Journal of Colloid And Interface Science (v.287, #2)
Editorial Board (CO1).
Gelling of otherwise nongelable polysaccharides by Yurii A. Shchipunov; Tat'yana Yu. Karpenko; Anna V. Krekoten; Irina V. Postnova (373-378).
It was shown first that solutions of nongelable polysaccharides, including such practically important ones as chitosan, hyaluronate, and cyclodextrin, can be gelled by generating silica in situ via sol–gel processing. This could be done owing to a novel silica precursor that is completely water-soluble and compatible with biopolymers. The gelation was caused by mineralization of carbohydrate macromolecules, which strengthened them and provided their cross-linking.
Keywords: Sol–gel; Chitosan; Hyaluronate; Cyclodextrin; Mineralization; Silica nanocomposite; Organic–inorganic nanocomposite; Hydrogel; Biomaterial;
Investigation of factors affecting the adsorption of functional molecules onto gel silicas by L. Diaz; C.M. Liauw; M. Edge; N.S. Allen; A. McMahon; N. Rhodes (379-387).
Flow microcalorimetry and infrared spectroscopy were used to study the surface structure and adsorptive properties of a series of calcined and uncalcined porous silicas. The adsorbates dl-menthol, (r)-(+)-limonene, ( + / − ) -citronellal and carvone were selected for their functionality, that included carbonyl, vinylic and hydroxyl groups. The amounts of probe retained by the silicas together with the energy exchange involved in the adsorption/desorption process were determined by flow microcalorimetry. The functional groups involved in these interactions were studied by means of infrared spectroscopy. It was observed that the strongest interactions with the silica surface took place through hydrogen bonding onto the surface silanol. The most retentive probes were found to be those with a carbonyl group in their structure. Adsorption onto calcined silicas was found to be less energetic than onto the equivalent calcined samples. The adsorption densities were compared with theoretical predictions based on molecular models. In all cases apart from citronellal monolayer coverage were not observed due to steric effects.
Keywords: Silica; Adsorption; Flow microcalorimetry; FMC; Surface;
Adsorption of n-butyl-substituted tetrathiafulvalene dodecanethiol on gold by Rodrigo M. Petoral; Karin Wermelin; Emma Dahlstedt; Jonas Hellberg; Kajsa Uvdal (388-393).
Tetrathiafulvalene (TTF) derivative substituted with two butyl- and two dodecylthiol chains is adsorbed on polycrystalline gold. The TTF-derived thiol adsorbates were characterized by ellipsometry, contact angle goniometry, infrared and X-ray photoelectron spectroscopy and cyclic voltammetry. The molecule is strongly anchored on the gold surface through the sulfur terminating the alkylthiol chains. On the average, the TTF moiety is oriented extended away from the gold surface. The topmost layer of the film containing the dibutyl chains is disordered with gauche defects. The molecule was organized with majority of the alkylthiol chains bound to the gold surface. There are indications of pinholes in the monolayer due to steric hindrance of the bulky TTF rings. The molecular systems consisting of an electroactive π-system such as TTF, are promising for thin-film field effect transistor application.
Keywords: Tetrathiafulvalenes; Thiols; XPS; IRAS; Cyclic voltammetry;
Recovery of gold from gold slag by wood shaving fly ash by Amphol Aworn; Paitip Thiravetyan; Woranan Nakbanpote (394-400).
Wood shaving fly ash was used as an alternative adsorbent for gold preconcentration from gold slag. The maximum gold adsorption capacity of wood shaving fly ash washed with tap water (WSFW) at 20, 30, 40, and 60 °C was 8.68, 7.79, 7.44, and 7.25 mgAu/gadsorbent, respectively, while of activated carbon it was 76.78, 60.95, 56.13, and 51.90 mgAu/gadsorbent, respectively. Deionized water at 100 °C could elute gold adsorbed onto WSFW to 71%. The effect of the increasing temperature of water, 30, 60, and 100 °C, implied that the adsorption mechanism was mainly physical adsorption. The negative values of enthalpy change ( Δ H ) and free energy change ( Δ G ) indicated an exothermic and spontaneous process, respectively. The positive values of entropy change ( Δ S ) indicated increasing disorder of the system. The advantages of wood shaving fly ash are the purification of gold and the easier recycling of gold from the gold-adsorbed adsorbent.
Keywords: Adsorption; Gold cyanide; Gold slag; Wood shaving; Fly ash;
Brownian dynamics simulation of adsorbed layers of interacting particles subjected to large extensional deformation by Luis A. Pugnaloni; Rammile Ettelaie; Eric Dickinson (401-414).
We present Brownian dynamics simulations of the compression and expansion of monolayers adsorbed at a planar interface. The surface-active species are modelled as monodisperse spherical particles that can form particle–particle elastic bonds. The objective is to model the large compression and expansion of viscoelastic protein films investigated in Langmuir trough experiments. We determine the stress–strain response of the system and the associated microstructural changes induced by the large deformation of the interface as a function of particle adsorption energy, and bond breakability and stiffness. We also study the effect of the velocity of compression and the type of compression (uniaxial or homogeneous) on the mechanism of collapse of the adsorbed films. Furthermore, we present simulations on complex mixed systems containing both bond-forming particles (modelling protein) and nonbond-forming particles (modelling surfactant). We find that the preferential desorption of one type of particle or the other, upon compression, is sensitive to the extent of bond breakability of the bond-forming species.
Keywords: Computer simulation; Adsorbed protein layers; Surface rheology; Film collapse;
In situ determination of thickness and electrical properties of multilayers from weak polyelectrolytes by Tsetska Radeva; Miglena Grozeva (415-421).
An electro-optical study of the role that the outermost layer plays in the behavior of a multilayer film of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) was carried out. The film surface was enriched with the chains of the last adsorbed polyelectrolyte when a fully ionized polymer was combined with nearly fully charged chains of the other polyelectrolyte. A distinct influence of the chain length on the critical frequency of relaxation of the electro-optical effect was demonstrated, indicating that polarization of condensed counterions of the last adsorbed polymer governs the behavior of the whole film. The multilayer growth, which was found to proceed via a series of adsorption–desorption steps, correlated well with the changes in the electro-optical effect. No indication was found, however, for participation of small ions from the film bulk in creation of the electro-optical effect.
Keywords: Polyelectrolyte multilayers; Thickness of multilayers; Electrical properties of multilayers; Counterion dynamics; Electro-optics of multilayers;
Competitive sorption behavior of copper(II) and herbicide propisochlor on humic acids by Zhonghou Xu; Manxiang Huang; Qingbao Gu; Yu Wang; Yunzhe Cao; Xiaoming Du; Duanping Xu; Qing Huang; Fasheng Li (422-427).
