Journal of Colloid And Interface Science (v.302, #2)
Editorial Board (CO1).
Removal of copper on composite sewage sludge/industrial sludge-based adsorbents: The role of surface chemistry by Mykola Seredych; Teresa J. Bandosz (379-388).
Sewage sludge and industrial waste oil sludge were pyrolyzed in an inert atmosphere at 650 or 950 °C, either as single components or as 50:50 mixtures. Composite materials were used as adsorbents of copper ions from aqueous solution. The capacity for copper removal was comparable to that of commercial activated carbon. To relate the performance of materials to their properties, the surface features were characterized using adsorption of nitrogen, thermal analysis, XRF, potentiometric titration, and elemental analysis. The results indicated that a high copper removal capacity could be linked to basic surface pH and specific compounds present on the surface. The high removal ability of materials obtained at 650 °C is attributed to cation exchange reactions between calcium and magnesium in aluminosilicates, formed on their surface during heat treatment, and copper. On the other hand, the high degree of mineralization of the surface of the materials obtained at 950 °C promotes copper complexation and its surface precipitation as hydroxides or hydroxylcarbonate entities.
Keywords: Industrial sludges; Pyrolysis; Copper adsorption; Surface chemistry; Porosity;
Determination of the parameters for the 1-pK triple-layer model of ion adsorption onto oxides from known parameter values for the 2-pK TLM by Wojciech Piasecki (389-395).
Prior knowledge of the model parameters describing the metal oxide/simple electrolyte interface is frequently crucial to successful application of surface complexation modeling. On the basis of the parameter values for the 2-pK triple-layer model recently published by Sverjensky, the parameters for the 1-pK TLM were determined. This was done by fitting (using the 1-pK model) the proton surface charge and ion adsorption isotherms generated by the 2-pK TLM. It was assumed that inner-layer capacitance was the same for both models. A strong correlation was found between ion adsorption constants of different electrolytes on the same oxide predicted by both models. Additionally, the 1-pK and 2-pK models predict different electrokinetic potentials in spite of very similar values of calculated surface charge and ion adsorption isotherms when the same value of outer-layer capacitance is assumed. Because the value of outer-layer capacitance practically does not influence surface charge and electrolyte adsorption isotherms, it can be treated as a freely adjusted parameter, the value of which can be estimated if we have measured the electrokinetic potential.Correlation between values of adsorption constants of monovalent anions sorbing on different oxides obtained by using the 1-pK and the 2-pK triple-layer model.
Keywords: 1-pK; 2-pK; Triple-layer model; Parameters; Ion adsorption; Metal oxide;
Use of statistical design of experiments to evaluate the sorption capacity of 7-amine-4-azaheptylsilica and 10-amine- 4-azadecylsilica for Cu(II), Pb(II), and Fe(III) adsorption by Camila G. Passos; Fernanda S. Ribaski; Nathália M. Simon; Araci A. dos Santos; Júlio C.P. Vaghetti; Edilson V. Benvenutti; Éder Cláudio Lima (396-407).
7-Amine-4-azaheptylsilica (AAH Si) and 10-amine-4-azadecylsilica (AAD Si) were prepared and used for removal of Cu(II), Pb(II), and Fe(III) from aqueous solutions. Full 23 factorial designs with two pseudo-central points were carried out in order to achieve the best conditions of the batch adsorption procedure for metallic ion uptake by the adsorbents. To continue the optimizations, central composite surface design was also employed. These two independent statistical designs of experiments lead to the following conditions: m = 30.0 mg of adsorbent; pH 6.0 for Cu(II) and Pb(II), pH 4.0 for Fe(III); t of contact 180 min to guarantee equilibration at higher adsorbate concentration. After optimization of the conditions, isotherms of the metallic ions adsorbed on the AAH Si and AAD Si adsorbents were obtained, which were fitted to nonlinear Langmuir and Freundlich isotherm models.Response surface for the metallic ions adsorption on AAH Si and AAD Si as adsorbents.
Keywords: Adsorption; Grafting silica gel; Cu(II), Pb(II), and Fe(III); Isotherm models; Statistical design of experiments;
Sorption of atrazine on conventional and surface modified activated carbons by P. Chingombe; B. Saha; R.J. Wakeman (408-416).
The sorption of atrazine from water has been studied using a conventional activated carbon, F400, an annealed carbon sample, F400AN, and an aminated carbon sample, F400NH2. Characterisation of the carbon samples showed that sample F400NH2 had the highest proportion of micropores, but had the lowest values of point of zero charge (PZC) and iso-electric point (IEP). This was attributed to the existence of a high proportion of oxygen containing functional groups. Sorption data showed that sample F400AN was superior in the sorption of atrazine to samples F400 and F400NH2. It was noted that pore size distribution alone was not the only contributing factor for the uptake of atrazine onto the activated carbons. The sorption data were fitted well using the Freundlich isotherm. The free energy change showed that sorption of atrazine on activated carbons is a spontaneous process. A pseudo-second order kinetic model was used for analysing the kinetic data, and it was concluded that adsorption of atrazine was controlled by a film diffusion mechanism.The sorption of atrazine from water was studied in detail using a conventional activated carbon, F400, an annealed carbon sample, F400AN and an aminated carbon sample, F400NH2. A pseudo-second order kinetic model was used for analysing the kinetic data.
Keywords: Activated carbon; Surface modification; Characterisation; Sorption; Atrazine; Adsorption isotherms; Kinetic studies; Pseudo-second order kinetic model;
Adsorption behavior and activity of hexokinase by S.M. Pancera; H. Gliemann; Th. Schimmel; D.F.S. Petri (417-423).
The study on the adsorption of hexokinase (HK) onto silicon wafers was carried out by means of in situ ellipsometry and atomic force microscopy in the liquid. The thickness values of the adsorbed HK layer determined by both techniques were in excellent agreement and evidenced HK monolayer formation. The adsorption of HK onto Si wafers was favored at low ionic strength, indicating that the adsorption is mainly driven by electrostatic forces, since salt screens not only the segment–segment repulsion but also the segment–surface attraction when the salt concentration increases. The enzymatic activity of free HK and of adsorbed HK was measured as a function of time. Free HK in solution lost activity upon storage. Contrarily, adsorbed HK kept its activity level even after 48 h storage at room temperature. This outstanding behavior was attributed to specific orientation of the HK active site to the solution.AFM in the liquid and in situ ellipsometry evidenced the formation of a smooth HK monolayer on Si wafers. Upon storing free HK lost activity, while immobilized HK kept enzymatic activity.
Keywords: Hexokinase; Ellipsometry; AFM; Adsorption; Enzymatic activity;
Sorption of AsV on aluminosilicates treated with FeII nanoparticles by Barbora Doušová; Tomáš Grygar; Alexandr Martaus; Lucie Fuitová; David Koloušek; Vladimír Machovič (424-431).
Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, three samples of clay minerals (natural metakaoline, natural clinoptilolite-rich tuff, and synthetic zeolite) in both untreated and Fe-treated forms were used for the sorption of arsenate from model aqueous solution. The treatment of minerals consisted of exposing them to concentrated solution of FeII. Within this process the mineral surface has been laden with FeIII oxi(hydroxides) whose high affinity for the AsV adsorption is well known. In all investigated systems the sorption capacity of FeII-treated sorbents increased significantly in comparison to the untreated material (from about 0.5 to >20.0 mg/g, which represented more than 95% of the total As removal). The changes of Fe-bearing particles in the course of treating process and subsequent As sorption were investigated by the diffuse reflectance spectroscopy and the voltammetry of microparticles. IR spectra of treated and AsV-saturated solids showed characteristic bands caused by FeIII ―SO4, FeIII ―O, and As―O vibrations. In untreated AsV-saturated solids no significant As―O vibrations were observed due to the negligible content of sorbed arsenate.Clays and aluminosilicates are not selective sorbents for anions thanks to a low pHZPC. A simple Fe-treatment of their surfaces improved the sorption properties significantly. Arsenic oxyanions have been bound to treated sorbent surfaces forming very stable inner-sphere complexes (see the mechanism of As sorption to Fe-hydrated oxides in the figure). The sorption efficiency of Fe-treated aluminosilicates exceeded 95% regardless of the sorbent used.
Keywords: Arsenic; FeII nanoparticles; Treated clays; Adsorption; IR spectra; Voltammetry; DRS-analysis;
Use of laterite for the removal of fluoride from contaminated drinking water by Mitali Sarkar; Aparna Banerjee; Partha Pratim Pramanick; Asit R. Sarkar (432-441).
The effects of different operational variables on the mechanistic function of laterite in removal of fluoride have been investigated. Thermodynamic parameters such as free energy change, enthalpy, and entropy of the process, as well as the sorption isotherm, were evaluated. The extent of solute removal is determined by initial solute concentration, operational conditions, laterite dose, and solution pH. For a fixed set of experimental conditions, a model equation is developed from which the percent removal corresponding to each load of fluoride is determined. The mechanism of fluoride adsorption is governed by the zero point charge of laterite and follows a first-order rate equation. pH has a vital role influencing the surface characteristics of laterite. To simulate the flow dynamics, fluoride solution was run through a fixed bed column. The pattern of breakthrough curves for different influent fluoride concentration, pH, and column bed height was characterized. The column efficiency was tested from the bed depth–service time model. The elution of the retained fluoride was studied and the effectiveness of column operation was determined by the retention–elution cycles.
Keywords: Fluoride; Adsorption; Laterite; Equilibrium; Kinetics; Dynamics;
Ligand and Charge Distribution (LCD) model for the description of fulvic acid adsorption to goethite by Liping Weng; Willem H. Van Riemsdijk; Luuk K. Koopal; Tjisse Hiemstra (442-457).
The LCD model (Ligand and Charge Distribution) has recently been proposed to describe the adsorption of humic substances to oxides, in which the CD-MUSIC model and the NICA model for ion binding to respectively oxides and humic substances are integrated. In this paper, the LCD model is improved by applying the ADAPT model (ADsorption and AdaPTation) to calculate the equilibrium distribution of the humic substances based on the change of the average chemical state of the particles. The improved LCD model is applied to calculate the adsorption of fulvic acid (Strichen) to goethite, in which it is assumed that the carboxylic type of groups of fulvic acid can form innersphere complexes with the surface sites. The charge of the carboxylic groups in the innersphere complexes is distributed between the 0- and d-plane, whereas the charge of the other carboxylic and phenolic groups is located in the d-plane. The average distribution of the carboxylic and phenolic groups among their various chemical states (carboxylic groups: innersphere complex, protonated and deprotonated; phenolic groups: protonated and deprotonated) depends on pH, ionic strength and loading, and are the outcome of the model. The calculation shows that the LCD model can describe sufficiently the effects of pH, ionic strength and loading on the adsorption of fulvic acid, using one adjustable parameter ( log K ˜ S , 1 ) . The model calculations indicate that the chemical complexation between fulvic acid and goethite is the main driving force of the adsorption, while the electrostatic repulsion between the particles and the surface is the major limiting factor for further adsorption.The LCD model combines the CD-MUSIC and NICA model and can be used to describe the adsorption of humic substances to oxide surface.
Keywords: LCD; CD-MUSIC; NICA; ADAPT; Humic acid adsorption; Humic; Fulvic; Iron (hydr)oxides; Variable charge particles;
Adsorptive removal of arsenites by a nanocrystalline hybrid surfactant–akaganeite sorbent by E.A. Deliyanni; L. Nalbandian; K.A. Matis (458-466).
Removal of toxic arsenite ions from aqueous solutions was investigated using an innovative hybrid nanocrystalline surfactant-modified akaganeite. This sorbent was prepared using ferric chloride as the precursor and a cationic surfactant, hexadecyltrimethylammonium bromide. From the experimental work, the material was found to be an effective adsorbent for the separation of arsenites. The chemical kinetics of the process was studied, described by a pseudo-second-order equation. The Freundlich adsorption isotherm was determined to examine the mechanism of sorption. FTIR measurements and XPS analysis gave useful information both on the sorbent synthesized and on the arsenite removal process.Adsorptive removal of arsenites by a nanocrystalline hybrid material
Keywords: Iron oxide hydroxide; Surfactant-modified adsorbent; Freundlich model;
Importance of bound water in hydration–dehydration behavior of hydroxylated poly(N-isopropylacrylamide) by Tomohiro Maeda; Kazuya Yamamoto; Takao Aoyagi (467-474).
In this study, a differential scanning calorimetric analysis was performed to investigate the role of water existing around the polymer chains on their thermoresponsive behaviors using the novel functional temperature-sensitive copolymer, poly(N-isopropylacrylamide-co-2-hydroxyisopropylacrylamide) (poly(NIPAAm-co-HIPAAm)). The HIPAAm comonomers were incorporated into the polymeric chains as hydrophilic parameters, and then the hydration states of poly(NIPAAm-co-HIPAAm) with various HIPAAm compositions were examined. Bound water, which is affected by the polymeric chains to some extent, was produced by adding the copolymers to the water, and the temperature due to the melting of the bound water decreased as the HIPAAm content increased. On the basis of this result, we considered that the interaction between the bound water and the polymeric chains is reinforced by the increasing HIPAAm composition. In addition, the cloud points of the copolymers shifted to a higher temperature, and the endothermic enthalpy for the phase transition decreased with increasing the HIPAAm content, suggesting that the number of water molecules disassociated from the polymeric chains decreased. Based on these results, we postulate that the changes in the interaction between the thermosensitive polymer and bound water exert a strong influence on its phase transition and/or separation, such as the cloud point or dehydration behavior.In poly(N-isopropylacrylamide)-based polymers, introducing the novel hydrophilic comonomer (2-hydroxyisopropylacrylamide) changed the interaction between water and the polymeric chains, which significantly affected the thermoresponsive behaviors of the polymers.
