Journal of Colloid And Interface Science (v.326, #1)
Analysis of uncertainties in manometric gas-adsorption measurements
by A. Badalyan; P. Pendleton (pp. 1-7).
We describe procedures to propagate the uncertainty in adsorption data andαS-values to generate uncertainty in apparent primary, secondary, and total micropore volumes for porous activated carbons exhibiting Type I and IV character. TheαS-data are interpolated from selected non-porous reference material (NPRM) adsorption isotherm data with some adsorbents exhibiting surface chemistry quite different from and some similar to that of the porous adsorbents (PA). We show that a statistically constant apparent total micropore volume can be determined independent of the NPRM surface chemistry. In contrast, NPRM surface chemistry appears to influence our ability to identify unequivocally the filling and condensation ranges of micropore filling, leading to statistically different apparent primary and secondary micropore volumes.αS-Plot analysis of FM1/250 using the non-porous reference materials: (1) carbon black; (2) Aerosil 200 silica; (3) graphite cloth.
Keywords: Experimental uncertainty; Nitrogen adsorption; α; S; -Method; Micropore volume
Applicability of waste materials—bottom ash and deoiled soya—as adsorbents for the removal and recovery of a hazardous dye, brilliant green
by Alok Mittal; Dipika Kaur; Jyoti Mittal (pp. 8-17).
Deoiled soya, an agricultural waste material, and bottom ash, a waste of power plants, have been successfully used for the removal and recovery of the hazardous water-soluble dye brilliant green from water. To remove the dye from water, batch adsorption studies have been carried out by observing the effects of pH, concentration, amounts of adsorbents, size of adsorbent particles, etc. Attempts have also been made to monitor the adsorption process through Langmuir, Freundlich, Tempkin, and D-R adsorption isotherm models. Relevant thermodynamic parameters have also been calculated from these models. The adsorption process has been found endothermic and feasible at all the temperatures. The kinetics of the adsorption was also recorded and indicates pseudo-second-order kinetics in both cases. Kinetic operations also reveal the involvement of a film diffusion mechanism for the deoiled soya adsorption at all the temperatures, while bottom ash undergoes through a particle diffusion mechanism at only 30 °C and at higher temperatures a film diffusion mechanism operates. Bulk removal of the dye has been carried out through column studies for both adsorbents. Attempts have also been made to recover the dye from exhausted columns by eluting sulfuric acid of pH 3.Bulk removal and recovery of the dye were carried out through column operations.
Keywords: Adsorption; Bottom ash; Deoiled soya; Brilliant green; Dyes
Dynamic adhesion behavior of micrometer-scale particles flowing over patchy surfaces with nanoscale electrostatic heterogeneity
by Ranojoy D. Duffadar; Jeffrey M. Davis (pp. 18-27).
The dynamic adhesion behavior of micrometer-scale silica particles is investigated numerically for a low Reynolds number shear flow over a planar collecting wall with randomly distributed electrostatic heterogeneity at the 10-nanometer scale. The hydrodynamic forces and torques on a particle are coupled to spatially varying colloidal interactions between the particle and wall. Contact and frictional forces are included in the force and torque balances to capture particle skipping, rolling, and arrest. These dynamic adhesion signatures are consistent with experimental results and are reminiscent of motion signatures observed in cell adhesion under flowing conditions, although for the synthetic system the particle–wall interactions are controlled by colloidal forces rather than physical bonds between cells and a functionalized surface. As the fraction of the surface ( Θ) covered by the cationic patches is increased from zero, particle behavior sequentially transitions from no contact with the surface to skipping, rolling, and arrest, with the threshold patch density for adhesion (Θcrit) always greater than zero and in quantitative agreement with experimental results. The ionic strength of the flowing solution determines the extent of the electrostatic interactions and can be used to tune selectively the dynamic adhesion behavior by modulating two competing effects. The extent of electrostatic interactions in the plane of the wall, or electrostatic zone of influence, governs the importance of spatial fluctuations in the cationic patch density and thus determines if flowing particles contact the wall. The distance these interactions extend into solution normal to the wall determines the strength of the particle–wall attraction, which governs the transition from skipping and rolling to arrest. The influence of Θ, particle size, Debye length, and shear rate is quantified through the construction of adhesion regime diagrams, which delineate the regions in parameter space that give rise to different dynamic adhesion signatures and illustrate selective adhesion based on particle size or curvature. The results of this study are suggestive of novel ways to control particle–wall interactions using randomly distributed surface heterogeneity.Dynamic adhesion behavior of micrometer-scale particles flowing over nanotextured surfaces.
Keywords: Dynamic adhesion; Particle deposition; Charge heterogeneity; Nanotextured surface; Colloidal interaction; DLVO; Electrostatic double layer; Sphere-flat plate; Patchy surface; Adhesion state diagram
A comparative study on the dispersion behaviors and surface acid properties of molybdena on CeO2 and ZrO2 (Tet)
by Haiqin Wan; Dan Li; Haiyang Zhu; Yanhua Zhang; Lihui Dong; Yuhai Hu; Bin Liu; Keqin Sun; Lin Dong; Yi Chen (pp. 28-34).
Dispersion of molybdena on CeO2, ZrO2 (Tet), and a mixture of CeO2 and ZrO2 (Tet), was investigated by using laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and temperature programmed reduction (TPR). The results indicate that molybdena is dispersed on both individual oxide support and mixed oxide support at the adopted molybdena loadings (0.2 and 0.8 mmol Mo6+/100 m2) and the structure of the supported molybdena species is intimate association with its loading amount. Two molybdena species are identified by Raman results, i.e. isolated MoO2−4 species at 0.2 mmol Mo6+/100 m2 and polymolybdate species at 0.8 mmol Mo6+/100 m2. IR spectra of ammonia adsorption prove that isolated MoO2−4 species are Lewis acid sites on the Mo/Ce and/or Zr samples, and the polymolybdate species are Brönsted acid sites on the Mo/Ce and/or Zr samples. Moreover, a combination of the Raman, IR and TPR results confirms that at 0.2 mmol Mo6+/100 m2 Ce+Zr, molybdena is preferentially dispersed on the surface of CeO2 when a mixed oxide support (CeO2 and ZrO2) is present, which was explained in term of the difference of the surface basicity between CeO2 and ZrO2 (Tet). Surface structures of the oxide supports were also taken into consideration.IR spectra of ammonia adsorption indicate that isolated MoO2−4 species are corresponding to Lewis acid sites and polymolybdate species are corresponding to Brönsted acid sites over the Mo/Ce and/or Zr samples.
Keywords: MoO; 3; CeO; 2; ZrO; 2; In situ FT-IR
Layer-by-layer assembled thin films composed of carboxyl-terminated poly(amidoamine) dendrimer as a pH-sensitive nano-device
by Shigeru Tomita; Katsuhiko Sato; Jun-ichi Anzai (pp. 35-40).
Dendrimer-containing multilayer thin films have successfully been prepared by a layer-by-layer deposition of carboxyl-terminated poly(amidoamine) dendrimer (PAMAM–COOH) and poly(methacrylic acid) (PMA) on a solid surface at pH 4.0, while the multilayer film did not form at pH 7.0. The PMA/PAMAM–COOH multilayer films prepared at pH 4.0 are decomposed at neutral pH due to electrostatic repulsion between negatively-charged carboxylate residues. The results suggest that the primary force for the successful deposition of PAMAM–COOH and PMA at pH 4.0 is hydrogen bonding between COOH residues on the surface of the dendrimer and PMA. The multilayer films are decomposed also at strongly acidic pH, suggesting an electrostatic force of attraction between the protonated tertiary amino groups in PAMAM–COOH and a small fraction of COO− residues in PMA contributes in part to the multilayer formation at pH 4.0. The PMA/PAMAM–COOH thin films can accommodate model dyes, Rose Bengal and 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonate, and the release can be controlled by changing pH.
