Effect of pore structure on surface characteristics of zirconium phosphate-modified silica

Three samples of silica of different pore structure-predominantly microporous, S1; mesoporous, S2; and nonporous, S3-were modified with zirconium phosphate and examined. Pore structure analysis showed that modification had taken place in wider pores of S1 leaving a totally microporous sample, and in large pores of S2 giving a mesoporous sample of narrower pore size distribution. The modification of the nonporous sample decreased the surface area and pore volume to a lower extent than in the other two samples, but resulted in a surface of lower energy toward N2. The different distribution of surface silanol groups on the surfaces of different porosity may result in variable pictures on the modified surfaces as reflected in the differences observed in Br?nsted acidity of modified surfaces. The use of these modified silica samples for amino acid adsorption (L-glutamic acid and L-alanine) indicated that both the isoelectric point of the amino acid and the distribution of surface groups on modified solids are controlling the adsorption process.     

Low temperature synthesis and characterization of porous anatase TiO2 nanoparticles

An ethanol solution of Ti-peroxy compounds was prepared from the ethanol solution of titanium isopropoxide (Ti(O-iPr)4) and H2O2. Heating of the ethanol solution of the Ti-peroxy compounds at 348 K formed a Ti-peroxy gel, and heat treatment of the gel at 348 K for more than 6 h formed gels that consisted of anatase nanoparticles. The diameter of the anatase nanoparticles increased from 9 to 15 nm as the heating time increased from 6 to 48 h. According to the results of the N2 adsorption measurement, the anatase nanoparticles had micropores, and the specific surface area (SBET) was in the range of 254 to 438 m2/g. The particle size, lattice strain, specific surface area, and photocatalytic activity of the anatase nanoparticles can be regulated by the heating time of the Ti-peroxy gel at 348 K.     

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.     

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.     

A structural study of amphiphilic PAMAM (poly(amido amine)) dendrimers in Langmuir and Langmuir-Blodgett films

Two amphiphilic PAMAM dendrimers are synthesized by attaching 12-hydroxydodecanoic acid (HA) chains to a poly(amido amine) (PAMAM) dendrimer core (including generation I and generation II). The limiting molecular area obtained from the surface pressure-area isotherm at the air/water interface suggests the edge-on configuration for both dendrimers in Langmuir films. The edge-on arrangement is also supported by the atomic force microscopic (AFM) studies of the Langmuir-Blodgett films.     

Thermodynamics of micellization of alkyldimethylbenzylammonium chlorides in aqueous solutions

Specific conductivities of alkyldimethylbenzylammonium chlorides (alkyl=decyl-, dodecyl-, tetradecyl-, and hexadecyl-) in aqueous solutions were measured as a function of molality and temperature. Critical micelle molalities (cmc) and degrees of ionization of the micelles, beta, were estimated from the dependence of the specific conductivity on molality. It was found that temperature dependence of cmc is U-shaped with a minimum shifting toward higher temperatures with a decrease in the chain length of the alkyl group. The temperature dependence of ln xcmc (where xcmc is the cmc in mole fraction units) was fitted to the equation of Muller, which we modified by taking into account the temperature dependencies both of beta and of change in heat capacity upon micellization. From the fitting parameters, Gibbs free energies, enthalpies, and entropies of micellization as a function of temperature were estimated.     

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.     

Use of the Gaussian Distribution Function as a Tool to Estimate Continuous Heterogeneity in Adsorbing Systems

In environmental engineering, adsorption and desorption are phenomena commonly referred to as responsible for pollution dispersion, retention, or retardation in soils, aquifers, and hydrologic systems. They are also used to remove organic pollutants from water or odorous compounds in gas deodorization. Most often, the characterization of the aqueous adsorption systems that are of engineering interest involves a narrow adsorbate concentration range and low values of the adsorbate concentration. The practice is to use the Freundlich equation that best fits most data and is considered sufficient to design adsorption contactors. However, no physical or chemical meaning can be associated with the values taken by the parameters. The present paper gives a new way of analyzing adsorption data, using an extension of the Freundlich equation and the Gaussian distribution function that makes it possible to associate parameter values of this extension with the adsorbate–adsorbent normal interaction energy, its heterogeneity, and to some extent the adsorbate–adsorbate lateral interaction energy.     

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.     

