbalance with dissipation monitoring and atomic force microscopy. Both adsorption kinetics and peptide rearrangement dynamics at the solid interface were significantly different on the surface-modified films compared to the untreated ones. Fibroblast cells cultures at short times and in a simplified environment, i.e., a medium-free solution, were prepared to distinguish interaction events at the interface between cell membrane and surface-immobilized peptide for the two cases. It turned out that the cell-adhesive effect of immobilized PHSRN was different for hydrophobic compared to hydrophilic ones. Early signatures of cell spreading were only observed on the hydrophilic substrates. These effects are explained in terms of different spatial arrangements of PHSRN molecules immobilized on the two types of surfaces.
Keywords: Cell-adhesive PHSRN; Peptide adsorption; Polymer surface modification; QCM-D; Surface free energy
Permeabilization of biological and artificial membranes by a bacterial dirhamnolipid produced by Pseudomonas aeruginosa
by Marina Sánchez; Francisco J. Aranda; José A. Teruel; María J. Espuny; Ana Marqués; Ángeles Manresa; Antonio Ortiz (pp. 240-247).
Dirhamnolipid causes hemolysis of human erythrocytes at various concentrations below the CMC ( μM, numbers on the curves). Pseudomonas aeruginosa, when cultured under the appropriate conditions, secretes rhamnolipids to the external medium. These glycolipids constitute one of the most interesting classes of biosurfactants so far. A dirhamnolipid fraction was isolated and purified from the crude biosurfactant, and its action on model and biological membranes was studied. Dirhamnolipid induced leakage of internal contents, as measured by the release of carboxyfluorescein, in phosphatidylcholine unilamellar vesicles, at concentrations below its CMC. Membrane solubilization was not observed within this concentration range. The presence of inverted cone-shaped lipids in the membrane, namely lysophosphatidylcholine, accelerated leakage, whereas cone-shaped lipids, like phosphatidylethanolamine, decreased leakage rate. Increasing concentrations of cholesterol protected the membrane against dirhamnolipid-induced leakage, which was totally abolished by the presence of 50mol% of the sterol. Dirhamnolipid caused hemolysis of human erythrocytes through a lytic mechanism, as shown by the similar rates of K+ and hemoglobin leakage, and by the absence of effect of osmotic protectants. Scanning electron microscopy showed that the addition of the biosurfactant changed the usual disc shape of erythrocytes into that of spheroechinocytes. The results are discussed within the frame of the biological actions of dirhamnolipid, and the possible future applications of this biosurfactant.
Keywords: Rhamnolipids; Biosurfactants; Phospholipid membranes; Permeabilization; Hemolysis; Pseudomonas aeruginosa
Catechol derivatives-coated Fe3O4 and γ-Fe2O3 nanoparticles as potential MRI contrast agents
by H. Basti; L. Ben Tahar; L.S. Smiri; F. Herbst; M.-J. Vaulay; F. Chau; S. Ammar; S. Benderbous (pp. 248-254).
TEM images of the colloids of Fe3O4 -DA and Fe3O4- CAL showing well dispersed particles in case of the dopamine ( DA) and aggregated ones in the case of the catechaldehyde ( CAL).Superparamagnetic iron oxide nanoparticles, Fe3O4 and γ-Fe2O3, were produced by the so-called polyol process. In order to stabilize the particles in a physiological environment as potential contrast agents for Magnetic Resonance Imaging ( MRI), the as-prepared particles were successfully transferred to an aqueous medium through ligand exchange chemistry of the adsorbed polyol species with the dopamine or the catechaldehyde. The ligands were able to participate in bidentate binding to the nanoparticles surface and to improve the stability of aqueous suspensions of the nanoparticles. Analysis was performed by various techniques including X-ray diffraction, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results of magnetic measurements and initial in vitro magnetic resonance imaging essays are presented for the pre- and post-surface modified nanoparticles, respectively and discussed in relation with their structure and microstructure.
Keywords: Iron oxide; Superparamagnetism; Catechol derivatives; Colloid; Magnetic resonance imaging
Osmotic-driven mass transport of water: Impact on the adhesiveness of hydrophilic polymers
by Annika Borde; Anna Bergstrand; Cecilia Gunnarsson; Anette Larsson (pp. 255-260).