Keywords: Dendrimer; Layer-by-layer film; Hydrogen bonding; pH-controlled release
Unusually high hydrophobicity and its changes observed on the newly-created surfaces of PNIPA/clay nanocomposite hydrogels
by Kazutoshi Haraguchi; Huan-Jun Li; Liyuan Song (pp. 41-50).
The surface wettability of cross-sections of polymeric hydrogels was studied, focusing particularly on poly( N-isopropylacrylamide) (PNIPA) hydrogels below their lower critical solution temperature (LCST). It was found that nanocomposite hydrogels (N-NC gels) with organic (PNIPA)/inorganic (clay) network structures exhibit extraordinarily high contact angles for water (θw) on newly-created, cross-sectional surfaces produced by cutting prior to measurement. Values ofθw for N-NC gels were observed in the range of 100°–131° and changed depending on the composition, the environment and the measuring time. It was shown that hydrophobic surfaces (highθw) are formed most effectively in N-NC gels with specific clay and water contents. Also, during long-term measurements, high values ofθw showed unique changes which strongly depended on the clay concentration (i.e. network density). Further, the hydrophobic surface of N-NC gels changed to hydrophilic in contact with surface water and rapidly reverted to hydrophobic on subsequent drying. Also, contrary to the conventional hydrophobic surfaces of solids, a water droplet on the hydrophobic surface of an N-NC gel did not fall, even on a vertical surface, because of the strong interaction between the droplet and the gel surface. The mechanism for creating high values ofθw was attributed to the amphiphilicity of PNIPA chain in PNIPA/clay networks below the LCST and, more specifically, to the spontaneous alignment of N-isopropyl groups of PNIPA chains at the gel–air interface.By alternating the environment between wet and dry (in-air) conditions, the contact angle to water of PNIPA-NC5 gel (cross-section) rapidly and reversibly changed between 0° and >100°, respectively.
Keywords: Hydrophobicity; Nanocomposite; Hydrogel; Wettability; Poly(; N; -isopropylacrylamide)
Hyperbranched polyamidoamine as stabilizer for catalytically active nanoparticles in water
by Jean-Daniel Marty; Elsa Martinez-Aripe; Anne-Françoise Mingotaud; Christophe Mingotaud (pp. 51-54).
Poly(amidoamine) hyperbranched polymers (HYPAM) were successfully used to synthesize platinum nanoparticles of ca. 1.8 nm and to stabilize these particles in water. Furthermore these hyperbranched-stabilized platinum nanoparticles proved to be effective and robust for hydrogenation reaction in water.Hyperbranched polymers were used to synthesize and stabilize platinum nanoparticles in water. Furthermore these particles proved to be effective and robust for hydrogenation reaction in water.
Keywords: Platinum nanoparticles; Hyperbranched polymers; Hydrogenation; Catalysis in water; Isophorone
Self-assembly of Nafion molecules onto silica nanoparticles formed in situ through sol–gel process
by Jingjing Pan; Haining Zhang; Mu Pan (pp. 55-60).
Self-assembly of Nafion onto in situ formed silica nanoparticles in ethylene glycol–water mixture solvent has been investigated in this study. It was found that the formation of silica nanoparticles depends on the concentration of Nafion in dispersions. At relatively low concentration, 0.8% in weight in this case, the existing Nafion is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the concentration of Nafion increased to 2% in weight, self-assembled Nafion layer on the surface stabilizes the initial formed silica nanoparticles and silica particles with average diameters of4.2±0.5 nm were found to be uniformly distributed in the dispersion. With further increasing the concentration of Nafion, the number of Nafion aggregates increases and silica nanoparticles were mainly formed inside the entangled Nafion chains, resulting in an observation of clusters of silica nanoparticles.In situ generation of silica nanoparticles in Nafion dispersion with different concentrations: (a) low concentration, (b) medium concentration, and (c) high concentration.
Keywords: Nafion–silica hybrid nanoparticles; Self-assembly; Sol–gel process; Proton exchange membrane; Fuel cells
Electrochemically produced responsive hydrogel films: Influence of added salt on thickness and morphology
by Johanna Bünsow; Diethelm Johannsmann (pp. 61-65).
We report on electrochemically prepared hydrogel layers of poly- N-isopropylacrylamide (pNIPAm) and on the influence that the supporting electrolyte has on their thickness and morphology. Ions that are destabilizing in the Hofmeister sense increase the thickness. The effect correlates well with the ion's tendency to lower the lower critical solution temperature (LCST) of pNIPAm films. AFM micrographs show small-scale globules. When the films were produced in the presence of a destabilizing salt (such as ammonium sulfate) one also observes larger features, resembling wrinkles. We attribute the globules to nucleated growth of surface-attached microgels, whereas the wrinkles presumably are produced by the collapse of hydrogen bubbles underneath a well-crosslinked film. Adding a chain transfer agent to the reactant solution reduces the lateral heterogeneities.
Keywords: Smart hydrogel; N; -isopropylacrylamide; Hofmeister series; Electrochemically induced polymerization; Added salt; Lower critical solution temperature; Surface morphology
Surfactant dependent morphology of polymeric capsules of perfluorooctyl bromide: Influence of polymer adsorption at the dichloromethane–water interface
by Emilia Pisani; Elias Fattal; Juliane Paris; Catherine Ringard; Véronique Rosilio; Nicolas Tsapis (pp. 66-71).
In a strategy to develop more stable ultrasound contrast agents (UCAs), we have designed a process to obtain nano/microcapsules with a single core of liquid perfluorocarbon within a biodegradable polymeric shell of homogeneous thickness. During the optimization of perfluorooctyl bromide (PFOB) encapsulation by solvent emulsion-evaporation, a marked influence of surfactants has been observed. While sodium cholate leads to spherical capsules of homogeneous thickness, sodium taurocholate induces to the formation of “acorn”-particles with one hemisphere of PFOB and another one of PLGA, and polyvinyl alcohol is responsible for the coexistence of both morphologies. Whereas the theoretical model proposed by Torza and Mason [J. Colloid Interface Sci. 33 (1970) 67] fails to predict the observed morphologies, microscopic observations of the evaporation and interfacial tension measurements provide an insight into the mechanism of formation of these structures. Most probably, there is a competition between PLGA and the surfactant stabilizing the emulsion at the dichloromethane–water interface. If PLGA is able to adsorb at the interface, the core–shell morphology is obtained, otherwise the acorn morphology is preferentially formed. When the surfactant rearrangement at the interface is long (>30 min), a coexistence of morphologies can be obtained.Final particle morphology, regular capsule or “acorn,” strongly depends on the ability of PLGA to adsorb or not at the dichloromethane–water interface.
Keywords: Polymeric capsules; Perfluorooctyl bromide; Encapsulation; Surfactant; Morphology
Preparation of polyaniline–metal composite nanospheres by in situ microemulsion polymerization
by Liang Li; Guoping Yan; Jiangyu Wu; Xianghua Yu; Qingzhong Guo (pp. 72-75).
