Journal of Colloid And Interface Science (v.295, #2)
Modification of a montmorilloniteâ€“illite clay using alkaline hydrothermal treatment and its application for the removal of aqueous Cs+ ions
by B. Öztop; T. Shahwan (pp. 303-309).
A montmorilloniteâ€“illite clay was modified using alkaline hydrothermal treatment (reflux method) and applied to the removal of aqueous Cs+ ions. The alkaline solutions were prepared by dissolving NaOH in seawater and in distilled water, and the effect of the two alkaline media on the sorption capacities of the modified clay was discussed. The modified materials were characterized using XRD, SEM/EDS, and FTIR. As a result of the modification, the original mineral was partially transformed into a zeolitic material with spherical morphology. The results showed that the modification improved the Cs+ uptake capacity of the starting clay, with the clay modified in distilled water medium demonstrating higher sorption capacity. The sorption data were adequately described using the Freundlich and Dubininâ€“Radushkevich isotherm models.A typical EDS spectrum showing the elemental distribution in a zeolited montmorilloniteâ€“illite clay following Cs+ sorption.
Keywords: Montmorillonite; Illite; Alkaline hydrothermal treatment; Sorption; Cs; +
Simple models of adsorption in nanotubes
by Sylwester Furmaniak; Artur P. Terzyk; Piotr A. Gauden; Gerhard Rychlicki (pp. 310-317).
We present two very simple models of adsorption in cylindrical pores. It is assumed that a layer-by-layer mechanism occurs similarly to that in the BET theory. The major assumption is that in the pores having an adsorption space with cylindrical geometry, the surface area of the upper surface (in comparison with the bottom surface) should be diminished in proportion to the radii of a cylinder. Two cases are considered: the adsorbateâ€“adsorbate interactions are neglected or they are taken into account according to the lattice model developed by Fowler and Guggenheim. It is shown that the data simulated by Ohba and Kaneko for adsorption of nitrogen in the internal space of carbon nanotubes are successfully described by our models. On the basis of the fitted data we show that the relation between the monolayer capacity in cylindrical pores and on flat surfaces is in excellent agreement with the equation developed recently by Salmas and Androutsopoulos. Moreover, our models are verified for two sets of experimental data reported by Kaneko et al. We obtain excellent agreement between the values of the pore diameters calculated by us and suggested by these authors (from HRTEM, the GCMC simulations, and the IDBdB model). It is concluded that proposed simple and fast models can be applied as a first approximation to the estimation of the internal nanotube diameters if they do not exceed ca. 5 nm and are slightly dispersed.
Keywords: Adsorption; Porosity; Nanotubes; Pore diameter; Cylindrical pore geometry
Creating mixed Fe/Al coatings on planar Î³-Al2O3 surfaces
by Christine F. Conrad; Michael J. Kelley; Catherine J. Chisholm-Brause (pp. 318-326).
Insufficient understanding of the interactions of reactive phases (e.g., Fe and Al oxides) with minerals, other reactive phases and sorbing species has made predicting and modeling metal sorption on natural sediment surfaces difficult. This work develops a method to create mixed Fe/Al planar oxide surfaces by coating well-characterized planar Î³-Al2O3 with ferric iron. The objective is to closely control the Fe/Al ratio as well as the distribution of Fe on the planar surface. Effects of starting Fe(III) concentration, reaction time and number of coating sequences were examined using XPS and ToF-SIMS. No observable trend was seen in Fe/Al ratios by varying the starting Fe(III) concentration or reaction time. For both 4- and 14-day reactions, lower concentrations of Fe(III) produced oxide phases with a homogeneous distribution of Fe at the surface as detected by ToF-SIMS. ToF-SIMS Fe elemental maps of the oxide phases resulting from the highest Fe(III) concentration showed areas of localized Fe deposition. A sequential coating procedure allowed for a closer control of the concentration and spatial distribution of Fe(III) in the resulting oxide phase. This work provides methodology that can be used to create Fe/Al oxide phases whose Fe/Al content can be controlled for use in subsequent sorption studies to better understand the effects of mixed phase oxides on metal ion uptake.Insufficient understanding of the interactions of reactive phases (e.g., Fe and Al oxides) with minerals, other reactive phases and sorbing species has made predicting and modeling metal sorption on natural sediment surfaces difficult. This work develops a method to create mixed Fe/Al planar oxide surfaces by coating well-characterized planar Î³-Al2O3 with ferric iron. The objective is to closely control the Fe/Al ratio as well as the distribution of Fe on the planar surface. Effects of starting Fe(III) concentration, reaction time and number of coating sequences were examined using XPS and ToF-SIMS. No observable trend was seen in Fe/Al ratios by varying the starting Fe(III) concentration or reaction time. For both 4- and 14-day reactions, lower concentrations of Fe(III) produced oxide phases with a homogeneous distribution of Fe at the surface as detected by ToF-SIMS. ToF-SIMS Fe elemental maps of the oxide phases resulting from the highest Fe(III) concentration showed areas of localized Fe deposition. A sequential coating procedure allowed for a closer control of the concentration and spatial distribution of Fe(III) in the resulting oxide phase. This work provides methodology that can be used to create Fe/Al oxide phases whose Fe/Al content can be controlled for use in subsequent sorption studies to better understand the effects of mixed phase oxides on metal ion uptake.
Keywords: Mixed oxide; Iron; Planar; Î³; -Al; 2; O; 3; Coating; XPS; ToF-SIMS
Changes of the porous structure of activated carbons applied in a filter bed pilot operation
by P.A. Gauden; E. Szmechtig-Gauden; G. Rychlicki; S. Duber; J.K. Garbacz; R. Buczkowski (pp. 327-347).