Water mass transport ( J) from an agarose gel into a Carbopol tablet controlled by the mutual diffusion constant ( D) and differences in osmotic pressure ( π1 and π2) generates adhesion.Adhesion is an important property for the functionality of many medical devices. One reason for the development of adhesive forces is dehydration caused by mass transport of water. Osmotic pressure is one main driving force for mass transport and the correlation between osmotic pressure and adhesive force has not been studied yet, which was the aim of the present study. A model system was used where a Carbopol tablet was lowered onto a 1% (w/w) agarose gel. The force required to detach the tablet (adhesive force) and the weight gain of the tablet (as a measure of transported water) were determined. Sodium chloride and mannitol were added to the agarose gel to decrease the osmotic pressure difference between the agarose gel and the partially hydrated Carbopol tablet. This resulted in a decrease of both mass transport and adhesive force. In addition, experiments with restricted water transport within the agarose gel were performed by preparing gels with different agarose concentrations. An increase of the agarose concentration resulted in decreased water transport and higher adhesive forces. Hence, the results confirmed our hypothesis that osmotic-driven mass transport and restricted mass transport of water correlate very well with the adhesive force.
Keywords: Bioadhesion; Adhesion mechanism; Osmotic pressure; Polyacrylic acid; Agarose gel
Effect of alkyl chain asymmetry on catanionic mixtures of hydrogenated and fluorinated surfactants
by Elena Blanco; Carlos Rodriguez-Abreu; Pablo Schulz; Juan M. Ruso (pp. 261-266).
Plateau modulus ( G0) and relaxation time ( τR) as a function of total concentration in CTAB-C8HONa systems (a) αF=0.4; (b) αF=0.6.In this work we studied and compared the physicochemical properties of the catanionic mixtures cetyltrimethyl-ammonium bromide–sodium dodecanoate, cetyltrimethyl-ammonium bromide–sodium perfluorodacanoate, octyltrimethylammonium bromide–sodium perfluorodacanoate and cetyltrimethyl-ammonium bromide–sodium octanoate by a combination of rheological, transmission electron microscopy (TEM) and polarized optical microscopy measurements. The binary mixtures of the surfactants have been analyzed at different mixed ratios and total concentration of the mixture. Mixtures containing a perfluorinated surfactant are able to form lamellar liquid crystals and stable spontaneous vesicles. Meanwhile, system containing just hydrogenated surfactants form hexagonal phases or they are arranged in elongated aggregates.
Keywords: Fluorinated; Hydrogenated; Catanionics; Rheology; Mixed
Phase behavior and rheology of oil-swollen micellar cubic phase and gel emulsions in nonionic surfactant systems
by Mohammad Mydul Alam; Yuki Sugiyama; Kei Watanabe; Kenji Aramaki (pp. 267-272).
Oil-swollen micellar cubic phase (sort of cubic (I1) microemulsion) could form in a nonionic surfactant system, which is highly dependent on the surfactant nature.We have studied the phase behavior and rheological property of the cubic phase and related gel emulsions in water/nonionic/dodecane systems. In the phase behavior study, it is pointed out that the formation of the discontinuous cubic phase (I1) is not common in all nonionic surfactant systems; however, a cubic phase (I1) with oil-swollen micelles or a cubic phase microemulsion is found in the water/C16EO6/dodecane system, which can solubilize large amount of oil. It was also observed that water/C16EO6/dodecane system forms stable gel emulsion. In the rheological study we have found an anomalous behavior of the I1 phase in the water/C12EO6/dodecane and the water/C16EO6/dodecane systems. In the water/C12EO6/dodecane system, the viscoelastic nature of the I1 phase has been observed, which is shifted to the elastic nature with the addition of dodecane, whereas, highly elastic nature was observed in the water/C16EO6/dodecane system. In both the cases shear-thinning behavior were seen. The elastic modulus, G′ and complex viscosity, | η∗| of the I1 phase increase with the dodecane concentration in the water/C12EO6/dodecane system, whereas, decreasing trend have been observed in the water/C16EO6/dodecane system. This anomalous behavior is suggested due to the nonspherical shape of micelles or polydispersity of the micelles in the water/C16EO6/dodecane system. The rheological behavior of the O/I1 gel emulsion was also studied in both the systems.