Nanosized metal and polyaniline (PANi) composite spheres have been prepared via the polymerization of aniline using PdCl2 or HAuCl4 as the oxidant in a microemulsion system. The oxidization of aniline and the reduction of metal ion happened together during the reaction, yielding PANi and elemental metal simultaneously. The results of FTIR spectra suggested that the oxidation degree of PANi was affected by the initial ratio of metal ions to monomer in the microemulsion system. The PANi–metal nanospheres were characterized using X-ray photoelectron spectroscopy and the conductivity of the composite nanospheres was measured by conventional four-probe method. Scanning and transmission electron microscopy were used to show the morphology of the composites.Conductive polyaniline–metal composite nanospheres of about 50 nm in diameter, containing dispersed metal nanoparticles of 2–5 nm in size, were prepared in a 1-step oxidative polymerization in microemulsion system.
Keywords: Polyaniline; Palladium; Gold; Microemulsion; Composite nanospheres
Temperature-induced intermicellization and contraction in aqueous mixtures of sodium dodecyl sulfate and an amphiphilic diblock copolymer
by Ramón Pamies; Kaizheng Zhu; Anna-Lena Kjøniksen; Kenneth D. Knudsen; Bo Nyström (pp. 76-88).
Aqueous solutions of a thermoresponsive amphiphilic diblock copolymer, containing poly( N-isopropylacrylamide), in the presence of the anionic sodium dodecyl sulfate (SDS) surfactant can undergo a temperature-induced transition from loose intermicellar clusters to collapsed core–shell nanostructures. The polymer–surfactant mixtures have been characterized with the aid of turbidity, small-angle neutron scattering (SANS), intensity light scattering (ILS), dynamic light scattering (DLS), shear viscosity, and rheo-small angle light scattering (rheo-SALS). In the absence of SDS, compressed intermicellar structures are formed at intermediate temperatures, and at higher temperatures further aggregation is detected. The SANS results disclose a structure peak in the scattered intensity profile at the highest measured temperature. This peak is ascribed to the formation of ordered structures (crystallites). In the presence of a low amount of SDS, a strong collapse of the intermicellar clusters is observed at moderate temperatures, and only a slight renewed interpolymer association is found at higher temperatures because of repulsive electrostatic interactions. Finally, at moderate surfactant concentrations, temperature-induced loose intermicellar clusters are detected but no shrinking was registered in the considered temperature range. At a high level of SDS addition, large polymer–surfactant complexes appear at low temperatures, and these species are compressed at elevated temperatures. The rheo-SALS results show that the transition structures are rather fragile under the influence of shear flow.
Keywords: Thermally responsive copolymer; Turbidity; Small-angle neutron scattering; Light scattering; Polymer–surfactant interactions; Rheo-small angle light scattering
Investigations on mixed micelles of binary mixtures of zwitterionic surfactants and triblock polymers: A cyclic voltammetric study
by Rakesh Kumar Mahajan; Kulwinder Kumar Vohra; Arifa Shaheen; Vinod Kumar Aswal (pp. 89-95).
Cyclic voltammetry has been employed to investigate the mixed micellar behavior of the binary mixtures of different zwitterionic surfactants such as 3-(N,N-dimethylhexadecylammonio)propane sulfonate (HPS), 3-(N,N-dimethyltetradecylammonio)propane sulfonate (TPS) and 3-(N,N-dimethyldodecylammonio)propane sulfonate (DPS) with three triblock polymers (L64, F127 and P65) by using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as an electroactive probe at 25 °C. Critical micellar concentration ( cmc) has been determined from the plots of variation in peak current (ip) versus the total concentration of surfactant/triblock polymer. Diffusion coefficient of the electroactive species has also been reported. The regular solution theory approximation has been used to determine various micellar parameters of ideal systems. The variation in micellar mole fraction (X1) of the zwitterionic surfactant supports the formation of mixed micelles, which are rich in triblock polymer component in the surfactant rich region of the mixture and vice versa. The regular solution interaction parameter ( β) suggests the formation of mixed micelles due to the synergistic interactions in case of HPS/TPS/DPS+F127/P65 systems and gets affected by EO/PO ratio of triblock polymers.Synergistic interactions in the mixed micelles of zwitterionic surfactants (HPS, TPS and DPS) and triblock polymers (L64, F127 and P65) have been investigated using cyclic voltammetry.
Keywords: Cyclic voltammetry; Zwitterionic surfactants; Triblock polymers; Synergistic interactions
Structure and dynamical mechanical properties of suspensions of sodium caseinate
by Anne Pitkowski; Dominique Durand; Taco Nicolai (pp. 96-102).
Sodium caseinate is derived from casein which is the major milk protein and forms small star-like aggregates in aqueous solution. The dynamic mechanical properties of dense sodium caseinate suspensions were studied by measuring the shear viscosity and the frequency dependent loss and storage shear modulus. The viscosity is shown to increase strongly above a concentration,Cc, due to jamming of the aggregates.Cc depends little on the pH or on the ionic strength. The repulsion between the aggregates increases with decreasing temperature leading to jamming at lower concentrations. As a consequence the viscosity decreases strongly with increasing temperature for concentrated suspensions. The frequency dependent shear modulus of concentrated suspensions shows a solid like behaviour at high frequencies. Shear thinning is observed at Peclet numbers larger than unity.Sodium caseinate forms star-like aggregates that jam in dense aqueous suspensions leading to a sharp increase of the viscosity with increasing concentration or decreasing temperature.
Keywords: Caseinate; Viscosity; Micelle
Comparative SERS effectiveness of silver nanoparticles prepared by different methods: A study of the enhancement factor and the interfacial properties
by M.V. Cañamares; J.V. Garcia-Ramos; S. Sanchez-Cortes; M. Castillejo; M. Oujja (pp. 103-109).
Different Ag nanoparticles were prepared by four different methods (chemical reduction with trisodium citrate, chemical reduction with hydroxylamine hydrochloride, laser ablation and laser in situ photoreduction) to compare their applicability in surface-enhanced Raman scattering (SERS), their stability and other interfacial characteristics such as the pH, surface availability and the surface potential. This study was conducted by using the anthraquinone dye alizarin as a molecular probe since this molecule is able to be adsorbed onto the metal through three different forms, which relative proportions depend on the interfacial properties of the exposed metal surfaces.SERS enhancement factor ( G) of Ag nanoparticles prepared by four different methods: chemical reduction with hydroxilamine (SH), chemical reduction with citrate (SC), laser ablation (SA) and laser photoreduction (SP).
Keywords: SERS; Enhancement factor; Silver nanoparticles; Ablation; Photoreduction; Adsorption on metals
A novel inverse method for determining the refractive indices of medium and dispersed particles simultaneously by turbidity measurement
by Shenghua Xu; Jie Liu; Zhiwei Sun; Pu Zhang (pp. 110-116).