The competitive sorption behavior of Cu2+ and propisochlor on humic acids (HA) was investigated using a batch method. The sorption equilibrium time of propisochlor on HA was 12 h when its initial concentration was 4 or 10 mg L−1. The results showed that the Langmuir model can best describe the sorption behavior of propisochlor on HA. The added Cu2+ reduced the solid-phase concentration of propisochlor on HA, and the Langmuir model can also describe the sorption behavior of propisochlor on HA when the Cu2+ concentration is 100 and 200 mg L−1. The sorption of propisochlor on HA did not remarkably affect the sorption of Cu2+ on HA when the concentration of propisochlor was below 20 mg L−1. Cu2+ may compete with propisochlor for the sorption sites of HA, such as carboxylic and phenolic groups. It can be concluded that Cu2+ fast adsorbed to the HA matrix, altered its physical and chemical properties, and thus decreased the solid-phase concentrations of propisochlor on HA. In natural water, Cu2+ may promote the release of propisochlor from HA, and thus affect its transport, transformation, and fate in the environment.
Keywords: Competitive sorption; Herbicide; Propisochlor; Cu2+; Humic acids;
Pore structure and adsorption performance of the KOH-activated carbons prepared from corncob by Ru-Ling Tseng; Szu-Kung Tseng (428-437).
Carbonaceous adsorbents with controllable surface area were chemically activated with KOH at 780 °C from chars that were carbonized from corncobs at 450 °C. The pore properties, including BET surface area, pore volume, pore size distribution, and mean pore diameter of these activated carbons, were characterized by the t-plot method based on N2 adsorption isotherms. Two groups are classified according to the types of adsorption/desorption isotherms. Group I corncob-derived activated carbons, with KOH/char ratios from 0.5 to 2, exhibited BET surface area ranging from 841 to 1221 m2 / g. Group II corncob-derived activated carbons, with KOH/char rations from 3 to 6, showed high BET surface areas, from 1976 to 2595 m2 / g. From scanning electron microscopic (SEM) results, the surface morphology of honeycombed holes on corncob-derived activated carbons was significantly influenced by the KOH/char ratios. The adsorption kinetics of methylene blue, basic brown 1, acid blue 74, 2,4-dichlorophenol, 4-chlorophenol, and phenol from water at 30 °C were studied on the two groups of activated carbons, which were suitably described by two simplified kinetic models, pseudo-first-order and pseudo-second-order equations. The effective particle diffusivities of phenols and dyes at the corncob-derived activated carbons of group II are higher than those of ordinary activated carbons. The high-surface-area activated carbons were demonstrated to be promising adsorbents for pollution control and for other applications.
Keywords: Activated carbons; KOH activation; Corncob; Pore properties; Adsorption;
Sorption of Na+, Ca2+ ions from aqueous solution onto unbleached kraft fibers—kinetics and equilibrium studies by Tuan D. Duong; Manh Hoang; Kien L. Nguyen (438-443).
The sorption of Na+ and Ca2+ from aqueous solutions onto unbleached kraft fiber was investigated. The sorption kinetics was found to be highly dependent on pH, initial concentration, and temperature. The sorption rate increased as the initial concentration and pH were increased. Thermodynamic and kinetic results indicated that the sorption of Na+ and Ca2+ onto kraft fiber was exothermic, reversible, and spontaneous with activation energies of 11.0 and 23.3 kJ/mol, respectively. The sorption kinetics followed a pseudo-second-order model and the equilibrium data followed the Langmuir isotherms. The fiber sorption capacities calculated from the Langmuir isotherms were similar to the fiber charges determined by potentiometric titration at pH > 7 .
Keywords: Kinetics; Thermodynamics; Sorption; Equilibrium; Kraft pulps; Fiber charges;
Sorption of aqueous carbonic, acetic, and oxalic acids onto α-alumina by Cyrille Alliot; Lionel Bion; Florence Mercier; Pierre Toulhoat (444-451).
The presence of organic complexing agents can modify the behavior of a surface. This study aims to better understand the impact of carboxylic acids (acetic, oxalic, and carbonic acids) issued from cellulose degradation and equally naturally present in soils. First, evidence of two different kinds of sites for chloride adsorption onto α-alumina and another for sodium sorption was provided. Consequently, no competition between these cation and anion sorptions occurs on α-alumina. The associated exchange capacities and ionic exchange constants were measured. Second, the adsorption behavior of the carboxylic acids was studied as a function of aqueous − log [ H + ] and 0.01 to 0.1 M ionic strength (NaCl), and modeled by using mass action law for ideal biphasic systems. The carboxylic acids were found to be adsorbed on the same sites as chloride ions. The competition between organic ligands and chloride ions was satisfactorily accounted for by the model assuming the deprotonated form of the ligands was sorbed on α-alumina. The model also allowed us to interpret the adsorption of all species under various conditions without any extra fitting parameters.
Keywords: Alumina; Acetate; Oxalate; Carbonate; Sorption; Ion-exchange theory;
Adsorption of argon on homogeneous graphitized thermal carbon black and heterogeneous carbon surface by D.D. Do; H.D. Do (452-460).
In this paper we investigate the effects of surface mediation on the adsorption behavior of argon at different temperatures on homogeneous graphitized thermal carbon black and on heterogeneous nongraphitized carbon black surface. The grand canonical Monte Carlo (GCMC) simulation is used to study the adsorption, and its performance is tested against a number of experimental data on graphitized thermal carbon black (which is known to be highly homogeneous) that are available in the literature. The surface-mediation effect is shown to be essential in the correct description of the adsorption isotherm because without accounting for that effect the GCMC simulation results are always greater than the experimental data in the region where the monolayer is being completed. This is due to the overestimation of the fluid–fluid interaction between particles in the first layer close to the solid surface. It is the surface mediation that reduces this fluid–fluid interaction in the adsorbed layers, and therefore the GCMC simulation results accounting for this surface mediation that are presented in this paper result in a better description of the data. This surface mediation having been determined, the surface excess of argon on heterogeneous carbon surfaces having solid–fluid interaction energies different from the graphite can be readily obtained. Since the real heterogeneous carbon surface is not the same as the homogeneous graphite surface, it can be described by an area distribution in terms of the well depth of the solid–fluid energy. Assuming a patchwise topology of the surface with patches of uniform well depth of solid–fluid interaction, the adsorption on a real carbon surface can be determined as an integral of the local surface excess of each patch with respect to the differential area. When this is matched against the experimental data of a carbon surface, we can derive the area distribution versus energy and hence the geometrical surface area. This new approach will be illustrated with the adsorption of argon on a nongraphitized carbon at 87.3 and 77 K, and it is found that the GCMC surface area is different from the BET surface area by about 7%. Furthermore, the description of the isotherm in the region of BET validity of 0.06 to 0.2 is much better with our method than with the BET equation.
