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PubMed1997

Preparation of Magnetic Inks: Adsorption of Macromolecular Dispersion Agents on Magnetic Metallic Iron Pigments and Electrical Charge Formation

The interaction between metallic iron pigments (MPs) and the actual constituents of magnetic ink is examined by first determining the adsorption isotherms and analyzing by FTIR the type of bonding that is established between the constituents and MP. Then, following the approach described in a previous paper using model compounds, the formation of electrical charges on MPs is examined through acoustophorometric (Electrokinetic amplitude or ESA) measurements. It is shown that the variation in ESA is related to charge transfer processes and reflects the MP-constituent interactions. Finally, adsorption competitions are shown and the importance of the method of preparation (order of mixing of the ingredients of the ink) is illustrated. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Adsorption of Thorium on Amorphous Silica: An EXAFS Study

Wet samples of Th(IV) sorbed on colloidal amorphous silica particles (Aerosil OX 200) have been studied with extended X-ray absorption fine structure spectroscopy (EXAFS) at the Th LIII edge (16.3 keV). The samples were collected with sample surface coverages ranging from 3.8 to 230%. No fundamental changes in the structural environment of Th in terms of the types and distances of nearest neighbors with increasing surface loading were detected, but the results indicate an increasing degree of structural disorder with increasing surface coverage. The O shell around Th shows a distorted configuration with two O atoms at 2.33 A distance and four to six O atoms at 2.55 A. Only one Si shell is observed, with two Si atoms at a distance of 3.8-3.9 A. These results have been interpreted with a double corner-sharing surface complex of Th on silica, where the Th atom shares one O atom with each of two coordinated SiO4 tetrahedra, accounting for the first O coordination shell detected as well as the Th-Si distances. The longer Th-O distances result from coordinated water molecules from solution. No Th-Th interactions could be detected in the EXAFS spectra. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Probing the Sol-Gel Conversion in the Tetraethoxysilane/Alcohol/Water System with the Aid of Diffusion-Controlled Fluorescence Quenching

The sol-gel conversion in the tetraethoxysilane/alcohol/water system can be probed by means of the diffusion-controlled fluorescence quenching of Py* by Cu2+ ions. In the course of tetraethoxysilane hydrolysis, the viscosity of the system increases, thereby causing the quenching rate to decrease and the mean lifetime of the excited state to elongate dramatically as the system approaches the gel-point. Incorporating the equation proposed by Vogelsberger et al. (1992) for the time-dependence of the viscosity of gelating systems into the Smoluchowsky kinetic equation, an equation has been proposed to describe the observed time-dependence of the Py* lifetime. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Interbubble Gas Diffusion and the Stability of Foams

Foam decay may arise from liquid drainage, whether gravitational, due to interbubble gas diffusion, or from rupture of the interbubble liquid lamellae. In our study of factors affecting foam stability, we focus on interbubble gas diffusion, which works against stability even given a stable lamella. We show that liquid drainage from the foam due to such diffusion (as distinct from that due to gravitation) can often be greatly reduced by adding a water-insoluble vapor to the foam-generating gas: the presence of such a vapor counterbalances the Ostwald ripening, thus stabilizing the system. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Influence of Particle Orientation on One-Dimensional Compression of Montmorillonite

Methods have recently been developed for calculating the double-layer repulsive and the van der Waals attractive forces between two nonparallel clay particles immersed in a fluid system. In the present study, these theories are used in an approximate model of one-dimensional compression to examine the role of particle orientation on the behavior of a montmorillonite. It is shown that consideration of nonparallel fabric could potentially explain the discrepancy observed in the past between experimental and theoretical behaviors. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Surface and Spectroscopic Properties of Acetylcholinesterase Monolayer at the Air/Water Interface

The behavior of the enzyme acetylcholinesterase was studied at the air/water interface. Surface pressure-area (pi-A) isotherms and UV-vis spectra recorded at different surface pressures were determined for different salt concentrations in the subphase. The ionic strength of the subphase does not influence the physical properties in consideration; however, the pH of the subphase has a great effect on its surface and optical properties. A subphase at pH 6.5 has shown that the enzyme is highly stable, based on the pi-A compression/decompression isotherms. No changes in the area per molecule were observed when the surface pressure was maintained constant at 16 mN/m for a period of 120 min. The long-term stability of acetylcholinesterase at the air/water interface was demonstrated for pH 6.5 and a salt concentration of 10(-2) M (KCl). The absorption spectra of the monolayer, measured directly at the air/water interface, are considered good evidence of the organization of the enzyme molecules. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Adsorption of Polycations on Clays: A Comparative in situ Study Using 133Cs and 23Na Solution Phase NMR