The refractive indices of particles and dispersion medium are important parameters in many colloidal experiments using optical techniques, such as turbidity and light scattering measurements. These data are in general wavelength-dependent and may not be available at some wavelengths fitting to the experimental requirement. In this study we present a novel approach to inversely determine the refractive indices of particles and dispersion medium by examining the consistency of measured extinction cross sections of particles with their theoretical values using a series of trial values of the refractive indices. The colloidal suspension of polystyrene particles dispersed in water was used as an example to demonstrate how this approach works and the data obtained via such a method are compared with those reported in literature, showing a good agreement between both. Furthermore, the factors that affect the accuracy of measurements are discussed. We also present some data of the refractive indices of polystyrene over a range of wavelengths smaller than 400 nm that have been not reported in the available literature.From the measured extinction cross sections for different sized particles, the refractive indices of medium and dispersed particles for different incident wavelengths can be simultaneously determined by the inverse method.
Keywords: Colloidal suspension; Refractive index; Polystyrene; Turbidity measurement; Light scattering
Growth kinetics for AgI nanoparticles in AOT reverse micelles: Effect of molecular length of hydrocarbon solvents
by Maxim G. Spirin; Sergei B. Brichkin; Vladimir F. Razumov (pp. 117-120).
The growth kinetics for AgI nanoparticles formed in the solutions of water/AOT reverse micelles in n-hexane, n-octane, n-decane, and n-dodecane were investigated. In small micelles, the rate of nanoparticles growth was found to be independent of the type of solvent, while in large micelles the growth rate grew with increasing length of solvent molecules. The effect was explained by a different amount of free water in the micelle pools of the same size.
Keywords: Reverse micelles; Nanoparticles; AgI; Hydrocarbon solvents
A facile method to prepare CdS/polystyrene composite particles
by Xinjian Cheng; Qiang Zhao; Yingkui Yang; Sie Chin Tjong; Robert K.Y. Li (pp. 121-128).
Nano-CdS/polystyrene composite particles were prepared via surfactant-free emulsion polymerization. 2-(Dimethylamino)ethyl methacrylate (DMEMA) was used as auxiliary monomer which co-polymerized with styrene (St) and provided the location for coordinating with Cd2+. By the coordination of Cd2+ ions to DMEMA, mono-disperse polystyrene with the Cd2+ ions on the particles surface were prepared successfully. With the release of S2− ions from the thioacetamide (TAA), cadmium sulfide (CdS) was formed. Nano-CdS/PS composite particles could be synthesized via this facile method. The order of materials addition and the amount of initiator both are playing important roles to the final morphologies of the composite particles. In the method proposed in this study, no surfactant was used, and the stable emulsion was successfully obtained. UV–vis absorption and fluorescence measurement indicated the quantum dot effect in the resulted nano-CdS/PS composite particles. The possible composite particle formation mechanism was presented.CdS/polystyrene composite particles synthesized by surfactant-free emulsion polymerization method.
Keywords: CdS/PS composite particles; Surfactant-free; Quantum dots; Fluorescence
Green fluorescent protein for in situ synthesis of highly uniform Au nanoparticles and monitoring protein denaturation
by Pallab Sanpui; Shivendra B. Pandey; Siddhartha Sankar Ghosh; Arun Chattopadhyay (pp. 129-137).
Purified recombinant green fluorescent protein (GFP) expressed in E. coli was used for single-step synthesis of gold nanoparticles (Au NPs) with extraordinary size specificity in aqueous medium. The fluorescence of GFP offered a probe for concomitant changes in the protein during the course of synthesis, in addition to the monitoring of the time-dependent formation of Au NPs by the surface plasmon resonance. Reaction of AuCl−4 with the protein produced spherical Au NPs having diameters ranging from 5–70 nm. Remarkably, addition of1.0×10−5M AgNO3 in the medium produced uniform spherical Au NPs with particle diameter of2.2±0.5nm. Fluorescence spectroscopic measurements suggest that during synthesis of Au NPs in absence of AgNO3, partial denaturation of the protein occurred resulting in the lowering of fluorescence intensity. On the other hand, when the NPs were synthesized in the presence of AgNO3 complete denaturation of the protein with complete loss of fluorescence could be observed, which was further confirmed by native and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE). However, use of AgNO3 only resulted neither in the formation of NPs nor had any significant effect on the fluorescence of GFP.Small and uniform Au nanoparticles of less than 5 nm are synthesized by GFP in presence of AgNO3 with concurrent denaturation of the protein.
Keywords: Green fluorescent protein; Gold nanoparticles; Green synthesis; Protein denaturation
Size-controllable synthesis of monodispersed colloidal silica nanoparticles via hydrolysis of elemental silicon
by Jianjun Guo; Xuehui Liu; Yuchuan Cheng; Yong Li; Gaojie Xu; Ping Cui (pp. 138-142).
A new method is presented for preparing monodisperse and uniform-size silica nanoparticles using a two-stage hydrolysis of silicon powder in aqueous medium. The influence of synthesis conditions including solution composition and temperature on the formation of silica nanoparticles were systematically investigated. The structure and morphology of the silica particles were characterized via transmission electron microscopy (TEM) and dynamic light scattering (DLS). Various-sized particles in the range 10–100 nm were synthesized. The size of the nanoparticles can be precisely controlled by using a facile regrowth procedure in the same reaction media.Highly monodispersed colloidal silica particles with diameter of 10–100 nm were obtained by hydrolysis of silicon powders.
Keywords: Colloidal silica; Nanoparticles; Silicon powder
Detachment of colloids from a solid surface by a moving air–water interface
by Prabhakar Sharma; Markus Flury; Jun Zhou (pp. 143-150).
Colloid attachment to liquid–gas interfaces is an important process used in industrial applications to separate suspended colloids from the fluid phase. Moving gas bubbles can also be used to remove colloidal dust from surfaces. Similarly, moving liquid–gas interfaces lead to colloid mobilization in the natural subsurface environment, such as in soils and sediments. The objective of this study was to quantify the effect of moving air–water interfaces on the detachment of colloids deposited on an air-dried glass surface, as a function of colloidal properties and interface velocity. We selected four types of polystyrene colloids (positive and negative surface charge, hydrophilic and hydrophobic). The colloids were deposited on clean microscope glass slides using a flow-through deposition chamber. Air–water interfaces were passed over the colloid-deposited glass slides, and we varied the number of passages and the interface velocity. The amounts of colloids deposited on the glass slides were visualized using confocal laser scanning microscopy and quantified by image analysis. Our results showed that colloids attached under unfavorable conditions were removed in significantly greater amounts than those attached under favorable conditions. Hydrophobic colloids were detached more than hydrophilic colloids. The effect of the air–water interface on colloid removal was most pronounced for the first two passages of the air–water interface. Subsequent passages of air–water interfaces over the colloid-deposited glass slides did not cause significant additional colloid removal. Increasing interface velocity led to decreased colloid removal. The force balances, calculated from theory, supported the experimental findings, and highlight the dominance of detachment forces (surface tension forces) over the attachment forces (DLVO forces).
Keywords: Colloids; Detachment; Surface tension forces; Air–water interface
Encapsulation of silica nanoparticles by redox-initiated graft polymerization from the surface of silica nanoparticles
by Huijun Wang; Mao Peng; Jun Zheng; Peng Li (pp. 151-157).