Keywords: Adsorption; Surface area; GCMC; BET; Carbon black; Nongraphitized carbon black; Surface mediation;
Microcalorimetric study on the influence of temperature on bacterial coaggregation by Florence Postollec; Willem Norde; Henny C. van der Mei; Henk J. Busscher (461-467).
Binding isotherms and heats of interaction have been determined at 15, 25, and 40 °C for a coaggregating and a non-coaggregating oral bacterial pair. Heats of interaction were measured upon three consecutive injections of streptococci into an actinomyces suspension using isothermal titration calorimetry. After each injection, the number of streptococci injected remaining free in suspension was quantified microscopically and the degree of binding between the two bacterial strains was established. The coaggregating pair shows positive cooperative binding. The highest cooperativity, at 25 °C, correlates with a strong, macroscopically visible coaggregation. The non-coaggregating pair shows low cooperativity and lacks macroscopically visible coaggregation. Interactions between the coaggregating partners seem to be mainly due to specific, enthalpically saturable and favorable binding sites. Even though the enthalpic part of the interaction is saturated, cooperativity increases with consecutive injections, implying that the coaggregation phenomenon is driven by entropy gain. The change in heat capacity ( Δ C p ) is positive for the non-coaggregating pair from 15–40 °C as well as for the coaggregating pair beyond 25 °C. At lower temperatures the coaggregating pair causes a negative Δ C p . The decrease in heat capacity together with an increase in entropy is considered to be indicative of hydrophobic interactions playing an important role in the formation of large coaggregates as observed for the coaggregating pair at 25 °C.
Keywords: Coaggregation; Streptococci; Actinomyces; Microcalorimetry; Hydrophobic effect; Binding isotherms;
Dynamic mechanical properties of suspensions of micellar casein particles by Maud Panouillé; Lazhar Benyahia; Dominique Durand; Taco Nicolai (468-475).
Small micellar casein particles, so-called submicelles, were obtained by removing colloidal calcium phosphate from native casein by adding sodium polyphosphate. Aqueous submicelle suspensions were characterized using light scattering and rheology as a function of concentration and temperature. The casein submicelles behave like soft spheres that jam at a critical concentration ( C c ) of about 100 g L−1. The viscosity does not diverge at C c , but increases sharply, similarly to that of multiarm star polymers. C c increases weakly with increasing temperature, which leads to a strong decrease of the viscosity close to and above C c . Concentrated submicelle suspensions show strong shear-thinning above a critical shear rate and the shear stress becomes independent of the shear rate. The critical shear rates at different temperatures and concentrations are inversely proportional to the zero-shear viscosity. At much higher shear rates, the shear stress fluctuates strongly in time indicating inhomogeneous flow. The frequency dependence of casein submicelle suspensions is characterized by elastic behavior at high frequencies (concentrations) and viscous behavior at low frequencies (concentrations).
Keywords: Casein; Submicelles; Rheology; Soft spheres; Jamming;
N-(1-Piperidinepropionyl)amphotericin B methyl ester (PAME)— a new derivative of the antifungal antibiotic amphotericin B: Searching for the mechanism of its reduced toxicity by K. Hąc-Wydro; P. Dynarowicz-Łątka; J. Grzybowska; E. Borowski (476-484).
N-(1-Piperidinepropionyl)amphotericin B methyl ester (in short, PAME), a low-toxicity amphotericin B derivative, has been investigated in Langmuir monolayers at the air/water interface alone and in mixtures with cellular membrane sterols (a mammalian sterol, cholesterol, and a fungal sterol, ergosterol) and a model phospholipid (DPPC). The analysis of the strength of interaction between PAME and both sterols as well as DPPC was based, on surface pressure measurements and analysis of the isothermal compressibility ( C s −1 ), the mean area per molecule ( A 12 ), the excess free energy of mixing ( Δ G Exc ) and the total free energy of mixing ( Δ G M ). It has been found that the interactions between PAME and sterols are attractive; however, their strength is significantly weaker for mixtures of PAME with cholesterol than with ergosterol. This casts light on the improved selectivity of PAME toward fungal cells. The strongest interactions, found for PAME/DPPC mixtures, proved an important role of DPPC in the mechanism of reduced toxicity of PAME as compared to amphotericin B. Due to stable complex formation between PAME and DPPC the antibiotic is immobilized with DPPC molecules, which reduces the concentration of free antibiotic, which is capable of interacting with membrane sterols.
Keywords: Langmuir monolayers; Air–water interface; Mixed monolayers; Interactions; Amphotericin B derivatives;
Preparation and properties of colloidal iron dispersions by K. Butter; K. Kassapidou; G.J. Vroege; A.P. Philipse (485-495).
We systematically study the properties of dispersions of iron-based colloids synthesized in a broad size range by thermal decomposition of ironcarbonyl using different stabilizing surfactants. The synthesis results in stable dispersions of monodomain magnetic colloids. Our particles appear to consist of an amorphous Fe0.75C0.25 alloy. Sizes of particles coated with modified polyisobutene or oleic acid can be easily controlled in the 2–10 nm range by varying the amounts of reactants. Extensive characterization with various techniques gives particle sizes that agree well with each other. In contrast to dispersions of small particles, which consist of single colloids, dynamic aggregates are present in dispersions of larger particles. On exposure to air, an oxide layer forms on the particle surface, consisting of a disordered Fe(III) oxide.
Keywords: Colloids; Ferrofluids; Magnetic particles; Synthesis and characterization; Size control; Dipolar model system; SAXS; Magnetization measurements; Dynamic susceptibility measurements; (cryo-)TEM;
Synthesis of silver nanoprisms in formamide by Anjana Sarkar; Sudhir Kapoor; Tulsi Mukherjee (496-500).
Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.
Keywords: Silver; Nanoprism; Formamide; Surface plasmon; Polyethylene glycol;
Nanoparticles fabricated by selective reaction of Fe100−x Pt x alloy films during imidization of polyamic acid by Sung K. Lim; C.S. Yoon; C.K. Kim; Young-Ho Kim (501-506).
