Journal of Colloid And Interface Science (v.300, #1)
Editorial Board (CO1).
Comparison of helical twisting powers of novel fluorinated amphiphilic enantiomers with their hydrogenated counterparts by Mahmut Acımış; E. Berna Karaman (1-6).
This is the first report on novel amphiphilic enantiomers as esters of alanine and serine with a partially fluorinated octyl chain (l-APFOE and l-SPFOE), which form intrinsic chiral nematic (N*) phases with water only and exhibit very high helical twisting powers (htps) compared to their hydrogenated counterparts, dodecylesters of l-alanine (l-ADDE) and l-serine (l-SDDE). They also exhibit a wider N* range than those known in the literature. Furthermore, the htps of the chiral dopants mandelic acid (MA) and hexahydromandelic acid (HHMA) in the racemic nematic phase of dl-SPFOE and dl-APFOE are remarkably higher than those in the hydrogenated counterparts. The tremendous increase in chirality (htps) of the same single chiral center is a new phenomenon in micellar N* phases and is attributed to a “pivot” effect of the fluoroalkyl chain. As a result, a “skewed micelle” model is proposed to explain why the htp value of l-APFOE is higher than that of l-SPFOE, and accordingly how the intermicellar chirality transfer (chiral induction) may be visualized. The simplicity of these binary mixtures and the enlargement in htp of the single chiral centers visualized as the “skewed micelle” model may provide a basis vital for future computer modeling of chiral lyotropics.
Keywords: Helical twisting powers; Fluorinated/hydrogenated chiral amphiphiles; Chiral lyotropic phases;
Sequestration of amitriptyline by liposomes by Marissa S. Fallon; Anuj Chauhan (7-19).
We study the uptake of amitriptyline, which is a common cause of overdose-related fatalities, in aqueous solutions by 1 , 2 -dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes and liposomes composed of a mixture of DMPC and 1 , 2 -dioleoyl-sn-glycero-3-[phospho-rac(1-glycerol)] (DOPG) lipids. The effect of drug concentration, liposomal charge, pH, salt, and protein presence on the drug uptake is investigated using two different methodologies, a precipitation and a centrifugation method. Furthermore, the time scale of the drug uptake is studied through qualitative observations at high pH and through conductivity measurements at neutral pH and found to be < 5 s . The results of the quantitative studies show that the fractional drug uptake decreases with increasing drug concentration, and for a given concentration it increases with the pH and decreases in the presence of salt. We find that a larger amount of drug is sequestered by negatively charged liposomes (those containing DOPG) than liposomes with no net charge (DMPC). We speculate that the mechanism of drug uptake is due to both electrostatic interactions as well as hydrophobic effects. The fractional uptake by DMPC:DOPG in a 70:30 ratio is as high as 95% in water and about 90% in physiological buffer. The fractional uptake is also measured in presence of 2% (w/w) bovine serum albumin (BSA), which is approximately the protein concentration in the intercellular fluid. In presence of protein the fractional uptakes by 70:30 DMPC:DOPG liposomes and 50:50 DMPC:DOPG liposomes are 82 and 90%, respectively, at 125 μM drug amitriptyline. In the absence of liposomes, 67% of the drug is taken up by the protein in a 2% (w/w) BSA, 125 μM amitriptyline solution. Thus, addition of 50:50 DMPC:DOPG liposomes reduces the free drug concentration by a factor of about 3.5, making them attractive candidates for drug detoxification.In this paper, we study the uptake of amitriptyline in aqueous solutions by liposomes consisting of a neutral lipid 1 , 2 -dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and a negatively charged lipid 1 , 2 -dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DOPG). Experiments suggest that the liposomes sequester drug partially by absorbing the drug into the annulus and partially by adsorbing the drug on the surface through ionic interactions.
Keywords: Liposomes; Drug; Amitriptyline; DMPC; DOPG; Absorption; Adsorption; pH; Protein; Albumin; Drug overdose treatment;
Successive interaction of pairs of soluble organics with nanosilica in aqueous media by V.M. Gun'ko; V.I. Zarko; E.F. Voronin; E.V. Goncharuk; L.S. Andriyko; N.V. Guzenko; L.V. Nosach; W. Janusz (20-32).
Successive interaction of different pairs of water-soluble polymers (poly(ethylene glycol) (PEG), poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA)), proteins (bovine serum albumin (BSA), ovalbumin, gelatin, and ossein), and smaller organics such as lecithin (1-stearoyl-2-oleoyl phosphatidylcholine, SOPC) and Aethonium (1,2-ethylene-bis(N-dimethyl carbodecyl oxymethyl) ammonium dichloride) with nanosilicas A-300 ( S BET = 232 and 297 m2 g−1) and A-50 ( S BET = 52 m 2 g −1 ) was studied using dynamic light scattering, adsorption, and infrared (FTIR) spectroscopy methods. Time-dependent rearrangement of particle size distributions (PSDs) depicts appearance of both smaller and larger aggregates for silica/PEG(I—first adsorbate)/BSA(II—second adsorbate) and silica/PVP(I)/BSA(II) (i.e., BSA adsorbs onto PEG/silica or PVP/silica) than that for silica/organic compound I. However, in the cases of PVA(I)–BSA(II) and PVA(I)–SOPC(II) a similar effect is not observed because only increased aggregation occurs. The successive equilibrium adsorption of similar pairs shows a diminution of the adsorption of the second compound (gelatin, ovalbumin) with increasing amount of the first adsorbed polymer (PEG or PVP).
Keywords: Nanosilica; BSA; Gelatin; Ovalbumin; Ossein; Poly(ethylene glycol); Poly(vinyl pyrrolidone); Poly(vinyl alcohol); Lecithin; Aethonium; Aqueous suspension; Particle size distribution; Successive adsorption;
Measurement and modeling of the surface potential evolution of hydrated cement pastes as a function of degradation by Ingmar Pointeau; Pascal Reiller; Nathalie Macé; Catherine Landesman; Nathalie Coreau (33-44).
Hydrated cement pastes (HCP) have a high affinity with a lot of (radio)toxic products and can be used as waste confining materials. In cementitious media, elements are removed from solution via (co)precipitation reactions or via sorption/diffusion mechanisms as surface complexation equilibria. In this study, to improve the knowledge of the surface charge evolution vs the degradation of the HCP particles, two cements have been studied: CEM-I (ordinary Portland cement, OPC) and CEM-V (blast furnace slag and fly ash added to OPC). Zeta potential measurements showed that two isoelectric points exist vs HCP leaching, i.e., pH. Zeta potential increases from −17 to +20 mV for pH 13.3 to pH 12.65 (fresh HCP states) and decreases from 20 to −8 mV for pH 12.65 to 11 (degraded HCP states). The use of a simple surface complexation model of C-S-H, limited in comparison with the structural modeling of C-S-H in literature, allows a good prediction of the surface potential evolution of both HCP. Using this operational modeling, the surface charge is controlled by the deprotonation of surface sites (>SO−) and by the sorption of calcium (>SOCa+), which brings in addition a positive charge. The calcium concentration is controlled by portlandite or calcium silicate hydrate (C-S-H) solubilities.
Keywords: Cement; C-S-H; Leaching; Degradation; Zeta potential; Surface complexation; Solubility;
Generalization of Kelvin's equation for compressible liquids in nanoconfinement by Y. Chen; T. Wetzel; G.L. Aranovich; M.D. Donohue (45-51).
The Kelvin equation for a compressible liquid in nanoconfinement is written in a form that takes into account not only Laplace's pressure, but also the oscillatory compression pressure. This leads to a simple analytical equation for pressure in nanocapillaries. The corrected equation is used to analyze properties of aqueous systems, including the oscillatory structural forces between attractive surfaces and inert surfaces, repulsive “hydration” forces between hydrophilic surfaces, and attractive “hydrophobic” forces between hydrophobic surfaces. Relative vapor pressure in a nanocapillary also is discussed.Analytical extension to the Kelvin equation is derived to predict oscillations around classical behavior in nanocapillary. The pressure predicted by proposed model for n-hexadecane in coordinates of ln ( p / p S ) vs 1 / r qualitative agree with direct measurements.
Keywords: Nanocapillarity; Adsorption compression; Oscillaroty structural force; Vapor pressure;
Geopolymeric adsorbents from fly ash for dye removal from aqueous solution by Lin Li; Shaobin Wang; Zhonghua Zhu (52-59).
Adsorbents from coal fly ash treated by a solid-state fusion method using NaOH were prepared. It was found that amorphous aluminosilicate geopolymers would be formed. These fly ash-derived inorganic polymers were assessed as potential adsorbents for removal of some basic dyes, methylene blue and crystal violet, from aqueous solution. It was found that the adsorption capacity of the synthesised adsorbents depends on the preparation conditions such as NaOH:fly-ash ratio and fusion temperature with the optimal conditions being at 1.2:1 weight ratio of Na:fly-ash at 250–350 °C. The synthesised materials exhibit much higher adsorption capacity than fly ash itself and natural zeolite. The adsorption isotherm can be fitted by Langmuir and Freundlich models while the two-site Langmuir model producing the best results. It was also found that the fly ash derived geopolymeric adsorbents show higher adsorption capacity for crystal violet than methylene blue and the adsorption temperature influences the adsorption capacity. Kinetic studies show that the adsorption process follows the pseudo second-order kinetics.Geopolymers were synthesised from fly ash using fusion method. The method shows much higher conversion of fly ash to product. Geopolymers also exhibit significantly higher adsorption capacity for basic dye removal than other adsorbents.
Keywords: Fly ash basic dyes; Aqueous solution; Adsorption; Fusion method; Geopolymer;
Formation and electrochemical characterization of 6-thioguanosine monolayers on the mercury surface by Zoraida González Arias; Jesús Luis Muñiz Álvarez; Juan Miguel López Fonseca (60-68).
The interfacial and electrochemical behavior of 6-thioguanosine—6-thioguanine riboside (6TGR)—on a hanging mercury drop electrode was studied with ac and cyclic voltammetry in a solution of 0.1 M Na2SO4 and 0.01 M sodium acetate buffer at pH 4.3. A self-assembled monolayer (SAM) of chemisorbed 6TGR molecules formed under determined adsorption conditions was characterized. A low-density monolayer of chemisorbed 6TGR molecules and a condensed monolayer of physisorbed ones, which are successively formed by reduction of the SAM, were also studied.A self-assembled monolayer (SAM) of chemisorbed 6-thioguanosine (6-thioguanine riboside (6TGR)) molecules, formed on hanging mercury drop electrode under determined adsorption conditions, was characterized.
Keywords: 6-Thioguanosine; Mercury; Self-assembled and condensed monolayers; ac voltammetry; Cyclic voltammetry;
Kinetics of polyelectrolyte adsorption onto polystyrene latex particle studied using electrophoresis: Effects of molecular weight and ionic strength by K. Aoki; Y. Adachi (69-77).