This study describes a facile and versatile method for preparing polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce4+) as an oxidant and an organic reductant immobilized on the surface of silica nanoparticles. The silica nanoparticles were firstly modified by 3-aminopropyltriethoxysilane, then reacted with poly(ethylene glycol) acrylate through the Michael addition reaction, so that hydroxyl-terminated poly(ethylene glycol) (PEG) were covalently attached onto the nanoparticle surface and worked as the reductant. Poly(methyl methacrylate) (PMMA), a common hydrophobic polymer, and poly( N-isopropylacrylamide) (PNIPAAm), a thermosensitive polymer, were successfully grafted onto the surface of silica nanoparticles by ‘grafting from’ polymerization initiated by the redox reaction of Ce4+ with PEG on the silica surface in acid aqueous solutions. The polymer-encapsulated silica nanoparticles (referred to as silica@PMMA and silica@PNIPAAm, respectively) were characterized by infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. On the contrary, graft polymerization did not occur on bare silica nanoparticles. In addition, during polymerization, sediments were observed for PMMA and for PNIPAAm at a polymerization temperature above its low critical solution temperature (LCST). But the silica@PNIPAAm particles obtained at a polymerization temperature below the LCST can suspend stably in water throughout the polymerization process.Polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce4+) as a oxidant and an organic reductant immobilized on the surface of silica nanoparticles.
Keywords: Surface-initiated polymerization; Core–shell structure; Redox; Ceric ion; Silica nanoparticles
Facile synthesis of ordered magnetic mesoporous γ-Fe2O3/SiO2 nanocomposites with diverse mesostructures
by Yangang Wang; Jiawen Ren; Xiaohui Liu; Yanqin Wang; Yun Guo; Yanglong Guo; Guanzhong Lu (pp. 158-165).
On the basis of a sol–gel process, a facile, low cost, and one-step approach for preparing ordered magnetic mesoporous γ-Fe2O3/SiO2 nanocomposites by an evaporation-induced self-assembly (EISA) approach is presented. Various mesostructured silica materials ( P6mm or Im3m) incorporated with different amounts of iron oxide (nSi/nFe=9/1, 8/2, 7/3, respectively) were synthesized and characterized by XRD, TEM, N2-sorption analyses, and superconducting quantum interference device (SQUID) magnetometer. The HCl-leaching experiments together with TEM micrographs and nitrogen sorption analysis suggested that most of the γ-Fe2O3 domains of several nanometers were embedded in the silica walls, rather than dispersed in the mesopores, which could cause the significant pore clogging reported in some studies. The release behaviors of lysozyme from these magnetic porous nanocomposites were investigated for the possible application of drug targeting and control release. The influence of iron precursors was also studied and a possible mechanism was proposed. The hydrolysis of Fe3+ ions under weakly acidic conditions and the induced formation of SiOFe bonds may account for the synthesis of this kind of nanocomposite. These multifunctional nanostructured materials would have a wide range of applications in toxin removal, catalysis, waste remediation, and biological separation as well as novel drug-carrier technologies.
Keywords: Sol–gel; Magnetic materials; Mesoporous materials; Nanocomposites
Modeling liquid porosimetry in modeled and imaged 3-D fibrous microstructures
by S. Jaganathan; H. Vahedi Tafreshi; B. Pourdeyhimi (pp. 166-175).
In this paper, an analysis to distinguish the geometric and porosimetric pore size distributions of a fibrous material is presented. The work is based on simulating the intrusion of nonwetting fluid in a series of 3-D fibrous microstructures obtained from 3-D image reconstruction or virtual geometries mathematically generated according to the properties of the media. We start our study by computing the pore size distribution of two typical hydroentangled nonwoven materials and present a theoretical model for their geometric pore size distributions based on Poisson line network model of the fibrous media. It is shown that the probability density function of the geometric pore size distribution can be approximated by a two-parametric Gamma distribution. We also study connectivity of the pore space in fibrous media by computing and comparing the accessible and allowed pore volumes in the form access function graphs. It is shown that the so-called ink-bottle effect can significantly influence the fluid intrusion in a porous material. The pore space connectivity of a homogeneous fibrous media is observed to be a function of thickness, solid volume fraction (SVF), and fiber diameter. It is shown that increasing the materials' thickness or SVF, while other properties are kept constant, reduces the pore space connectivity. On the other hand, increasing the fiber diameter enhances the connectivity of the pores if all other parameters are fixed. Moreover, modeling layered fibrous microstructures; it is shown that the access function graphs can be used to detect the location of the bottle neck pores in a layered/composite porous material.The work is based on simulating the intrusion of nonwetting fluid into 3-D fibrous microstructures obtained from digital volumetric imaging. A novel analysis on pore size distribution and pore space connectivity is presented.
Keywords: Pore size distribution; 3-D imaging; Access function; Gamma distribution; Fibrous media; Filtration; Ink-bottle effect; Hydroentangling; Porosimetry
Characterization of physical structure of silica nanoparticles encapsulated in polymeric structure of polyamide films
by Puyam S. Singh; Vinod K. Aswal (pp. 176-185).
Polyamide nanocomposite films were prepared from nanometer sized silica particles and trimesoyl chloride– m-phenylene diamine based polyamides. The type of silica nanoparticles used is commercial LUDOX® HS-40 and the particle size characterized by the radius of gyration(Rg) is about 66 Å. The immediately prepared films were easily broken into particles to form colloidal-like dilute suspension of the silica–polyamide composite particles in D2O–H2O solutions for SANS measurements, that in this dilute system SANS data the complication of scattering data from the interacting particles is minimized. At about 60% D2O of the sample solution, the silica is contrasted out, therefore the SANS profiles are predominantly from the organic polyamide scattering. The SANS profile of the sample solutions measured at 90% D2O clearly indicates scattering from both silica and polymer. The scattering heterogeneities for two-phase system were evident from the validity of the Debye–Bueche expression in case of the nanocomposite with high silica loading. At limited silica loading of the nanocomposite, interaction between the silica and polymer chains forming core–shell morphology was observed. The transport properties of the membranes made from the nanocomposite films were measured on a batch type test kit with an aqueous solution of 500 ppm dioxane concentration at pressures ranging from 50 to 200 psig, and correlated to their composite structure.Nanoscale morphology of silica nanoparticles encapsulated in the trimesoyl chloride– m-phenylene diamine based polyamide films has been investigated by SANS study.
Keywords: Silica nanoparticles; Polyamide film; Nanocomposite membrane; SANS
Investigation of the effect of calcination temperature on HMDS-treated ordered mesoporous silica film
by Tae-Jung Ha; Hyung-Ho Park; Sang-Bae Jung; Hojun Ryu; Byoung-Gon Yu (pp. 186-190).
To reduce signal delay in ultra-large-scale integrated circuits, an intermetal dielectric with low dielectric constant is required. Ordered mesoporous silica film is appropriate for use as an intermetal dielectric due to its low dielectric constant and superior mechanical properties. To reduce the dielectric constant, an ordered mesoporous silica film prepared by a tetraethoxysilane/methyltriethoxysilane silica precursor and Brij-76 block copolymer was surface-modified by hexamethyldisilazane (HMDS) treatment. HMDS treatment substitutedOH withSi(CH3)3 groups on the silica surface. After treatment, ordered mesoporous silica films were calcined at various calcination temperatures, and the calcination temperature to obtain optimal structural, electrical, and mechanical properties was determined to be approximately 300 °C.Though substitutedSi(CH3)3 groups induce stress on silica wall in pore structure, calcination over 300 °C can reduce the stress and enhance the dielectric and mechanical properties of mesoporous film.
Keywords: Ordered mesoporous silica film; HMDS; Calcination; MTES; Brij-76
Effect of various additives on the performance of a newly developed PVC based potentiometric sensor for anionic surfactants
by Rakesh Kumar Mahajan; Arifa Shaheen (pp. 191-195).