Keywords: Cubic phase; Gel emulsion; Rheology; Phase behavior; Nonionic surfactant
Modulating the catalytic activity of Au/micelles by tunable hydrophilic channels
by De’an Xiong; Zhe Li; Lu Zou; Zhenping He; Yang Liu; Yingli An; Rujiang Ma; Linqi Shi (pp. 273-279).
Hydrophilic channels were constructed in the corona of the polymeric micelles and used to tune the catalytic activity of the supported gold nanoparticles.Polymeric micelles with a polystyrene core, poly(acrylic acid)/poly(4-vinyl pyridine) (PAA/P4VP) complex shell and poly(ethylene glycol) & poly(N-isopropylacrylamide) (PEG & PNIPAM) mixed corona were synthesized and used as the supporter for the gold nanoparticles (GNs). It was concluded from the result of1H NMR characterization that hydrophilic channels formed around PEG chains when PNIPAM collapsed above its lower critical solution temperature. The density of the channels in the corona can be tuned by changing the weight ratios of PEG chains to PNIPAM chains. The GNs were set in the PAA/P4VP complex layer and the catalytic activity of the GNs can be modulated by the channels. The catalytic activity increased with increasing the density of the channels in the corona. Meanwhile, the whole Au/micelle nanoparticles were stabilized by the extended PEG chains.
Keywords: Temperature sensitive; Multi-layered micelles; Catalyst carrying; Modulating the catalytic activity; Channels
Unusual buffer action of free-standing nanoscopically confined water
by Kylin Liao; Xiaozhou Xu; Xuezhong Du (pp. 280-285).
Nanoscopic water confined in black soap films (BSFs) showed unusual buffer action resistant not only to acidic/alkaline solutions but also to buffer solution.The acid–base properties of nanoscopic water confined in the black soap films (BSFs), which were prepared from aqueous solutions of sodium dodecylsulphate (SDS) with the dye neutral red (NR) as a pH probe, were investigated using a combination of UV–vis and FTIR spectroscopy. For the SDS micellar solutions at pH 1.0–9.5 adjusted with HCl/NaOH solutions and at pH 9.4 with ammonium buffered solution, the aqueous core thicknesses in the corresponding BSFs ranged from 2.7 to 6.2nm, and the nanoscopically confined water exhibits unusual buffer action resistant not only to acidic/alkaline solutions but also to standard buffer solution. In the heavily water-depleted confined zones, it is most likely that charge pairs in proton-transfer reactions could not be formed effectively and proton transfer was prohibited in the absence of sufficient solvating ability. Theoretical analyzes indicated that the buffer action of the nanoscopic water originated from the confinement effect of two charged surfaces of the BSFs. These results might inspire deeper understanding and further studies of biobuffering, enzyme superactivity, acid-catalyzed reactions, and Nafion fuel cell membranes.
Keywords: Soap film; Confined water; Buffer action; Molecular spectroscopy
Competitive adsorption between SDS and carbonate on tetrahydrofuran hydrates
by J.S. Zhang; C. Lo; P. Somasundaran; J.W. Lee (pp. 286-288).
This figure presents competitive adsorption between DS− and carbonate on hydrate particles when SDS is first added and then carbonate. DS−: round head and line tail, carbonate: small filled circle, and hydrate particle: large yellow filled circle.Sodium dodecyl sulfate (SDS) has been well known as a promoter for the formation of hydrates. However, the use of SDS to enhance the formation of CO2 hydrates has not been effective. This work will present an idea of competitive adsorption that will provide insights into the nonpromoting effect of SDS under high carbonate concentrations. The competitive adsorption is studied between DS− monomers and carbonate ions on tetrahydrofuran (THF) hydrates. The adsorption is qualitatively investigated by using pyrene fluorescence measurements. The SDS concentration at which hydrophobic domains occur on the hydrate surface increases with the increased carbonate concentration and this trend is less dependent on the order of addition of these two species. This concentration is 0.17mM at carbonate concentrations less than 2μM and it shifts to 3.47mM at carbonate concentrations higher than 2.5μM. Thus, using carbonate with its concentration higher than 2.5μM would be enough to displace the hydrophobic domains formed by SDS up to the solubility limit.