The paper investigates the changes in porosity (i.e., in the accessible adsorption capacity of carbonaceous adsorbents for pollutants during filter bed maturation) of three activated carbons applied in a filter bed pilot operation. The results of this investigation may help to reduce operating costs, increase granular activated carbon bed life, maximize the useful life of biofilters, and understand the mechanism of water purification by carbon adsorbents. The analysis of the pore structure was limited to the first year of service of the beds, since this was when the largest decrease in the available pore capacity occurred. Low-temperature nitrogen adsorption isotherms were used to evaluate the structural parameters and pore size distributions (PSDs) of carbon samples (virgin (reference) and mature adsorbents for different periods of water treatment) on the basis of the Nguyen and Do (ND) method and density functional theory (DFT). These results were compared with small-angle X-ray scattering (SAXS) investigations (PSDs calculated by Glatter's indirect transformation method (ITP)). The results show that in general, the ND and ITP methods lead to almost the same qualitative distribution curve behavior. Moreover, the enthalpy of immersion in water, mercury porosimetry, densities (true and apparent), and the analysis of ash are reported and compared to explain the decrease in adsorptive capacity of the carbons investigated. On the other hand, the efficacy of TOC (total organic carbon, i.e., a quantity describing the complex matrix of organic material present in natural waters) removal and the bacteria count were analyzed to explain the role of adsorption in the elimination of contaminants from water. Finally, a mechanism of organic matter removal was suggested on the basis of the above-mentioned experimental data and compared with mechanisms reported by other authors.
Keywords: Adsorption; Activated carbon; Porosity; Water treatment
Growth of calcium hydroxyapatite (Ca-HAp) on cholesterol and cholestanol crystals from a simulated body fluid: A possible insight into the pathological calcifications associated with atherosclerosis
by Dougal F. Laird; Michael R. Mucalo; Yoshiyuki Yokogawa (pp. 348-363).
An experimental study into calcium phosphate (CP) nucleation and growth on cholesterol and cholestanol surfaces from a supersaturated simulated body fluid (SBF) is presented with the overall aim of gaining some fundamental insights into the pathological calcifications associated with atherosclerosis. Soaking of pressed cholesterol disks at physiological temperature in SBF solutions was found to lead to CP nucleation and growth if the disks were surface roughened and if an SBF with concentrations of the calcium and hydrogen phosphate ions at 2.25Ã— physiological concentrations was used. The CP phase deposited was shown via SEM micrographs to possess a florette type morphology akin to that observed in earlier reported studies. The use of recrystallised cholesterol and cholestanol microcrystals as substrates for soaking in SBF facilitated the observation of CP deposition. In general, cholesterol recrystallised from polar solvents like 95% ethanol as a cholesterol monohydrate phase which was a better substrate for CP growth than cholesterol recrystallised from more non-polar solvents (e.g., benzene) which produced anhydrous cholesterol phases. CP was also observed to form on recrystallised cholestanol microcrystals, a molecule closely related to cholesterol. Inductively coupled plasma optical emission spectrometry (ICP-OES) data gave confirmation that Ca:P mole ratios of the grown CP were 1.3â€“1.5 suggesting a mixed phase of octacalcium phosphate (OCP) and Ca-deficient HAp and that the CP coating grows (with time of soaking) on the substrates after nucleation in the SBF growth medium. Infrared (IR) spectra of the extracted coatings from the cholesterol substrates confirmed that the CP phase deposited is a semi crystalline HAp with either carbonate substituted into its structure or else co-deposited as calcium carbonate. Soaking experiments involving modified cholesterol substrates in which theOH group in the molecule was replaced with the oleiyl or phosphonate group showed no CP nucleation and growth. This observation illustrates the importance of the known epitaxial relationship between cholesterol and HAp (which theoretically predicts favourable deposition of one phase upon the other) and the consequences of its destruction (by chemical modification of the cholesterol). In the case of the phosphorylated cholesterol, failure of this substrate to nucleate CP phases may have also been caused by the reduction in concentration of free solution Ca2+ in the SBF medium by complexation with the phosphonate groups on the phosphorylated cholesterol. This would have reduced the ion product of Ca2+ and inorganic phosphate and lowered the degree of supersaturation in the SBF medium.This is a study of calcium phosphate nucleation and growth on cholesterol and cholestanol disk and microcrystal surfaces from a supersaturated simulated body fluid solution.
Keywords: Cholesterol; Cholestanol; Hydroxyapatite; Simulated body fluid; Atherosclerosis; Nucleation
Atomistic simulation studies of magnetite surface structures and adsorption behavior in the presence of molecular and dissociated water and formic acid
by T.K. Kundu; K. Hanumantha Rao; S.C. Parker (pp. 364-373).
Static energy minimization techniques have been used to elucidate the surface structures of magnetite crystals in pure and hydroxylated forms. Adsorption energy values in the presence of molecular water, dissociate water and simple carboxylic group molecule (formic acid) are calculated and we found that the carboxylic group do not adsorb strongly in most of the pure and hydroxylated surfaces in comparison to water. Since the associated calcium minerals are floated from magnetite using fatty acid collector, our calculations corroborate the flotation practice of removing these impurity minerals from magnetite.Static energy minimization techniques have been used to elucidate the surface structures of magnetite crystals in pure and hydroxylated forms. Adsorption energy values in the presence of molecular water, dissociate water and simple carboxylic group molecule (formic acid) are calculated and we found that the carboxylic group do not adsorb strongly in most of the pure and hydroxylated surfaces in comparison to water. Since the associated calcium minerals are floated from magnetite using fatty acid collector, our calculations corroborate the flotation practice of removing these impurity minerals from magnetite.
Keywords: Atomistic simulation; Magnetite; Surfaces; Adsorption; Flotation
Viscosity and yield stress reduction in non-colloidal concentrated suspensions by surface modification with polymers and surfactants and/or nanoparticle addition
by Maricel Marquez; Amanda Robben; Brian P. Grady; Ian Robb (pp. 374-387).