A new poly(vinyl chloride) PVC membrane electrode to determine monomer concentrations of dodecylbenzenesulphonate ions (DBS−) based on a neutral ion-pair carrier complex of dodecyltrimethylammonium–dodecylbenzenesulphonate (DTA+–DBS−), is reported here. The electrode exhibits a slope of 51.25 mV per decade for DBS− ions. The DBS− ion selective electrode (ISE) can determine monomer units down to concentrations as low as 3.32×10−4 M. The effect of three kinds of additives, i.e. alcohols, glycols and triblock polymers on the performance of the surfactant selective electrode is studied systematically. The effect of foreign anions along with primary ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined using the fixed interference method (FIM) at 1.0×10−2 M concentration of foreign anions. The sensor responds well to the surfactant ions in the presence of additives at lower concentration. The Gibbs free energy of micelle formation (Δ Gm) of sodium dodecylbenzenesulphonate (SDBS) in the presence of various additives is calculated and found to vary differently with respect to the increase in the amount of additives. The sensor worked in the acidic pH range with a short response time of 30 s. The lifetime of the sensor is more than three months. The sensor was further used to determine the amount of DBS− in local detergents. This method of determining anionic surfactants was found to be quite accurate when compared with classical methods.Typical potentiometric response curve of a dodecylbenzenesulphonate ion selective electrode (DBS−-ISE) based on a neutral ion-pair carrier complex of dodecyltrimethylammonium–dodecylbenzenesulphonate.
Keywords: Ion selective electrode; Potentiometry; Additive effect; Dodecyltrimethylammonium–dodecylbenzenesulphonate sensor; Free energy of micellization
The head-on colliding process of binary liquid droplets at low velocity: High-speed photography experiments and modeling
by Feng-Chao Wang; Jiang-Tao Feng; Ya-Pu Zhao (pp. 196-200).
The experimental and theoretical studies are reported in this paper for the head-on collisions of a liquid droplet with another of the same fluid resting on a solid substrate. The droplet on the hydrophobic polydimethylsiloxane (PDMS) substrate remains in a shape of an approximately spherical segment and is isometric to an incoming droplet. The colliding process of the binary droplets was recorded with high-speed photography. Head-on collisions saw four different types of response in our experiments: complete rebound, coalescence, partial rebound with conglutination, and coalescence accompanied by conglutination. For a complete rebound, both droplets exhibited remarkable elasticity and the contact time of the two colliding droplets was found to be in the range of 10–20 ms. With both droplets approximately considered as elastic bodies, Hertz contact theory was introduced to estimate the contact time for the complete rebound case. The estimated result was found to be on the same order of magnitude as the experimental data, which indicates that the present model is reasonable.A droplet collides with another one resting on a PDMS substrate and exhibits remarkable elasticity. The estimated contact time is on the same order of magnitude as the experimental result.
Keywords: Droplet collision; Rebound; Coalescence; Conglutination; Contact time; Hertz contact theory
Wetting in the nanoscale: A continuum mechanics approach
by F. Barberis; M. Capurro (pp. 201-210).
A continuum mechanics model has been developed to study the equilibrium shape of nanometric droplets on a planar solid substrate and how, in this scale, the contact angle depends on the drop size. The drop is modeled as a liquid volume enclosed in an inextensible membrane, subject to an isotropic tension (the surface tension) and to a field of surface forces including, in the proximity of the solid, the liquid-to-solid interactions, envisaged as a generic potential force per unit surface directed normally to the solid surface (i.e. vertically). The only conditions required to solve the problem are those of mechanical and thermodynamic equilibrium. The predictions of the model are discussed in comparison with data on nanodrops retrieved by a special AFM device for a number of different liquid–solid systems.A continuum mechanics model has been developed to study the equilibrium shape of nanometric droplets on a planar solid substrate and how, in this scale, the contact angle depends on the drop size.
Keywords: Liquids; Amorphous oxides; Capillary phenomena; Wetting; Surface energy; Atomic force microscopy (AFM)
Preparation of highly concentrated nanostructured dispersions of controlled size
by Stefan Salentinig; Anan Yaghmur; Samuel Guillot; Otto Glatter (pp. 211-220).
This article presents the use of a shearing procedure for the preparation of stable nanostructured dispersions of lipid mesophases. This new application of the shearing technique is compared with the well-established ultrasonication method for the emulsification of these mesophases in water in terms of particle size, particle size distribution and available concentration range. With a laboratory-built shear device based on a Couette cell, it was possible to produce high quantities of internally self-assembled emulsion particles of controlled size at concentrated hydrophobic phase contents (ϕo) of up to 70 wt%. The concentration limit of 70 wt% could be reached however, the maximum attainable concentration depended on the internal structure type of the particles. The limit was thus easily attained for emulsified microemulsions (EME) as well as for the emulsified inverse hexagonal phase (H2), whereas it was found to be lower for emulsified discontinuous ( Fd3m) and bicontinuous ( Pn3m) cubic phases. Moreover, by shearing, it was possible to keep the size of the particles relatively constant when increasingϕo, whereas the particle size significantly increased withϕo when ultrasonication was employed. By means of ultrasonication, the hydrodynamic radius of the particles could be tuned linearly between 85 to 180 nm as a function ofϕo up to a maximum of 20 to 30 wt%. Below the maximum concentration limit, particles displayed a well-controlled size.Hydrodynamic radius for nanostructured dispersions made from Dimodan U and R(+)limonene formed by ultrasonication and shearing as functions of the dispersed phase content.
Keywords: Emulsified liquid crystalline phases; Emulsified microemulsion; SAXS; Dynamic light scattering; Hexosomes; Cubosomes; Shearing; Ultrasonication
Shear rheology and porous media flow of wormlike micelle solutions formed by mixtures of surfactants of opposite charge
by Mario R. Rojas; Alejandro J. Müller; A. Eduardo Sáez (pp. 221-226).
The rheology of solutions of wormlike micelles formed by oppositely charged surfactant mixtures (cationic cetyl trimethylammonium p-toluene sulfonate, CTAT, and anionic sodium dodecyl sulfate, SDS), in the dilute and semi-dilute regimes, were studied under simple shear and porous media flows. Aqueous mixtures of CTAT and SDS formed homogeneous solutions for SDS/CTAT molar ratios below 0.12. Solutions of mixtures exhibited a strong synergistic effect in shear viscosity, especially in the semi-dilute regime with respect to wormlike micelles, reaching a four order of magnitude increase in the zero-shear rate viscosity for solutions with 20 mM CTAT. Oscillatory shear results demonstrated that the microstructure of CTAT wormlike micelles is sensitive to SDS addition. The cross-over relaxation times of wormlike micelles of 20 mM CTAT solutions increased by three orders of magnitude with the addition of up to 2 mM of SDS, and the solutions became increasingly elastic. The shear thickening process observed in shear rheology became more pronounced in porous media flow due to the formation of stronger cooperative structures induced by the extensional component of the flow.Shear viscosity as a function of shear rate for CTAT/SDS mixtures. The concentration of CTAT is fixed at 20 mM while that of SDS is indicated in the legend.
Keywords: CTAT; SDS; Wormlike micelles; Surfactant mixtures
Interactions of phenol with cationic micelles of hexadecyltrimethylammonium bromide studied by titration calorimetry, conductimetry, and1H NMR in the range of low additive and surfactant concentrations
by Radhouane Chaghi; Louis-Charles de Ménorval; Clarence Charnay; Gaëlle Derrien; Jerzy Zajac (pp. 227-234).