Keywords: Competitive adsorption; SDS; Carbonate; THF hydrates
Phosphate uptake behavior of ZnAlZr ternary layered double hydroxides through surface precipitation
by P. Koilraj; S. Kannan (pp. 289-297).
Phosphate uptake over ZnAlZr LDHs results in the layered hopeite (Zn3(PO4)3·4H2O) by the surface precipitation of dissolved zinc ion through the outer-sphere complex formation of phosphate.Tetravalent Zr4+ ion incorporated ZnAl hydrotalcite-like material with varying Zn/(Al+Zr) atomic ratio (2–4) and Al/Zr atomic ratio 0.7:0.3 withCO32- as interlayer anion were successfully synthesized and characterized by various physicochemical methods. The phosphate uptake studies were carried out over these materials by batch method with the objective of enhancing the uptake through creation of higher positive charge on brucite-like layers by the incorporation of Zr4+. The studies revealed that ternary ZnAlZr hydrotalcites show good uptake capacity for phosphate, among which ZnAlZr4-HT depicts a maximum uptake of around 91mgP/g. We observed that phosphate uptake results in the formation of layered hopeite mineral (Zn3(PO4)3·4H2O) on the surface of material by the surface precipitation of dissolved zinc ion through the outer-sphere complex formation of phosphate. The phosphate uptake increases with a decrease in Zn/Al and Zn/(Al+Zr) atomic ratios. Effects of initial phosphate concentration, contact time, adsorbent amount and temperature variation on phosphate uptake were studied. Co-presence of competitive anion like nitrate enhances the uptake of phosphate to 148mgP/g. Recycle studies of the material shows a decrease in the uptake of phosphate with the number of cycles due to an increase in the crystallinity. Very high uptake of phosphate by these materials even in the presence of other anions/cations suggests their potential role in waste water remediation.
Keywords: Layered double hydroxides; Phosphate removal; Surface precipitation; Hopeite; Zirconium
Adsorption of sodium polyacrylate in high solids loading calcium carbonate slurries
by Joshua J. Taylor; Wolfgang M. Sigmund (pp. 298-302).
The fate of high solids loading slurries (>55wt.%) are different from low solids loadings. The bridging state for bonds is increased with solids loading and age of slurry. These phenomena seem not to occur in dilute conditions.The adsorption of sodium polyacrylate (NaPAA) in slurries with up to 75wt.% calcium carbonate was investigated with the use of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and adsorption of probe molecules. Analysis of the IR spectra demonstrated that the carboxylate groups of NaPAA adsorbed onto ground calcium carbonate (GCC) in three different modes. These modes were shown to be dependent on the solids loading and age of the slurry. Further investigation lead to the determination of the chelating ability of NaPAA at high solids loading.
Keywords: Calcium; Carbonate; Slurry; Infrared; Polyacrylate; Carboxylate; Adsorption; Solids; ATR-FTIR
A novel catalyst based on electrospun silver-doped silica fibers with ribbon morphology
by Haigang Kang; Yihua Zhu; Xiaoling Yang; Yujia Jing; Anezka Lengalova; Chungzhong Li (pp. 303-310).
The silver-doped mesoporous silica nanobibbons had been synthesized by combining the electrospinning technique and sol–gel method, which demonstrated high catalytic efficiency for reduction reaction of methylene blue dye (MB).Mesoporous silica nanofibers and Ag-doped composite nanoribbons were synthesized by a facile combination of an electrospinning technique and the sol–gel method. Tetraethyl orthosilicate, polyvinylpyrrolidone (PVP), triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), copolymer Pluronic P123, and silver nitrate (AgNO3) were the components of sol for the production of Ag-doped hybrid silica ribbons. Heat removal of structure-directing agent P123 in the hybrid fibers at high temperatures resulted in a mesoporous morphology, and the degradation of PVP caused AgNO3 to convert into silver in the form of nanoparticles. The size and content of the particles in the hybrid ribbons could be controlled by the concentration of AgNO3 and thermal treatment conditions. Scanning electron microscopy, N2 adsorption–desorption isotherm, transmission electron microscopy, X-ray diffraction, and UV–Vis spectroscopy were used to characterize the composite ribbons. The catalytic activity of the ribbons was evaluated by reduction of methylene blue dye and found to be better than in previous studies.