The kinetics of the adsorption of a cationic polymer flocculant onto negatively charged polystyrene latex (PSL) particles were measured by means of electrophoresis as a function of the molecular weight of the polyelectrolyte and the ionic strength of the solution. In the experiment, the dispersion of bare PSL particles was mixed with a polyelectrolyte solution by means of end-over-end rotation in which the mixing intensity was evaluated in terms of the collision frequency between the colloidal particles. The rate of electrophoretic mobility of a PSL particle, which remained as a singlet, was measured against the mixing steps, which was equivalent to the time elapsed after the onset of flocculation. The shape of the kinetic curves is typical: a linear increase for a short period followed by a plateau, implying the saturation of the colloidal surface by the adsorbed polyelectrolyte. In the case of low ionic strength, the plateau value was dependent on the molecular weight of the polyelectrolyte. That is, a lower plateau value was detected when the molecular weight of the polyelectrolyte was smaller and its concentration was lower. However, the amount of adsorption was kinetically controlled only for the case of higher molecular weight. In the case of high ionic strength, the plateau value of electrophoresis was constant, regardless of the polyelectrolyte concentration and molecular weight. These data will ultimately be useful in further analysis of the flocculation behavior of colloidal particles with a polyelectrolyte.A reconformation process of adsorbed polyelectrolytes on the colloidal surface is affected by the molecular weight and ionic strength, resulting in variation in the adsorbed state of the polyelectrolytes.
Keywords: Polyelectrolyte; Adsorption; Ionic strength; Molecular weight; Electrophoretic mobility;
Strontium binding by calcium silicate hydrates by J. Tits; E. Wieland; C.J. Müller; C. Landesman; M.H. Bradbury (78-87).
In the present study the binding of strontium with pure calcium silicate hydrates (C-S-H) has been investigated using batch-type experiments. Synthetic C-S-H phases with varying CaO:SiO2 (C:S) mol ratios, relevant to non-degraded and degraded hardened cement paste, were prepared in the absence of alkalis (Na(I), K(I)) and in an alkali-rich artificial cement pore water (ACW). Two types of experimental approaches have been employed, investigating sorption and co-precipitation processes, respectively. The Sr(II) sorption kinetics were determined as well as sorption isotherms, the effect of the solid to liquid ratio and the composition (C:S ratio) of the C-S-H phases. In addition, the reversibility of the Sr(II) sorption was tested. It was shown that both the sorption and co-precipitation tests resulted in Sr(II) distribution ratios which were similar in value, indicating that the same sites are involved in Sr(II) binding. In alkali-free solutions, the Sr(II) uptake by C-S-H phases was described in terms of a Sr2+–Ca2+ ion exchange model. The selectivity coefficient for the Sr2+–Ca2+ exchange was determined to be 1.2 ± 0.3 .In this work it has been shown that the sorption of strontium by calcium silicate hydrates (C-S-H) can be described with an ion-exchange model involving the exchange of Ca2+ on silanol sites on the surface of the C-S-H particles for Sr2+.
Keywords: Strontium; Calcium silicate hydrates; Cement; Sorption; Co-precipitation; Ion exchange;
Removal of arsenious ion by calcined aluminum oxyhydroxide (boehmite) by Fumihiko Ogata; Naohito Kawasaki; Takeo Nakamura; Seiki Tanada (88-93).
Aluminum oxyhydroxide (boehmite, BE) shows adsorption ability of arsenious ion. In this study, we calcined BE in the temperature range 200–1150 °C, and examined the amount of arsenious ion adsorbed and adsorption mechanism. As a result, the adsorption amount of arsenious ion by BE calcined at 400 °C showed the highest value as compared with those by BE calcined at other temperatures. On the other hand, the amounts of arsenious ion adsorbed onto BE showed lower values at 200, 600, and >1000 °C than that by BE before calcination. The amount of surface hydroxyl group of calcined BE showed the highest value at the calcination temperature of 400 °C. As a result of X-ray analysis, BE showed boehmite structure at less than the calcination temperature of 300 °C, while BE was converted to the transitional state of aluminum oxide at more than 400 °C. From the result of the amount of arsenious ion adsorbed and FT-IR, it turned out that calcined BE dissociated water molecule when suspended in the water, hydroxyl group was generated on the surface, and the amount of arsenious ion adsorbed was increased because of the ion exchange of these hydroxyl groups with arsenious ions. It was clarified that an adsorbent with high adsorption ability of arsenious ion was obtained by calcination of BE.The adsorption of arsenious ion onto calcined boehmite was investigated. The structure of boehmite calcined at temperature range 200–1150 °C and the adsorption mechanisms of arsenious ion onto them was discussed.
Keywords: Arsenious ion; Adsorption mechanism; Boehmite; Calcinations;
Synthesis, characterization, and sorption properties of silica gel-immobilized pyrimidine derivative by Mohamed E. Mahmoud; Sawsan S. Haggag; Abdelrahman H. Hegazi (94-99).
5-Benzylidene-2-thiobarbituric acid (BzTBA), a pyrimidine derivative, was used to modify the surface of silica gel–chloropropyltrimethoxysilane (Si-Cl) via chemical immobilization to produce a new pyrimidine silica phase (Si-BzTBA). Identification of the surface modification was characterized and performed on the basis of infrared as well as elemental analysis. Thermal desorption method was found to give 0.129–0.143 mmol g−1 as surface coverage values. Metal sorption properties of Si-BzTBA were also studied and the evaluated results refer to the high metal sorption of Si-BzTBA for copper(II), mercury(II), cadmium(II), and lead(II) with the same order. These four Si-BzTBA–metal complexes were also synthesized and the stoichiometric ratios were identified as 1:1 except lead complex was found to give a 1:2 ratio. Electron impact–mass spectrometric analysis (EI-MS) with 70 eV ionization energy was used as a potential thermal method for the confirmation of surface modification of Si-BzTBA and its metal complexes based on fragmentation elucidation of thermally desorbed ion peaks. The EI-MS of Si-BzTBA was found to show several characteristic fragment ion peaks that are directly related to the chemical binding of BzTBA to SiCl phase. Differential scanning calorimetry study (DSC) was also performed to evaluate the various kinetic and thermodynamic parameters of thermal degradation processes and have been enumerated. The results of EI-MS and DSC are very similar in many respects.5-Benzylidene-2-thiobarbituric acid (BzTBA) is a pyrimidine derivative and characterized by the presence of N, O, and S donor atoms. BzTBA was synthesized and used to modify the surface of silica gel via chemical immobilization technique.
Keywords: Silica gel; 5-Benzylidene-2-thiobarbituric acid; Selectivity; EI-MS; DSC;
Biosorption of Cd(II), Cr(III), and Cr(VI) by saltbush (Atriplex canescens) biomass: Thermodynamic and isotherm studies by Maather F. Sawalha; Jose R. Peralta-Videa; Jaime Romero-González; Jorge L. Gardea-Torresdey (100-104).
The biosorption data of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass were fit on the Freundlich and Langmuir adsorption isotherms at 297 K. The Cd(II) and Cr(III) solutions were adjusted to pH 5.0 and the Cr(VI) solution was adjusted to pH 2.0. The correlation coefficient values indicated that the data fit better the Freundlich model. The maximal capacities ( K F ) were found to be 5.79 × 10 −2 , 3.25 × 10 −2 , and 1.14 × 10 −2 mol / g for Cr(III), Cd(II), and Cr(VI), respectively. Similar results were obtained using the Langmuir and the Dubinin–Radushkevick equations. Thermodynamic parameters calculated from the Khan and Singh equation and from the q e vs C e plot show that the equilibrium constants for the biosorption of the metals follow the same order of the maximal capacities. The negative Gibbs free energy values obtained for Cd(II) and Cr(III) indicated that these ions were biosorbed spontaneously. The mean free energy values calculated from the Dubinin–Radushkevick equation (10.78, 9.45, and 9.05 for Cr(III), Cr(VI), and Cd(II), respectively) suggest that the binding of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass occurs through an ionic exchange mechanism.Biosorption on saltbush biomass obeys both the Freundlich and the Langmuir isotherms, maximum capacity and equilibrium constants were for Cr(III) > Cd(II) > Cr(VI), and occurs through ionic exchange mechanism.
Keywords: Saltbush; Metal ions biosorption; Ion-exchange; Isotherm; Thermodynamic;
Interaction between poly(ethylene glycol) and two surfactants investigated by diffusion coefficient measurements by R. López-Esparza; M.-A. Guedeau-Boudeville; Y. Gambin; C. Rodríguez-Beas; A. Maldonado; W. Urbach (105-110).
Dynamic light scattering (DLS) and fluorescence recovery after pattern photobleaching (FRAPP) were used to study the interaction of low molecular weight poly(ethylene glycol) (PEG) with micelles of two different surfactants: tetradecyldimethyl aminoxide (C14DMAO, zwitterionic) and pentaethylene glycol n-dodecyl monoether (C12E5, non-ionic). By using an amphiphilic fluorescent probe or a fluorescent-labeled PEG molecule, FRAPP experiments allowed to follow the diffusion of the surfactant–polymer complex either by looking at the micelle diffusion or at the polymer diffusion. Experiments performed with both fluorescent probes gave the same diffusion coefficient showing that the micelles and the polymer form a complex in dilute solutions. Similar experiments showed that PEG interacts as well with pentaethylene glycol n-dodecyl monoether (C12E5).
Keywords: Polymer–surfactant interactions; Poly(ethylene glycol); Dynamic light scattering; Fluorescence recovery after pattern photobleaching;
Fabrication of UV-blocking nanohybrid coating via miniemulsion polymerization by Haifeng Lu; Bin Fei; John H. Xin; Ronghua Wang; Li Li (111-116).
A novel convenient approach to fabricate ZnO@polystyrene nanohybrid coating on cotton fabrics is reported. The as-prepared core–shell nanohybrid coating was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), and UV-blocking. The cotton fabrics treated in this study provided ultrahigh UV protection and superior wash fastness. Therefore, this new nanohybrid material and its synthesis method are highly potential to various functional treatments of flexible surfaces.The fabrication and characterization of UV-blocking nanohybrid coating on cotton fabrics by in situ polymerization method in miniemulsion is presented.
Keywords: Nanohybrid coating; In situ polymerization; Miniemulsion;
Facile fabrication of poly(p-phenylene ethynylene)/colloidal silica composite for nucleic acid detection by Joong Ho Moon; William McDaniel; Lawrence F. Hancock (117-122).