A custom-designed apparatus termed the yield stress adaptor (YSA) has been used to evaluate the effect of polymerâ€“surfactant coatings, and the addition of nanoparticles of different size, shape and surface chemistry, on the rheological properties of large hydrophilic particulates, sand, with the aim of reducing interparticle friction forces. Experimental results show that the flow properties of sand slurries at high volume fractions of sand (>50%) can be significantly enhanced by adding nanoparticles, and by surface modification with polymer/surfactant mixtures. A lesser effect is observed for polymer-only and surfactant-only coated samples. X-ray photoelectron spectroscopy was used to determine the concentration of organic species at the surface. The effect of polymer/surfactant concentration, adsorption time, polymer molecular weight, as well as surfactant charge and chemical structure were also addressed.A custom-designed apparatus termed the yield stress adaptor (YSA) has been used to evaluate the effect of polymerâ€“surfactant coatings, and the addition of nanoparticles of different size, shape and surface chemistry, on the rheological properties of large hydrophilic particulates, sand, with the aim of reducing interparticle friction forces.
Keywords: Non-colloidal suspensions; Surface modification; Nanoparticles; Viscosity; Yield stress
Highly-ordered layered organo-mineral materials prepared via reactions of n-alkylphosphonic acids with apatite
by Mikhail Y. Gelfer; Christian Burger; Benjamin S. Hsiao; Susan C. D'Andrea; Alexander Y. Fadeev (pp. 388-392).
This work describes a novel class of layered organo-mineral materials manufactured via a single-step solution-phase reaction of n-alkylphosphonic acids (C nH2 n+1P(O)(OH)2) with calcium hydroxyapatite mineral (CaHAP). TEM, SAXS, WAXS, FTIR, and Vapor Phase Adsorption data suggest that these alkyl-CaHAP materials present a surface-modified CaHAP matrix coated with ordered layers of calcium alkylphosphonates that are strongly adhered to the surface. Interlayer spacing increases from 1.47 (C3-CaHAP) to 4.77 nm (C18-CaHAP). According to FTIR, ordering of alkyl chains improves with the alkyl chain length. The organic loads in these alkyl-CaHAP can be controlled over a wide range (up to âˆ¼60%) by varying alkyl chain and the concentration of alkylphosphonic acids in the solution.
Effect of the crosslinking degree and the nickel salt load on the thermal decomposition of poly(2-hydroxyethyl methacrylate) hydrogels and on the metal release from them
by César Teijón; Rosa Olmo; M. Dolores Blanco; José M. Teijón; Arturo Romero (pp. 393-400).
Polymeric matrices of poly(2-hydroxyethyl methacrylate) (PHEMA) crosslinked with different percentages of ethylene glycol dimethacrylate (EGDMA) as well as different loads of nickel salt were synthesized. Nickel release from the polymeric systems, and their thermal stability were analyzed. A high percentage of the nickel loaded was released, although strong interactions between the polymeric matrices and the nickel ion must be established since a total nickel release did not take place. The values of the diffusion coefficients showed that nickel release depended on the amount of nickel salt loaded in the polymeric matrix and also on the crosslinking degree of the gels. On the other hand, the presence of nickel salt induced an evident thermal instability in the polymeric matrices, although all the polymeric systems can be considered thermally stable.Polymeric matrices of poly(2-hydroxyethyl methacrylate) (PHEMA) crosslinked with different percentages of ethylene glycol dimethacrylate (EGDMA) as well as different loads of nickel salt were synthesized. Nickel release from the polymeric systems, and their thermal stability were analyzed. A high percentage of the nickel loaded was released, although strong interactions between the polymeric matrices and the nickel ion must be established since a total nickel release did not take place. The values of the diffusion coefficients showed that nickel release depended on the amount of nickel salt loaded in the polymeric matrix and also on the crosslinking degree of the gels. On the other hand, the presence of nickel salt induced an evident thermal instability in the polymeric matrices, although all the polymeric systems can be considered thermally stable.
Keywords: Hydrogel; Nickel; Release; Swelling; Thermal degradation
Mercaptoethane sulfonate protected, water-soluble gold and silver nanoparticles: Syntheses, characterization and their building multilayer films with polyaniline via ionâ€“dipole interactions
by Xiangqin Zou; Haifeng Bao; Hongwei Guo; Lei Zhang; Li Qi; Junguang Jiang; Li Niu; Shaojun Dong (pp. 401-408).
Mercaptoethane sulfonate protected, water-soluble gold and silver nanoparticles (Au-MES and Ag-MES) are synthesized by one-phase method and characterized by TEM, TGA and XPS techniques, UVâ€“vis and FTIR spectra. Both Au-MES and Ag-MES nanoparticles are soluble in the water up to 2.0 mg/ml and the stability of Au-MES is much better than that of Ag-MES. When dissolved in the water, they behave like a polyanion and can be used to build multilayer films with polyaniline (PANI) by way of layer-by-layer. A new approach is presented to fabricate the multilayer films of Au-MES/PANI and Ag-MES/PANI. The assembly mechanism of these multilayer films is also discussed. We anticipate highly conducting PANI films can be obtained by doping with these nanoparticles.
Keywords: Conducting polymer; Polyaniline; Monolayer-protected clusters; Mercaptoethane sulfonate; Water soluble; Layer-by-layer
Comparison of the surface characteristics of polypropylene films treated by Ar and mixed gas (Ar/O2) atmospheric pressure plasma
by Oh-June Kwon; Sung-Woon Myung; Chang-Soo Lee; Ho-Suk Choi (pp. 409-416).
In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such asCO,CO, andCOO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.The Ar plasma treatment is slightly more effective in improving the wettability of a PP film than the Ar/O2 plasma treatment but the polar contribution of the surface-free energy of the PP film increases with increasing O2 content in the gas mixture.
Keywords: Atmospheric pressure plasma; Contact angle measurements; Surface-free energy; Surface morphology; Surface roughness; Polypropylene
A small-angle neutron scattering study of sodium dodecyl sulfate-poly(propylene oxide) methacrylate mixed micelles
by Guillaume Bastiat; Bruno Grassl; Oleg Borisov; Alain Lapp; Jeanne François (pp. 417-426).