Keywords: Silver-doped composite; Nanoribbon; Electrospinning; Sol–gel method; Porous materials; Catalytic reduction
Interaction between tetracycline and smectite in aqueous solution
by Zhaohui Li; Po-Hsiang Chang; Jiin-Shuh Jean; Wei-Teh Jiang; Chih-Jen Wang (pp. 311-319).
Desorption of metal cations and co-adsorption of H+ accompanying tetracycline adsorption confirmed experimentally that cation exchange was the major mechanism of tetracycline intercalation in smectite minerals even in zwitterionic form.The fate and transport of commonly used antibiotics in soil and groundwater have attracted renewed studies due to increased sensitivities of analytical instruments and thus frequent detections of these compounds even in treated wastewater. Smectite, an important soil component, has large surface area and high cation exchange capacity, while tetracycline (TC) can exist in different forms and charges under different pH conditions. Thus, the interaction between smectite and TC in aqueous systems is of great importance. This research focused on elucidating the mechanisms of TC uptake by smectite, in terms of TC adsorption, cation desorption, and pH changes associated with TC adsorption by smectite and intercalation in smectite. TC adsorption onto smectite was a relatively fast process even though most of the adsorption sites were in the interlayer position involved in intercalation as confirmed by the expansion of d001 spacing. The TC adsorption capacity was equivalent to 0.74–1.11 times the cation exchange capacity for three of the four smectite minerals studied. Accompanying TC adsorption was simultaneous adsorption of H+, resulting in protonation of TC on the dimethylamine group. At higher TC input concentrations further adsorption of H+ resulted in the ratio of H+ adsorbed to TC adsorbed greater than one, suggesting that additionally adsorbed H+ could serve as counterions to partially offset the negative charges on the tricarbonyl or phenolic diketone functional groups. The positive correlations between cations desorbed and TC adsorbed, as well as TC adsorbed and H+ adsorbed, provided a first time evidence to confirm cation exchange as the main mechanism of TC uptake, even under neutral pH conditions.
Keywords: Adsorption; Cation exchange; Desorption; Intercalation; Protonation; Smectite
In situ synthesis of Ag nanoparticles in aminocalixarene multilayers
by Shuiying Gao; Daqiang Yuan; Jian Lü; Rong Cao (pp. 320-325).
The formation of Ag nanoparticles depends on cation–π interaction and hydrogen bonding between tetraamino-calixarenes. The layer-by-layer assembled thin films were used as nanoreactor to synthesize in situ Ag nanoparticles.The layer-by-layer (LbL) assembled thin films containing tetraamino-thiacalixarenes (1) and tetraamino-calixarenes (2) were used as nanoreactor to synthesize in situ Ag nanoparticles (Ag NPs). UV–vis spectra and AFM images demonstrate that Ag NPs are included in the (1/Ag NPs) n and (2/Ag NPs) n multilayer films. The silver ions are absorbed through cation–π interaction and calixarene-metal ion coordination interaction and are reduced into Ag NPs by calixarenes. TEM images indicated that Ag NPs within aminocalixarene multilayers were highly dispersed and uniform. Moreover, the mean size of Ag NPs is smaller than 10nm.
Keywords: Films; Calixarene; Ag nanoparticles; Layer-by-layer self-assembly
Droplets wetting on filament rails: Surface energy and morphology transition
by Xiang-Fa Wu; Amol Bedarkar; K. Abraham Vaynberg (pp. 326-332).