Keywords: Thermoresponsive polymers; N-isopropylacrylamide; Cloud point; Differential scanning calorimetry; Bound water;
Influence of collagen denaturation on the nanoscale organization of adsorbed layers by Elzbieta Gurdak; John Booth; Clive J. Roberts; Paul G. Rouxhet; Christine C. Dupont-Gillain (475-484).
Adsorption (at 37 °C) of type I collagen, in native and heat-denatured (30 min at 40 and 90 °C) forms, on polystyrene was studied using quartz crystal microbalance with energy dissipation monitoring (QCM-D), atomic force microscopy (AFM) in tapping mode and X-ray photoelectron spectroscopy (XPS). The significance of the parameters deduced from QCM-D data was examined by comparing different approaches. The adsorbed layer of native collagen has a complex organization consisting of a thin mat of molecules near the surface, in which fibrils develop depending on concentration and time, and of a thicker overlayer containing protruding molecules or bundles which modify noticeably the local viscosity. As a result of drastic denaturation, the ability of collagen to assemble into fibrils in the adsorbed phase is lost and the protrusion of molecules into the aqueous phase is much less pronounced. The adsorbed layer of denatured collagen appears essentially as a monolayer of flattened coils. At low concentration, this is easily displaced upon drying, leading to particular dewetting figures; at high concentration, aggregates add to the first layer. Moderate denaturation leads to an adsorbed phase which shows properties intermediate between those observed with native and extensively denatured collagen, regarding the ability to form fibrillar structures and the adlayer thickness and viscosity.Adsorbed layers of native and denatured collagen were examined using QCM-D, AFM, and XPS. The ability to form fibrils and to protrude in solution was lost for extensively denatured collagen.
Keywords: Collagen; Adsorption; Denaturation; Self-assembly; Polystyrene; Nanostructure; Quartz crystal microbalance with dissipation monitoring (QCM-D); Atomic force microscopy (AFM); X-ray photoelectron spectroscopy (XPS);
Hydroxyapatite organofunctionalized with silylating agents to heavy cation removal by Oberto G. da Silva; Edson C. da Silva Filho; Maria G. da Fonseca; Luiza N.H. Arakaki; Claudio Airoldi (485-491).
Hydroxyapatite surface silylation with organosilane derivatives (H3CO)3SiR, R being the corresponding organic moieties ―CH2CH2CH2NH2, ―CH2CH2CH2NHCH2CH2NH2, and ―CH2CH2CH2NHCH2CH2NHCH2CH2NH2, was carried out to yield organofunctionalized nanomaterials, named HApR1, HApR2, and HApR3, respectively. The products were characterized by elemental analysis, infrared spectroscopy, X-ray diffraction, thermogravimetry, and 31P and 13C NMR in the solid state. The amounts of groups grafted onto surfaces were 0.75 ± 0.05 , 2.35 ± 0.14 , and 2.48 ± 0.18 mmol g −1 for HApRx ( x = 1 , 2 , 3 ) surfaces, respectively. Linear correlations between elemental analysis, mass loss, 31P chemical shift data, and the characteristics of the chain of each alkoxysilane were observed. The organic basic centers distributed onto the external surface have the ability to adsorb divalent copper and cobalt cations from aqueous solution. The degree of adsorption obtained from batchwise processes showed the best performance of these synthesized nanomaterials when compared with the pristine hydroxyapatite.
Keywords: Organofunctionalization; Alkoxysilanes; Adsorption; Hydroxyapatite;
Iron-oxide-modified nanosized diamond: Preparation, characterization, and catalytic properties in methanol decomposition by Tanya Tsoncheva; Ljubomira Ivanova; Daniela Paneva; Momtchil Dimitrov; Ivan Mitov; Stavry Stavrev; Christo Minchev (492-500).
Nanosized diamond (UDD), obtained by a detonation procedure, was modified with iron from the corresponding acetylacetonate precursor under various pretreatment conditions. Nitrogen physisorption, X-ray diffraction, temperature-programmed reduction, and FTIR and Mössbauer spectroscopy were used for their characterization. The samples' catalytic behavior in methanol decomposition was also studied. The physicochemical and catalytic properties of the obtained materials (Fe/UDD) were compared with those of other iron-oxide-modified mesoporous supports with different nature and functionality (MCM-48 silica and CMK-1 carbon). The highest catalytic activity and stability was achieved with air-pretreated Fe/UDD.The state of iron oxide nanoparticles on various supports is determined by both the surface properties (nature and functionality) and the pore structure of the support, the former factor probably being of primary importance. The combined unique properties of nanosize iron oxide particles with nanosize diamond support lead to the formation of highly active and stable catalysts for methanol decomposition.
Keywords: Iron-oxide-modified nanosize diamond; Mössbauer spectroscopy; TPR study; Methanol decomposition;
Characterization of nano-cerias synthesized in microemulsions by N2 sorptiometry and electron microscopy by Ali Bumajdad; Mohamed I. Zaki; Julian Eastoe; Lata Pasupulety (501-508).
A surfactant-stabilized microemulsion method was used to prepare nano-sized particles (<10 nm) of cubic-CeO2 exposing surfaces of not only highest specific areas (142–201 m2/g) ever reported for polycrystalline ceria, but also high thermal stability at 800 °C. Three different surfactants, a non-ionic, an anionic and a cationic, were used to form the microemulsions. Then, N2 sorptiometry and pore volume distribution calculations, were used to reveal microporous and mesoporous structures of these cerias as a function of surfactant type. Transmission electron microscopy was used to visualize consequent particle behaviors. Suggestions have been made as to the textural attributes of the high surface area and thermal stability. Accordingly, cationic surfactants, in the presence or absence of added non-ionic surfactant, are seen to assist in producing cerias of promising surface textural properties for the chemical makeup of combustion catalysts. Nano-CeO2 particles (size ⩽6 nm) synthesized near ambient conditions in microemulsions stabilized by mixed non-ionic (Brij) and cationic (DDAB) surfactants were found to suffer considerable loss of surface accessibility ( 201 → 29 m 2 / g ) due to sintering ( ⩽ 6 → ∼ 40 nm ) at 800 °C, whereas those synthesized in the sole presence of the cationic surfactant only suffered mild agglomeration ( ⩽ 10 → ∼ 15 nm ), thus retaining a higher surface accessibility ( 142 → 45 m 2 / g ) at 800 °C.
Keywords: Nano-cerias; Microemulsion synthesis; Nitrogen sorptiometry; Transmission electron microscopy; Surface texture assessment;
Synthesis and characterization of ultrafine CeF3 nanoparticles modified by catanionic surfactant via a reverse micelles route by Hui Zhang; Hongfei Li; Deqian Li; Shulan Meng (509-515).
