Transport Properties of Compact Clays: I. Conductivity and Permeability

Conductivity and permeability of model and natural clays have been studied experimentally. Local properties such as porosity and zeta potentials were measured as functions of the electrolyte solutions. Whenever possible, experimental data were compared to numerical data obtained for random packings of grains of arbitrary shape, and a good agreement was found between them.     

Flow of water through channels filled with deformable polymer gels

A mathematical model is developed for the flow of water through a channel impregnated with a polymer gel that is treated as an elastic and deformable porous medium. The model uses a Brinkman equation along with an experimentally observed velocity-dependent permeability. Numerical and approximate analytical solutions are given. These results show that the gel intrinsic properties, i.e., gel reference permeability and elastic index, control the water flow. First, the permeability of water flow through the gel increases with an increase of gel reference permeability. Second, the velocity of water decreases when the gel velocity exponent increases. Our theoretical results show that the velocity-dependent permeability of water flow through polymer gels is in fact an intrinsic property of the gel rather than a property of the channel or some interaction between the gel and the pore walls.     

Characterization of Titania/Silica Gel by Means of Low-Pressure Nitrogen Adsorption

Adsorbents synthesized by grafting of titania onto mesoporous silica gel surfaces at different temperatures were studied by means of nitrogen adsorption–desorption and water desorption. The pore size distribution f(R_p) of titania/silica gel depends on the titania concentration (C_TiO2) and the temperature of titania synthesis. Nonuniformity of TiO₂ phase is maximal at a low C_TiO2 value (3.2 wt.% anatase deposited at 473 K), and two peaks of the fractal dimension distribution f(D) are observed at such a concentration of titania, but at larger C_TiO2 values, only one f(D) peak is seen. More ordered filling of pores and adsorption sites by nitrogen, reflecting in the shape of adsorption energy distributions f(E) at different pressures of adsorbate, is observed for adsorbent with titania (rutile+anatase) grafted on silica gel at a higher temperature (673 K).     

Advective flow and floc permeability

This work monitored advection flow through a floc by bubble tracking. Close examination of the motion of a swarm of hydrogen bubbles that passed over a free-falling floc allowed the extent of advection flow to be estimated at 53% for the original activated sludge floc, and 12% for the flocculated floc. The interior permeability of the sludge flocs was estimated from this information. The fluid force exerted on the falling floc was also considered.     

Fluidification of Concentrated Aqueous Colloidal Silica Suspensions by Adsorption of Low-Molecular-Weight Poly(ethylene oxide)

This paper deals with the effect of different low-molecular-weight poly(ethylene oxide)s on the rheology of concentrated aqueous colloidal silica suspensions (volume fraction >0.2) with the aim of obtaining well-dispersed media. Results are correlated with the physico-chemical characteristics of the systems that govern the ranges of the various operating interactions, i.e., mainly surface coverage, molecular weight of the polymer, and ionic strength of the medium. Optimization of the fluidification occurs to be strongly linked to these parameters. An unexpected effect of free polymer bulk concentration leads to improved fluidification when the characteristic lengths of the system are correctly adjusted; it has been interpreted in the frame of recent theories.     

Interactions between Poly(ethylene oxide) and Sodium Alkylcarboxylates As Studied by Conductivity and Gel Permeation Chromatography

The interactions between PEO and sodium alkylcarboxylates (octyl, decyl, and dodecyl) have been investigated by conductivity measurements and gel permeation chromatography (GPC). Also included in the study was sodium dodecyl sulfate. From the conductivity measurements the critical aggregation concentration, ionization degree, and binding ratios were determined; the binding ratio was also determined from GPC. PEO–surfactant interactions were observed for all the studied surfactants, except sodium octanoate. For the polymer–surfactant complexes the ionization degree was in all cases observed to be about 0.2 higher than the ionization degree for the corresponding aqueous micelles. Further, the binding ratio decreased somewhat with decreasing chain length of the alkylcarboxylate. The Gibbs free energy showed that the polymer–surfactant interaction decreases with decreasing chain length of the alkylcarboxylates and is weaker for alkylcarboxylate compared to alkylsulfate of similar chain length.     