Nanoparticles with different morphology and composition were fabricated inside a polyimide (PI) matrix based on selectively oxidizing a layer of Fe100−x Pt x alloy metal film sandwiched between two PI precursor layers. γ-Fe2O3, Pt, and Fe3Pt nanoparticles were formed in a monolayer between two PI layers, depending on the alloy film composition and curing conditions. These particles were well-crystallized and sized between 4 and 10 nm. X-ray photoelectron spectroscopy confirmed that Fe in the film preferentially reacted with the organic matrix whereas Pt remained metallic throughout the curing process, which enabled fabrication of particles different morphology and composition. This process can be easily extended to other alloy films, which provides an opportunity to fabricate nanoparticles relatively easily with desired composition and morphology embedded in an inert organic matrix.
Keywords: Metallic particle; Nanoparticle; Pt nanoparticle; Fe3Pt; Polyimide;
Interaction forces in bitumen extraction from oil sands by Jianjun Liu; Zhenghe Xu; Jacob Masliyah (507-520).
Water-based extraction process (WBEP) has been successfully applied to bitumen recovery from Athabasca oil sand ore deposits in Alberta. In this process, two essential steps are involved. The bitumen first needs to be “liberated” from sand grains, followed by “aeration” with air bubbles. Bitumen “liberation” from the sand grains is controlled by the interaction between the bitumen and sand grains. Bitumen “aeration” is dependent, among other mechanical and hydrodynamic variables, on the hydrophobicity of the bitumen surface, which is controlled by water chemistry and interactions between bitumen and fine solids. In this paper, the interaction force measured with an atomic force microscope (AFM) between bitumen–bitumen, bitumen–silica, bitumen–clays and bitumen–fines is summarized. The measured interaction force barrier coupled with the contacted adhesion force allows us to predict the coagulative state of colloidal systems. Zeta potential distribution measurements, in terms of heterocoagulation, confirmed the prediction of the measured force profiles using AFM. The results show that solution pH and calcium addition can significantly affect the colloidal interactions of various components in oil sand extraction systems. The strong attachment of fines from a poor processing ore on bitumen is responsible for the corresponding low bitumen flotation recovery. The identification of the dominant non-contact forces by fitting with the classical DLVO or extended DLVO theory provides guidance for controlling the interaction behavior of the oil sand components through monitoring the factors that could affect the non-contact forces. The findings provide insights into megascale industrial operations of oil sand extraction.
Keywords: Bitumen extraction; Oil sands; Fines; Slime coating; Clays; Colloidal interactions; Zeta potential distribution; Surface force; AFM;
Synthesis of fluorescent silica-coated gibbsite platelets by Chantal Vonk; S. Martijn Oversteegen; Judith E.G.J. Wijnhoven (521-525).
We describe the fluorescent labeling of gibbsite particles. Gibbsite particles are first stabilized with polyvinyl pyrrolidone. Subsequently the particles are covered with a silica layer in which a fluorescent dye is incorporated. Both fluorescein and rhodamine dyes have been used. The fluorescent labeling is applicable to gibbsite particles of various sizes. Particles are transferred to dimethyl formamide by vacuum distillation after dialysis. These particles are used for confocal scanning laser microscopy and confocal fluorescence-recovery after photobleaching.
Keywords: Colloidal gibbsite; Fluorescence; Silica coating;
Preparation of agglomeration-free hematite particles coated with silica and their reduction behavior in hydrogen by Motoyuki Iijima; Yuichi Yonemochi; Mitsumasa Kimata; Masahiro Hasegawa; Mayumi Tsukada; Hidehiro Kamiya (526-533).
To prepare silica-coated hematite particles without agglomeration, the effects of solid fraction, ion content in solution, and designed layer thickness on agglomeration and dispersion behavior after silica coating were examined. Since the ion concentration remained high in suspension after the hematite particles were prepared, these particles formed aggregates by the compression of an electric double layer on the hematite and silica layer produced a solid bridge between primary hematite particles. Silica bridge formation and agglomeration were almost completely prevented by decreasing the ion concentration and solid fraction of the hematite particles. Furthermore, the effects of the silica-layer thickness and structure on the reduction of hematite to iron under hydrogen gas flow and the iron core stability under air were discussed. When the solid fraction was low in suspension to prevent agglomeration during coating, a densely packed structure of nanoparticles formed by heterogeneous nucleation was observed on the silica-layer surface. Since this structure could not completely prevent oxide diffusion, the layer thickness was increased to 40 nm to obtain a stable iron core under air. Although a dense uniform layer was produced at a high solid fraction during coating, its thickness was reduced to 20 nm to completely reduce hematite to iron.
Keywords: Hematite; Silica coating; Agglomeration; Layer structure; Reduction; Iron;
Formation and characterization of different ceria/silica composite materials via dispersion of ceria gel or soluble ceria precursors in silica sols by Kamal M.S. Khalil; Leena A. Elkabee; Brian Murphy (534-541).
Composite ceria/silica materials of 10 and 20% (w/w) were prepared by calcination, at 650 °C for 3 h, of the xerogels obtained by mixing the corresponding amount of a ceria precursor with freshly prepared sols of spherical silica particles (Stöber particles) in their mother liquors. Two different ceria precursors were examined in this investigation. The first was a gel produced by the prehydrolysis of cerium(IV) isopropoxide in isopropanol medium, and the second was an aqueous solution of cerium(IV) ammonium nitrate. Different textural and morphological characteristics that developed by calcination were investigated by TGA, FTIR, XRD, SEM, and analyses of N2 adsorption isotherms. The results indicated that ceria dispersion and formation of mesoporous textural composite materials produced by the second precursor, cerium(IV) ammonium nitrate, are better than those produced by the first precursor, prehydrolyzed cerium(IV) isopropoxide. The results are discussed in terms of the effect of precursors and mixing media on nucleation and growth of ceria particles and their protection from sintering on calcination at the test temperature.
Keywords: Sol–gel; Ceria/silica; CeO2/SiO2; Thermal stability; Adsorption isotherms; Mesoporous materials;
Stress jumps on weakly flocculated dispersions: Steady state and transient results by K. Dullaert; J. Mewis (542-551).
Weakly flocculated, thixotropic suspensions have been investigated by means of fast stress jump experiments. With a suitable procedure, reliable stress relaxation data could be collected starting 20 ms after cessation of flow. This technique has been used to determine the elastic and hydrodynamic contributions to the shear stress. Steady state as well as transient flows have been studied for suspensions containing either fumed silica or carbon black particles in a Newtonian medium. In both systems, the elastic stress totally dominates the response at low shear rates and consequently also the apparent yield stress. This stress contribution becomes negligibly small at high shear rates. The hydrodynamic contribution to the viscosity has finite limits at both the low and high shear rate ends. The data are relevant for testing rheological models. As an illustration, it is shown that the data agree qualitatively with the model proposed by Potanin et al. (J. Chem. Phys. 102 (14) (1995) 5845–5853).