Morphology transition of droplets wetting on filament rails.The morphology of liquid droplets wetting on filaments depends on the filament configuration, droplet volume, and contact angle. A stable morphology is the one that minimizes the potential energy of the droplet–filament system, while morphology transition may happen when an intermediate state exists which corresponds to a higher potential energy. This paper aims to explore such morphology transition of droplet wetting on filament rails made of two parallel identical microfilaments. Detailed numerical simulations were performed to extract the surface energy of the droplet–filament system at varying filament spacings, droplet volumes, and contact angles. Critical conditions of the morphology transition between two symmetrical wetting morphologies (i.e., liquid droplet bridge and barrel-shaped droplet) were determined. A family of characteristic curves in terms of the dimensionless droplet volume vs the filament spacing at varying contact angles was obtained, which can be used as a universal law to govern the morphology transition for such droplet–filament rail systems. The results and concepts presented in this work can be extended to broad wetting systems and utilized for the analysis and design of microfluidic devices and testers based on droplet–filament systems.
Keywords: Wetting and spreading; Droplets; Filament rails; Morphology transition
Ligand-stabilized metal nanoparticles in organic solvent
by Sudip Nath; Subhra Jana; Mukul Pradhan; Tarasankar Pal (pp. 333-352).
Chain length-dependent stability of Au–organosol. Ligands with longer chains preferentially stabilize Au nanoparticles in organic solvent.This critical review reports the fundamental behavior of metal nanoparticles in different organic solvents, i.e., metal organosol. An overview on metal organosol and then their smart synthetic approaches, characterization, and potential applications in the fields of catalysis and spectroscopy with special emphasis on SERS are embodied. Aspects of organosol fabrication, stabilization, morphology control, growth mechanisms, and physical properties as mono- and bimetallic nanoparticles are discussed. The article inspires the repetitive usage of metal nanoparticles as stable deliverable organic and molecular compounds.
Keywords: Nanoparticles; Organosol; Catalysis; SERS
Encapsulation of polyaniline in 3-D interconnected mesopores of silica KIT-6
by Yu-Qian Dou; Yunpu Zhai; Fanwu Zeng; Xiao-Xia Liu; Bo Tu; Dongyuan Zhao (pp. 353-358).
Polyaniline (PANI) was encapsulated into the 3-D interconnected pore channels of mesoporous silica, KIT-6. The composite showed enhanced electrical conductivity and potential applications in humidity sensors.Composite material PANI/KIT-6, with polyaniline (PANI) chains encapsulated in the 3-D interconnected pore channels of mesoporous silica, KIT-6, has been synthesized via a gas-phase method. The composite formation and the presence of PANI inside the pore channels of KIT-6 were evidenced by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), small-angle X-ray scatter (SAXS), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms. The PANI/KIT-6 composite showed good electrical conductivity (2.4×10−3S/cm) due to the formation of 3-D networks of PANI inside the 3-D interconnected channels of KIT-6. The resistance of PANI/KIT-6 composite at different relative humidities (RH) was investigated. An essentially linear relationship between the relative resistance of the composite and the relative humidity of the environment was found from 11.3% to 97.3% RH.
Keywords: Mesoporous materials; Polyaniline; Composite; Electrical conductivity; Humidity sensor
Novel synthesis of high-surface-area ordered mesoporous TiO2 with anatase framework for photocatalytic applications
by Li-Heng Kao; Tzu-Chien Hsu; Kuo-Kuang Cheng (pp. 359-365).
Ordered mesoporous TiO2 materials with an anatase framework and a hexagonal mesostructure showing efficient photocatalytic efficiency have been successfully synthesized via a cationic surfactant-assisted sol–gel synthesis under hydrothermal condition.Ordered mesoporous TiO2 materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C16TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S+ and the negatively charged inorganic framework I− (S+I− type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO2 materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO2 possesses an anatase crystalline framework having a maximum pore size of 6.9nm and a maximum Brunauer–Emmett–Teller specific surface area of 284m2g−1. This ordered mesoporous anatase TiO2 also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.