Numerical simulations of capillary-driven flows in nonuniform cross-sectional capillaries

In this study the wetting behavior of converging-diverging and diverging-converging capillaries is investigated numerically using an in-house written, finite-element code. An interface tracking procedure based on the predicted change in the total liquid volume, to update the interface location, and Cox's formulation, to determine the dynamic contact angle and the interface shape, is proposed and used. Flow simulations revealed that both converging-diverging and diverging-converging capillaries exhibit significantly slower wetting behavior than straight capillaries and that any deviation in the capillary diameter necessarily tends to slow the overall wetting speed. This behavior was attributed to local regions of very low capillary pressure and high viscous retardation force when the capillary diameter at the interface was significantly larger than the capillary diameter over the upstream fluid. Though the local wetting velocities were different, when equivalent capillaries were compared it was found that both converging-diverging and diverging-converging capillaries had the same total fill time independent of the number of irregular regions, suggesting that the simple model is sufficient for predicting the overall effect. The influence of surface tension and contact angle on the total wetting time was found to be similar for both straight and irregularly shaped capillaries.     

Electroosmosis through a Cation-Exchange Membrane: Effect of an ac Perturbation on the Electroosmotic Flow

Electroosmosis experiments through a cation-exchange membrane have been performed using NaCl solutions in different experimental situations. The influence of an alternating (ac) sinusoidal perturbation, of known angular frequency and small amplitude, superimposed to the usual applied continuous (dc) signal on the electroosmotic flow has been studied. The experimental results show that the presence of the ac perturbation affects the electroosmotic flow value, depending on the frequency of the ac signal and on the solution stirring conditions. In the frequency range studied, two regions have been observed where the electroosmotic flow reaches a maximum value: one at low frequencies (Hz); and another at frequencies of the order of kHz. These regions could be related to membrane relaxation phenomena.     

H(2)O Outgassing Properties of Fumed and Precipitated Silica Particles by Temperature-Programmed Desorption

Temperature-programmed desorption was performed at temperatures up to 850 K on as-received fumed and precipitated silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 38–61 kJ/mol. However, the activation energies of desorption for chemisorbed water varied from 80 to >247 kJ/mol for fumed silica, Cab-O-Sil-M-7D, and 96 to 155 kJ/mol for precipitated silica, Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>126 kJ/mol) will not escape silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (80–109 kJ/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies <126 kJ/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1–0.4 wt% of water in silica-reinforced polysiloxane formulations containing 21% Cab-O-Sil-M-7D and 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that the adsorbed H₂O and the Si–OH bonds on the silica surfaces are the major contributors to water outgassing from these types of silica-filled polymers.     

Contribution to the Determination of Kinetic Parameters of the Sol-Gel Transformation by Rheological Measurements

The system tetraethoxysilane(TEOS)–water–ethanol has been studied by rheological measurements. Different molar ratios of TEOS : water (1 : 4, 1 : 10, and 1 : 20) are studied at different temperatures (30, 40, and 50°C). The dynamic viscosity (rotating mode) at a constant shear rate (100 s⁻¹) and the elastic and viscous moduli (oscillating mode) at a constant frequency (1 Hz) are determined. The viscosity–time curves are evaluated by application of a nucleation and particle growth model. Good agreement between experiments and theory is observed. The model allows the determination of the complex rate constant of silica precipitation. The temperature-dependent measurements gave the possibility to determine the apparent energy of activation by common methods. The results are in agreement with data from the literature. The gel time defined as intersection point of elastic and plastic moduli and its dependence on temperature are evaluated by the Smoluchowski model. The energy of activation for the coagulation was determined and found to be in the correct order of magnitude.     