Keywords: Thixotropy; Stress jump; Elastic stress; Fumed silica; Carbon black; Flocculated suspension;
Long-term phosphorus effects on evolving physicochemical properties of iron and aluminum hydroxides by Konstantinos C. Makris; Willie G. Harris; George A. O'Connor; Hassan El-Shall (552-560).
Iron (Fe) and aluminum (Al) hydroxides are highly reactive components in environmental processes, such as contaminant fate and transport. Phosphorus (P) sorption by these components can decrease environmental problems associated with excess accumulation of P in soils. The long-term stability of P sorbed by Fe/Al hydroxides is of major concern. Synthetic Fe and Al hydroxides coprecipitated with P (1:1 metal:P molar ratio) were incubated at 70 °C for 24 months to simulate natural long-term weathering processes that could influence the stability of sorbed P. Heat incubation (70 °C) of the untreated (no P) Al hydroxides resulted in drastic decreases (within the first month of incubation) in oxalate–Al extractability, specific surface area (SSA), and micropore volume with time. These changes were consistent with the formation of pseudoboehmite. Untreated Fe hydroxides showed no formation of crystalline components following heating (70 °C) for 24 months. Much smaller changes in oxalate-Al, P extractability, and SSA values were observed in the P-treated Al particles when compared with the untreated. Phosphorus treatment of both Fe and Al hydroxides stabilized the particle surfaces and prevented structural arrangements toward a long-range ordered phase. Slight reduction in SSA of the P-treated particles was related to dehydration phenomena during heating at 70 °C. Monitoring of physicochemical properties of the solids after heating at 70 °C for 2 years showed that sorbed P may be stable in the long-term. Understanding long term physicochemical properties may help engineers to optimize the Fe/Al hydroxides performance in several environmental/industrial applications.
Keywords: Iron and Al hydroxides; Stability; Heat incubations; Microporosity; Specific surface area;
Novel optical and statistical methods reveal colloid–wall interactions inconsistent with DLVO and Lifshitz theories by Poul Martin Hansen; Jakob Kisbye Dreyer; Jesper Ferkinghoff-Borg; Lene Oddershede (561-571).
We present an experimental method based on video microscopy to perform nanometer scale position detection of a micrometer bead in the direction along the propagation of the detection light. Using the same bead for calibration and detection significantly improves the in depth resolution in comparison to video microscopy methods from literature. This method is used together with an optical trap to measure interaction potentials between a glass surface and colloids made of polystyrene or silica at different electrolyte concentrations. The results are confirmed by an independent method where the optical trap is used in connection with a quadrant photodiode. Also, we present a maximum likelihood analysis method which considerably improves the spatial resolution of interaction potentials by optimizing the underlying potential function to fit all observed position distributions. The measured interaction potentials agree well with DLVO theory for small electrolyte concentrations; however, for larger electrolyte concentrations the potentials differ qualitatively from both DLVO and Lifshitz theory.
Keywords: Interactions; Potentials; Optical tweezers; Video; Colloid; Surface; DLVO; Lifshitz; Maximum likelihood;
Water structure in aqueous solutions of alkali halide salts: FTIR spectroscopy of the OD stretching band by Z.S. Nickolov; J.D. Miller (572-580).
Water structure making/breaking studies in solutions of five alkali halide salts (KF, KI, NaI, CsF and CsCl) in 4 wt% D2O in H2O mixtures have been performed by FTIR analysis of the OD stretching band in the full solubility range. The proposed method gives a microscopic picture of the water structure making/breaking character of the salts in terms of the hydrogen bonding between the water molecules in the solution. With the exception of CsCl, there is a very good correlation of the structure making/breaking character of the salts determined by FTIR analysis, and the viscosity coefficients of the solutions. The results fully support and explain previous studies of bubble attachment to microscopic salt particles of the above salts. The investigations support the primary importance of interfacial water structure in the explanation of the flotation of alkali halide salts in their brines.
Keywords: Interfacial water structure; Salt flotation; FTIR; Alkali halides; Water structure makers and breakers;
Limitations of potentiometric studies to determine the surface charge of gibbsite γ-Al(OH)3 particles by Marie-Camille Jodin; Fabien Gaboriaud; Bernard Humbert (581-591).
Surface charges of gibbsite particles were probed by potentiometric titration and subsequently analyzed to estimate intrinsic proton affinity constants of OH surface groups. A detailed spectroscopic characterization of the molecular structure of surface OH groups yielded estimates of bond lengths and bond valences of O―H surface sites. Based on these results, the effects of the setting parameters of a MUSIC calculation have been shown in comparison with previous predictions yielding higher p K a values ( 2 < − p K a < 4 ) for the protonation of basal doubly coordinated OH surface groups and lower p K a values ( 7.9 < − p K a < 9.9 ) for the protonation of lateral singly coordinated OH surface groups. Comparison with experimental data is complicated by reproducible hysteresis between acid and base addition in optimal raw potentiometric titration curves at different ionic strengths. Such effects prevented the determination of a univocal intersection point to provide the global point of zero charge of gibbsite particles, even though the ionic strength dependence of the point of zero net proton charge and the different crossovers between curves indicated that the point of zero charge could be estimated between 8.1 and 9.6, in relative agreement with the lateral affinity constant calculated with the MUSIC model. Still, two main drawbacks remained to differentiate the reactivity of lateral singly and basal doubly coordinated surface groups. First, significant kinetic effects observed in acidic media indicated a dissolution process and/or protonation of basal surface groups. Second, the choice of specific surface areas, especially for a heterogeneous sample, led to several cases for the calculation of the absolute surface charge of particles. Therefore, our results demonstrated the heterogeneous reactivity of gibbsite particles and that the prediction and the experimental determination of respective surface groups are still complex even if some trends emerge.
Keywords: Gibbsite; Hydroxide; Surface charge; Point of zero charge; Potentiometric titrations; Morphology; Surface sites; Heterogeneity;
Electrochemistry of diphenylditelluride at the hanging mercury drop electrode in a protic medium by Jesús L. Muñiz Álvarez; Josefa A. García Calzón; Juan Miguel López Fonseca (592-596).
The electrochemical behavior of diphenylditelluride, Φ 2 Te 2 , at a hanging mercury drop electrode has been studied in an aqueous–ethanol solution at pH 7 by means of cyclic and ac voltammetry. The appearance of two cathodic peaks has been attributed to the reversible reduction of the first and all the successive monolayers of a film of ΦTe–Hg, which is formed by adsorption of Φ 2 Te 2 at the mercury/solution interface. The different electrochemical properties of such monolayers have been explained.