Mixed micelle of protonated or deuterated sodium dodecyl sulfate (SDS and SDSd25, respectively) and poly(propylene oxide) methacrylate (PPOMA) are studied by small-angle neutron scattering (SANS). In all the cases the scattering curves exhibit a peak whose position changes with the composition of the system. The main parameters which characterize mixed micelles, i.e., aggregation numbers of SDS and PPOMA, geometrical dimensions of the micelles and degree of ionisation are evaluated from the analysis of the SANS curves. The positionqmax of the correlation peak can be related to the average aggregation numbers of SDSâ€“PPOMA and SDSd25â€“PPOMA mixed micelles. It is found that the aggregation number of SDS decreases upon increasing the weight ratio PPOMA/SDS (or SDSd25). The isotopic combination, which uses the â€œcontrast effectâ€? between the two micellar systems, has allowed us to determine the mixed micelle composition. Finally, the SANS curves were adjusted using the RMSA for the structure factorS(q) of charged spherical particles and the form factorP(q) of spherical coreâ€“shell particle. This analysis confirms the particular coreâ€“shell structure of the SDSâ€“PPOMA mixed micelle, i.e., a SDS â€œcoreâ€? micelle surrounded by the shell formed by PPOMA macromonomers. The structural parameters of mixed micelles obtained from the analysis of the SANS data are in good agreement with those determined previously by conductimetry and fluorescence studies.
Keywords: Mixed micelle; Sodium dodecyl sulfate; Small-angle neutron scattering; RMSA method; Spherical coreâ€“shell structure
Mixed self-assembled monolayers (SAMs) consisting of methoxy-tri(ethylene glycol)-terminated and alkyl-terminated dimethylchlorosilanes control the non-specific adsorption of proteins at oxidic surfaces
by Christian Hoffmann; Günter E.M. Tovar (pp. 427-435).
Monolayers from the newly synthesized compound methoxy-tri(ethylene glycol)-undecenyldimethylchlorosilane (CH3O(CH2CH2O)3(CH2)11Si(CH3)2Cl, MeO(EG)3C11DMS) and dodecyldimethylchlorosilane (DDMS), both pure and mixed, were prepared by self-assembly from organic solution in the presence of an organic base. The films obtained were characterized by advancing and receding contact angle measurements and ellipsometry to confirm the formation of self-assembled monolayers (SAMs). The resulting data on the covalently attached dimethylsilanes were compared to known oligo(ethylene glycol) (OEG)-terminated SAM systems based on terminal alkenes, thiolates or trihydrolyzable silanes. The composition of the mixed SAMs was found to depend directly and linearly on the composition of the silanization solution. Enhanced protein repellent properties were found for the SAMs using a variety of proteins, including the Ras Binding Domain (RBD), a protein with high relevance for cancer diagnostics. Roughly a RBD protein monolayer amount was adsorbed to silicon oxide surfaces silanized with DDMS or non-silanized silicon wafers, and in contrast, no RBD was adsorbed to surfaces silanized with MeO(EG)3C11DMS or to mixed monolayers consisting of DDMS and MeO(EG)3C11DMS if the content of OEG-silane overcame a critical content ofXEGâ‰ˆ0.9.
Keywords: Self-assembled monolayer; Organosilane; Oligo(ethylene glycol); Non-specific binding; Protein adsorption
Nano-fibriform production of silica from natural chrysotile
by Lijuan Wang; Anhuai Lu; Changqiu Wang; Xishen Zheng; Dongjun Zhao; Rui Liu (pp. 436-439).
Nano-fibriform silica was extracted from chrysotile by the acid-leaching method. The acid-leached residue of chrysotile has been studied by TEM, XRD, FT-IR, and thermal analysis techniques, etc. When the magnesium leaching degree (MLD) is over 90%, the nano-fibriform silica consists of hydrous silicon dioxide (above 90%) with small amount of magnesium trapped inside the SiO network. The amount of hydroxyl on surface of nano-fibriform silica is 6 unitâ€‰nmâˆ’2. This value is between the values of fumed and precipitated silica. This study shows that nano-fibriform silica is a kind of amorphous matter with a high special surface area (368 m2/g), a high adsorption (330 cm3/g), and a larger pore volume (0.51 cm3/g). The diameter of a single silica fiber is 20â€“30 nm. The nitrogen adsorption isotherm is similar to Type IV curve. The nano-fibriform silica is one of mesopores materials.Nano-fibriform silica (MLD > 90%) was extracted from chrysolite by the acid-leaching method. Experimental results give evidence that nano-fibriform silica, one of mesopores material, is a kind of amorphous matter with a high special surface area, a high adsorption, and a larger pore bulk.
Keywords: Silica; Nano-fibriform; Magnesium leaching degree; Chrysotile
Shape-controlled synthesis and characterization of InVO4 particles
by Limiao Chen; Younian Liu; Zhouguang Lu; Dongming Zeng (pp. 440-444).
InVO4 powders in the shape of rod-like, cubic-like, irregular particle and brick-like have been successfully synthesized by a hydrothermal method in the presence of different organic additives, namely, CTAB, SDS, PVP, and EDTA. The products were characterized by X-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscope (SEM). From the experimental results, it has been revealed that there is optimal pH range(pHâ©½7.0) for the formation of pure InVO4 and the organic additives play a key role in the formation of the products with different morphologies and sizes. Gas sensing behavior of this material to ethanol and ammonia has been studied. The gas sensors constructed by the InVO4 particles with different morphologies show different sensitivity to ethanol. It is also found that the sensor based on InVO4 is more sensitive to ethanol than to ammonia.TEM images of the products obtained: (a) in the presence of SDS, pH 6; (b) in the presence of CTAB, pH 6; (c) in the presence of CTAB, pH 7; (d) in the presence of PVP, pH 6; (e) in the presence of EDTA, pH 6.
Keywords: InVO; 4; Hydrothermal synthesis; Gas-sensors
Electrooptics of Î²-FeOOH particle in aqueous media
by Viktor Peikov; Ryo Sasai; Masato Tanigawa; Ivana Petkanchin; Kiwamu Yamaoka (pp. 445-456).