In this article, we firstly reported on the synthesis and characterization of ultrafine CeF3 nanoparticles (NPs) modified by catanionic surfactant via a reverse micelles-based route. The catanionic surfactant PN was prepared by mixing the di(2-ethylhexyl) phosphoric acid (DEHPA) and primary amine (N1923) with 1:1 molar ratio. It exhibited a high surface activity and formed much small reverse micelles in comparison with its individual component (DEHPA or N1923). The PN reverse micelles were then used as templates to prepare ultrafine CeF3 NPs. The narrow distributed nanoparticles have an average diameter 1.8 nm. FTIR spectra indicated that there existed strong chemical interactions between nanoparticles and the adsorbed surfactants. The modification resulted in the FTIR peak position of P＝O shifting to lower energy. Due to the effect of modification and small size, the CeF3 NPs showed a remarkable red shift of 54 nm in the fluorescence emission in comparison with that of bulk material and a red shift of 18 nm in contrast with that of the normal CeF3 NPs with an average diameter of 16 nm.A catanionic surfactant PN was prepared and used to form reverse micelles to prepare CeF3 NPs. The ultrafine CeF3 NPs with average size of 1.8 nm were modified by catanionic surfactant. The modification as well as small size of the CeF3 NPs resulted in a huge red shift 54 nm in contrast to the emission peak of bulk materials in fluorescence spectroscopy.
Keywords: Catanionic surfactant; Reverse micelles; Cerium fluoride; Nanoparticles; Modification; Fluorescence;
Scavenging DPPH radicals catalyzed by binary noble metal–dendrimer nanocomposites by Takeshi Endo; Takae Fukunaga; Tomokazu Yoshimura; Kunio Esumi (516-521).
Catalytic activity of gold–platinum, gold–palladium, and platinum–palladium dendrimer nanocomposites for scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals was investigated. The gold–platinum and gold–palladium dendrimer nanocomposites were prepared via simultaneous reduction by sodium borohydride in the presence of poly(amidoamine) (PAMAM) dendrimers with amine or carboxyl terminal groups. The particles were not mixtures of monometallic particles but alloyed bimetallic particles. Bimetallic particles exhibited higher catalytic activity than monometallic ones.DPPH scavenging catalyze by bimetallic nanoparticles stabilized by PAMAM dendrimer were investigated. Bimetallic nanoparticles have higher catalytic activity than monometallic ones.
Keywords: Bimetallic nanoparticles; DPPH scavenging; Gold; Platinum; Palladium; PAMAM dendrimer;
Colloidal stability of Pluronic F68-coated PLGA nanoparticles: A variety of stabilisation mechanisms by M.J. Santander-Ortega; A.B. Jódar-Reyes; N. Csaba; D. Bastos-González; J.L. Ortega-Vinuesa (522-529).
Poloxamers are a family of polypropylene oxide (PPO) and polyethylene oxide (PEO) tri-block copolymers that are usually employed in the micro- and nanoparticulate engineering for drug delivery systems. The aim of this work is to study the electrophoretic mobility ( μ e ) and colloidal stability of complexes formed by adsorbing a poloxamer (Pluronic F68) onto poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles. A variety of stabilisation mechanisms have been observed for the Pluronic-coated PLGA nanoparticles, where DLVO interactions, solvent–polymer segment interactions and hydration forces play different roles as a function of the adsorbed amount of Pluronic. In addition, the μ e and stability data of these complexes have been compared to those obtained previously using a PLGA–Pluronic F68 blend formulation. As both the μ e and the stability data are identical between the two systems, a phase separation of both components in the PLGA–Pluronic blend formulation is suggested, being the PLGA located in the core of the particles and the Pluronic in an adsorbed shell.
Keywords: PLGA; Nanoparticle; Poloxamer adsorption; Colloidal stability; DLVO interactions; Steric interactions; Hydration interactions;
Solvothermal synthesis and characterization of anatase TiO2 nanocrystals with ultrahigh surface area by Rajeev K. Wahi; Yunping Liu; Joshua C. Falkner; Vicki L. Colvin (530-536).
Phase-pure, ultrafine nanocrystalline anatase with high specific surface area (up to 250 m2 g−1) was obtained upon injection of a titanium alkoxide precursor into ethanol with designed volume of water under mild solvothermal conditions (<200 °C, 2 h). Primary particle sizes were tuned by adjusting various reaction parameters, with the smallest grain sizes occurring at low temperatures (140–150 °C), low initial alkoxide concentrations, and intermediate hydrolysis ratios ( r ≡ [H2O]/[Ti(OR)4] = 5–10). Additionally, variations in the reaction temperature result in changes in particle morphology and distribution, with high-temperature samples exhibiting bimodal distributions of small spherical and larger cubic particles that suggest grain growth via Ostwald ripening. A crystalline product with high thermal stability and specific surface area up to 5 times that of commercial nano-titania can be obtained at a relatively low temperature of 150 °C. The physical properties of the titania samples obtained in this study suggest they might be well suited for catalytic applications.Mild solvothermal synthesis of nanoscale TiO2 in ethanol with designed volume of water produces phase-pure anatase with ultrahigh surface area and tunable physical properties.
Keywords: Titanium dioxide; Nanocrystal; Anatase; Solvothermal synthesis; Characterization; Ultrahigh surface area;
Soft water-soluble microgel dispersions: Structure and rheology by A. Omari; R. Tabary; D. Rousseau; F. Leal Calderon; J. Monteil; G. Chauveteau (537-546).
The size and structural characteristics of polyacrylamide-based water-soluble microgel dispersions were investigated by optical and rheological methods. Microgel hydrodynamic radii R h were measured by light scattering and derived from intrinsic shear viscosity [ η ] 0 . The variations of R h 3 and [ η ] 0 with the crosslink density N x , follow the scaling law R h 3 ≅ N x − α with α close to 0.63, in good agreement with the simple structural model proposed in this paper showing how the exact value of α depends on inner structural details of the microgel. The plateau viscosity versus particle apparent volume fraction shows a monotonous change from hard sphere dispersions (high crosslink density of microgels) to flexible linear polymer solutions. Measurements of the first normal stress difference N 1 show that increasing the microgel crosslink density affects the system viscosity more than its elasticity. Under oscillatory shear flow, loss and storage moduli undergo both qualitative and quantitative changes with crosslink density. At moderate concentrations, the elastic modulus is the most affected and its slope in low frequency regime decreases from two to less than one as N x increases. We discuss the experimental results within the frame of knowledge on linear, branched polymer solutions and soft microgel suspensions.We investigate the effects of change of crosslink density on the structural and rheological properties of well-characterized microgel dispersions. A wide range of crosslink density was explored, from linear polymer to highly crosslinked microgels.
Keywords: Microgel; Crosslink; Shear viscosity; Loss modulus; Storage modulus; First normal stress difference;
Theoretical study of the acid–base properties of the montmorillonite/electrolyte interface: Influence of the surface heterogeneity and ionic strength on the potentiometric titration curves by Piotr Zarzycki; Fabien Thomas (547-559).