Keywords: Diphenylditelluride; Mercury; Adsorption; Multilayer films; Cyclic and ac voltammetry;
Enhancement of electrodialysis performances using pulsing electric fields during extended period operation by Hong-Joo Lee; Seung-Hyeon Moon (597-603).
Many methods have been considered for mitigating and minimizing fouling potentials in the electrodialysis process, because fouling of ion exchange membranes is one of the significant considerations in process design and operation. In the observation of foulant behaviors, it was observed that the humate was deposited and formed a loosely packed fouling layer on the anion-exchange membrane surfaces, thus having reversible fouling effects on the process. In order to investigate the effects of the frequencies on the electrodialysis performance during fouling experiments in the presence of humate, the square-wave powers having various frequencies in the electric fields were employed. The results showed that the pulsing electric fields mitigated the fouling potential and that there exists an optimal frequency for the minimization of the fouling potential. Also, the pulsation of the electric field with an optimal frequency reduced the fouling potential of the already fouled membrane systems in the continuous batch runs. It was suggested that the electric field with pulsing effects enhanced the electrophoretic mobilities of the charged foulants, thus decreasing fouling potentials.
Keywords: Electrodialysis; Fouling; Fouling mitigation; Humate; Pulsing electric field;
Silver nanocomposite layer-by-layer films based on assembled polyelectrolyte/dendrimer by Zelin Liu; Xudong Wang; Hongying Wu; Chenxi Li (604-611).
Silver nanocomposite multilayer films were prepared through the in situ method. Multilayer thin films, prepared through the sequential electrostatic deposition of a positively charged third-generation poly(amidoamine) dendrimer (PAMAM) and negatively charged poly(styrenesulfonate) (PSS) and poly(acrylic acid) (PAA), were utilized as nanoreactors for the formation of silver nanoparticles. The silver ions were preorganized in layer-by-layer (LBL) films composed of PAMAM dendrimers and subsequently reduced with hydrogen to prepare the silver nanoparticles. The UV–vis spectrum and profilometer were used to characterize the regular growth of bilayers. UV–vis absorption from plasmon resonance at 435 nm and TEM images indicated the formation of the silver nanoparticles in the multilayer films. The silver nanocomposite LBL films were also constructed on the indium tin oxide-glass and investigated using cyclic voltammetry. The silver nanoparticles in the multilayer films have a stronger negative redox potential. The silver nanocomposite LBL films may have a potential application in the catalysis of reduction of 4-nitrophenol with sodium borohydride.
Keywords: Layer-by-layer; Multilayer films; Dendrimer; Nanoparticles; Catalysis; Polyelectrolyte; Cyclic voltammetry; Silver; PAMAM; ITO–glass;
Effects of organic solvents on ultrafiltration polyamide membranes for the preparation of oil-in-water emulsions by L. Giorno; R. Mazzei; M. Oriolo; G. De Luca; M. Davoli; E. Drioli (612-623).
Hydrophilic ultrafiltration membranes made of polyamide with molecular weight cutoff 10 and 50 kDa have been studied for the preparation of oil-in-water emulsions by a cross-flow membrane emulsification technique. Isooctane and phosphate buffer were used as disperse and continuous phase, respectively. The permeation of apolar isooctane through the polar hydrophilic membrane was achieved by pretreatment of membranes with a gradient of miscible solvents of decreasing polarity to remove water from the pores and replace it with isooctane. Four different procedures were investigated, based on the solvent mixture percentage and contact time with membranes. After pretreatment, the performance of the membranes in terms of pure isooctane permeate flux and emulsion preparation was evaluated. The influence of organic solvents on polyamide (PA) membranes has been studied by SEM analysis, which showed a clear change in the structure and morphology of the thin selective layers. The effects proved stronger for PA 10 kDa than for 50 kDa. In fact, similar pretreatment procedures caused larger pore size and pore size distribution for PA 10 kDa than for 50 kDa. The properties of emulsions in terms of droplet size distribution reflected the membrane pore sizes obtained after pretreatment. The correlation between pore size and droplet size, for the physicochemical and fluid dynamic conditions used, has been evaluated.
Keywords: Membrane emulsification; O/W emulsion; Polyamide membrane; Solvent effect; Membrane pretreatment;
Rupture of thin stagnant films on a solid surface due to random thermal and mechanical perturbations by Ganesan Narsimhan (624-633).
A generalized formalism for the rupture of a nondraining thin film on a solid support due to imposed random thermal and mechanical perturbations, modeled as a Gaussian white noise, is presented. The evolution of amplitude of perturbation is described by a stochastic differential equation. The average film rupture time is the average time for the amplitude of perturbation to equal to the film thickness and is calculated by employing a first passage time analysis for different amplitudes of imposed perturbations, wavenumbers, film thickness, van der Waals and electrostatic interactions and surface tensions. The results indicate the existence of an optimum wavenumber at which the rupture time is minimum. A critical film thickness is identified based on the sign of the disjoining pressure gradient, below which the film is unstable in that the rupture time is very small. The calculated values of rupture time as well as the optimum wavenumber in the present analysis agree well with the results of linear stability analysis for immobile as well as completely mobile gas–liquid film interfaces. For stable films, the rupture time is found to increase dramatically with film thickness near the critical film thickness. As expected, the average rupture time was found to be higher for smaller amplitudes of imposed perturbations, larger surface potentials, larger surface tensions and smaller Hamaker constants.
Keywords: Thin film rupture; Thermal fluctuations; Pressure fluctuations; First passage time; Van der Waals forces; Electrostatic forces; Disjoining pressure; Stagnant thin film;
Superhydrophobicity of 2D ZnO ordered pore arrays formed by solution-dipping template method by Yue Li; Weiping Cai; Guotao Duan; Bingqiang Cao; Fengqiang Sun; Fang Lu (634-639).
Large-scale 2-dimensional ZnO ordered pore arrays (films) were fabricated by a solution-dipping colloidal monolayer method. The morphologies of the films are precursor-concentration-dependent. Higher concentration leads to rougher morphology. The wettability of such ordered porous films was studied. It was shown that the ordered pore structure of as-prepared samples can effectively enhance the hydrophobicity of ZnO and the water contact angle (CA) on the film surface increases from 125° to 143° with the rise of precursor concentration from 0.3 to 1.0 M, indicating concentration-controlled hydrophobicity. Meanwhile, a photoinduced reversal transition of wettability between hydrophobicity and hydrophilicity was observed on these films. The difference between hydrophobic and hydrophilic CAs can be tuned from 89° to 138° by precursor concentration. After surface modification by fluoroalkylsilane, these ordered pore arrays demonstrate superhydrophobicity with water CAs from 152° to 165°, depending on the precursor concentration. Especially for the ordered porous film fabricated by high precursor concentration (1.0 M), the large water CA (165°) and small sliding angle (less than 5°) were obtained. This work has demonstrated that if such ordered pore arrays are used for some micro- or nanodevices, they will be waterproof and even self-cleaning.