23Na solution phase NMR has been evaluated as an in situ probe to study the adsorption of tetramethylammonium (TMA+) and two polycations, FL17 ([(Me2NCH2CHOHCH2)n]n+Cln) and Magnafloc 1697, ([(CH2CHCH2N(Me)2CH2&Cmacr;HCH2)n]n+Cln), onto clays in aqueous suspensions containing 2.5 mass% low iron Texas bentonite. The NMR data shows the effectiveness of the organocations at displacing Na+ from the bentonite surface. This information has been correlated with that obtained from particle-size and electrophoretic measurements in aqueous solution, together with information from adsorption isotherms. These results have been compared to those obtained in parallel studies using 133Cs solution phase NMR. FL17 and 1697 both exhibited high affinity adsorption isotherms on Na+- and Cs+-clay, whereas the adsorption of TMA+, which represents the cationic portion of the polymers was of lower affinity. Na+-bentonite adsorbed almost twice the amount of polycation required to fulfill the cation-exchange capacity (CEC) of the bentonite. The electrophoretic and particle size data indicated significant differences in the size of the polycation/clay flocs and the amount of polymer adsorbed on the external faces of the flocs in the presence of Na+- and Cs+-exchange ions. Correlation of this data with the NMR results suggests that the Na+-bentonite/polycation flocs are large, of low density, and that the polycation is concentrated in the interior while the Na+-ions occupy exchange sites on the external faces. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Adsorption of Pb(II), NTA, and Pb(II)-NTA onto TiO2

Nitrilotriacetic acid (NTA) is extensively used in different industries because of its excellent chelating properties. Introduction of NTA into the natural environment is a concern because of mobilization of heavy metal species that may be otherwise bound to natural particulate matter. The present study investigates the adsorption behavior of Pb(II) and NTA, both as individual species and as complex species onto titanium dioxide. This adsorption information is important in considering the TiO2-assisted photocatalytic treatment of these metal-organic complexes. Pb(II) shows a typical cationic type of adsorption behavior, whereas NTA demonstrates an anionic type of adsorption trend. Results from stoichiometric ternary systems show a gradual increase in Pb(II) adsorption and a decrease in NTA removal with an increase in pH. However, for the cases of Pb(II) > NTA, increased NTA adsorption as compared to pure NTA systems was noted even at higher pH. Model predictions employing MINTEQA2 software followed the experimental trends. Experimental and model results from ternary systems suggest adsorption of free Pb(II) and NTA, as well as ternary Ti-NTA-Pb(II) and Ti-O-Pb(II)-NTA2- species. The cationic-type complexation, i.e., Ti-O-Pb(II)-NTA2-, was essential for the successful NTA adsorption modeling, especially at higher pH and for Pb > NTA systems, where significant NTA adsorption was noted even at very high pH values. Most of the previous metal-ligand adsorption studies did not consider such a surface complexation. However, the present results indicate that any groundwater transport modeling of such pollutants will require the inclusion of cationic-type surface complexation, in addition to other surface species. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Solubilization of Gases by Polyethoxylated Octyl Phenols

Measurements have been made to determine the solubilities of a number of gases in aqueous solutions of commercially available polyethoxylated octyl phenols at temperatures ranging from 25°C to 45°C (298-318 K). The solubilities determined for each gas increase linearly with surfactant concentration. The intramicellar gas solubilities derived from these data are found to be relatively insensitive to temperature and sodium chloride in the external aqueous phase. When analyzed in terms of surfactant composition, the intramicellar gas solubilities are found to depend solely on the octyl phenol content of each surfactant. This suggests that the ethylene oxide chains of the micellized surfactant molecules do not contribute directly to the solubilization process, even under conditions near the cloud point. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Low-Frequency Dielectric Dispersion from Ion Permeability of Membranes