The parallel shape of the potentiometric titration curves for montmorillonite suspension is explained using the surface complexation model and taking into account the surface heterogeneity. The homogeneous models give accurate predictions only if they assume unphysically large values of the equilibrium constants for the exchange process occurring on the basal plane. However, the assumption that the basal plane is energetically heterogeneous allows to fit the experimental data (reported by Avena and De Pauli [M. Avena, C.P. De Pauli, J. Colloid Interface Sci. 202 (1998) 195–204]) for reasonable values of exchange equilibrium constant equal to 1.26 (suggested by Fletcher and Sposito [P. Fletcher, G. Sposito, Clay Miner. 24 (1989) 375–391]). Moreover, we observed the typical behavior of point of zero net proton charge (pznpc) as a function of logarithm of the electrolyte concentration ( log [ C ] ). We showed that the slope of the linear dependence, pznpc = f ( log [ C ] ) , is proportional to the number of isomorphic substitutions in the crystal phase, which was also observed in the experimental studies.
Keywords: Electrical double layer; Montmorillonite; Potentiometric titration of clays; Surface heterogeneity; Exchange process;
Buffer salt effect on pH in the interior of an anion exchange resin by A.M. Hardin; C.F. Ivory (560-567).
The internal pH of Q Sepharose Fast Flow anion exchange resin in equilibrium with a bis–tris acetate buffer solution is investigated as a function of buffer salt concentration. Direct evidence of a resin phase pH shift is presented. At low buffer salt concentrations of 20 mM NaCl the resin phase pH is found to be as much as 1.1 pH units greater than that of the buffer phase, approaching to within 0.1 units of the buffer phase at salt concentrations greater than 250 mM. An ideal model with no adjustable parameters based on the Boltzmann distribution and the electroneutrality condition provides excellent agreement with experimental observations. The model assumes that small ions do not bind to the resin fixed charge sites and the agreement between the model predictions and observed resin internal pH suggests that strong electrolytes do not form ion pairs with the resin fixed charge sites.The internal pH of an anion exchange resin is seen to be higher than that of the surrounding buffer. This offset decreases as the buffer salt concentration is increased.
Keywords: Ion exchange; Strong electrolyte; Chlorine; Q Sepharose; NaCl; pH shift; Boltzmann;
Heterogeneous Suzuki cross-coupling reactions over palladium/hydrotalcite catalysts by Manuel Mora; César Jiménez-Sanchidrián; J. Rafael Ruiz (568-575).
The efficiency of various heterogeneous solids consisting of palladium supported on hydrotalcite as catalysts in the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid was studied. Based on the catalytic activity results, the reaction develops to an acceptable extent with 100% selectivity at moderate temperatures in the presence of some of the catalysts. The best results were provided by a catalyst consisting of an acetate–pyridine complex of Pd supported on hydrotalcite that gave high conversion values even after three reuses. The reactions conditions were very mild (a temperature of 55 °C and atmospheric pressure). In fact, the catalyst provided conversion and selectivity results surpassing those of existing heterogeneous phase catalysts and most homogeneous phase catalysts for the same purpose.
Keywords: Palladium catalyst; Suzuki cross-coupling reaction; Hydrotalcite; Phenylboronic acid; Bromobenzene;
Ni/SiO2 promoted growth of carbon nanofibers from chlorobenzene: Characterization of the active metal sites by Mark A. Keane; Gary Jacobs; Patricia M. Patterson (576-588).
The temporal changes to supported Ni sites during the growth of graphitic carbon nanofibers (GCNs) via the decomposition of chlorobenzene over Ni/SiO2 at 873 K have been investigated. The reaction of chlorobenzene with hydrogen also generated benzene, via catalytic hydrodechlorination, as the principal competing reaction. Reaction selectivity was found to be time dependent with a switch from a preferential hydrodechlorination to a predominant decomposition that generated an increasingly more structured carbon product over prolonged time-on-stream. These findings are discussed in terms of Cl/catalyst interaction(s) leading to metal site restructuring, the latter manifest in a sintering and faceting of the Ni metal particles. The pressure exerted on the metal/support interface due to fiber formation was of sufficient magnitude to extract the Ni particle from the support; the occurrence of an entrapped Ni particle at the fiber tip is a feature common to the majority of GCNs with the incorporation of Ni fragments along the length of the GCN. Metal site restructuring has been probed by temperature-programmed reduction of the passivated samples, H2 chemisorption/temperature-programmed desorption (TPD) and XANES/EXAFS analyses. This restructuring serves to enhance destructive chemisorption and/or facilitate carbon diffusion to generate the resultant GCN. The nature of the carbonaceous product has been characterized by a combination of TEM-EDX, SEM, XRD and temperature-programmed oxidation (TPO).Temporal changes to supported Ni during the growth of carbon nanofibers (see figure) from a chlorobenzene feed are demonstrated via TPR, H2 chemisorption/TPD and XANES/EXAFS analyses and attributed to Cl/surface interactions.
Keywords: Carbon nanofibers; Ni/SiO2; Chlorobenzene decomposition; Temperature-programmed reduction; TEM-EDX; SEM; XRD; H2 chemisorption/TPD; XANES/EXAFS;
Transport properties of some cationic polysaccharides by Luminita Ghimici; Marieta Nichifor (589-596).
The charge density effect on the behavior of some cationic polysaccharides in aqueous and nonaqueous (methanol) solutions was studied by viscometric and conductometric measurements. The polyelectrolytes investigated contain quaternary ammonium salt groups, N-alkyl- N , N -dimethyl-2-hydroxypropylene ammonium chloride, attached to a dextran backbone. This new class of polyelectrolytes has various linear charge density parameters, ξ, located below and above the critical threshold value of counterions condensation, ξ c = 1 ( ξ = 0.25 – 3.18 ) . The viscometric data revealed that all copolymers exhibit a polyelectrolyte behavior and were plotted in the terms of Rao equation. The conductometric measurements of solutions of these copolymers were presented as a function of polymer concentration and charge density. The results were analyzed within the Manning's theory and lower experimental values of the equivalent conductivity than the theoretical ones were found. Possible reasons of this discrepancy have been discussed. The interaction parameters were evaluated and these were found to depend on both the polymer concentration and the charge density. The conductometric behavior of these cationic polysaccharides has shown that counterion condensation is not a threshold phenomenon, their association to the charged groups of the polyions taking place for ξ > 1 as well as ξ < 1 .The viscometric and conductometric behavior of some cationic polysaccharide solutions have been investigated. It was found that counterion condensation was not a threshold phenomenon for the samples under study.
Keywords: Cationic polysaccharides; Electrolytic conductivity; Charge density; Dielectric constant; Interaction parameter;
Electrical conductance study of θ-liquid bridges by Sotiris P. Evgenidis; Margaritis Kostoglou; Thodoris D. Karapantsios (597-604).