Adsorption of 1,4-Benzenedithiol on Gold and Silver Surfaces: Surface-Enhanced Raman Scattering Study

The adsorption behavior of 1,4-benzenedithiol (1,4-BDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). 1,4-BDT chemisorbed dissociatively on both gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of 1,4-BDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag–S bonds. On the gold surface, the monothiolate species,1,4-BDT⁻¹, appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of 1,4-BDT was close to that required for a full-monolayer coverage limit, a band assignable to the S–S stretching vibration appeared at 536 cm⁻¹ in the gold sol SERS spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to tetralayers could be assembled on gold in 1 mM n-hexane solution of 1,4-BDT while at best a bilayer formed in either methanol or ethanol solution. The different adsorbate structure of 1,4-BDT on gold and silver was overall quite comparable to that of p-xylene-α,α′-dithiol.     

Effect of structural stress on the intercalation rate of kaolinite

Particle size in kaolinite intercalation showed an inverse reactivity trend compared with most chemical reactions: finer particles had lower reactivity and some of the fine particles cannot be intercalated. Although this phenomenon was noted in the early 1960s and several hypotheses have been reported, there is no widely accepted theory about the unusual particle size response in the intercalation. We propose that structural stress is a controlling factor in the intercalation and the stress contributes to the higher reactivity of the coarser particles. In this study, we checked the structural deformation spectroscopically and indirectly proved the structural stress hypothesis. A Georgia kaolinite was separated into nine size fractions and their intercalations by hydrazine monohydrate and potassium acetate were investigated with X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The apical Si-O band of kaolinite at 1115 cm(-1) shifted to 1124 cm(-1) when the mineral was intercalated to 1.03 nm by hydrazine monohydrate, and its strong pleochroic properties became much weaker. Similar reduction in pleochroism was observed on the surface OH bands of kaolinite after intercalation. Both the bending vibrations of the inner OH group at 914 cm(-1) and of the surface OH group at 937 cm(-1) shifted to 903 cm(-1) after intercalation by hydrazine. A new band for the inner OH group appeared at 3611 cm(-1) during the deintercalation of the 1.03 nm hydrazine kaolinite complex. Pleochroism change in the apical Si-O band suggested the tetrahedra had increased tilt with respect to the (001) plane. The tilt of the Si-O apical bond could occur only if the octahedra had also undergone structural rearrangement during intercalation. These changes in the octahedral and tetrahedral sheets represent some change in the manner of compensation for the structural misfit of the tetrahedral sheet and octahedral sheet. As the lateral dimensions of a kaolinite particle increases, the cumulative degree of misfit increases. Intercalation breaks the hydrogen bonds between layers and allows for the structure to reduce the accumulated stress in some other manner. The reversed size effect on intercalation probably was not caused by crystallinity differences as reported in the literature, because the Hinckley and Lietard crystallinity indices of the four clay fractions were very close to each other. Impurities, such as dickite- or nacrite-like phases are not significant in the studied sample as suggested by the XRD and IR results, they are not the main reasons for the lower reactivity of the finer particles.     

Formation and Characterization of Reversed Micelles Composed of Phospholipids and Fatty Acids

The formation of reversed micellar systems composed of phosphatidylcholine (PC) and fatty acid was newly demonstrated by a significant increase in water content in the organic ethyl oleate phase when the micelles were prepared by the contact method. The solubilized water concentration in the reversed micellar organic phase reached 3 wt%. The new systems are expected to be used as highly biocompatible reversed micellar systems. The structure of the reversed micelles composed of PC and oleic acid was characterized by determining the water concentration and by small-angle X-ray scattering analysis. The reversed micelles composed of PC and oleic acid formed in ethyl oleate were spherical. The radius of gyration was between 30 and 50 Å. The size of the reversed micelles decreased with an increase in the oleic acid concentration and was independent of the PC concentration. Experimental results indicated that the structure of the reversed micellar system was determined by the oleic acid concentration. An increase in the PC concentration caused an increase in the number of reversed micelles of the same size. These reversed micellar systems are expected to be used as solubilization media in pharmaceutical and food industries because they are not toxic.     