Fabrication, characterization, and application of poly(phenylene ethynylene) (PPE)/silica composite particles are described. PPE is a class of conjugated polymers, which has been used for various sensory materials. However, its hydrophobic nature makes its application difficult in the aqueous phase, especially for biological substance detection. In this report, we utilized non-aqueous soluble PPE, 15 nm of colloidal silica particles, and aminosilane to fabricate a biosensory platform. The resulting composite showed high aqueous compatibility, large surface area, high quantum efficiency, and versatile chemical modification including oligonucleotide coupling. By monitoring the fluorescence quenching of PPE, we could detect a quencher-labeled target oligonucleotide specifically. Stern–Volmer (SV) analysis showed different accessibility of fluorophores (PPE) to a quencher labeled target oligonucleotide. The accessibility of fluorophores and SV constant are determined to be 0.54 and 4.2 × 10 7 M −1 , respectively, from a modified SV plot. This method will broaden the capability of conjugated polymers for the sensitive detection of biological substances.Functional composite of organic soluble PPE/silica was fabricated and utilized for sensitive and specific oligonucleotide detection.
Keywords: Poly(phenylene ethynylene); Nanoparticle; Fluorescence quenching; Stern–Volmer analysis; Nucleic acid detection;
Control of silica shell thickness and microporosity of titania–silica core–shell type nanoparticles to depress the photocatalytic activity of titania by Ahmed Mohamed El-Toni; Shu Yin; Tsugio Sato (123-130).
Titania is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of its excellent UV light absorption properties. Its high photocatalytic activity, however, facilitates the generation of reactive oxygen species, which can oxidize and degrade other ingredients during its formulation, raising safety concerns. Dense coating of titania nanoparticles with a silica layer could help in depression of their photocatalytic activity by disturbing the formation of radicals produced by the reaction of oxygen and/or water with the electron–hole pair. Depression of the high photocatalytic activity of titania necessitates that the silica shell has to be thick, with minimum microporosity. Coating parameters were optimized to attain greater amounts of precipitated silica and thicker shells with lower microporosity, which in turn resulted in great depression of photocatalytic activity. Silica-coated titania nanoparticles were characterized by TEM, XPS, FT-IR, EDX, and microporosity measurements. The photocatalytic activity was evaluated for the coated powder to investigate the efficiency of the silica coating as well.Depression of high photocatalytic activity of titania necessitates that silica shell has to be thick with minimum microporosity. Additionally, the mode of arrangement of silica nuclei in silica shell has significant impact on microporosity of silica shell to reduce the electron–hole pair reaction with water and oxygen.
Keywords: Silica coating; Titania nanoparticles; Seeded polymerization; Photocatalytic activity;
Adhesion force between calcium oxalate monohydrate crystal and kidney epithelial cells and possible relevance for kidney stone formation by Yakov I. Rabinovich; Madhavan Esayanur; Saijit Daosukho; Karen J. Byer; Hassan E. El-Shall; Saeed R. Khan (131-140).
AFM interaction force measurements have been performed between calcium oxalate monohydrate crystal (COM) colloidal probes and monolayers of renal epithelial cells (on a polymer substrate) in artificial urine (AU) solutions. The adhesion force was measured for the COM/MDCK cell interaction, while no adhesion force was found for the COM/LLC-PK1 cell interaction. Long-range repulsive forces for both lines of cells were measured in the range of 2–3 μm. After removal of the cell from the substrate by the AU flow, the basal membrane (BM), with a thickness of 100–200 nm, remained on the substrate. In this case, the shorter-range repulsive forces were found on the extending (approaching) portion of force/indentation curves. Similar to the COM/MDCK cell interaction, the retracting portions of curves for COM/basal membranes have shown the existence of the attractive force of adhesion for the interaction of COM with a BM of MDCK cells, while no adhesion was found for COM/BM LLC-PK1 cells interaction. No adhesion force was found for the interaction of a BM (of any cells) with the silicon nitride tip. Besides the hydrodynamic reasons, the adhesion difference between LLC-PK1 and MDCK cells possibly explains the preferential deposition of crystals only in collecting ducts (lined with MDCK-type cells) and the lack of the crystal deposition in the proximal tubules (lined with LLC-PK1-type cells). Previous treatments of cells with oxalate alone increased the adhesion force COM/BM MDCK; however, even after oxalate treatment there was small or no adhesion between COM and BM LLC-PK1 cells. Note that the adhesion force for COM/BM MDCK is practically independent of the probe velocity, i.e., does not have the viscous origin. Evaluation of the adhesion energy shows that this force should be related to the ionic or hydrogen bonds of samples.
Keywords: AFM, MDCK and LLC-PK1 cells; Calcium oxalate monohydrate; Adhesion force and kidney stone;
Mechanism of oil-in-water emulsification using a water-soluble amphiphilic polymer and lipophilic surfactant by Eri Akiyama; Akio Kashimoto; Hajime Hotta; Tomohito Kitsuki (141-148).
A new O/W (oil-in-water) emulsification system was developed using the amphiphilic polymer HHM-HEC (hydrophobically–hydrophilically modified hydroxyethylcellulose) and a lipophilic surfactant. HHM-HEC was used as a thickener and polymeric surfactant, and the addition of small quantities of various types of nonionic lipophilic surfactant (hydrophilic–lipophilic balance <5) decreased the droplet size of several types of oil due to a lowering of the tension at the water/oil interface. The oil droplets were held by the strong network structure of the aqueous HHM-HEC solution, preserving the O/W phase without inversion. These stable O/W emulsions were prepared without the addition of hydrophilic surfactants and thus show improved water repellency.The combination of amphiphilic polymer HHM-HEC and lipophilic surfactant made a new unique emulsification system. The network structure of HHM-HEC held oil particles stably and lipophilic surfactant lowered the interfacial tension and made oil particles small.
Keywords: HHM-HEC; Water-soluble polymer; Oil-in-water emulsion; Lipophilic surfactant;
One-dimensional assemblies of platinum nanoparticles on a graphite surface using nonionic/ionized mixed hemicylindrical micelle templates by Hideya Kawasaki; Masafumi Uota; Takumi Yoshimura; Daisuke Fujikawa; Go Sakai; Tsuyoshi Kijima (149-154).
One-dimensional (1-D) self-assemblies of Pt nanoparticles on a graphite surface have been synthesized via a template-directed sintering process of individual nanoparticles, using nonionic/cationic mixed hemicylindrical micelle templates of dodecyldimethylamine oxide surfactant at graphite/solution interfaces. The dimension and morphology of Pt nanoparticles can be widely controlled by the concentration of Pt ions equivalent to the mixing ratio of nonionic and cationic species in the surfactant micelle. This approach could be extended to fabricate a wide range of self-assembling metallic nanostructures on surfaces using various nonionic/cationic mixed micelle-like self-assemblies carrying metal ions at interfaces, while providing a fundamental insight into a 1-D self-assembly from individual nanoparticles.One-dimensional self-assemblies of platinum (Pt) nanoparticles on a graphite surface have been synthesized via a template-directed sintering process of individual nanoparticles, using nonionic/cationic mixed hemicylindrical micelle templates of dodecyldimethylamine oxide surfactant at graphite/solution interfaces. The dimension and morphology of Pt nanoparticles can be widely controlled by the concentration of Pt ions equivalent to the mixing ratio of nonionic and cationic species in the surfactant micelle.
Keywords: Self-assembly; Interface; Thin films; Platinum; Template synthesis;
Gelation and internal dynamics of colloidal rod aggregates by Ali Mohraz; Michael J. Solomon (155-162).
The internal dynamics of fractal cluster gels of colloidal boehmite rods with aspect ratios r = 3.9 , 8.6, and 30.1, and colloidal polystyrene spheres ( r = 1 ) are reported. Increasing r decreases the minimum colloid volume fraction for gelation. The behavior of the dynamic structure factor of rod gels is consistent with the internal dynamics of a constrained Brownian fractal object. Colloidal boehmite gels display an abrupt transition from floppy to brittle dynamics at ϕ ∼ 10 −4 . Moreover, the fractal cluster size of rod gels is not the determinant of the relaxation time of density fluctuations as it is in spherical particle gels. Instead, the relative behavior of the magnitude and time scale of the constrained fluctuations suggests that the fractal rod network is viscously coupled only on local, rather than cluster, scales. We hypothesize that noncentral forces between the anisometric particles are responsible for this anomalous behavior.The gelation and internal dynamics of fractal cluster gels of boehmite rods of different aspect ratios is reported, and the effect of particle shape in mediating the gel internal dynamics is investigated.
Keywords: Anisometric particles; Fractal gel dynamics;
Characterization of concentrated colloidal ceramics suspension: A new approach by Bimal P. Singh; Ruben Menchavez; Masayoshi Fuji; Minoru Takahashi (163-168).
The dispersion behavior of a concentrated ceramic suspension (Al2O3) has been investigated in terms of capillary suction time (CST) with varying solids concentration both in the absence as well as in the presence of dispersant (APC). The CST value is found to be the lowest at the pHiep whereas it increases as the pH is changed either to the acid side or alkaline side due to the repulsive forces acting among the neighboring particles keeping them in more dispersed state. It has been further observed that the CST value increases with increasing concentration of solids in the suspension. The dispersability of the suspension has been quantified in terms of dispersion ratio (DR). The higher the dispersion ratio of a particular system above unity, the better is the dispersability and vice versa. Further, quantification of dispersion stability by the CST technique is found to be useful and practical for optimization of different parameters concerning suspension stability. A correlation is found among the CST, zeta potential, colloidal stability, and maximum solids loading. It has been finally concluded that the CST method could be potentially employed as a quantitative and diagnostic technique for characterizing concentrated ceramic suspension.The dispersability of the suspension has been quantified in term of dispersion ratio (DR). The higher the dispersion ratio of a particular system above unity, the better is the dispersability and vice versa. It has been concluded that the CST method could be potentially employed as a quantitative and diagnostic technique for characterizing concentrated ceramic suspension.
Keywords: Dispersion; Capillary suction time; Iso-electric point (iep); Colloidal stability; CST; Dispersion ratio; Solids loading; Alumina; Surface charge;
Facile size-regulated synthesis of silver nanoparticles by controlled thermolysis of silver alkylcarboxylates in the presence of alkylamines with different chain lengths by Yukiyasu Kashiwagi; Mari Yamamoto; Masami Nakamoto (169-175).
Controlled thermolysis of silver alkylcarboxylates with primary alkylamines was investigated as a facile synthetic method of silver nanoparticles. A series of silver alkylcarboxylates, C7H15COOAg, C13H27COOAg, and C17H35COOAg, have been prepared and the thermolysis of those silver alkylcarboxylates in the presence of various alkylamines, C8H17NH2, C12H25NH2, and C18H37NH2, with no use of solvent was conducted at 120 or 180 °C for 5 h, providing spherical silver nanoparticles stabilized by alkylcarboxylates and alkylamines. The size and dispersibility of nanoparticles depend on the alkyl chain length of the precursors, alkylcarboxylates and alkylamines.Controlled thermolysis of silver alkylcarboxylates in the presence of primary alkylamines without solvents was investigated as the facile size-regulated synthesis of silver nanoparticles.