This work investigates the behavior of small liquid bridges that are formed between two horizontal supporting surfaces, aligned at the vertical direction. The contact lines of the liquid bridges are not edge-pinned but free to move across the supporting surfaces with the contact angle as a parameter (θ-bridges). An a.c. electrical conductance technique coupled with high resolution optical images is used to characterize the geometrical details of constant volume liquid bridges when their length is increased gradually until rupture. A mathematical framework is developed for the identification of the geometrical characteristics of θ-liquid bridges explicitly from conductance data. Theoretical predictions show good agreement with measurements for most of the bridge lengths (separation distance between supports) except close to the rupture point where the bridge is highly stretched. It is further shown that for short and moderate separation distances the present model can be used with confidence to determine the bridge volume and neck radius from the electrical signal.
Keywords: Liquid bridge; Electrical conductance; Contact angle;
Modeling of the moving deformed triple contact line: Influence of the fluid inertia by V.S. Nikolayev; S.L. Gavrilyuk; H. Gouin (605-612).
For partial wetting, motion of the triple liquid–gas–solid contact line is influenced by heterogeneities of the solid surface. This influence can be strong in the case of inertial (e.g., oscillation) flows where the line can be pinned or move intermittently. A model that takes into account both surface defects and fluid inertia is proposed. The viscous dissipation in the bulk of the fluid is assumed to be negligible as compared to the dissipation in the vicinity of the contact line. The equations of motion and the boundary condition at the contact line are derived from Hamilton's principle. The rapid capillary rise along a vertical inhomogeneous wall is treated as an example.Contact line motion for the partial wetting case is modeled. We take into account both surface defects and fluid inertia. The rapid capillary rise along a vertical wall with a stripe “defect” of a higher wettability is shown.
Keywords: Wetting; Spreading; Pinning; Wetting hysteresis;
Surface modification and characterization of indium–tin oxide for organic light-emitting devices by Z.Y. Zhong; Y.D. Jiang (613-619).
In this work, we used different treatment methods (ultrasonic degreasing, hydrochloric acid treatment, and oxygen plasma) to modify the surfaces of indium–tin oxide (ITO) substrates for organic light-emitting devices. The surface properties of treated ITO substrates were studied by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), sheet resistance, contact angle, and surface energy measurements. Experimental results show that the ITO surface properties are closely related to the treatment methods, and the oxygen plasma is more efficient than the other treatments since it brings about smoother surfaces, lower sheet resistance, higher work function, and higher surface energy and polarity of the ITO substrate. Moreover, polymer light-emitting electrochemical cells (PLECs) with differently treated ITO substrates as device electrodes were fabricated and characterized. It is found that surface treatments of ITO substrates have a certain degree of influence upon the injection current, brightness, and efficiency, but hardly upon the turn-on voltages of current injection and light emission, which are in agreement with the measured optical energy gap of the electroluminescent polymer. The oxygen plasma treatment on the ITO substrate yields the best performance of PLECs, due to the improvement of interface formation and electrical contact of the ITO substrate with the polymer blend in the PLECs.The surface properties of treated ITO substrates were characterized and the effects of surface modifications of ITO substrates on the performance of organic light-emitting devices were investigated.
Keywords: Indium–tin oxide; Surface modification; Organic light-emitting device;
A novel pH-controlled transfer process of 5,10,15-tri(4-hydroxyphenyl)-20-(4-hexadecyloxyphenyl) porphyrin in CTAB micelles by Lin Guo (620-624).
By analysis of the UV–visible and fluorescence spectra of 5,10,15-tri(4-hydroxyphenyl)-20-(4-hexadecyloxyphenyl)porphyrin (P) in different microenvironments of micelle and solvent solutions, a novel pH-controlled transfer process of P in CTAB micelle was reported. In neutral CTAB micelles, porphyrins may locate at the inner layers of micelles. With pH increases to 11.19, the porphyrin can be completely deprotonated and transfers to the outer surface of CTAB micelle. The investigation of kinetics of porphyrin complexing with Cu(II) indicates that the metallation rate of porphyrins in CTAB micelles could also be controlled by changing pH.
Keywords: Porphyrin; CTAB; Micelle; Location; Metallation;
Interaction between flavonoid, quercetin and surfactant aggregates with different charges by Weiya Liu; Rong Guo (625-632).
The interactions of flavonoid, quercetin with sodium dodecyl sulfate (anionic surfactant) and cetyltrimethyl ammonium bromide (cationic surfactant) micelles were investigated. The average location site of quercetin in different micelles was determined by the cyclic voltammetry method with the aid of molecular optimization. The interaction parameters of quercetin with micelles of different charges such as binding constant K and normal binding energy ΔG were calculated. Furthermore, the morphologic change of the SDS and CTAB spherical micelles and rod-like micelles upon their interaction with quercetin was also observed.
Keywords: Quercetin; SDS micelle; CTAB micelle; Cyclic voltammetry; Binding constant; Morphologic change;
Structural variations in a family of orthodialkoxyarenes organogelators by Pierre Terech; Gilles Clavier; Henri Bouas-Laurent; Jean-Pierre Desvergne; Bruno Demé; Jean-Luc Pozzo (633-642).
A series of low mass organic gelators (LMOGS) 1 to 6 whose chemical structures have in common an orthodialkoxyarene feature was prepared in order to compare the shape of their fibrillar network as investigated by small-angle neutron scattering (SANS) experiments. All members of the family exhibit a pronounced tendency to bundle formation by merging isolated fibers in extended packets of average diameter >500 Å. Variations of the 2D packing symmetry are observed from hexagonal to square orderings with close derivatives of the reference member 2,3-didecyloxyanthracene (DDOA). Networks in which the fraction of isolated fibers is significant enough to allow for their SANS identification are those for 6,7-dichloro-2,3-didecyloxyanthracene (Cl2DDOA) and 2,3-dodecyloxy-9,10-anthraquinone (5). For this latter, the monodispersity of the cross-sections (thickness = 74 Å) is remarkable and the rectangular shape ( b / a ∼ 0.12 ) accounts for a merging mechanism into anisotropic bundles (ribbons).Neutron scattering studies characterize the solid-like gel network made up of ribbon-like aggregates with elliptical sections ( b / a = 0.12 , a = 308 Å ) and radially polydisperse cylindrical bundles ( R = 450 Å ) acting as nodal zones.
Keywords: Gel; Neutron scattering; Structures; Network; Fiber; Bundles;
Mixed fluorinated–hydrogenated surfactant-based system: Preparation of ordered mesoporous materials by J.L. Blin; N. Henzel; M.J. Stébé (643-650).