Influence of Sodium Periodate and Tyrosinase on Binding of Alginate to Adlayers of Mytilus edulis Foot Protein 1

Mytilus edulis foot protein 1 (Mefp-1) is the most well-characterized component of this sea mussel's adhesive plaque. The plaque is a condensed, heterogeneous mixture consisting of a large proportion of cross-linked biopolymers that bonds the mussel to a chosen mooring. Mefp-1 is densely populated with lysine and -3,4-dihyroxyphenylalanine ( -dopa) residues incorporated into a repeating amino acid sequence motif. It has been proposed that one plaque cross-linking reaction is the nucleophilic addition of the ε-amino groups of the lysine residues into the oxidized catechol (o-diphenol) functionality (quinone) of the -dopa residues. In order to determine if this reaction occurs in adlayers of Mefp-1, a previously developed assay for ε-amino groups was applied. Adlayers of Mefp-1 were exposed to an oxidant, either the enzyme, mushroom tyrosinase, or sodium periodate. Binding of alginate to adlayers was used to probe for accessibility of ε-amino groups. It was found that lysine residues lose the ability to bind alginate after exposure to sodium periodate, but that this loss is not clearly due to a reaction with -dopa residues. There is a slight decrease of binding of alginate to adlayers of Mefp-1 exposed to either active or thermally deactivated mushroom tyrosinase, probably due to the obstruction of binding sites by bound enzyme. Adsorption kinetics of mushroom tyrosinase onto adlayers of Mefp-1 for active and thermally inactivated enzyme were nearly identical. Attenuated total reflection Fourier transform infrared spectroscopy was used to characterize these interactions at a germanium (Ge) interface.     

Polydispersity and Functional Group Distribution of Dispersant Polymer: Adsorption Properties and Magnetic Paint Dispersion

The quantitative analysis examining the functional group distribution of a dispersant polymer for magnetic paints is conducted by statistical estimation and adsorption experiments. The dispersant polymer contains averagely one or two functional groups on the chain, and has generally large polydispersity. By the calculation based on the random distribution of the functional group and the molecular weight, a typical design of the dispersant polymer is found to contain a significant amount of nonfunctionalized chains and highly functionalized ones. In adsorption experiments, the adsorbed amount of the polymer mass and the functional group are separately measured to determine the functional group distribution. The distribution is also evaluated by a sequential adsorption experiment, in which the chains are fractionated by the adsorption strength. Obtained experimental results agree with the calculated results. A practical method for increasing the effective chains in the paint is to make use of a preferential adsorption of the functionalized chain.     

Assembly of Alternated Multivalent Ion/Polyelectrolyte Layers on Colloidal Particles. Stability of the Multilayers and Encapsulation of Macromolecules into Polyelectrolyte Capsules

Alternating adsorption of multivalent ions and oppositely charged polyelectrolytes on colloid particles has been investigated. Multilayer films composed of Tb³⁺/polysterene sulfonate (PSS) and 4-pyrene sulfate/polyallylamine (PAH) were successfully assembled on polysterene sulfonate (PS) and melamine formaldehyde (MF) latex particles. The amount of assembled material was estimated by fluorescence and the linear growth of the film versus the number of layers was demonstrated. These multilayers are not stable and can be decomposed by salt and temperature. Dissolution of MF particles leads to formation of hollow capsules consisting of multivalent ion/polyelectrolyte multilayers. Comparative analysis of the capsules was done by confocal and scanning force microscopy. Complex hollow spheres consisting of Tb³⁺/PSS or 4-PS/PAH as an inner shell and stable PSS/PAH as an outer shell were produced. Due to selective permeability of the outer shell after degradation of the inner shell the multivalent ions are released out of the capsule while the polyelectrolytes fill the capsule interior. This is indicative of swelling of the capsule by osmotic pressure. The filled capsules were studied by confocal and scanning electron microscopy. Possibilities of encapsulating macromolecules in defined amounts per capsule are discussed.     