Steady-state and decay birefringence, expressed in terms of the optical phase retardation per cell lengthÎ´/d, was measured on Î²-FeOOH in aqueous ionic media at 633 nm and at 25â€‰Â°C by an electric square-pulse technique over a wide range of field strength E to ca. 6 kV/cm. The field-strength dependence of bothÎ´/d and field-free rotational relaxation time Ï„ was determined at the sample concentrations between 0.0011 and 0.055 g/L and in the 0.02â€“2.0 mM NaCl concentration range. Extrapolation of bothÎ´/d and Ï„ values to infinitely high fields (E2â†’âˆž) could yield birefringence- and weight-average quantities, respectively. Observed Ï„ values were decreased at weak fields but leveled off to ca. 0.3 ms at very high fields due to a slight polydispersity regarding the length and volume of particles. The weight-average relaxation timeâŒ©Ï„âŒªw was calculated with Perrin's expressions theoretically from the length, width, and volume of Î²-FeOOH particles estimated in the dried state from electron micrograph. These quantities were variously averaged. The size distribution was discussed in terms of observed discrete histogram and theoretical (Weibull and Lansingâ€“Kraemer) distribution functions. The sign of observedÎ´/d value was always positive. The infinitely high-field(Î´/d)âˆž values and the reduced optical anisotropy factorÎ”g/n were evaluated by fitting to theoretical orientation functions. The intrinsic birefringence (n3âˆ’n1) could be estimated with the mean refractive indexnp reported in the literature. For the spindle-shaped particle with an axial ratio of ca. 4, the sign ofÎ”g/n is always positive, whereas the quantity (n3âˆ’n1) was either negative (np>2.35) or positive (np<2.05) in sign or nearly zero (ca.np=2.26), depending critically on thenp values.The light extinction at 633 nm of Î²-FeOOH suspension per unit absorption cell length against particle concentration in the absence of applied electric field. The apparent Lambertâ€“Beer law holds over the entire concentration region. The concentration of NaCl in the suspension is kept in the 0.03â€“0.1 mM range. The solid line represents a linear fit through the origin of measured points (squares).
Keywords: Î²; -FeOOH in NaCl solution; Particle size distribution; Electric birefringence decay; Rotational relaxation time; Steady-state birefringence; Optical anisotropy factors
Ceramic encapsulated latex composites
by Åž. UÄŸur; E. Pehlivan; F. Tepehan; Ã–. Pekcan (pp. 457-463).
This work reports the encapsulation of latex particles in Al2O3â€“polystyrene (PS) composite films. These films were prepared from PS particles in Al2O3 dispersion at room temperature in various latex contents. Composite films were annealed at elevated temperatures in 10 min time interval above the glass transition temperature (Tg) of polystyrene. Transmitted photon intensities,Itr were monitored after each annealing step. AFM micrographs were also used to observe the physical changes of the composite films during annealing. It was observed that latex particles are encapsulated above a critical Al2O3 content of 33 wt% which corresponds to the critical occupation probability ofpc=0.33 at which the film obey the site-percolation model with a critical exponent of 0.45. Belowpc, it was seen that complete latex film formation process took place, where transparency of the film was increased by annealing.
Keywords: Latex; Encapsulation; Percolation; Critical exponents
Encapsulation method for the dispersion of NiO onto ordered mesoporous silica, SBA-15, using polyethylene oxide (PEO)
by Younggeun Park; Taewook Kang; Pil Kim; Jongheop Yi (pp. 464-471).
An effective method for dispersing NiO onto ordered mesoporous silica, SBA-15, is described. The procedure involves the use of polyethylene oxide (PEO) as an encapsulating agent. It can be expected that encapsulation between PEO and Ni2+ ions mainly involves complexes between PEO and Ni2+ ions. Both N2 adsorption/desorption isotherm and TEM analyses indicate that a 2-dimensionally hexagonal pore structure with a distinct pore symmetry (space group P6mm) is maintained throughout the procedure, even though both Ni2+ ions and PEO are present in the middle of the self-assembly of mesostructured silica. The particle size of the NiO increases slightly as a function of PEO concentration. When the ratio of PEO to the templating agent (triblock copolymer, polyethylene oxideâ€“polypropylene oxideâ€“polyethylene oxide) reaches a value of 4.5, ordered mesoporous silica with NiO is hardly formed.The effective method for dispersing NiO onto ordered mesoporous silica, SBA-15, is described. The procedure involves the use of polyethylene oxide (PEO) as an encapsulating agent. Both N2 adsorption/desorption isotherm and TEM analyses indicate that the 2-dimensionally hexagonal pore structure with a distinct pore symmetry (space group P6mm) is maintained throughout the procedure, even though bot Ni2+ and PEO are present in the middle of the self-assembly of mesostructured silica.
Keywords: NiO; Encapsulation; Polyethylene oxide; Mesostructured silica; Hexagonal pore structure; Self-assembly
Influence of physical and chemical heterogeneity shape on thin film rupture
by David Simmons; Anuj Chauhan (pp. 472-481).
It is known that the breakup times for thin liquid films on solid surfaces can be substantially smaller if the surface is heterogeneous, either chemically or physically. In this paper we explore issues related to the effect of the shape of the physical and chemical heterogeneities on the breakup time and the thinning behavior. We consider two shapes, sinusoidal and exponential, for both physical and chemical gradients and compare the breakup times for these two different forms of gradients. Furthermore, the wavelength of the sinusoidal gradients and the length scale of the exponential gradients are varied and the effects of these on the breakup times and the film evolution are determined. For the sinusoidal gradients, we also obtain analytical results for shape evolution that are valid at short times and for small amplitude perturbation of the physical/chemical heterogeneities. The fastest growing modes are determined for spinodal breakup and also for both shapes (sinusoidal and exponential) of physical and chemical heterogeneities. The breakup times for the fastest growing modes from the linear and the nonlinear studies are compared for spinodal breakup and these results are also compared with those for both chemical and physical heterogeneities, of both sinusoidal and exponential shapes. Results show that the presence of heterogeneities, in general, accelerates the breakup of the film. In the linear regime, the growth rates are the same for the chemical and physical heterogeneities and spinodal breakup, and the effect of the heterogeneities is manifested as increased amplitude of initial perturbation. The effect of the chemical and physical heterogeneities dominate the film dynamics at early times, becoming less important at later times. The growth rates and equivalently the breakup times for the films on heterogeneous surfaces depend on the length scale over which physical/chemical gradients occur, and as the length scale approaches zero, which implies that the gradients become very steep, the effect of the heterogeneities on the breakup times becomes small.This paper investigates the effect of chemical heterogeneities (dashed line in the figure) and similar physical heterogeneities on the breakup of thin liquid films (solid lines show the temporal film evolution).