Low-frequency dielectric behavior of membrane/electrolyte systems was studied with artificial membranes made from thin plastic films and NaCl electrolyte of various concentrations. A low-frequency dielectric dispersion or relaxation, which is associated with membrane pores and membrane permeability, was observed and investigated. A qualitative explanation is proposed. Membrane structure characteristics, such as thickness, pore size, and number, were found to affect significantly the low-frequency dielectric dispersion, which indicates some potential applications for low-frequency dielectric measurements in membrane- or tissue-related areas. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Elution Behavior of Chemically Different Probes on the Evaluation of Surface Properties of Cellulose by Inverse Gas Chromatography

The inverse gas chromatography (IGC) technique has been employed to examine adsorption behavior of cellulose surfaces from elution characteristics of chemically different adsorbates. The neutral probes were eluted completely during IGC measurements while acidic, amphoteric, and basic probe molecules were eluted incompletely. In this work, complete elution is defined by the flat postpeak FID signal within the noise limits of the detector. An understanding of incomplete elution is thereby reached by introducing a precisely controlled, very small quantity of individual probes into the column. A strong correlation is found between elution efficiency of vapors and their enthalpies of acid-base interactions. Delayed elution of acid-base vapors is interpreted as being due to nonequilibrium sorption process, and calculations have shown that diffusion into the bulk is unlikely under the measurement conditions. The chromatographic process is simulated and it is found that the contribution of nonequilibrium adsorption to the retention is responsible for observed peak tailing and thereby delayed elution of acid-base probes. Results of the study indicate that characterization of acid-base (electron acceptor-donor) type of stationary phase material surfaces by IGC needs careful attention and is an area for future work. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Spatial Distribution of Chemical Components in Aerosol Particles as Determined from Secondary Electron Yield Measurements: Implications for Mechanisms of Multicomponent Aerosol Crystallization

Secondary electron yield measurements were used to determine the distribution of chemical components in multicomponent aerosol particles formed by crystallization from aqueous solution droplets. Yield measurements were made by measuring the charge acquired by a beam of particles as they passed through an electron beam (100-600 eV energy) inside a high-vacuum apparatus. Yields were sufficiently different for certain compounds that measurements made on two-component particles could be used to obtain information on the spatial distribution of components. Variations in chemical composition as a function of depth beneath the particle surface were ascertained from the energy dependence of the measured yields, since the electron penetration depth, and therefore the probe depth, increases with electron energy. The results for mixed NaCl-NH4Cl particles indicate that the distribution of components within these particles is relatively homogeneous, while measurements made on mixed NaCl-NaNO3 particles are indicative of particles having a heterogeneous core-shell morphology. Results for mixed Na2SO4-(NH4)2SO4 particles are ambiguous, probably because of the complexity of the phase diagram of this system. It appears that the mechanism by which aerosol particles crystallize, and therefore the resulting distribution of chemical components within particles, is strongly dependent on particle composition and environmental variables. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Surface Element Integration: A Novel Technique for Evaluation of DLVO Interaction between a Particle and a Flat Plate

A novel method, the surface element integration (SEI), is developed to determine the van der Waals and electrostatic double layer interactions between a particle and an infinite flat plate from the corresponding interactions per unit area between two infinite flat plates. Comparison with the Hamaker expression for nonretarded van der Waals interaction reveals that the new technique gives the exact interaction energy between a spherical particle and a flat plate. Available analytical expressions for the electrostatic double layer interaction energy between two infinite flat plates, based on the linearized Poisson-Boltzmann equation, are used in SEI to obtain the sphere-flat plate interaction energy. These sphere-flat plate interaction energies determined using SEI are compared with the corresponding interaction energies obtained from a detailed numerical solution of the Poisson-Boltzmann equation based on finite element analysis. The comparisons reveal that SEI scales the flat plate interaction to the corresponding sphere-flat plate geometry exactly, while the scaling based on the conventional Derjaguin approximation technique grossly overpredicts the interaction energy for small particles and low electrolyte concentrations. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Hysteresis Thermodynamics of Capillary Condensation in Mesopores