Interactions of phenol (PhOH) with micellar aggregates of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions at surfactant concentrations close to the CMC and phenol contents of 1, 5, or 10 mmol kg−1 have been investigated at 303 K by means of titration calorimetry, solution conductimetry, and1H NMR spectroscopy. Estimates of the main thermodynamic parameters related to HTAB micellization were made for PhOH/HTAB/H2O systems based on the specific conductivity measurements and calorimetric determination of the cumulative enthalpy of dilution as functions of the surfactant concentration at a fixed additive content. The combined analysis of the results obtained in H2O solutions pointed to the preferential location of PhOH in the outer micelle parts by an enthalpy-driven mechanism. Additional PhOH molecules were located increasingly deeper within the micelle core. The1H NMR study of PhOH solubilization by 1.5 mmol kg−1 HTAB solutions in D2O indicated that the two categories of the solubilization site became saturated with the solubilizate already at the lowest additive content. Dissimilar amounts of the solubilized material in H2O and D2O solutions were ascribed to the difference in the initial micelle structures formed in the two solvents, as inferred from calorimetry and1H NMR studies of the HTAB micellization in D2O and H2O.Phenol is located preferentially in the outer portions of cationic micelles by an enthalpy-driven solubilization mechanism, but some additional molecules are forced to penetrate deeper into the micellar structures.
Keywords: Micellar solubilization; Hexadecyltrimethylammonium micelles; Phenol solubilization loci; Phenol–micelle interactions; Titration calorimetry; Conductimetry; 1; H NMR spectroscopy
Novel highly fluorinated sulfamates: Synthesis and evaluation of their surfactant properties
by Khaled Debbabi; Frédéric Guittard; Serge Geribaldi (pp. 235-239).
Two synthetic pathways have been elaborated to prepare new series of highly fluorinated sulfamates with excellent yields. Surface tension measurements at the air/water interface showed that these compounds constitute new excellent non-ionic surfactants exhibiting high surface activity in the range of the best non-ionic fluoro surfactants already described in the literature. The most important feature of this work is that, in comparison with the classical non-ionic fluoro surfactants, these sulfamates are easily synthesized in a monodisperse form from classical and relatively non-toxic starting materials. The critical micelle concentration (CMC), the maximum surface excess concentration(Γ) and the minimum area per molecule(a) have been calculated from the surface tension measurements on surfactant aqueous solutions. Relationships have been established between the length of both the fluorinated tail and hydrocarbon spacer linking the hydrophobic tail to the hydrophilic head, and the interfacial properties.A new class of sulfamates bearing a hydrophobic and lipophobic perfluorinated chain linked to the functional group OSO2NH2 by a hydrocarbon spacer has been prepared by two efficient pathways with excellent yields. Their interfacial behaviour in aqueous solutions shows that these compounds constitute a news series of excellent fluorinated surfactants.
Keywords: Sulfamates; Non-ionic surfactants; Surface tension; Fluorinated surfactants; Synthesis of; Critical micelle concentration; Maximum surface excess concentration
The dielectric response of a colloidal spheroid
by C. Chassagne; D. Bedeaux (pp. 240-253).
In this article, we present a theory for the dielectric behavior of a colloidal spheroid, based on an improved version of a previously published analytical theory [C. Chassagne, D. Bedeaux, G.J.M. Koper, Physica A 317 (2003) 321–344]. The theory gives the dipolar coefficient of a dielectric spheroid in an electrolyte solution subjected to an oscillating electric field. In the special case of the sphere, this theory is shown to agree rather satisfactorily with the numerical solutions obtained by a code based on DeLacey and White's [E.H.B. DeLacey, L.R. White, J. Chem. Soc. Faraday Trans. 2 77 (1981) 2007] for all zeta potentials, frequencies andκa⩾1 where κ is the inverse of the Debye length and a is the radius of the sphere. Using the form of the analytical solution for a sphere we were able to derive a formula for the dipolar coefficient of a spheroid for all zeta potentials, frequencies andκa⩾1. The expression we find is simpler and has a more general validity than the analytical expression proposed by O'Brien and Ward [R.W. O'Brien, D.N. Ward, J. Colloid Interface Sci. 121 (1988) 402] which is valid forκa≫1 and zero frequency.We derived the dipolar coefficientsβi for an ellipsoidal colloid as a function of the different complex conductivities (Ki) and depolarization factors (Li).
Keywords: Colloidal spheroids; Dielectric spectroscopy; Complex conductivity; Electrokinetics; Dipolar coefficient; Double layer polarization; Zeta potential
Shear and extensional rheology of solutions of mixtures of poly(ethylene oxide) and anionic surfactants in ionic environments
by Miguel F. Torres; Alejandro J. Müller; Miklos A. Szidarovszky; A. Eduardo Sáez (pp. 254-260).
Interactions between a high molecular weight poly(ethylene oxide) (PEO) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions were investigated by shear and extensional rheometry. Results for mixtures between PEO and sodium dodecyl sulfate (SDS) are also presented for comparison purposes. Addition of anionic surfactants to PEO solutions above the critical aggregation concentration (CAC), at which micellar aggregates attach to the polymer chain, results in an increase in shear viscosity due to PEO coil expansion, and a strengthening of interchain interactions. In extensional flows, these interactions result in a decrease of the critical shear rate for the onset of the characteristic extension thickening of the PEO solutions that is due to transient entanglements of polymer molecules. The relaxation times associated with these transient entanglements are not directly proportional to the shear viscosity of the solutions, but rather vary more rapidly with surfactant concentration. In the presence of an electrolyte, coil contraction results in lower shear viscosities and a decrease in the extension thickening effects at surfactant concentrations just beyond the CAC. The relaxation times associated with transient entanglement reach a minimum at the same surfactant concentration as the shear viscosity, which indicates that coil contraction is responsible for the observed effects in both types of flow. However, the increase in extensional-flow entanglement relaxation times is much more abrupt than the decrease in shear viscosity. All these results point to a greater sensitivity of extensional flows on the molecular conformation of PEO/surfactant complexes.Simultaneous plot of low-shear rate shear viscosity (open symbols) and apparent extensional viscosity in the extension thickening regime (solid symbols) for 100 ppm PEO/SDBS solutions and 0.1 M NaCl. The same solution reaches a minimum viscosity in the two flows at the point of maximum contraction of the PEO coils induced by attachment of micellar aggregates to the polymer chain.
Keywords: Polymer/surfactant interactions; Elongational flows; Poly(ethylene oxide); Sodium dodecyl sulfate; Sodium dodecyl benzene sulfonate
Characterization of crystal structure in binary mixtures of latex globules
by Lei Liu; Shenghua Xu; Jie Liu; Zhiwei Sun (pp. 261-266).
Colloidal crystals formed by two types of polystyrene particles of different sizes (94 and 141 nm) at various number ratios (94:141 nm) are studied. Experiments showed that the formation time of crystals lengthens as the number ratio of the two components approaches 1:1. The dependence of the mean interparticle distance(D0), crystal structure and alloy structure on the number ratio of the two types of particles was studied by means of Kossel diffraction technique and reflection spectra. The results showed that as the number ratio decreased, the mean interparticle distance(D0) became larger. And the colloidal crystal in binary mixtures is more preferably to form the bcc structure. This study found that binary systems form the substitutional solid solution (sss)-type alloy structure in all cases except when the number ratio of two types of particles is 5:1, which results instead in the superlattice structure.Kossel pattern and reflection spectra were used to systematically study the effect of the number ratio of the two types of particles on the characteristics of binary colloidal crystals.