Keywords: Thin film stability; Thin film breakup; Wettability gradients; Surface roughness
Effect of embedded metal compound on porosity of silica colloids prepared by spray reaction of silicon tetrachloride
by Hiroshi Isobe; Yoshiyuki Hattori; Tomoe Hayano; Hirofumi Kanoh; Kohzoh Yamamoto; Katsumi Kaneko (pp. 482-489).
Attempts to prepare macroporous silica particles and metal-compound-nanoparticle-embedded silica microspheres were carried out using reactions between silicon tetrachloride and ultrasonic generating microdroplets including metal (Na, K, Al, Ni, Ti, Pt) compounds. Samples were collected by dry and wet processes. In the case of using nickel and aluminum compounds, acid-treated samples were also prepared. The obtained samples were characterized by scanning electron microscopy, X-ray fluorescence spectroscopy, powder X-ray diffractometry, mercury porosimetry, and the nitrogen adsorption method. The macroporous silica particles were prepared by removing the salt crystals, such as NaCl and KCl, formed in the silica frame. For acid-resistant metals, platinum- and titanium-compound nanoparticles are easily embedded in silica microspheres using these metal-compound solutions. For acid-soluble metals, aluminum- and nickel-compound-nanoparticle-embedded silicas were prepared by applying neutralization of the collection water. Micropores and mesopores were produced in wet-process samples. Acid treatment induced the increase of micropore volumes.
Keywords: Porous silica; Nanoparticle; Silicon tetrachloride; Ultrasonic spray method
Unsmooth cuticles of soil animals and theoretical analysis of their hydrophobicity and anti-soil-adhesion mechanism
by Xian Jia (pp. 490-494).
Soil adhesion is a natural phenomenon, and it is harmful to terrain machines and tillage equipment that have soil as their work medium, such as automobiles, tractors, earth-moving machines, spades, hoes, and plows. Soil adhesion increases motion resistance and energy consumption, quickens damage to the soil-engaging components, and lowers work quality. The biomimetic research has provided a promising method to solve the soil adhesion problem. In this work, the cuticles of typical soil animals were observed by scanning electron microscopy (SEM) and their wettability and mechanism of antiadhesion were analyzed in theory. The results of experimental observation have shown that the cuticles of soil animals have different unsmooth appearances, such as pimple-shaped, pit-like, and undee structures. But for the cross sections of the unsmooth cuticles, their common character is undee. Theoretical analysis has indicated that the larger the ratio of the amplitude of the wave to the period of the wave, the stronger the hydrophobicity, the more easily the composite interface between the liquid and the unsmooth cuticles forms, and the function of reducing soil adhesion of the unsmooth cuticles will be better.
Keywords: Adhesion; Surfaces; Wettability; Soil animals
Effect of surfactant sucrose ester on physical properties of dairy whipped emulsions in relation to those of O/W interfacial layers
by A. Tual; E. Bourles; P. Barey; A. Houdoux; M. Desprairies; J.-L. Courthaudon (pp. 495-503).
Dairy foams were manufactured on a pilot plant with various sucrose ester contents. Oil-in-water emulsions were produced by high-pressure homogenisation of anhydrous milk fat (20 wt%) with an aqueous phase containing skim milk powder (6.5 wt%), sucrose (15 wt%), hydrocolloids (2 wt%), and sucrose esters. Sucrose ester content was varied from 0 to 0.35 wt%. Firmness and stability of dairy foams were determined. The fraction of protein associated with emulsion fat droplets and the compression isotherms of those droplets were determined as a function of sucrose ester content. With less than 0.1 wt% sucrose ester, no foam could be produced. The most firm and stable foams were obtained with ca. 0.1 wt% sucrose ester. The fraction of protein associated with emulsion droplets suddenly falls from 60% at a sucrose ester content lower than 0.1125% down to ca. 10â€“20% for higher surfactant content. Compression isotherms of emulsion droplets at the airâ€“water interface show that, in the presence of surfactant, emulsion droplets disrupt and spread at the interface whilst without surfactant they become dispersed. This means that the presence of sucrose ester causes some destabilisation of fat droplet interfacial layers. There is hence an optimal sucrose ester content that allows some destabilisation of the oilâ€“water interface without concomitant protein displacement from that interface. Consequently, with the recipe and manufacturing process used to produce dairy foams, there exists a compromise in sucrose ester content with regards to manufacture and shelf-life of dairy foams.
Keywords: Dairy foam; Sucrose ester; Protein adsorption; Airâ€“water interface; Foam stability
Electroviscous cylinderâ€“wall interactions
by S.M. Tabatabaei; T.G.M. van de Ven; A.D. Rey (pp. 504-519).
A theoretical analysis is presented to determine the forces of interaction between an electrically charged cylindrical particle and a charged plane boundary wall when the particle translates parallel to the wall and rotates around its axis in a symmetric electrolyte solution at rest. The electroviscous effects, arising from the coupling between the electrical and hydrodynamic equations, are determined as a solution of three partial differential equations, derived from R.G. Cox's general theory [J. Fluid Mech. 338 (1997) 1], for electroviscous ion concentration, electroviscous potential, and electroviscous flow field. It is assumed a priori that the double layer thickness surrounding each charged surface is much smaller than the length scale of the problem. Using the matched asymptotic expansion technique, the electroviscous forces experienced by the cylinder are explicitly determined analytically for small particleâ€“wall distances for low and intermediate Peclet numbers. It is found that the tangential force usually increases the drag above the purely hydrodynamic drag, although for certain conditions the drag can be reduced. Similarly the normal force is usually repulsive, i.e., it is an electrokinetic lift force, but under certain conditions the normal force can be attractive.