Keywords: Nanoparticles; Silver alkylcarboxylates; Controlled thermolysis; Size regulation; Alkylamines;
Core–shell structured SiO2@YVO4:Dy3+/Sm3+ phosphor particles: Sol–gel preparation and characterization by H. Wang; M. Yu; C.K. Lin; J. Lin (176-182).
Spherical SiO2 particles have been coated with YVO4:Dy3+/Sm3+ phosphor layers by a Pechini sol–gel process, leading to the formation of core–shell structured SiO2@YVO4:Dy3+/Sm3+ particles. X-ray diffraction (XRD), Fourier-transform IR spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting SiO2@YVO4:Dy3+/Sm3+ core–shell phosphors. The obtained core–shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 300 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (20 nm for one deposition cycle). The core–shell particles show strong characteristic emission from Dy3+ for SiO2@YVO4:Dy3+ and from Sm3+ for SiO2@YVO4:Sm3+ due to an efficient energy transfer from YVO4 host to them. The PL intensity of Dy3+ and Sm3+ increases with raising the annealing temperature and the number of coating cycles.Spherical SiO2 particles have been coated with YVO4:Dy3+/Sm3+ phosphor layers by a Pechini sol–gel process. The PL intensity of Dy3+ and Sm3+ increases with raising the annealing temperature and the number of coating cycles.
Keywords: Silica; YVO4; Dysprosium; Samarium; Core–shell; Luminescence;
Iron oxide modified diamond blends containing ultradispersed diamond by Tanya Tsoncheva; Momtchil Dimitrov; Ljubomira Ivanova; Daniela Paneva; Dimitar Mitev; Boiko Tsintsarski; Ivan Mitov; Stavri Stavrev; Christo Minchev (183-189).
Iron oxide modified diamond blends containing different amounts of ultradispersed diamond were prepared and characterized by nitrogen physisorption, X-ray diffraction, temperature programmed reduction, Mössbauer and IR spectroscopy. The catalytic behavior of these composite materials in methanol decomposition to hydrogen, carbon monoxide, and methane has been also studied. The initial state and phase transformations of the supported highly dispersed iron oxide particles in various pretreatment media, as well as their reductive and catalytic properties, strongly depend on the ultradispersed diamond content in the diamond blends.The surface properties of diamond blends (DB) determine their application as suitable supports for highly dispersed iron oxide particles—their phase composition, reductive properties, and catalytic behavior in methanol decomposition being substantially affected by the presence of ultradispersed diamond carbon in them.
Keywords: Ultradispersed diamond; Diamond blends; Highly dispersed iron oxide; Methanol decomposition; Mössbauer spectroscopy;
Au–Pt bimetallic nanoparticles formation via viologen-mediated reduction on polymeric nanospheres by Lian Cen; K.G. Neoh; Qinjia Cai; E.T. Kang (190-199).
Poly(vinylbenzyl chloride) nanospheres prepared via emulsion polymerization were surface functionalized with viologen moieties. Several methods were investigated to achieve the desired high surface concentration of viologen moieties with minimal aggregation of the nanospheres. The viologen-functionalized nanospheres were used for photoinduced reduction of gold ions and platinum ions, either individually, simultaneously or sequentially, to result in the formation of well-distributed Au–Pt nanoparticles of a few nanometers on the surface of the nanospheres. UV–visible absorption spectroscopy and XPS analyses of these bimetallic nanoparticles were carried out. The reaction time and the sequence of the reduction process play an important role in determining the composition of the bimetallic nanoparticles. High-resolution transmission electron microscopy analysis reveals the highly crystalline nature of the bimetallic nanoparticles.
Keywords: Viologen; Polymeric nanospheres; Crystalline; Bimetallic nanoparticles; Gold; Platinum;
Contribution of static light scattering to the textural characterization of large aggregates by M. Bizi; G. Baudet (200-209).
The industrial processes of water clarification often imply flocs of millimeter length. The principal motivation of this work relates to the characterization of these large flocs with laser diffractometry, for which the authors propose particular experimental approaches. In addition, a reformulation of the various properties of the flocs accessible by laser diffractometry is presented, in particular for the determination of the size, density, porosity, volume fraction, and fractal dimension. By way of illustration, these experimental and theoretical developments are applied to the characterization of flocs obtained by flocculation of a commercial kaolin. The size, fractal dimension, and density of kaolin floc were examined under various flocculant concentrations. Measurements reveal important variations of the granulometric and textural properties of large flocs in response to flocculation, opening ways of optimization for the associated industrial processes.Fractal dimension versus distribution spreading index in volume for various concentrations of flocculant (CF). This relation makes it possible to determine the optimal concentration. It also indicates the saturation of the adsorption sites and the presence of an excess of flocculant beyond the concentration corresponding to D F MAX .
Keywords: Density; Floc size distribution; Fractal dimension; Kaolin; Light scattering; Obscuration; Porosity;
Preparation of AgCl–polyacrylamide composite microspheres via combination of a polymer microgel template method and a reverse micelle technique by Ying Zhang; Yu Fang; Huiyun Xia; Yuxia Xie; Ruifang Wang; Xuejun Li (210-218).
A new route was created for the preparation of AgCl–polyacrylamide (AgCl–PAM) composite microspheres with patterned surface structures. The route is a combination of a polymer microgel template method and a reverse micelle technique. The size of the AgCl nanoparticles existing on the surfaces of the composite microspheres and the clearness of the surface patterns of the composite microspheres can be altered by simply adjusting the amount of precipitated AgCl and the rate of the deposition reaction. The route can be also used for the preparation of other water-insoluble salt–polymer composite microspheres, such as BaSO4–PAM. It is expected that the composite microspheres with patterned surface structures may not only combine the advantages of polymers and those of inorganic compounds, but also combine the advantages of microspheres in the micrometer size range and those in the nanometer size range.AgCl–polyacrylamide (AgCl–PAM) composite microspheres with fancy surface structures were prepared by combing a polymer microgel template method and a reverse micelle technique.
Keywords: Composite materials; Microgels; Reverse micelles; Template method; AgCl nanoparticles;
A simple route utilizing surfactant-assisted templating sol–gel process for synthesis of mesoporous Dy2O3 nanocrystal by Thammanoon Sreethawong; Sumaeth Chavadej; Supachai Ngamsinlapasathian; Susumu Yoshikawa (219-224).
A simple route of combined sol–gel process with surfactant-assisted templating technique was successfully employed for the first time to synthesize nanocrystalline mesoporous Dy2O3 with narrow monomodal pore size distribution under mild conditions. The nanocrystalline Dy2O3 with monomodal mesoporous characteristic was ultimately achieved by controlling the hydrolysis and condensation steps of dysprosium n-butoxide modified with acetylacetone in the presence of laurylamine hydrochloride surfactant aqueous solution. The synthesized material was methodically characterized by thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), N2 adsorption–desorption, Brunauer–Emmett–Teller (BET) surface area analysis, and Barrett–Joyner–Halenda (BJH) pore size distribution analysis. The particle size of the synthesized Dy2O3 in nanosized range obtained from the SEM and HRTEM micrographs was in good accordance with the crystallite size estimated from the XRD result. The N2 adsorption–desorption result exhibited hysteresis pattern with single loop, indicating the existence of monomodal mesopore. The extremely narrow pore size distribution with mean pore diameter in the mesopore region of the synthesized Dy2O3 was also confirmed by the BJH result.A simple route of surfactant-assisted templating sol–gel process was successfully utilized to synthesize nanocrystalline monomodal mesoporous Dy2O3. N2 adsorption–desorption analysis of the synthesized Dy2O3 exhibited IUPAC type IV pattern with hysteresis loop indicating the presence of prevalent mesopore, and pore size distribution was also extremely narrow and monomodal.
Keywords: Dysprosium oxide; Mesoporous material; Nanocrystal; Surfactant template; Sol–gel process;
Control on size and adsorptive properties of spherical ferric phosphate particles by Kazuhiko Kandori; Takanori Kuwae; Tatsuo Ishikawa (225-231).
Ferric phosphate particles were prepared by aging a solution dissolving Fe(ClO4)3 and H3PO4 at 40–80 °C for 16 h in a Teflon-lined screw-capped Pyrex test tube. The spherical or agglomerated fine particles were only precipitated with an extremely fast rate of reaction. The spherical particles were only produced at a very narrow region in fairly low pH solutions. TEM observation revealed that these particles grew in spherical structure by aggregation of primary small particles. The size of spherical particles was decreased by increase in the solute concentration or raising the aging temperature. Therefore, the formation of spherical particles was explained by a polynuclear layer mechanism proposed by Nielsen. The uniform spherical particles produced are amorphous, but they were crystallized to FePO4 after calcining above 600 °C. It was suggested that the voids between the primary particles within the secondary agglomerated particles constitute mesopores. The Fe/P molar ratio determined and weight loss in TG curves gave the chemical formulas of the particles as Fe(PO4) x (H2PO4) y ⋅nH2O (x: 0.93–1.00, y: 0–0.22, n: 2.4–2.7). The amorphous spherical ferric phosphate particles showed a high selective adsorption of H2O by penetration of H2O molecules into ultramicropores, produced after outgassing pretreatment, of that size is smaller than N2 molecule. The more particles grew, the more adsorption selectivity of H2O became remarkable.The size of spherical ferric phosphate particles, grew by aggregation of primary small particles, was controlled. They showed mesoporosity and high selective adsorption of H2O.
Keywords: Spherical ferric phosphate; Size control; Mesoporosity; Adsorptive properties;
Study of the formation of perovskite type lanthanum ruthenates by heating their hydrous precursor by Nitin K. Labhsetwar; V. Balek; E. Večerníková; P. Bezdička; J. Subrt; T. Mitsuhashi; S. Kagne; S. Rayalu; H. Haneda (232-236).
Emanation thermal analysis (ETA), differential thermal analysis (DTA), thermogravimetry (TG), evolved gas analysis with mass spectrometric detection (EGA-MS), and X-ray diffraction (XRD) were used to investigate the formation of perovskite type lanthanum ruthenates on heating their hydroxide precursor in argon from 20 to 1200 °C. The co-precipitated lanthanum–ruthenium mixed hydroxide containing a small amount of carbonates was used as a precursor. The mass loss corresponding to the release of water and CO2 from the precursor was determined by TG and EGA (MS), respectively. The ETA characterized the exposure of sample surface after release of water and CO2, as well as microstructure development corresponding to the crystallization and structure ordering of LaRuO3 and La3.5Ru4.0O13 perovskite phases. The obtained information on formation of phases and their transformation is useful for optimizing their synthesis protocols for achieving the desired physical properties, and to estimate the thermal stability of these materials to be used as catalysts.Emanation thermal analysis, DTA, TG-EGA, and XRD were used to study the formation of perovskite type lanthanum ruthenates on heating their hydroxide precursor. The ETA characterized the microstructure development corresponding to the crystallization and structure ordering of LaRuO3 and La3.5Ru4.0O13 perovskite phases.