Molecular Interactions in Mixed Monolayers of Octadecanoic Acid and Three Related Amphiphiles

Binary mixed monolayers of octadecanoic acid and three related amphiphilic compounds (octadecanamide, octadecylamine, octadecylurea) have been investigated at the air/water interface by surface pressure–area (Π–Â) isotherms and their resistances to water evaporation (r). In addition, the excess free energies of mixing (ΔG^E) were calculated using the Goodrich method. Both the ln r vs x and ΔG^E vs x plots exhibit marked deviations from linearity, indicating a high degree of miscibility and nonideal behavior of the components in the mixed films. For all of these binary systems the excess free energies of mixing have been found to be minimum for a certain composition corresponding almost to a maximum in evaporation resistances. Weak interactions were detected in octadecanoic acid/octadecanamide monolayers, whereas significant condensation effects were observed in 1 : 1 mixed films containing octadecanoic acid and octadecylamine. This is attributed to an acid–base equilibrium followed by the formation of a well-ordered arrangement of COO⁻ and NH₃⁺ head groups bound to each other by electrostatic forces. The unusual polymorphism of octadecylurea monolayers could be influenced by adding small amounts of octadecanoic acid. The formation of the low-temperature phase (β-phase) is completely suppressed, if the acid content exceeds 8 mol%. The octadecanoic acid seems to induce the formation of the high-temperature phase (α-phase), which is characterized by a vertical orientation of the hydrocarbon chains.     

Investigation of Calcium Carbonate Scaling Inhibition and Scale Morphology by AFM

The calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has been studied in two heat transfer systems: recirculating cooling water and pool boiling systems. It is found that PBTCA has a better inhibition effect than PAA under identical conditions. The inhibition effect increases with increasing fluid velocity for the cooling water system, whereas in the presence of inhibitors, the fluid velocity has less effect on the scaling behavior. When the initial surface temperature increases, the inhibition efficiency decreases. In the presence of inhibitors, the scaling behavior is insensitive to the change of surface temperature. The relationship between the inhibition effect and the fractal dimension has also been investigated. The results show that the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher the fractal dimension. XRD and FTIR analyses demonstrate that for the CaCO₃ formed in the pool boiling system, the content of vaterite increases with the increase of inhibition effects. The metastable crystal forms of vaterite and aragonite are stabilized kinetically in the presence of inhibitors. The step morphology has been observed by atomic force microscopy. It is shown that the step space on the CaCO₃ surface increases in the presence of inhibitors. Moreover, with the increase in inhibition effect, both the step space and the fractal dimension increase. Step bunching is also found and discussed in this paper.     

Effects of Nonionic and Mixed Cationic-Nonionic Micelles on the Rate of Alkaline Hydrolysis of 4-Nitrophthalimide

Pseudo-first-order rate constants (k_obs) for alkaline hydrolysis of 4-nitrophthalimide show a monotonic decrease with increase in [C₁₂E₂₃]_T (total concentration of Brij 35) at constant [CH₃CN] and [NaOH]. This micellar effect is explained in terms of a pseudophase micelle model. The rate of hydrolysis becomes too slow to monitor at [C₁₂E₂₃]_T≥0.03 M in the absence of cetyltrimethylammonium bromide (CTABr) and at [C₁₂E₂₃]_T≥0.04 M in the presence of 0.006–0.02 M CTABr at 0.01 M NaOH. The plots of k_obs versus [C₁₂E₂₃]_T show minima at 0.006 and 0.01 M CTABr, while such a minimum is not visible at 0.02 M CTABr.