Keywords: Electrokinetics; Electroviscous forces; Electrokinetic lift; Electroviscous drag; Particleâ€“wall interactions; Cylinderâ€“wall interactions
Sedimentation of a circular disk in power law fluids
by S. Nitin; R.P. Chhabra (pp. 520-527).
The continuity and momentum equations have been solved numerically for the two-dimensional steady flow of power law fluids over a thin circular disk oriented normal to the direction of flow. Extensive results on the individual and total drag coefficients are obtained as functions of the power law flow behavior index (0.4â©½nâ©½1.0), Reynolds number (1â©½Reâ©½100) and the blockage ratio, disk-to-cylinder diameter ratio (0.02â©½eâ©½0.5), which can be used to estimate the settling velocity of a circular disk. The numerical predictions of drag are consistent with the scant experimental results available in the literature.The continuity and momentum equations have been solved numerically for the two-dimensional steady flow of power law fluids over a thin circular disk oriented normal to the direction of flow. Extensive results on the individual and total drag coefficients are obtained as functions of the power law flow behavior index (0.4â©½nâ©½1.0), Reynolds number (1â©½Reâ©½100) and the blockage ratio, disk-to-cylinder diameter ratio (0.02â©½eâ©½0.5), which can be used to estimate the settling velocity of a circular disk. The numerical predictions of drag are consistent with the scant experimental results available in the literature.
Keywords: Disk; Drag; Wall effects; Power law liquids; Sedimentation velocity
Electrically induced anisotropy in a colloidal dispersion of nanospheres as measured by electric birefringence
by C. Chassagne; D. Bedeaux; J.P.M. v.d. Ploeg; G.J.M. Koper (pp. 528-534).
Electrically induced birefringence experiments were performed on dispersions consisting of sulfate latex nanospheres of two different sizes and charges dispersed in an electrolyte solution, at various ionic strengths. The induced birefringence was found to have an important contribution increasing as a quadratic power law of the volume fraction of the spheres. This shows that interparticle interactions play a role in the observed birefringence. The data were analyzed, using a theory from Hafkenscheid and Vlieger [Physica 75 (1974) 57], in terms of the changes of the interparticle separations in the directions parallel and perpendicular to the applied electric field.Electrically induced birefringence experiments were performed on dispersions consisting of sulfate latex nanospheres of two different sizes and charges dispersed in an electrolyte solution, at various ionic strengths. The induced birefringence was found to have an important contribution increasing as a quadratic power law of the volume fraction of the spheres. This shows that interparticle interactions play a role in the observed birefringence. The data were analyzed, using a theory from Hafkenscheid and Vlieger [Physica 75 (1974) 57], in terms of the changes of the interparticle separations in the directions parallel and perpendicular to the applied electric field.
Keywords: Birefringence; Kerr effect; Colloidal suspensions; Electrokinetics
Effect of electrical potential on the electro-demulsification of oily sludge
by Maria Elektorowicz; Shiva Habibi; Rozalia Chifrina (pp. 535-541).
Oily sludge, produced mostly in petroleum refineries and petrochemical industries, is one of the major industrial wastes that require treatment. Typically, these sludge wastes are water-in-oil emulsions that are stabilized by fine solids. These fine particles adsorb at the droplet surface and by lowering the demulsification rate constant, act as a barrier to prevent droplet coalescence. In this investigation, the effects of different electrical potential gradients and amphoteric surfactant on effectiveness of phase separation were investigated. It was concluded that lower electrical potential (0.5 V/cm) produced a higher demulsification rate. The solid phase remaining after the experiment was of a more compact and stable consistency. It was concluded that application of the amphoteric surfactant does not improve the total efficiency of the process. The role of oil constituents in stabilizing water-in-oil emulsions, and their effect on the dynamics of the process, were considered in every step of the experiment. Analysis of pH changes, resistance evolution, and hydrocarbon polarity analysis confirmed that the application of lower electrical gradient results in better phase separation.In this paper, the effects of different electrical potential gradients and amphoteric surfactant on oily sludge were investigated. Results of this study have demonstrated a new and effective process for the separation of sludge phases: water, hydrocarbons, and solids. Electro-separation process can be monitored by resistance changes along the electrokinetic cell. Cell SE (0.5), which had lower electrical potential and did not contain an additive, represented the optimum condition (Fig. 2d).
Keywords: Oily sludge; Electrokinetics; Waste management; Phase separation; Demulsification
Experimental and modeling study of Newtonian and non-Newtonian fluid flow in pore network micromodels
by Christian L. Perrin; Philippe M.J. Tardy; Ken S. Sorbie; John C. Crawshaw (pp. 542-550).
The in situ rheology of polymeric solutions has been studied experimentally in etched silicon micromodels which are idealizations of porous media. The rectangular channels in these etched networks have dimensions typical of pore sizes in sandstone rocks. Pressure drop/flow rate relations have been measured for water and non-Newtonian hydrolyzed-polyacrylamide (HPAM) solutions in both individual straight rectangular capillaries and in networks of such capillaries. Results from these experiments have been analyzed using pore-scale network modeling incorporating the non-Newtonian fluid mechanics of a Carreau fluid. Quantitative agreement is seen between the experiments and the network calculations in the Newtonian and shear-thinning flow regions demonstrating that the â€˜shift factor,â€™ Î±, can be calculated a priori. Shear-thickening behavior was observed at higher flow rates in the micromodel experiments as a result of elastic effects becoming important and this remains to be incorporated in the network model.
Keywords: Micromodel; Pore network modeling; Non-Newtonian rheology; HPAM; Carreau model; Shear thinning; Rectangular capillary
Transient electroosmotic flow induced by AC electric field in micro-channel with patchwise surface heterogeneities
by Win-Jet Luo (pp. 551-561).