Keywords: Lanthanum ruthenate; Emanation thermal analysis; DTA; Crystallization;
Synthesis, characterization, and catalytic activity of phosphomolybdic acid supported on hydrous zirconia by Sujata Mallik; Suswati S. Dash; Kulamani M. Parida; B.K. Mohapatra (237-243).
A series of ecofriendly solid acid catalyst was synthesized by phosphomolybdic acid impregnated on hydrous zirconia (ZPMA) by an incipient wetness impregnation technique. The support and the resulting catalysts were characterized by X-ray diffraction, FTIR, EPMA, BET surface area, acid sites, etc. These studies indicate that the phosphomolybdic acid keeps its Keggin-type structure unaltered up to 500 °C. Catalytic activities of the material were evaluated for the esterification of acetic acid reaction. The 12 wt% of phosphomolybdic acid supported on hydrous zirconia shows highest surface area, acid sites and gives about 86% conversion with 100% selectivity of n-butyl acetate.With increase of the reaction time from 60 to 300 min, the percentage of conversion of acetic acid increases from 25 to 65% and 35 to 89% for zirconia and 12 wt% ZPMA, respectively. The selectivity toward butyl acetate nearly 100% in all cases.
Keywords: Hydrous zirconia; Phosphomolybdic acid; Esterification; n-Butyl acetate; Rate constant;
Photocatalytic degradation of aniline at the interface of TiO2 suspensions containing carbonate ions by Anil Kumar; Nupur Mathur (244-252).
The degradation of aniline has been investigated using aqueous TiO2 suspensions containing carbonate ions as photocatalyst. The addition of carbonate to Degussa P-25 increased the number of active adsorption sites at its surface. For the TiO2 suspensions containing carbonate ions the intensity of adsorption of aniline increased to 6.9 × 102 from 5.5 × 102 mol−1 dm3 in case of bare TiO2 suspensions. This in turn results in the increased interfacial interaction of the photogenerated charge carriers with the adsorbed aniline and thus enhancing the rate of its photodecomposition to 6.5 × 10−6 mol dm−3 s−1 compared to 2.7 × 10−6 mol dm−3 s−1 in the absence of Na2CO3. The maximum efficiency of this photocatalyst has been obtained upon addition of 0.11 mol dm−3 of Na2CO3 at pH 10.8. The photocatalytic action is understood by the simultaneous interaction of intermediates, •OH and CO• − 3, and their reactivity with aniline. Azobenzene, p-benzoquinone, nitrobenzene, and NH3 have been identified as the major products of the photooxidation of aniline. Both the reactant and products have been followed kinetically. The photodegradation follows Langmuir–Hinshelwood Model. The mechanism of the occurring reactions has been analyzed and discussed. In the presence of Na2CO3, 3 × 10−3 mol dm−3 of aniline could be photodegraded completely in about 6 h while all organic intermediates decomposed completely within about 10 h.The addition of CO2− 3 to the TiO2 suspensions enhances the photocatalytic degradation of aniline due to increased active adsorption sites and interfacial interaction of photogenerated intermediates, •OH and CO• − 3 with aniline.
Keywords: Photocatalysis; Photodegradation; Aniline; TiO2 suspensions; Suspensions carbonate; Bicarbonate; Adsorption; Interfacial interaction; Azobenzene; Ammonia; Alkalinity;
Preparation and characterization of long-lived anode catalyst for direct methanol fuel cells by Yuzuru Shimazaki; Yoshio Kobayashi; Masatoshi Sugimasa; Shinji Yamada; Takeyuki Itabashi; Takao Miwa; Mikio Konno (253-258).
Entry of direct methanol fuel cells into the market requires anode catalyst with stable activity. This paper presents a novel method for stabilizing the activity by immobilizing silica on the catalytic PtRu nanoparticles. Characterization was performed by STEM-EDX, XRD, and ICP. The silica-immobilized PtRu nanoparticles showed high and stable activity toward methanol oxidation. The activity was maintained for 1000 h in sulfuric acidic solution, while the activity of the catalyst with “bare” PtRu nanoparticles decayed after 100 h, showing high durability of the silica-immobilized PtRu nanoparticles catalyst in quasi-anodic acidic environment.The DMFC anode catalyst prepared with silica-immobilized PtRu nanoparticles showed stable catalytic activity for 1000 h, while the activity of the catalyst with “bare” PtRu nanoparticles decayed after 100 h.
Keywords: Direct methanol fuel cell; Anode catalyst; PtRu nanoparticle; Silica; STEM-EDX; XRD; ICP;
Electrical properties of polypyrrole wires measured by scanning probe microscope by Mun-Sik Kang; Kyo-Hyeok Kim; Il Sub Chung; Yongkeun Son (259-263).
Hybrid wires composed of metal and conducting polymer (polypyrrole, Ppy) were electrochemically synthesized using a template synthesis method. We showed that the dimensions of the hybrid wires can be tailored by controlling the time of electrolysis. The electrical properties of Ppy having different lengths were measured using a scanning probe microscope (SPM) tip as an electrode without aligning the hybrid wires on a substrate. Especially, temperature-dependent characteristics of the I – V curve were determined. As we expected, the shorter the Ppy wire is, the better the current response produced. The activation energy of each Ppy wire is determined. It is confirmed that the electrical properties of a single wire of Ppy can be measured by SPM.
Keywords: Hybrid wires; Polypyrrole; Template synthesis; SPM; I – V characteristics; Activation energy;
Structure of montmorillonite cointercalated with stearic acid and octadecylamine: Modeling, diffraction, IR spectroscopy by P. Čapková; M. Pospíšil; M. Valášková; D. Měřínská; M. Trchová; Z. Sedláková; Z. Weiss; J. Šimoník (264-269).
Structural analysis of Na-montmorillonite co-intercalated with octadecylamine and stearic acid was carried out using combination of experiment: X-ray powder diffraction and IR spectroscopy with molecular modeling (force field calculations) in Cerius2 modeling environment. Results of structure analysis revealed the chemical reaction of guest compounds leading to the formation of octadecylammonium stearate. This reaction may occur even before the intercalation out of the interlayer space of montmorillonite. The presence of octadecylammonium stearate in the samples was clearly confirmed by IR spectroscopy and X-ray diffraction. Present results also showed that: (1) Stearic acid itself does not intercalate into Na-montmorillonite; (2) cointercalation with octadecylamine led to the formation of octadecylammonium stearate, which was successfully intercalated into the interlayer space of montmorillonite, and (3) Na-montmorillonite intercalated with octadecylammonium stearate does not create a stable structure. Intercalated samples in ambient conditions undergo gradual decomposition, accompanied by the release of octadecylammonium stearate from the interlayer space and rearrangement of the interlayer structure. Co-intercalation of STA and ODA to lower the octadecylamine content and consequently to suppress the unfavorable effect of amine groups on the polymer matrix in nanocomposite, was investigated.
Keywords: Polymer–clay nanocomposites; Intercalation; Montmorillonite; Octadecylamine; Stearic acid; Molecular modeling; IR spectroscopy; X-ray diffraction;
Mesoporous silica–titania composed materials by Paula V. Messina; Marcela A. Morini; María B. Sierra; Pablo C. Schulz (270-278).
Titania mesosized particles were obtained by TiCl4 hydrolysis in Aerosol OT/water/n-hexane microemulsion. These particles were incorporated in surfactant templated silica mesoporous materials of MCM-41 and MCM-50 structures. Results depended on the surfactant: hexadecyltrimethylammonium bromide templated materials retained the honeycomb structure with small modifications in their characteristics. The dodecyltrimethylammonium bromide templated material changed from honeycomb to lamellar structure when the titania particles were included, with dramatic changes in the structure characteristics. The didodecyldimethylammonium bromide templated lamellar structure was retained after TIO2 inclusion, with a slight increase in the specific area, pore diameter and pore walls thickness.Titania particles were sinthesized with Cl4Ti in an inverse microemulsion Aerosol OT/n-hexane/water. The titania particles were then included in the sinthesis of mesoporous silica materials. The obtained materials were characterised by electron microscopy and nitrogen adsorption. The inclusion of titania produced changes in the structure, specific area and wall thickness of the resulting material.
Keywords: Mesoporous material; Silica–titania material; Inverse microemulsion templated particles;
Synthesis of flexible silica aerogels using methyltrimethoxysilane (MTMS) precursor by A. Venkateswara Rao; Sharad D. Bhagat; Hiroshi Hirashima; G.M. Pajonk (279-285).
The experimental results on the synthesis of flexible and superhydrophobic silica aerogels using methyltrimethoxysilane (MTMS) precursor by a two-step (acid–base) sol–gel process followed by the supercritical drying, are reported. The effects of various sol–gel parameters on the flexibility of the aerogels have been investigated. The aerogels of different densities were obtained by varying the molar ratio of MeOH/MTMS ( S ) from 14 to 35, with lower densities for larger S values. It has been observed that the Young's modulus ( Y ) decreased from 14.11 × 10 4 to 3.43 × 10 4 N / m 2 with the decrease in the density of the aerogels from 100 to 40 kg/m3. Simultaneously, the aerogels are superhydrophobic with a contact angle as high as 164°. The superhydrophobic aerogels are thermally stable up to a temperature of 530 K, above which they become hydrophilic. The aerogels have been characterized by bulk density, percentage volume shrinkage, and porosity measurements. The microstructures of the aerogels have been studied using the transmission electron microscopy (TEM). The Young's modulus of the aerogels has been determined by an uniaxial compression test. The variation of physical properties of the aerogels has been explained by taking into consideration the hydrolysis, condensation reactions, the resulting colloidal clusters and their network formation.
Keywords: Silica aerogels; Elastic properties; TEM; Superhydrophobicity; Flexible aerogels;
Surface modification of phenolphthalein poly(ether sulfone) ultrafiltration membranes by blending with acrylonitrile-based copolymer containing ionic groups for imparting surface electrical properties by Meng Wang; Li-Guang Wu; Xing-Cun Zheng; Jian-Xiong Mo; Cong-Jie Gao (286-292).
Asymmetric ultrafiltration membranes were fabricated from the blends of phenolphthalein polyethersulfone (PES-C) and acrylonitrile copolymers containing charged groups, poly(acrylonitrile-co-acrylamido methylpropane sulfonic acid) (PAN-co-AMPS). From the surface analysis by XPS and ATR-FTIR, it was found that the charged groups tend to accumulate onto the membrane surface. This result indicated that membrane surface modification for imparting surface electrical properties could be carried out by blending charged polymer. Furthermore, with the help of a relatively novel method to measure membrane conduction, the true zeta potentials calculated on the basis of the streaming potential measurements were used to reflect the charge state of membrane surface. In addition, it was noteworthy that, from the profiles of zeta potential versus pH curves and the magnitude of zeta potentials, the determination of zeta potential was dependent not only on the electrical properties of membrane surface but also on its hydrophilicity. At last, based on a relatively elaborate study on the electrostatic interaction between the membrane surface and protein, it was found that these charged membranes could meet different demands of membrane applications, such as resisting protein fouling or protein separation, through adjusting solution pH value.The surface charge state of membrane samples was reflected by using zeta potentials calculated neglecting system total conduction in the former case and considering it in the latter case.