Keywords: Superhydrophobicity; ZnO; 2D ordered pore arrays; Solution-dipping template method;
Dynamic surface tensions of Athabasca bitumen vacuum residue including the effect of dissolved air by X.-S. Li; J.A.W. Elliott; W.C. McCaffrey; D. Yan; D. Li; D. Famulak (640-646).
The pendant drop technique was used to measure the equilibrium and dynamic surface tensions of Athabasca bitumen vacuum residue (500 °C+) (AVR) between 150 and 280 °C. A significant (16%) slow (over hours) decrease from initial to equilibrium values was found. In addition, the effect of dissolved air on surface tension was studied at 150 °C by comparing dynamic surface tensions of air- or nitrogen-saturated AVR in contact with air or nitrogen. It was found that the presence of dissolved air significantly decreases the dynamic change in surface tension (from 16 to 5%). In order to perform the surface tension studies, the density of AVR was required. Archimedes method was used to measure the density of AVR from 98 to 335.8 °C.
Keywords: Dynamic surface tension; Density; Bitumen vacuum residue; Bitumen upgrading; Oxygen;
Capillary penetration failure of blood suspensions by Ronghui Zhou; Hsueh-Chia Chang (647-656).
Blood suspension fails to penetrate a capillary with radius R less than 50 μm even if the capillary is perfectly wettable. This invasion threshold is attributed to three red blood cells (RBCs) segregation mechanisms—corner deflection at the entrance, the intermediate deformation-induced radial migration and shear-induced diffusion within a packed slug at the meniscus. The shear-induced radial migration for deformable particles endows the blood cells with a higher velocity than the meniscus to form the concentrated slug behind the meniscus. This tightly packed slug has a higher resistance and arrests the flow. Rigid particles and rigidified blood cells result in wetting behavior similar to that seen for homogeneous liquids, with decreased RBC migration towards the capillary centerline and reduction of packing. Corner deflection with a radial drift velocity accelerates the radial migration for small capillaries. However, deformation-induced radial migration is the key mechanism responsible for penetration failure. This sequence of mechanisms is confirmed through videomicroscopy and scaling theories were applied to capture the dependence of the critical capillary radius as a function of RBC concentrations.
Keywords: Suspension rheology; Diagnostic kits; Blood rheology;
Calculation of wetting angles in crude oil/water/quartz systems by K.M. Askvik; S. Høiland; P. Fotland; T. Barth; T. Grønn; F.H. Fadnes (657-663).
A method for the determination of water-advancing wetting angles has been developed and tested. The method allows measurements in black oils, as opposed to traditional techniques which substitute transparent model oils prior to measurements. The method is based on the Laplace equation and axisymmetric drop shape analysis. The main source of error is the determination of the drop volume. Results in transparent systems are comparable to results using other techniques. Wetting angles are determined for water in two different crude oil systems, using quartz as the substrate. The quartz surfaces are water wet over large pH ranges, but it is possible to accurately identify pH intervals where the surfaces are intermediate or oil wet.
Keywords: Wetting angle; Crude oil;
Contact angle studies on anodic porous alumina by Rocío Redón; A. Vázquez-Olmos; M.E. Mata-Zamora; A. Ordóñez-Medrano; F. Rivera-Torres; J.M. Saniger (664-670).
The preparation of nanostructures using porous anodic aluminum oxide (AAO) as templates involves the introduction of dissolved materials into the pores of the membranes; one way to determine which materials are preferred to fill the pores involves the measurement of the contact angles ( θ ) of different solvents or test liquids on the AAOs. Thus, we present measurements of contact angles of nine solvents on four different AAO sheets by tensiometric and goniometric methods. From the solvents tested, we found dimethyl sulfoxide (DMSO) and N , N ′ -dimethylformamide (DMF) to interact with the AAOs, the polarity of the solvents and the surfaces being the driving force.
Keywords: Contact angle; Anodic porous alumina; Ordered porous materials; Polarity;
Investigation of the micropolarity in reverse micelles of nonionic poly(ethylene oxide) surfactants using 4-nitropyridine-N-oxide as absorption probe by Rodica Bandula; Marilena Vasilescu; Helge Lemmetyinen (671-677).
The micropolarities of the reverse micelle (RM) interior of nonionic poly(ethylene oxide) surfactants of the alkyl ether type (poly(ethylene oxide) lauryl ether (C12E4, Brij 30)), alkyl–aryl ethers (poly(ethylene oxide) nonylphenyl ether (C9ΦE4), poly(ethylene oxide) nonylphenyl ether (C9ΦE5), and poly(ethylene oxide) octylphenyl ether (C8ΦE5)), and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers (Pluronics P123, F127) were investigated as a function of the water content by applying the absorption probe technique, using 4-nitropyridine-N-oxide (NP) as a probe. The change in the micellar aggregate micropolarity in different solvents (cyclohexane, decane, n-butanol, and n-butyl acetate) at various water contents has been investigated. The research was focused on the determination of the effects of surfactant structure and solvent type on the hydration degrees of the PEO chains in the region at the core limit, where the NP probe was located. All results regarding the polarities in RM and PEO/water calibration mixtures have been expressed in terms of Kosower's Z values, using the linear dependence of E NP on Kosower's Z. The PPO/butanol mixtures have also been used for RM in butanol as a reference system. The data revealed that local polarity in RM is dependent on the surfactant type, block copolymer composition, solvent nature, and water content. At the same water content, the results clearly indicate a lower hydration degree of triblock copolymers, as compared to the surfactants of the alkyl ether and alkyl–aryl ether type, but for P123 and F127 Pluronics in n-butanol the hydration is higher owing to the behavior of butanol as cosurfactant and to its hydration.
Keywords: 4-Nitropyridine-N-oxide; Micropolarity; Reverse micelles;
Controlling the agglomeration of anisotropic Ru nanoparticles by the microwave–polyol process by R. Harpeness; Zhao Peng; Xiansong Liu; Vilas G. Pol; Yuri Koltypin; Aharon Gedanken (678-684).