This paper investigates two-dimensional, time-dependent electroosmotic flow driven by an AC electric field via patchwise surface heterogeneities distributed along the micro-channel walls. The time-dependent flow fields through the micro-channel are simulated for various patchwise heterogeneous surface patterns using the backwards-Euler time stepping numerical method. Different heterogeneous surface patterns are found to create significantly different electrokinetic transport phenomena. The transient behavior characteristics of the generated electroosmotic flow are then discussed in terms of the influence of the patchwise surface heterogeneities, the direction of the applied AC electric field, and the velocity of the bulk flow. It is shown that the presence of oppositely charged surface heterogeneities on the micro-channel walls results in the formation of localized flow circulations within the bulk flow. These circulation regions grow and decay periodically in phase with the applied periodic AC electric field intensity. The location and rotational direction of the induced circulations are determined by the directions of the bulk flow velocity and the applied electric field.
Keywords: Electroosmotic flow; Patchwise surface heterogeneity
A hybrid rheological model for particulate suspension in zeolite crystal growth
by Hongwei Song; Olusegun J. Ilegbusi; Albert Sacco Jr. (pp. 562-568).
A hybrid constitutive model is developed to represent the thixotropic behavior of particulate suspension during zeolite crystallization from solution. This model is valid over the complete solid fraction range typical for such a process. It employs two internal variables, agglomeration and contiguity, to describe the degree to which the gel particles form short- and long-range networks. The contiguity is used to weigh the effects of hydrodynamic to chain-like network deformation on the suspension viscosity. Heterogeneous nucleation and surface reaction-controlled crystal growth are assumed to describe the evolution of microstructure and solid fraction of gel and crystals. Such a model successfully captures the thixotropic behavior of zeolite particulate suspension by comparison of the predictions with a set of experimental data.A hybrid constitutive model is developed to represent the thixotropic behavior of particulate suspension during zeolite crystallization from solution. This model is valid over the complete solid fraction range typical for such a process. It employs two internal variables, agglomeration and contiguity, to describe the degree to which the gel particles form short- and long-range networks. The contiguity is used to weigh the effects of hydrodynamic to chain-like network deformation on the suspension viscosity. Heterogeneous nucleation and surface reaction-controlled crystal growth are assumed to describe the evolution of microstructure and solid fraction of gel and crystals. Such a model successfully captures the thixotropic behavior of zeolite particulate suspension by comparison of the predictions with a set of experimental data.
Keywords: Zeolites; Particulate suspension; Rheology; Gel dissolution
Polydispersed O/W emulsions in porous media: Segregation at low-tension conditions
by János Török; János Tóth; Gyula Gesztesi (pp. 569-577).
The segregation of polydispersed oil was studied in theoretical models, sand packs, and plugs from consolidated cores at low tension and atmospheric conditions. The height of the oil belt formed at the top of the porous column and its change in time were measured. The analysis of the segregation curves indicates the subsequent appearance and rise of three pseudo-phases. The primary phase, which contains the dominant fraction of oil in the system, rises with a relatively high steady state velocity. Unsteady state and decreasing velocity characterize the transitional secondary phase which is a lean emulsion left behind. The ternary phase, which follows it with a semi-steady state low velocity, is a lean emulsion of the smallest oil blobs present in low concentration. The process terminates at the segregation of the mobile oil particles in the subsequent phases where a small fraction of the total oil content remains in the porous bed, mainly from the last stage of segregation due to the entrapment in suitable microstructures. According to the postulated mechanism, the decreasing probability of the repeated coalescence in pore bodies and dispersion at the connecting pore throats are responsible for the development of the mobile phases at the sufficiently low-tension conditions. The structure of the pore network, the size-distribution of the oil droplets, the density of their population, and the length of paths affect the mechanism, properties, and behaviour of the systems.
Keywords: Polydispersed emulsion; Segregation; Pseudo-phases; Pore effects; Mechanism; Low-tension waterflooding; EOR
Influence of the interfacial adsorptions on the imbibition of aqueous solutions of low concentration of the non-ionic surfactant Triton X-100 into calcium fluoride porous medium
by L. Labajos-Broncano; J.A. Antequera-Barroso; M.L. González-Martín; J.M. Bruque (pp. 578-582).
The imbibition of aqueous solution of Triton X-100 in porous columns of calcium fluoride has been carried out in order to investigate the surfactant influence on the capillary rise. Experiments have consisted of the measurement of the increase in the weight of the porous columns caused by the imbibition of the solutions. From their analysis, it has been found that the capillary rise velocity does not depend on the surfactant concentration, and that imbibition of these solutions behaves as in the case of water. This unexpected finding can not be attributed to depletion of the surfactant molecules from the advancing meniscus, since this effect can not be caused by the adsorption at the solid. This lack of surfactant adsorption on the solid is precisely the reason that justifies the observed behaviour. So, it has been proved that the driving force for the capillary rise movement will remain unaltered despite the surfactant addition whenever the free energies of the solid interfaces are not modified by the adsorption on the solid. Therefore, it is concluded from this study that only if adsorption on the solid happened, the imbibition could be influenced by the surfactant concentration.Imbibition of aqueous solutions of Triton X-100 in porous columns of a non-adsorbent solid: Study of the phenomenon by a new procedure based on the analysis of the velocity profile.
Keywords: Imbibition; Adsorption; Free energy; Surfactant; Porous media
Buildup of gold nanoparticle multilayer thin films based on the covalent-bonding interaction between boronic acids and polyols
by Ying Ma; Lei Qian; Haizhen Huang; Xiurong Yang (pp. 583-588).
A novel method for the fabrication of gold nanoparticle multilayer films based on the covalent-bonding interaction between boronic acid and polyols, poly(vinyl alcohol) (PVA), was developed. The multilayer buildup was monitored by UVâ€“vis absorbance spectroscopy, which showed a linear increase of the film absorbance with the number of adsorbed Au layers and indicated the stepwise and uniform assembling process. The atomic force microscopy (AFM) image showed that a compact gold multilayer thin film was successfully assembled. The residual boronic acid group on the surface of thin film could incorporate glycosylated-protein horseradish peroxidase (HRP), and good catalytic activity for H2O2 could be observed.
Keywords: Boronic acid; Poly(vinyl alcohol); Nanoparticles; Self-assembly; Biosensors
by Arthur Hubbard (pp. 589-589).