Keywords: Surface modification; Blends; Charged membrane; Zeta potential; Protein adsorption behavior;
Patterning in rapidly evaporated polymer solutions: Formation of annular structures under evaporation of the poor solvent by Edward Bormashenko; Roman Pogreb; Albina Musin; Oleg Stanevsky; Yelena Bormashenko; Gene Whyman; Zahava Barkay (293-297).
Patterning in the intensively evaporated polymer solutions based on polystyrene and poor solvent (acetone) was investigated. SEM and AFM studies demonstrated that annular elements of the surface topography are formed in this case, in contrast to the honeycomb patterns obtained under the evaporation of the good solvent (chloroform). The authors suggest that the theory of viscous dewetting developed by de Gennes explains the phenomenon satisfactorily.
Keywords: Polymer solutions; Poor solvent; Viscous dewetting; Annular structures; Patterning;
Two-dimensional “nano-ring and nano-crystal” morphologies in Langmuir monolayer of phthalocyaninato nickel complexes by Qingyun Liu; Hongguo Liu; Yongzhong Bian; Xueying Wang; Yanli Chen; Jianzhuang Jiang; Xiyou Li (298-303).
Three 1,8,15,22-tetrasubstituted phthalocyaninato nickel complexes Ni[Pc(α-OR)4] [H2Pc(α-OC5H11)4 = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine; H2Pc(α-OC7H15)4 = 1,8,15,22-tetrakis(2,4-dimethyl-3-pentyloxy)phthalocyanine; H2Pc(α-OC10H7)4 = 1,8,15,22-tetrakis(2-naphthyloxy)phthalocyanine] (1–3) have been prepared by treating the corresponding metal-free phthalocyanines H2Pc(α-OR)4 with Ni(acac)2⋅2H2O in refluxing n-pentanol. Structures of the Langmuir monolayers of these compounds at different temperature have been investigated. Compound 1 formed nano-ring structures with the outer diameter of 70–150 nm and inner diameter of 50 nm at 25.0 °C while 2 and 3 formed round particles. This difference can be ascribed to the different substituents at α position. The morphologies of the aggregates of 1 in monolayers have been found to change with temperature. Decreasing in temperature induced the formation of regular quadrate crystals. UV–vis absorption spectra revealed strong intermolecular interactions in the nano-ring aggregates. Polarized UV–vis absorption spectra suggest a titled orientation with respect to the surface of substrate for phthalocyanine macrocycles in the nano-ring aggregates.
Keywords: Nano-ring; Nano-crystal; Langmuir; Phthalocyaninato nickel;
Temperature effect on water intrusion/expulsion in grafted silica gels by Loïc Coiffard; Valentin Eroshenko (304-309).
Water intrusion–expulsion cycles within a hydrophobic silica gel system were observed at various temperatures. The hysteresis phenomenon revealed an attenuation effect growing with temperature. A simple model derived from the Laplace–Washburn equation made it possible to characterize the observed phenomena both qualitatively and quantitatively. The model involves advancing and receding contact angles increasing with temperature, which influence the hysteresis phenomenon very differently, depending on their value.
Keywords: Nonwetting; Contact angle hysteresis; Hydrophobic silica gel; Water intrusion; Water expulsion;
Aggregation of quaternary ammonium gemini surfactants C12-s-C12⋅2Br in n-heptane/n-hexanol solution: Effect of the spacer chains on the critical reverse micelle concentrations by Ou Zheng; Jian-Xi Zhao; Rui-Ting Chen; Xian-Ming Fu (310-313).
The critical reverse micelle concentrations of C12-s-C12⋅2Br ( s = 2 , 3 , 4 , 5 , 6 , 8 , 12 ) in n-heptane/n-hexanol solutions, cmcI s, have been determined by absorption spectrum method using iodine as probe. The values of cmcI s are smaller than those of the critical micelle concentrations (cmcaq s) in aqueous solution and reach a maximum at s = 4 , which is similar to the variation of cmcaq with s. The variation of cmcI with s is attributed to the alteration in the spacer chain conformation, i.e. when the spacer is short enough, it may adopt stretch configuration and when the spacer is long, it tends to bend towards the continuous oil phase to achieve a more densely packing of the quaternary ammonium heads on the surface of the core.The gemini surfactants C12-s-C12⋅2Br ( s = 2 , 3 , 4 , 5 , 6 , 8 , 12 ) form reverse micelles in n-heptane with the assistance of n-hexanol. The variation of the critical reverse concentration (cmcI) with s is attributed to the change of folded conformation of the spacer chain.
Keywords: Quaternary ammonium gemini surfactants; n-Heptane/n-hexanol solution; Reverse micelle;
Effects of cholesterol component on molecular interactions between paclitaxel and phospholipid within the lipid monolayer at the air–water interface by Lingyun Zhao; Si-Shen Feng (314-326).
Cholesterol is a main component of the cell membrane and could have significant effects on drug–cell membrane interactions and thus the therapeutic efficacy of the drug. It also plays an important role in liposomal formulation of drugs for controlled and targeted delivery. In this research, Langmuir film technique, atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) are employed for a systematic investigation on the effects of cholesterol component on the molecular interactions between a prototype antineoplastic drug (paclitaxel) and 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) within the cell membrane by using the lipid monolayer at the air–water interface as a model of the lipid bilayer membrane and the biological cell membrane. Analysis of the measured surface pressure (π) versus molecular area ( a ) isotherms of the mixed DPPC/paclitaxel/cholesterol monolayers at various molar ratios shows that DPPC, paclitaxel and cholesterol can form a non-ideal miscible system at the air–water interface. Cholesterol enhances the intermolecular forces between paclitaxel and DPPC, produces an area-condensing effect and thus makes the mixed monolayer more stable. Investigation of paclitaxel penetration into the mixed DPPC/cholesterol monolayer shows that the existence of cholesterol in the DPPC monolayer can considerably restrict the drug penetration into the monolayer, which may have clinical significance for diseases of high cholesterol. FTIR and AFM investigation on the mixed monolayer deposited on solid surface confirmed the obtained results.AFM images of the cholesterol monolayer transferred onto the mica surface at 30 mN/m surface pressure: (left) 3D image; (right) 2D image and cross section measurement.
Keywords: Anticancer drugs; Atomic force microscopy (AFM); Drug–membrane interactions; Drug penetration; Fourier Transform Infrared Spectroscopy (FTIR); Langmuir trough; Taxol®;
Model for Plateau border drainage of power-law fluid with mobile interface and its application to foam drainage by Zebin Wang; Ganesan Narsimhan (327-337).
A model for drainage of a power-law fluid through a Plateau border is proposed which accounts for the actual Plateau border geometry and interfacial mobility. The non-dimensionalized Navier–Stokes equations have been solved using finite element method to obtain the contours of velocity within the Plateau border cross section and average Plateau border velocity in terms of dimensionless inverse surface viscosity and power-law rheological parameters. The velocity coefficient, the correction for the average velocity through a Plateau border of actual geometry compared to that for a simplified circular geometry of the same area of cross section, was expressed as a function of dimensionless inverse surface viscosity and flow behavior index of the power-law fluid. The results of this improved model for Plateau border drainage were then incorporated in a previously developed foam drainage model [G. Narsimhan, J. Food Eng. 14 (1991) 139] to predict the evolution of liquid holdup profiles in a standing foam. Foam drainage was found to be slower for actual Plateau border cross section compared to circular geometry and faster for higher interfacial mobility and larger bubble size. Evolution of liquid holdup profiles in a standing foam formed by whipping and stabilized by 0.1% β-lactoglobulin in the presence of xanthan gum when subjected to 16g and 45g centrifugal force fields was measured using magnetic resonance imaging for different xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Measured bubble size, surface shear viscosity of β-lactoglobulin solutions and literature values of power-law parameters of xanthan gum solution were employed in the current model to predict the evolution of liquid holdup profile which compared well with the experimental data. Newtonian model for foam drainage for zero shear viscosity underpredicted drainage rates and did not agree with the experimental data.A model for Plateau border drainage of a power-law fluid accounting for actual geometry and interfacial mobility is proposed and is applied to drainage of a standing foam.
Keywords: Plateau border drainage; Power-law fluid; Interfacial mobility; Surface shear viscosity; Foam drainage; Liquid holdup profile; Magnetic resonance imaging; Protein stabilized foam; β-Lactoglobulin; Xanthan gum;
Disconnected lamellar phases ( L α ) in pseudobinary water–non-ionic surfactant systems: A general phenomenon by Dharmesh Varade; Hironobu Kunieda; Reinhard Strey; Cosima Stubenrauch (338-347).
This study provides new experimental evidence for the disconnection of the lamellar phase ( L α ) in pseudobinary water–non-ionic surfactant systems. To prove that the disconnection is indeed a general phenomenon the phase behavior of the pseudobinary system water–pentaethylene glycol dodecyl ether/hexaethylene glycol dodecyl ether (H2O–C12E5/C12E6) was investigated as a function of the surfactant composition δ and the total surfactant concentration γ. At a fixed γ of 0.10 the extension of the highly diluted L α phase shrank continuously with increasing amount of C12E6, i.e., increasing δ, until it disappeared at δ = 0.60 . The γ–T phase diagram of this particular surfactant mixture was found to have a disconnected L α phase. For the first time, SAXS measurements were carried out to monitor structural changes related to the disconnection. For this purpose the interlayer spacing d and the effective cross-sectional area a s were determined from the SAXS data along characteristic paths through the L α phase.Schematic drawing of a phase diagram, in which a disconnected L α phase is formed. Undulating bilayers of the dilute L α phase (left) and stacked monolayers of the concentrated L α phase (right).
Keywords: Non-ionic surfactants; Phase diagram; Lyotropic liquid crystals; Dilute lamellar phase; Disconnected lamellar phase; SAXS;
Effect of temperature on dynamic rheological behavior of discontinuous cubic liquid crystal by Hongxia Wang; Gaoyong Zhang; Zhiping Du; Qiuxiao Li; Wanxu Wang; Diansheng Liu; Xinwei Zhang (348-353).