Keywords: Colloidal crystal; Polystyrene; Kossel diffraction; Reflection spectra; The mean interparticle distance; Binary system
Solvent-tuned multiple self-assembly of a new sugar-appended gelator
by Jiaxi Cui; Jia Zheng; Wenqiang Qiao; Xinhua Wan (pp. 267-274).
4-(4′-Butoxyphenyl)phenyl- β- O-d-glucoside was synthesized as a low-molecular-mass gelator. It was able to immobilize a variety of aqueous and organic solvents in large amounts through the formation of three-dimensional self-assembled fibrillar networks. The morphologies of the aggregates depended on the nature of solvent where they were formed. Planar ribbons were observed in water, while helical ribbons were dominant in toluene and sheets in CHCl3. The xerogel from water exhibited a lamellar structure with a d-spacing of 2.45 nm as demonstrated by 1D-WAXD, indicating a bilayer structure interdigitated with butoxy tails, whereas the xerogel from CHCl3 or toluene yielded a lamellar structure with a d-spacing of 3.05 nm, implying a bilayer structure interdigitated with glycosyl heads. Increasing the content of 1,4-dioxane in water caused a gradual transformation from planar to twisted ribbons and then tubes.
Keywords: Sugar; Low-molecular-mass gelator; Self-assembly; Twisted ribbon; Nanotube
Morphological transformation of self-assembled nanostructures prepared from cholesteryl acyl didanosine and the optimal formulation of nanoparticulate systems: Effects of solvents, acyl chain length and poloxamer 188
by Yiguang Jin; Ping Ai; Rui Xin; Dawei Chen (pp. 275-282).
Self-assembled nanostructures were obtained through injecting cholesteryl-succinyl didanosine (CSD) solutions in tetrahydrofuran (THF) into water. The incorporation of THF leads to CSD flexible bilayers. Spherical vesicles of CSD initially formed based on hydrophobic interaction and transformed to short nanotubes with THF leaving. A large proportion of THF led to formation of long flexible nanoribbons, also transforming to short nanotubes after removing THF because of rigid bilayers recovering. Cholesteryl-adipoyl didanosine (CAD) only formed spherical vesicles due to its long and flexible tails. A triblock copolymer, poloxamer 188 (P188) could insert into CSD monolayers at the air/water interface. P188 stabilized CSD nanoparticulate systems by incorporation and adsorption. The optimal formulation of nanoparticulate systems was identified and the appropriate ratio of CSD/P188 and CSD concentration in injected solutions were the keys. A highly concentrated system had a narrow size distribution, allowing heat sterilization at 100 °C, and resisting aggregation under high gravity accelerations in spite of the low zeta potential of −18.5 mV. A gel–liquid crystalline phase transition at 47 °C occurred. The system may become promising self-assembled drug delivery systems (SADDS) for anti-HIV therapy.Spherical vesicles are formed by injecting cholesteryl-succinyl didanosine solutions in THF into water. THF in bilayers improves spherical vesicles to fuse to long flexible nanoribbons further transforming to short nanotubes.
Keywords: Bilayers; Cholesteryl derivatives; Didanosine; Drug delivery; Nanoribbons; Nanotubes; Poloxamer; Tetrahydrofuran; Self-assembly; Vesicles
Photocatalytic formulations for protein fibers: Experimental analysis of the effect of preparation on compatibility and photocatalytic activities
by Wing Sze Tung; Walid A. Daoud (pp. 283-288).
In this article, we report an optimization study of a photocatalytic self-cleaning sol–gel formulation. In particular we studied the effect of formulation preparation time on the formation of anatase titanium dioxide sol and its compatibility to protein keratin-type wool fibers. The sols were formed by a low temperature sol–gel process. The nucleated anatase was characterized by UV–vis transmission, particle size distribution, X-ray diffraction, and transmission electron microscopy. The compatibility between the formulations and wool fibers is evaluated by field-emission scanning electron microscopy, UV transmission, and mechanical properties. The photocatalytic self-cleaning activity of coated fibers and its reproducibility are also discussed.Nanocrystalline anatase titanium dioxide was successfully deposited on protein keratin-type wool fibers with good compatibility and reproducible self-cleaning activities by a simple dip-coating sol–gel process.
Keywords: Titanium dioxide; Photocatalysis; Self-cleaning; Nano-coating; Wool
Synthesis and surface characterization of yttrium doped boehmite nanofibers
by Yanyan Zhao; Ray L. Frost (pp. 289-299).
Yttrium doped boehmite nanofibers with varying yttrium content have been synthesized at low temperatures using a soft-chemistry route in the presence of polyglycol ether surfactant. The effect of yttrium content, hydrothermal temperature on the growth of boehmite nanostructures was systematically studied. Nanofibers were formed in all samples with varying doped Y% treated at 100 °C; large Y(OH)3 crystals were also formed at high yttrium doping. Treated at an elevated temperatures resulted in a remarkable changes in size and morphology for samples with the same doped Y content. The resultant nanofibers were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray analysis (EDX), N2 adsorption and thermogravimetric analysis. The detailed characterization and discussion on the Y doped nanostructures are presented.
Keywords: Boehmite; Surface characterization; Nanofiber; Surface area; Transmission electron microscopy
by Arthur Hubbard (pp. 300-300).
Probing of polyelectrolyte monolayers by zeta potential and wettability measurements
by M. Kolasińska; M. Zembala; M. Krasowska; P. Warszyński (pp. 301-304).
Detection of the very first step of polyelectrolyte adsorption onto a solid support is of great importance for understanding mechanisms of solid surface modification. It was shown that streaming potential and contact angle measurements can be successfully used for polyelectrolyte (PE) adsorption characterization in a broad range of surface coverage. Cationic polyallylamine hydrochloride (PAH) was used for the formation of the layer. The electrokinetic characteristics of the substrate covered by the PAH layer were compared with contact angles measured under wet (captive air bubble/substrate in water) and dry (sessile water droplet/dried substrate) conditions. It has been demonstrated that contact angle values determined under both conditions are in good agreement. The observed rapid increase in the contact angle from zero for the bare mica surface to the value close to one characteristic of the PAH monolayer appears in the same PAH coverage range as zeta potential value changes due to adsorption. These results show that wettability can be as sensitive to the presence of small amounts of adsorbed species as electrokinetic measurements.Streaming potential and wettability measurements performed for polyelectrolyte-covered solid substrates proved that both techniques can be used for detection of very small amounts of adsorbed species.
Keywords: PAH adsorption; Streaming potential; Wetting characteristics
New explanation of the high electron concentration at the surface of a carbon electrode
by E.V. Veitsman (pp. 305-305).
It is pointed out that the high surface electron concentration in the carbon electrode gives rise to surface repulsion forces between ensembles of electrons and carbon atoms.The interface as the three-dimensional area. ρ is the density of medium,ρ1,ρ2 are densities of electrons at the boundary points 1 and 2 accordingly, X is the coordinate axis, 1–2 is the width of the interface.
Keywords: Electron; Electrode; Surface; Repulsion forces