We have investigated a mixed fluorinated–hydrogenated surfactant-based system [C8F17C2H4(OC2H4)9–C12H25(OC2H4)8] in water. The phase diagram exhibits that the micellar domain can be divided into three parts: above 80 wt% of water both hydrogenated and fluorinated surfactants are completely miscible and they formed mixed micelles in all proportion. When the water concentration is decreased from 80 to 60 wt% a gap of miscibility appears and two micellar zones, one fluorocarbon-rich micelles and one hydrocarbon-rich micelles are observed. The liquid crystal domain is composed of one fluorocarbon-rich (HF 1) and one hydrocarbon-rich (HH 1) hexagonal phase. The hydrophobic radius and the cross-sectional area remain constant in the HH 1 and in the HF 1 domains. Moreover, SAXS measurements proved that the hydrophobic chains in the liquid crystal phases adopt rather an extended conformation. Then the mixture of surfactants was used as template for the preparation of mesoporous materials. Mesostructured silicas with a well hexagonal array of their channels were prepared via a cooperative templating mechanism (CTM), if the loading of fluorinated surfactant is larger than 50%. Decreasing the proportion of the fluorinated amphiphile in the mixture leads to the formation of mesoporous silica with a disordered structure. In this case the channel arrangement is no longer governed by the fluorinated surfactant but by the hydrogenated one.A mixed fluorinated–hydrogenated surfactant-based system in water has been investigated for the preparation of mesoporous materials. Fluorinated surfactant governed the channel arrangement if its concentration is higher than 50%.
Keywords: Nonionic surfactant; Hydrogenated surfactant; Fluorinated surfactant; Mixed system; Phase diagram; Mesoporous; Silica;
The microwave absorption of emulsions containing aqueous micro- and nanodroplets: A means to optimize microwave heating by Christian Holtze; R. Sivaramakrishnan; Markus Antonietti; J. Tsuwi; Friedrich Kremer; Klaus D. Kramer (651-657).
The microwave absorption at frequencies between 10 MHz and 4 GHz is measured for aqueous brine droplets dispersed in a dielectric medium ( ε ′ = 2.0 ). By varying the size of the droplets, ion type and ion concentration, it is found that the microwave absorption goes through a maximum which depends on the type of ions and their concentration. The absorption process is attributed to the polarization of the microdroplets through surface charges. Means to optimize microwave heating in emulsions is discussed.The dielectric relaxation of water-in-oil droplets was analyzed in dependence of droplet size and salt content. Strong surface polarization was found for droplets in the micrometer range.
Keywords: Microwave heating; Interface polarization;
Room-temperature decomposition of 2,2′-azobis(isobutyronitrile) in emulsion gels with and without silica by Gu Xu; Rakesh R. Nambiar; Frank D. Blum (658-661).
The decomposition of 2,2′-azobis(isobutyronitrile) (AIBN) at room temperature was studied in emulsion gels, with and without silica, using UV/visible spectroscopy. The emulsion gels consisted of toluene, AIBN, an aqueous solution of a surfactant (either hexadecyltrimethylammonium bromide, CTAB, or sodium dodecyl sulfate, SDS), and, in some cases, fumed silica. The AIBN compositions were determined in the opaque emulsion gels by converting them to transparent microemulsions. The decomposition rate constants for AIBN were determined to be 3.7 × 10 −8 s −1 ( ± 0.6 × 10 −8 s −1 ) for the emulsion gels and 10.2 × 10 −8 s −1 ( ± 1.3 × 10 −8 s −1 ) for the silica-containing emulsion gels. These rate constants were significantly greater than that in toluene solution, which, by our technique, is below our measurement threshold (effectively 0).
Keywords: 2,2′-Azobis(isobutyronitrile) (AIBN); Initiator decomposition; Polymerization; Emulsion gel; Kinetics; CTAB; SDS; Silica;
Structural changes in poly(ethyleneimine) modified microemulsion by Carine Note; Joachim Koetz; Sabine Kosmella (662-668).
The influence of branched poly(ethyleneimine) on the phase behavior of the system sodium dodecylsulfate/toluene–pentanol (1:1)/water has been studied. The isotropic microemulsions still exist when water is replaced with aqueous solutions of PEI (up to 30% in weight), but their stability is significantly influenced. From a polymer concentration of 20 wt%, the polymer enhances the solubilization of water in oil, changes the sign of the spontaneous curvature of the surfactant film, and induces an inversion of the microemulsion type from water-in-oil (L2) to oil-in-water (L1), by the formation of a bicontinuous channel. Further investigations show that the addition of polymer in the L2 phase changes the droplet–droplet interactions as the conductivity drops and the percolation disappears. In the bicontinuous channel, higher viscosities can be detected, as well as a weak percolation followed by a steep increase of the conductivity, which can be related to evident structural changes in the system. DSC measurements allow then to follow the changes of the water properties in the system, from interfacial-water in the L2 phase to free-water in the sponge-like phase. Finally, all the measurements performed permit to characterize the structural transitions in the system and to understand the role of the added polymer.
Keywords: Polyelectrolyte; Microemulsion; Bicontinuous phase;
The accurate QSPR models for the prediction of nonionic surfactant cloud point by Yueying Ren; Huanxiang Liu; Xiaojun Yao; Mancang Liu; Zhide Hu; Botao Fan (669-672).
Quantitative structure–property relationship models were developed to predict cloud points and study the cloud phenomena of nonionic surfactants in aqueous solution. Four descriptors were selected by the heuristic method as the inputs of multiplier linear regression and support vector machine (SVM) models. Very satisfactory results were obtained. SVM models performed better both in fitness and in prediction capacity. For the test set, they gave a predictive correlation coefficient (R) of 0.9882, root mean squared error of 4.2727, and absolute average relative deviation of 9.5490, respectively. The proposed models can identify and provide some insight into what structural features are related to the cloud points of compounds, i.e., the molecular size, structure, and isomerism of the hydrocarbon moiety and the degree of oxyethylation. They can also help to understand the cloud phenomena of nonionic surfactants in aqueous solution. Additionally, this paper provides two simple, practical, and effective methods for analytical chemists to predict the cloud points of nonionic surfactants in aqueous solution.Plot of predicted CP values vs experimental CP values for the training set and test set based on the 4-parameter model by SVM.
Keywords: Quantitative structure–property relationships; Nonionic surfactants; Cloud point; Heuristic method; Support vector machine;
A promising system of mixed single- and double-short-tailed PEO ether phosphate esters: Phase behavior and vesicle formation by Zaiwu Yuan; Jingcheng Hao; Heinz Hoffmann (673-681).