A thermodynamic approach based on mass, energy, and entropy balances is developed for capillary condensation hysteresis in porous media. Processes of fluid condensation and evaporation are considered as quasi-isothermal irreversible transitions between equilibrium states of the capillary system. The corresponding balances express the equilibrium interfacial properties of the system through the work and heat measured in capillary process and, thus, may be used for evaluating the vapor-condensed phase interface area as a function of pressure, surface area of the porous solid, its pore size distribution, and surface fractal properties. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Cationic Surfactant Adsolubilization of 2-Naphthol and Naphthalene with Titanium Dioxide Having Dodecyl Chain

Adsolubilization of 2-naphthol and naphthalene by cationic surfactant-adsorbed layers formed on titanium dioxides with or without a dodecyl chain was investigated. The cationic surfactants used were dodecyltrimethylammonium bromide and 1,2-bis(dodecyldimethylammonio) ethane dibromide (2RenQ). It was found that the adsolubilized amounts of 2-naphthol and naphthalene increase and reach a maximum and then decrease for both surfactants and titanium dioxides with or without the dodecyl chain, where in the absence of surfactants the incorporated amount of naphthalene on the titanium dioxide with the dodecyl chain is markedly large. The adsolubilized amounts of 2-naphthol and naphthalene were enhanced with the titanium dioxide with the dodecyl chain by adsorption of surfactants, in particular 2RenQ. The admicellar partitioning coefficients also showed that naphthalene is adsolubilized preferentially rather than 2-naphthol and the surface treatment with the dodecyl chain enhances the adsolubilization for two adsolubilizates. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Characterization and CO2 Adsorptivity of Acid-Washed and Cation-Exchanged Natural Mordenites

A Japanese natural mordenite was modified by acid washing as well as cation-exchange. Crystal structure, porosity, and active sites of the modified natural mordenites were characterized, and their CO2 adsorptivity were examined. Contraction as well as expansion of the mordenitic unit cell in the natural zeolite and distortion of zeolite structure by acid washing are plausibly shown by XRD. Long-term washing by nitric acid induces enlargement of micropore volume, increasing the micropore dimension but decreasing the large pore dimension over the mesoporous range. The degree of dehydration has an important role in CO2 adsorption. Metal ionic sites affect both the irreversible CO2 adsorption and the CO2 equilibrium adsorption at low concentration. Li+ ion-exchange brings about a great CO2 adsorption but reduces the CO2-surface interaction due to molecular size effect. Ca2+ ion-exchange has its main effect in the enhancement of CO2 desorption energy. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Monolayer Assemblies and Optical Properties of Europium(III) Complexes with beta-Diketones Containing Various Substituents

Europium(III) complexes with beta-diketones containing various substituents were newly synthesized and their monolayer behaviors on the water surface were studied in situ by a Brewster angle microscopy (BAM) together with surface pressure-area isotherms. Some BAM images look like a thin soap film on the flat surface, consisting of gas and liquid phases. The monolayer assemblies of these complexes could be deposited by both LB and horizontal lifting techniques. The emission probability from the excited singlet state 5D1 increased in the film as compared to the lowest excited state 5D0, and the symmetrically forbidden transition 5D0-->7F0 was enhanced in comparison with those in the solutions and the crystallines. This effect on the fluorescence was observed significantly for the complex with an asymmetrically substituted ligand rather than that with a symmetrically substituted one. These results can be ascribed to the fact that the thermal deactivation of the higher excited state is decreased and also the symmetries of these complexes are slightly distored in the monolayer assemblies. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Nonideal Mixing in Adsorbed Film and Micelle of Ionic-Nonionic Surfactant Mixtures

The surface tension of aqueous solutions of dodecylammonium chloride-octyl methyl sulfoxide (OMS) and dodecyltrimethylammonium bromide-OMS mixtures was measured as a function of the total molality of surfactants and the composition of OMS. The results were analyzed according to our thermodynamic procedure; the phase diagrams of adsorption and micelle formation and the diagram illustrating the composition relation between the micelle and the adsorbed film at the critical micelle concentration were drawn. The activity coefficient and excess Gibbs energy in the adsorbed film and the micelle were defined and then evaluated from the phase diagrams. They were found to give useful information on the deviation from ideal mixing and intermolecular interaction in the adsorbed film and micelle. Copyright 1997 Academic Press. Copyright 1997Academic Press

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