The dynamic rheological properties of discontinuous cubic liquid crystal, formed by nonionic surfactant C12–14E12, were investigated in the discrete and continuous patterns of raising temperature. In the discrete pattern, the discontinuous cubic phase appears in two types of viscoelastic behaviors under the melting points of cubic phase: elastic gel and viscoelastic liquid. When the discontinuous cubic phase begins to melt, it has the weak polymer-like viscoelasticity. Temperature and shear frequency have completely different effects on the ratio of viscous and elastic components of samples in these three states. At low temperature, the samples dominate in elasticity and temperature and shear frequency has hardly any effect on viscoelasticity. At moderate temperature, its ratio of viscous and elastic components increases with increasing temperature and decreasing shear frequency. At the vicinity of the melting point of cubic liquid crystal, the cubic liquid crystal appears to have almost equaled viscous and elastic component; shear has obvious effect on the ratio of viscoelasticity at low frequency. The results from the continuous pattern of raising temperature are consistent with those from the discrete pattern.In region I, the discontinuous cubic liquid crystal is elastic gel, temperature has little effect on G ′ but makes G ″ smoothly increase; in region II, it is viscoelastic liquid, G ′ and G ″ decrease with temperature; and in region III, weak polymer-like viscoelastic liquid, G ′ and G ″ sharply drop.
Keywords: Discontinuous cubic liquid crystalline phase; Dynamic rheological behaviors; Temperature;
Self-diffusion study of micelles in poly(oxyethylene)–polydimethylsiloxane diblock copolymer and poly(oxyethylene) alkyl ether systems by Kenji Aramaki; Ulf Olsson (354-360).
Self-diffusion constants of amphiphilic molecules in D2O solutions of mixed poly(oxyethylene)–polydimethylsiloxane diblock copolymer (POE–PDMS, Si m C 3 EO n ) and poly(oxyethylene) dodecyl ether ( C 12 EO n ) were measured by pulsed-field-gradient NMR method. In the D2O/Si25C3EO51.6/C12EO8 or D2O/Si52C3EO51.6/C12EO8 systems, small and large micelles coexist in a wide range of Si m C3EO51.6 fraction in total amphiphiles, whereas such a coexisting phenomenon does not take place in the D2O/Si5.8C3EO51.6/C12EO8 system. The coexisting phenomenon also takes place in the D2O/Si25C3EO51.6/C12EO5 system although the range of mixing fraction is limited. By obtaining each contribution of surfactant and copolymer molecules to the attenuation decay of the echo signal from the proton of the poly(oxyethylene) chain, we could evaluate the composition of the mixed micelles in the D2O/Si25C3EO51.6/C12EO8 system. The copolymer content in the mixed micelle increases proportionally to the copolymer mole fraction in the aqueous solution. From the series of self-diffusion measurements, we can conclude that the miscibility of Si m C 3 EO n and C 12 EO n in aqueous micelles becomes poor and the coexisting phenomenon takes place when the PDMS chain becomes much longer than the dodecyl chain of C 12 EO n or the POE chain of C 12 EO n becomes long. Furthermore it is also revealed that very few silicone copolymer molecules can be incorporated in small surfactant micelles.
Keywords: Micelle; Self-diffusion study; POE–PDMS block copolymer; Poly(oxyethylene) alkyl ether; Coexisting micelles; Micelle composition;
Phase behavior of mixtures of polyoxyethylene(10) stearyl ether (Brij-76), 1-butanol, isooctane, and mixed polar solvents by Debdurlav Nandy; Rajib K. Mitra; Bidyut K. Paul (361-367).
The isothermal phase diagram of the quaternary system polyoxyethylene(10) stearyl ether (Brij-76)/1-butanol/isooctane/water has been constructed at 30 °C with equal amounts of oil and water. A regular fishtail diagram was obtained, confirming the establishment of hydrophile–lipophile balance (HLB) in the system. Mixing of formamide (FA) [or N , N -dimethyl formamide (DMF)] with water as a cosolvent altered the HLB and decreased the solubilization capacity of the quaternary system. No three-phase body appeared at high FA or DMF content. Similar observations were noted for temperature-induced phase diagrams. The effect of DMF was more pronounced than that of FA in reducing the maximum solubilization capacity. The results have been summarized on the basis of HLB and mutual solubility of the components.Phase behavior of the mixture of polyoxyethylene(10) stearyl ether (Brij-76)/1-butanol/isooctane/water has been investigated in presence of mixed solvents (water + formamide) and (water + N , N -dimethyl formamide).
Keywords: Phase behavior; Quaternary microemulsion; Maximum solubilization capacity; Formamide; N , N -dimethyl formamide; Effect of temperature;
A thermodynamic study to evidence the α , ω -dichloroalkane/ block copolymer mixed aggregates formation: Effect of the copolymer architecture by R. De Lisi; G. Lazzara; S. Milioto; N. Muratore (368-374).
The thermodynamics of α , ω -dichloroalkanes in aqueous solutions of (ethylene oxide)11(propylene oxide)16(ethylene oxide)11 (L35) and (propylene oxide)8(ethylene oxide)23(propylene oxide)8 (10R5) was determined at 298 and 305 K. Modeling the experimental data allowed to calculate the standard free energy ( Δ G D o / w ) and the volume ( Δ V D / w ) for the additive–copolymer mixed aggregates formation per additive molecule. Δ G D o / w for Cl2CH2 and Cl2(CH2)2 evidenced that the process is controlled by the forces exercising between the chlorine atoms and the OH groups of the copolymer micelles protruded into the aqueous phase. Cl2(CH2)3 experiences both the hydrophilic and hydrophobic domains into the aggregates. The hydrophobic interactions are more significant in 10R5 whereas the hydrophilic ones are more significant in L35. Temperature increase does not influence Δ G D o / w in 10R5, whereas, it does influence Δ G D o / w in L35, enhancing the ability of the aggregate to extract the chlorinated compounds from the aqueous phase. The Δ V D / w values are consistent with the free energy results. These insights agree with those predicted by the Flory liquid lattice theory. The calculations extended to several α , ω -dichloroalkanes showed that Cl2CH2 and Cl2(CH2)2 prefer poly(ethylene oxide) (PEO), Cl2(CH2)3 exhibits the same affinity for both PEO and poly(propylene oxide) (PPO), whereas the more hydrophobic additives show a preference for PPO. The copolymer architecture plays a relevant role in the α , ω -dichloroalkane solubilization into the polymeric aggregates.Volume and free energy showed that the extraction ability of polymeric micelles, based on ethylene oxide and propylene oxide units, of α , ω -dichloroalkanes from the aqueous phase is a relevant function of the copolymer architecture.
Keywords: (Ethylene oxide)11(propylene oxide)16(ethylene oxide)11; (Propylene oxide)8(ethylene oxide)23(propylene oxide)8; α , ω -Dichloroalkanes; Volume; Standard free energy; Temperature;
Preparation of highly monodisperse W/O emulsions with hydrophobically modified SPG membranes by Chang-Jing Cheng; Liang-Yin Chu; Rui Xie (375-382).
Experimental investigations on the hydrophobic modification of SPG membranes and the preparation of monodisperse W/O (water-in-oil) emulsions using the modified membranes were carried out. Effects of the osmotic pressure of disperse phase, the average pore size of membranes, emulsifier concentrations in continuous phase and the transmembrane pressure on the average size, size distribution and size dispersion coefficient of emulsions were systematically studied. The stability of W/O emulsions was also investigated. The results showed that SPG membranes took on excellent hydrophobicity through the modification by silane coupler reagent (octyltriethoxysilane) or by silicone resin (polymethylsilsesquioxane). Monodisperse W/O emulsions with size dispersion coefficient of about 0.25, which meant high monodispersity, were successfully prepared by using the hydrophobically modified SPG membranes with average pore sizes of 1.8, 2.0, 2.5, 4.8 and 11.1 μm. When the osmotic pressure was lower than 0.855 MPa, the average size of emulsions was gradually increased while the size dispersion coefficient δ gradually decreased with the osmotic pressure; when the osmotic pressure was higher than 0.855 MPa, both the coefficients kept unvarying. When kerosene was saturated with disperse phase in advance, the average size of emulsions became larger and the monodispersity of emulsions was slightly better than that prepared using unsaturated kerosene. The smaller the pore size of SPG membranes was, the better the monodispersity of the W/O emulsions. The average size and size dispersion coefficient δ were nearly independent on the emulsifier concentrations when the PGPR concentration was in the range from 0.5 to 5.0 wt%, whereas both of them slightly increased as the PGPR concentration was below 0.5 wt%. The effect of the transmembrane pressure on size distributions was slight. Both the average size and size dispersion coefficient δ slightly increased to some extent with the increase of the transmembrane pressure in the experimental range. The stability of the W/O emulsions was dependent on the storage time. The mean size of W/O emulsions decreased gradually with the increase of storage time at the first 35 days, and then kept constant; while the size dispersion coefficient of W/O emulsions was nearly not changed.Highly monodisperse water-in-oil emulsions were prepared with hydrophobically modified Shirasu porous glass membranes.
Keywords: W/O emulsions; Monodisperse; SPG membranes; Hydrophobic modification; Membrane emulsification;
Colloid dispersion in a uniform-aperture fracture by Marissa D. Reno; Scott C. James; Susan J. Altman (383-390).
This research investigates the dispersion of colloids through fracture systems by exploring experimentally and numerically the transport and dispersion of 1.0-, 0.11-, and 0.043-μm diameter fluorescent carboxylate-modified microspheres and chloride at various flow rates through variable-length, synthetic Plexiglas fractures (flow cells). A dimensionless number describing each experiment is varied by changing the colloid size, flow rate, and fracture length. Surface characteristics of the microspheres and Plexiglas favor repulsive interactions, thereby minimizing the chance of colloid filtration and remobilization. Full recovery of the colloids is typically observed, thereby supporting the assumption of negligible colloid filtration. In comparison to chloride transport, there is increased tailing for colloid plumes traveling through the flow cell. This increased tailing is attributed to Taylor dispersion phenomena (dispersion due to an advection gradient). In the synthetic fractures investigated here, colloid dispersion due to the velocity gradient is evident, but fully developed Taylor conditions are not realized. A particle-tracking algorithm is run inversely to estimate the effective dispersion rate for the colloid plume in each experiment as a function of the experimental parameters (flow rate, fracture length, and colloid size). Results suggest that the log of the effective dispersion rate of the colloid plume increases linearly with the log of the dimensionless number comprising experimental parameters.This work looks at the transport of colloids through synthetic fractures. A relationship between effective dispersion rate and a dimensionless number comprising experimental parameters is presented to help distinguish between different tailing mechanisms.
Keywords: Dispersion; Colloids; Transport; Uniform-aperture fracture;
The similarity of electric double-layer interaction from the general Poisson–Boltzmann theory by Junfeng Zhang; Astrid Drechsler; Karina Grundke; Daniel Y. Kwok (391-395).