Keywords: Ordered mesoporous TiO; 2; Anatase framework; Cetyltrimethylammonium bromide; Peroxytitanates; Photocatalytic activity
Gap-mode SERS studies of azobenzene-containing self-assembled monolayers on Au(111)
by Ulrich Jung; Mathias Müller; Norihiro Fujimoto; Katsuyoshi Ikeda; Kohei Uosaki; Ursula Cornelissen; Felix Tuczek; Claudia Bornholdt; Dordaneh Zargarani; Rainer Herges; Olaf Magnussen (pp. 366-375).
Gap-mode SERS spectra of azobenzene-containing alkane thiol SAMs on Au(111) surfaces with the azobenzene moieties (a) in trans and (b) in cis configuration.Self-assembled monolayers of azobenzene-containing thiols on smooth Au(111) surfaces were studied by gap-mode surface-enhanced Raman spectroscopy (gap-mode SERS). By adsorption of colloidal Au nanoparticles on top of the organic adlayer highly reproducible spectra with strongly enhanced intensities are obtained. The observed bands indicate a trans conformation of the azobenzene moieties and are in agreement with structural data for the molecular layer. A characteristic dependency on the terminal and the spacer groups of the molecules is found. Samples prepared during illumination with UV light show pronounced spectral differences that can be attributed to azobenzene in cis conformation.
Keywords: Surface-enhanced Raman spectroscopy; Gap-mode SERS; Self-assembled monolayers; Azobenzene; Photoswitching
Hydrodynamic interactions induce movement against an external load in a ratchet dimer Brownian motor
by José A. Fornés (pp. 376-379).
An elastically coupled dimer Brownian motor in a ratchet potential under the load force, thermal noise and an unbiased thermal fluctuation; with and without hydrodynamic interactions.We use the Brownian dynamics with hydrodynamic interactions simulation in order to describe the movement of a elastically coupled dimer Brownian motor in a ratchet potential. The only external forces considered in our system were the load, the random thermal noise and an unbiased thermal fluctuation. For a given set of parameters we observe direct movement against the load force if hydrodynamic interactions were considered.
Keywords: Dimer Brownian motors; Hydrodynamic interactions; Brownian dynamics; Molecular motors; Coupled Brownian motors; Transport of two coupled particles
Evaluation of the Zn2+ transport properties through a cation-exchange membrane by chronopotentiometry
by I. Herraiz-Cardona; E. Ortega; V. Pérez-Herranz (pp. 380-385).
Effect of the concentration of ZnSO4on the transport numbers of Zn2+ through the cation-exchange membrane.In this work the effect of zinc concentration, pH, and boric acid concentration on the zinc transport properties through an IONICS 67-HMR-412 cation-exchange membrane was evaluated. The limiting current density and the transport numbers were determined by means of chronopotentiometry. A model between the limiting current density and the bulk zinc concentration was established, assuming a potential relationship between the zinc transport number through the membrane and the bulk zinc concentration together with the Levich equation for the DBL thickness. A decrease in the initial pH value of the solutions causes considerable modifications both in the plateau region and in the overlimiting current density region of the current–membrane potential curves. The results show that the presence of boric acid produces the precipitation of zinc metaborate on the anodic layer of the cation-exchange membrane.
Keywords: Zn; 2+; transport; Chronopotentiometry; Cation-exchange membrane; Boric acid
Self assembly of anastomosis-like superstructures in fatty acid/guanidine hydrochloride aqueous dispersions
by Jean-Paul Douliez; Bérénice Houinsou-Houssou; Anne-Laure Fameau; Bruno Novales; Cédric Gaillard (pp. 386-389).
We report the formation of interconnected nanostructures in fatty acid mixtures having the appearance of an anastomosis-like superstructure.A mixture between 1% sodium myristate and guanidine hydrochloride at a molar ratio of 1 in water forms a gel of membranes below a phase transition of ca. 21°C and a viscous limpid and isotropic solution above. As observed by both TEM and AFM, we report the formation of interconnected superstructures in that latter phase. Those assemblies exhibit a size of ca. 4–40nm width and several tens of μm length with unexpected disconnections and re-connections between them having the appearance of an anastomosis-like superstructure.
Keywords: Fatty acids; Self assembly; Tubules; Fibrils; Anastomosis