A rapid polyol process for the synthesis of ruthenium nanoparticles was developed using microwave irradiation. A colloidal solution of monodispersed anisotropic Ru metal nanoparticles (mean particle size 2–6 nm) with different aspect ratios was obtained first. Particles with different degrees of agglomeration have also been synthesized using monodisperse particles as seeds and PVP (poly-N-vinyl-2-pyrrolidone) as the stabilization reagent. The stabilization mechanisms of different protective reagents were studied by UV–vis spectra. The HRTEM images indicated that dendritic particles formed by controlling agglomeration consisted of single-crystal domains with a random crystalline orientation.
Keywords: Nanoparticles; Ruthenium; Anisotropic; Stabilization reagent; Polyol process; Microwave irradiation;
Effects of micelle-to-vesicle transitions on the degree of counterion binding by Yousuke Ono; Hideya Kawasaki; Masahiko Annaka; Hiroshi Maeda (685-693).
Effects of micelle-to-vesicle transitions on the degree of counterion binding (β) were investigated on three systems. For the concentration-dependent micelle-to-vesicle transition in the didodecyldimethylammonium bromide (DDAB)/water system, in the region of coexistent micelles and vesicles, less than 3 mM, the β values increased significantly with DDAB concentration: β (0.07 mM) = 0.35 and β (3 mM) = 0.93. In the coexistent region, activities of the bromide ion, a Br , were almost independent of the DDAB concentration, suggesting the pseudo-phase nature of both micelles and vesicles. In the concentration-dependent vesicle-to-lamellar transition region above 5 mM, where multilamellar vesicles were prevailing, on the other hand, the β values were only little affected by this transition. This suggests that the increase in the layer number of DDAB multilamellar vesicles scarcely affects the β values. This was also supported by the fact that the destruction of multilamellar vesicles by ultrasonication did not change the β values. These results strongly suggest that the inner and outer monolayers of DDAB multilamellar vesicles are characterized by similar β values. The second system, cetyltrimethylammonium bromide (CTAB)/DDAB mixtures, showed composition-dependent transitions depending on the mole fraction of DDAB X DDAB : spherical micelles ( 0 < X DDAB < 0.2 ) → rodlike micelles ( 0.2 < X DDAB < 0.4 ) → vesicles ( 0.6 < X DDAB < 1 ). Values of β increased with both the sphere-to-rodlike micelle transition and the micelle-to-vesicle transition. The increase in the β value was larger for the latter than for the former transition. Little effects of ultrasonication on β was also observed for the multilamellar vesicles of CTAB/DDAB mixtures. In the third system of the mixtures of two single chain surfactants, protonated and non-protonated of oleyldimethylamine oxide, the dependence of β on the degree of ionization (α) can be well described with a theoretical curve, derived on the basis of the linear relation between the surface charge density and the α value, despite the occurrence of the micelle-to-vesicle transition.
Keywords: Micelles; Vesicles; Counterion binding; Micelle–vesicle transition; Didodecyldimethylammonium bromide; Amine oxides;
A method for the characterization of emulsions, thermogranulometry: Application to water-in-crude oil emulsion by D. Clausse; F. Gomez; C. Dalmazzone; C. Noik (694-703).
Emulsions are used in a wide range of applications and industries. Their size distribution is an important parameter because it influences most of the emulsion properties of emulsions. Several techniques of characterization are used to determine the granulometric distribution of emulsions, but they are generally limited to dilute samples and are based on complex algorithms. We describe a method that allows characterization of the droplet size distribution of emulsions using thermal analysis (thermogranulometry). This method permits the use of very concentrated samples without any dilution or perturbation of the system. We first define our method by a thermodynamic and kinetic approach. We studied a real system, i.e., crude oil emulsions, which form very concentrated, viscous, and opaque emulsions with water. We present a correlation between the size of droplets and their freezing temperature, corresponding to our system. Then we compare the size distributions obtained by our method with those derived by direct microscopy observations. The results obtained show that thermogranulometry may be an interesting method of characterization of emulsions, even for concentrated systems.
Keywords: Emulsion; Granulometry; Thermal analysis; Crude oil;
Estimation of degree of counterion binding and thermodynamic parameters of ionic surfactants from cloud point measurements by using triblock polymer as probe by Mandeep Singh Bakshi; Jasmeet Singh; Jagnandan Kaur (704-711).
Cloud point ( C P ) was measured for ternary mixtures of different ionic surfactants such as sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12–2–12) plus triblock polymer (TBP) ((PEO)2(PPO)15.5(PEO)2) plus water, keeping the concentration of TBP constant and varying the surfactant concentration from pre- to postmicellar regions. These experiments were also performed in the presence of different fixed amounts of NaBr to evaluate the salt effect on the clouding behavior of these ternary mixtures. The C P value of TBP exhibits a drastic change at the cmc of each surfactant. The cmc values thus obtained both in the absence and in the presence of NaBr were used to evaluate counterion binding (β) with the Corrin–Harkins method. β values were also used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the β values evaluated using this method, especially at low [TBP], are in good agreement with those reported in the literature.
Keywords: Cloud point measurements; Counterion binding; Triblock polymers; Ionic surfactants; Thermodynamic parameters;
Water partitioning in “dry” poly(ethylene oxide) alcohol (C m E n ) nonionic surfactant—a proton NMR study by Markus M. Hoffmann; Megan E. Bennett; Jack D. Fox; Donald P. Wyman (712-716).
A proton NMR titration study is presented where in small increments quantities of water were added to “dry” C m E n nonionic surfactant. For a particular range of compositions, two resonances for the water/hydroxyl protons were observed that display large chemical shift increases as water content is increased indicating that water must partition between two chemical environments with a surprisingly slow chemical exchange rate. A detailed mechanism of how the increasing amounts of water are incorporated into the surfactant medium is presented accounting for all observed spectral changes.
Keywords: C m E n nonionic surfactants; 1H NMR; Hydrogen exchange;
Short-time synthesis of SBA-15 using various silica sources by Pasquale F. Fulvio; Stanisław Pikus; Mietek Jaroniec (717-720).
A short-time synthesis of SBA-15 is reported by using two different silica sources, sodium metasilicate (Na2SiO3⋅9H2O) and tetraethyl orthosilicate (TEOS). The SBA-15 samples obtained from both silica sources were highly ordered as evidenced by SAXS spectra showing five reflection peaks characteristic for p6mm symmetry group. While the surface areas of these samples were similar, the pore volume of the sample prepared from TEOS was slightly larger than that from sodium metasilicate. However, the latter exhibited higher microporosity and thicker pore walls. It was shown that a significant reduction of time of the self-assembly step from 24 to 2 h had no detrimental influence on the quality of SBA-15 materials.
Keywords: Mesoporous silica; Nitrogen adsorption; SBA-15; Sodium metasilicate; Tetraethyl orthosilicate;
by Arthur Hubbard (721).
Author Index for Volume 287 (722-723).