We studied electric double-layer (EDL) interactions in electrolytes with different valence combinations. Our results show that the interactions are similar for electrolytes with the same co-ion valences and concentrations and such similarity increases with the co-ion valence and surface potential. A scaled surface potential was defined and found to be useful in characterizing the difference in EDL interaction. These results show that co-ions play a more important role than counterions in determining EDL potential and interaction in an electrolyte solution, especially for systems with high co-ion valence and/or high surface potentials.
Keywords: Poisson–Boltzmann equation; Electric double layer; Interaction force; Asymmetric electrolyte;
Generation current of charged micelles in nonaqueous liquids: Measurements and simulations by Filip Strubbe; Alwin R.M. Verschueren; Luc J.M. Schlangen; Filip Beunis; Kristiaan Neyts (396-403).
Electrically charged species in nonaqueous media still hold many questions. Recent studies and applications show the need for a better understanding of the origin and nature of these charged species. Transient current measurements have been used to study the conductivity of nonaqueous liquid containing charged inverse micelles. At small time scales (1–100 ms) drift and diffusion of charged species are the main contributions to the measured current. At larger timescales (above 1 s) a nonzero quasi steady-state current at high voltages (above 0.5 V) remains. This indicates that besides drift and diffusion an additional process occurs. The dependence of the quasi steady-state current on the applied voltage, micelle concentration, and device thickness has been investigated. Experimental results have been compared to simulations and analytical calculations. It is concluded that the quasi steady-state current results from a bulk disproportionation reaction between neutral micelles that generates charged micelles. And therefore this technique allows for direct quantification of the reaction kinetics from which the charged species originate.Charged species in a nonaqueous medium with added surfactant have been found to originate from a disproportionation reaction between neutral inverse micelles that generate charged micelles.
Keywords: Nonaqueous media; Electrical charges; Disproportionation; Transient current; Generation; Electrophoretic displays;
Growth of ultrathin films of cadmium telluride and tellurium as studied by electrochemical atomic force microscopy by Ruxandra Vidu; Jie-Ren Ku; Pieter Stroeve (404-412).
Time dependent, cathodic electrodeposition of ultrathin CdTe and Te films has been studied in 50 mM H2SO4 + 1 mM CdSO4 + 0.1 mM TeO2 solutions at room temperature under potential control using electrochemical atomic force microscopy (EC-AFM). The films were also characterized electrochemically and with X-ray diffraction. The growth mechanism and the composition of the films depends on the applied potentials. Island-like growth mode was observed for CdTe films when the deposition potential was − 0.35 V (SHE). At a more positive deposition potential of 0.138 V (SHE), Cd was not codeposited into the film but affected the dynamic growth mode of the deposit. At this voltage smooth Te films were obtained. Depending on the applied potential, Cd acts either as a codeposition element for CdTe film growth, or as a mediator for layer-by-layer growth of Te films.
Keywords: Ultrathin films; Electrochemical deposition; Smooth nanometer films; Dynamic electrochemical atomic force microscopy; Dynamic EC-AFM; Tellurium; Cadmium telluride; Film growth mechanism; Codeposition element; Deposition mediator; Cyclic voltammetry; XRD;
Modulation of electroosmotic flows in electron-conducting microchannels by coupled quasi-reversible faradaic and adsorption-mediated depolarization by Shizhi Qian; Jérôme F.L. Duval (413-428).
A theoretical model is proposed for the description of steady electroosmotic flows within a cylindrical electron-conducting microchannel that is depolarized by faradaic and adsorption-mediated processes. The bipolar electron-transfer (e.t.) reactions are examined in the general situation where the electrolyte contains a quasi-reversible redox couple. The rate of the e.t. reactions is governed by transversal convective diffusion of the electroactive species to/from the surface and a position-dependent degree of reversibility. The nonuniform distribution of the electric field in solution, that is intimately coupled to that of the local faradaic current density, alters the double layer composition along the conducting surface via the occurrence of simultaneous electronic and ionic double layer charging processes. This in turn generates a nonlinear distribution of the zeta potential, which affects the electroosmotic flow. The highly coupled spatial profiles for the concentrations of the electroactive species, the faradaic current density, the electrokinetic potential, the electric field and the electroosmotic velocity in/along the metallic channel are solved by consistent numerical analysis of (i) the convective-diffusion equation, (ii) the generalized Butler–Volmer expression that includes mass transport and electron-transfer kinetic contributions, (iii) the continuity and Navier–Stokes equations, and (iv) the Poisson equation for finite currents. The results reported as a function of the surface properties of the channel and the kinetic characteristics of the e.t. reaction illustrate the deviations of the electroosmotic flow profiles as compared to the typical pluglike distribution predicted by Smoluchowski's equation and encountered for homogeneous and dielectric channels. Manipulation of the flow patterns by bipolar electrochemical means is a promising way to control and optimize the local detection and separation of electroactive molecules or molecules dyed with electroactive elements.A theoretical model is presented for the determination of electroosmotic flow profiles within a cylindrical electron-conducting microchannel depolarized by quasi-reversible faradaic and adsorption-mediated processes. The former results from the bipolar functioning of the channel as induced by the applied electric field while the latter originates from the impact of the interfacial potential drop on the local double layer composition. The chemical contribution to the interfacial depolarization depends on the degree of amphifunctionality (or, equivalently, polarizability) of the interface metallic substrate/solution. The faradaic component is governed by the kinetics of the local electron-transfer reactions and the mass transport of the electroactive species by transversal diffusion and lateral electroosmotic/induced-pressure convection.
Keywords: Bipolar electrode; Faradaic electrochemical reaction; RedOx; Electroosmosis; Microfluids;
Electroosmotically enhanced mass transfer through polyacrylamide gels by Marvi A. Matos; Lee R. White; Robert D. Tilton (429-436).
We present an internal pumping strategy to enhance solute fluxes in polymer gels. The method is based on electroosmotic flow driven by an electric field applied across a gel that has been doped with charged colloidal inclusions. This work is motivated by the need to enhance the transport in gel-based biosensor devices whose response dynamics are often mass transfer limited. In this case, polyacrylamide gel slabs were doped with immobilized, charged silica colloids, and the flux of a fluorescent tracer was measured as a function of applied field strength, the volume fraction and size of the colloidal silica inclusions, and the bulk electrolyte composition. Significant flux enhancements were achieved with applied electric currents on the order of a few mA. Control experiments indicated that the flux enhancement was not due to any distortion of the gel diffusional properties in response to the presence of the inclusions. At a constant inclusion volume fraction, the electroosmotic solute flux enhancement was strongest for the smallest particle sizes that provide the highest total surface area, consistent with the electroosmotic mechanism whereby fluid flow is generated along the solid/liquid interface.Electroosmotic convection pumped by charged silica nanoparticle inclusions is demonstrated as a means to enhance mass transport through crosslinked polyacrylamide gels.
Keywords: Electroosmosis; Mass transport; Flux enhancement; Nanoparticles; Silica; Polyacrylamide; Crosslinked gels; Hydrogel; Particle immobilization;
Removal of bromide and iodide anions from drinking water by silver-activated carbon aerogels by M. Sánchez-Polo; J. Rivera-Utrilla; E. Salhi; U. von Gunten (437-441).
The aim of this study is to analyze the use of Ag-doped activated carbon aerogels for bromide and iodide removal from drinking water and to study how the activation of Ag-doped aerogels affects their behavior. It has been observed that the carbonization treatment and activation process of Ag-doped aerogels increased the surface area value ( S N 2 ), whereas the volume of meso-( V 2 ) and macropores ( V 3 ) decreased slightly. Chemical characterization of the materials revealed that carbonization and especially activation process considerably increased the surface basicity of the sample. Original sample (A) presented acidic surface properties (pHPZC = 4.5) with 21% surface oxygen, whereas the sample that underwent activation showed mainly basic surface chemical properties (pHPZC = 9.5) with only 6% of surface oxygen. Carbonization and especially, activation process considerable increased the adsorption capacity of bromide and iodide ions. This would mainly be produced by (i) an increase in the microporosity of the sample, which increases Ag-adsorption sites available to halide anions, and (ii) a rise of the basicity of the sample, which produces an increase in attractive electrostatic interactions between the aerogel surface, positively charged at the working pH (pHsolution < pHPZC), and the corresponding halide. To test the applicability of these aerogels in water treatment, adsorption of bromide and iodide was studied under dynamic conditions using waters from Lake Zurich. Results obtained showed that the carbonization and activation processes increased the adsorptive capacity of the aerogel sample. However, results showed that the adsorption capacity of the aerogel samples studied was considerably lower in water from Lake Zurich. Results showed X 0.02 (amount adsorbed to initial breakthrough) values of 0.1 and 4.3 mg/g for chloride anion and dissolved organic carbon (DOC), respectively, during bromide adsorption process in water from Lake Zurich. This indicates that the adsorptive capacity reduction observed may be due to (i) blocking of the porosity, caused by adsorption of dissolved organic matter on the aerogel surface, that would impede the access of bromide and iodide ions to Ag-adsorption sites, and (ii) the competition of chloride anions for the same adsorption sites. Bromide- and iodide-saturated columns were regenerated with NH3 (0.02 M), observing little change in column characteristics. Moreover, the organic polymer precursors were not dissolved and the concentration of surface Ag-adsorption sites is not significantly changed after two adsorption/regeneration cycles. According to these results, Ag-doped activated carbon aerogels could be a very promising agents to remove bromide and iodide from drinking water.The results obtained indicate that the carbonization process and the activation treatment considerably increased the bromide adsorption capacity of Ag-aerogel in aqueous phase.
Effect of ion-exchange nanofiber fabrics on water splitting in bipolar membrane by Yuji Wakamatsu; Hidetoshi Matsumoto; Mie Minagawa; Akihiko Tanioka (442-445).
In the present study, the effect of ion-exchange fiber fabric made by electrospray deposition (ESD) on water splitting in a composite bipolar membrane (CBM) was investigated. Cation- and anion-exchange fiber (CEF and AEF) fabrics, which were composed of very thin fibers, were prepared by ESD and postdeposition chemical modification and then used as the intermediate layer of a CBM. The current–voltage characteristics under reverse bias conditions showed that the AEF fabrics enhanced water splitting. The water dissociation is accelerated by the AEF fabric, which contains both tertiary pyridyl groups and quaternary pyridinium groups and has a high specific surface area. On the other hand, the CEF fabric, which contains sulfonic acid groups and has an insufficient specific surface area, reduced water splitting. These results indicate that fiber fabric with catalytic activity and a high surface area obtained by ESD can improve the performance of a CBM.The effect of cation- and anion-exchange fiber (CEF and AEF) fabric made by electrospray deposition on water splitting in a composite bipolar membrane was investigated
Keywords: Electrospray deposition; Ion exchange; Nanofiber; Bipolar membrane; Water splitting;
Corrigendum to “Lattice Poisson–Boltzmann simulations of electro-osmotic flows in microchannels” [J. Colloid Interface Sci. 296 (2006) 729–736] by Moran Wang; Jinku Wang; Zhixin Li (446).