Acidic surfactants, single- and bi-2-methylheptanol polyethenoxy ether phosphate esters, H2PO3(OCH2CH2) n OCH2CH2CH2CH2CH2CH(CH3)2 (u-MHPEPE) and HPO3[(OCH2CH2) n OCH2CH2CH2CH2CH2CH(CH3)2]2 (d-MHPEPE), where n ≈ 4 , were synthesized. Phase behavior of u- and d-MHPEPE (u- and d-MHPEPE mixtures were abbreviated as MHPEPE) mixtures in aqueous solutions and vesicle formation were determined. Surface tension measurements showed that u-MHPEPE and MHPEPE have low surface tensions at critical micelle concentrations. γ cmc = 29.0 mN m −1 and cmc = 16.0 mmol L −1 for u-MHPEPE, MHPEPE has two transition points suggesting the mixtures of u- and d-MHPEPE with γ cmc1 = 30.5 mN m −1 and cmc1 = 4.0 mmol L −1 , and γ cmc2 = 27.3 mN m −1 and cmc2 = 42.0 mmol L −1 . These values, specific γ cmc , are much lower than those of traditionally cationic or anionic surfactants such as cetyltrimethylammonium bromide (CTAB, γ cmc = 37.1 mN m −1 at cmc = 0.92 mmol L −1 ) and sodium dodecyl sulfate (SDS, γ cmc = 39.0 mN m −1 at cmc = 8.1 mmol L −1 ). Rich phase behavior was observed with increasing MHPEPE concentration, an isotropic L1-phase (micelle solution), an unstable emulsion-region (with time, the samples separate into two-phase), a transparently bluish and birefringent Lα-phase up to 200 mmol L−1 with unilamellar and multilamellar vesicles. These unilamellar and multilamellar vesicles were demonstrated by using staining transmission electron microscopy (staining-TEM), which were compared to freeze-fracture TEM (FF-TEM). The vesicle-phase is stable for at least 1 year. Vesicle formation possibly could be explained in harmonization of the hydrophobic force of acidic surfactant tails, the hydrogen bonding (H-bonding) and the electrostatic interaction among polar headgroups of PEO ether phosphate ester. Phase transition from the flow birefringent unilamellar vesicles induced by addition of HCl, NaCl, NaOH, and increasing temperature has been observed. Surprisingly, for u-MHPEPE or d-MHPEPE in water, we just observed L1-phase (micelle solution) with increasing u-MHPEPE or d-MHPEPE concentration.A typical FF-TEM image of multilamellar vesicles, the multilamellar vesicles are polydisperse in size. The interlamellar spacing between the bilayers is rather uniform and in the range of about 500 Å.
Keywords: Acidic surfactants; Phase behavior; Vesicles; Freeze-fracture TEM;
Chemico-electromechanical coupling in microporous media by A. Revil; N. Linde (682-694).
We determine the macroscopic transport properties of isotropic microporous media by volume-averaging the local Nernst–Planck and Navier–Stokes equations in nonisothermal conditions. In such media, the excess of charge that counterbalances the charge deficiency of the surface of the minerals is partitioned between the Gouy–Chapman layer and the Stern layer. The Stern layer of sorbed counterions is attached to the solid phase, while the Gouy–Chapman diffuse layer is assumed to have a thickness comparable to the size of the pores. Rather than using Poisson–Boltzmann distributions to describe the ionic concentrations in the pore space of the medium, we rely on Donnan distributions obtained by equating the chemical potentials of the water molecules and ions between a reservoir of ions and the pore space of the medium. The macroscopic Maxwell equations and the macroscopic linear constitutive transport equations are derived in the vicinity of equilibrium, assuming that the porous material is deformable. In the vicinity of thermodynamic equilibrium, the cross-coupling phenomena of the macroscopic constitutive equations of transport follow Onsager reciprocity. In addition, all the material properties entering the constitutive equations depend only on two textural properties, the permeability and the electrical formation factor.The coupled constitutive equations describing the transport of ions and water in a microporous deformable medium are obtained by volume-averaging the Nernst–Planck and Navier–Stokes equations.
Keywords: Streaming potential; Coupling processes; Osmotic pressure; Porous media; Shale; Onsager's reciprocity; Maxwell equations; Electroosmosis; Navier–Stokes equation; Nernst–Planck equation;
Adsorption behavior of propylamine on activated carbon fiber surfaces as induced by oxygen functional complexes by Byeoung-Ku Kim; Seung-Kon Ryu; Byung-Joo Kim; Soo-Jin Park (695-697).
In this study, the surfaces of activated carbon fibers (ACFs) were modified by nitric acid to introduce surface oxygen complexes and to observe the influence of those complexes on the propylamine adsorption of the ACFs. It was found that the oxygen complexes including carboxylic and phenolic groups were predominantly increased, resulting in the increase of total surface acidity. However, the specific surface areas and the total pore volumes of the modified ACFs were decreased by 5–8% due to the increased blocking (or demolition) of micropores in the presence of newly introduced complexes. Despite the decrease of textural properties, it was found that the amount of propylamine adsorbed by the modified ACFs was increased by approximately 17%. From the XPS results, it was observed that propylamine reacted with strong or weak acidic groups, such as COOH or OH, on the ACF surfaces, resulting in the formation of pyrrolic-, pyridonic-, or pyridine-like structures.The figure above illustrates the adsorption isotherms of PA on the V-ACFs at 298 K. It was found that the amount of adsorbed PA rapidly increased as a result of the micropore filling effects under 0.1 relative pressure, and then reached a plateau at 1.0 of relative pressure, as representative of a typical Type I isotherm.
Keywords: Activated carbon fibers; Surface oxygen complexes; Propylamine; Surface treatment;
Metabolic mimics: Thiol responsive drug release by Imma Andorra Solsona; Robert B. Smith; Callum Livingstone; James Davis (698-701).
A new approach to the design of selective release interfaces is assessed in which a hydrophobic component is functionalised with a receptor reactive toward reduced thiol peptides—principally glutathione. The assembly has been characterised using electrochemical techniques and its ability to form a coherent, water insoluble coating is demonstrated. The subsequent reaction with glutathione creates a supramolecular conjugate that exploits the hydrophilic nature of the amino acid chain as a route through which the protective coating can be eroded and hence the underlying substrate exposed. The efficacy of the release process has been critically assessed with a view to establishing the action and selectivity of the trigger mechanism.
Keywords: Naphthoquinone; Adamantane; Glutathione; Drug release; Delivery;
The ‘Einstein correction’ to the bulk viscosity in n dimensions by Aditya S. Khair (702-703).
We calculate the effective bulk viscosity of a dilute dispersion of rigid n-dimensional hyperspheres in a compressible Newtonian fluid at zero Reynolds number.The effective bulk viscosity, κ eff , of a dilute dispersion of rigid n-dimensional hyperspheres in a compressible Newtonian fluid at zero Reynolds number is determined. The final result is κ eff = κ + 2 ( n − 1 ) n η ϕ , where κ and η are the bulk and shear viscosities of the fluid, respectively, and ϕ is the volume fraction of hyperspheres.
Keywords: Colloidal dispersion; Bulk viscosity; Hypersphere; Compressible fluid; Low-Reynolds-number flow; Effective properties; Two-phase material;
Corrigendum to “On the solidification of a supercooled liquid droplet lying on a surface” [J. Colloid Interface Sci. 272 (2004) 225–234] by S. Tabakova; F. Feuillebois (704).
Corrigendum to “Synthesis of flexible silica aerogels using methyltrimethoxysilane (MTMS) precursor” [J. Colloid Interface Sci. 300 (2006) 279–285] by A. Venkateswara Rao; Sharad D. Bhagat; Hiroshi Hirashima; G.M. Pajonk (705).
by Arthur Hubbard (706).
Author Index for Volume 302 (707-708).