Electrooptics of β-FeOOH Particles in Aqueous Media: 1. Reversing-Pulse Electric Birefringence in the Low Field Region

Reversing-pulse electric birefringence (RPEB) of a nearly monodisperse iron(III) hydroxide oxide sample in the β-form (β-FeOOH) was measured at 25°C and at a wavelength of 633 nm in aqueous media in the presence of NaCl. The concentrations of β-FeOOH and added NaCl varied between 0.00111 and 0.0555 g/L and 0.03 and 2.0 mM, respectively. Except for the suspensions with high salt concentrations, each RPEB signal showed a dip or minimum in the reverse process upon electric field reversal, together with a smooth rise in the buildup and a fall in the decay process. The observed signals were analyzed with a new RPEB theory, which takes into account not only the permanent electric dipole moment (μ) but also the root-mean-square ionic dipole moment (m^21/2) due to the ion fluctuation in ion atmosphere, in addition to the field-induced electronic (covalent) dipole moment Δα′ E. The results showed that the slowly fluctuating moment of m^21/2 is by far the most predominant one for the field orientation of the β-FeOOH particle, though the permanent dipole moment μ may not be completely excluded. The rotational relaxation time of the whole particle was evaluated from the decay signal, while the relaxation time for fluctuating ions was estimated from RPEB signal fitting. The sign of the steady-state birefringence for β-FeOOH suspensions was positive without exception under the present conditions. The birefringence signals in the steady state (δ/d) were proportional to the second power of the applied field strength (E) in the low field region; thus, the Kerr law was verified to hold for β-FeOOH suspensions. The specific Kerr constant was evaluated for each suspension by extrapolating the values of δ/d to zero field (E→0).     

Effect of β-Cyclodextrin on the Photoinduced Charge Transfer in Sodium 1-Anilino-8-naphthalene Sulfate (ANS)/CdS Colloidal System

The S-center radical (ANS^·) of sodium 1-anilino-8-naphthalene sulfate (ANS) generated by photoinduced charge transfer in ANS/CdS and ANS/CdS/β-cyclodextrin(β-CD) systems has been studied by using spin trapping electron spin resonance techniques, UV-visible spectroscopic methods, and fluorescence spectroscopic methods. It was found that the S-centered radical (ANS^·) was produced by the charge transfer reaction between the ground state ANS and the positive hole h⁺(CdS) from the valence band of CdS colloids, by the charge transfer from the excited singlet state ¹ANS* to the conduction band of CdS colloids, or by both in the ANS/CdS and ANS/CdS/β-CD systems. The ESR signal intensity of the spin adduct (5,5′-dimethyl-1-pyrroline-N-oxide (DMPO)–ANS)^·, which is formed from ANS^· trapped by DMPO, in the latter system is 15 times stronger than that in the former system. The apparent association constants between ANS and CdS colloids in the absence and presence of β-CD determined from fluorescence quenching experiments are 1097 and 1606 M⁻¹, respectively. From ESR and fluorescence results, it is estimated that the efficiency of photoinduced charge transfer from ANS to CdS colloids in the ANS/CdS/β-CD system is 12.5 times that in the ANS/CdS system.     

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.     

The Heavy-Atom Effect on the Photophysics of Aromatic Hydrocarbons in the Presence of Solid Clays

The exchange of the original cation present on a Laponite clay (usually Na⁺) for heavy atoms such as Rb⁺, Cs⁺, and Tl⁺ significantly alters the emission characteristics of some aromatic hydrocarbons (p-terphenyl, naphthalene, pyrene, and biphenyl). The increase of the atomic mass of the cation induces a decrease of the fluorescence emission simultaneous with an increase of the emission in the region of lower energies of the spectra, ascribed to the phosphorescence of those hydrocarbons. Time-resolved experiments for the pyrene–clay system showed a decrease of singlet lifetimes for the heavier atoms. Hydrocarbon aggregates were also detected from both the emission spectra and the time-resolved studies. The “excimer-like” emission showed longer lifetimes (10–25 ns) than the monomolecular hydrocarbons (1–3 ns), as already found for other similar systems. The amount of aggregates increased for the heavier cations due to the smaller surface available on the clay particles. Experiments increasing the amount of Tl⁺ in samples containing a constant concentration of naphthalene allowed evaluation of the distance between the heavy atoms and the probe on the clay surface. The Perrin model treatment was used and resulted in approximately R₀=9.2 Å.     

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.     

Novel sintering behavior of polystyrene nanolatex particles in the filming process

The filming process of polystyrene nanolatex (NPS) particles was studied by a combination of various methods. For a constant annealing time of 1 h, the AFM images showed that the deformation and interdiffusion temperatures of NPS particles were ca. 90 and 100-110 degrees C, respectively. In spin-lattice relaxation measurements of solid state NMR, it is found that T1L, T1S, and PL increased significantly after annealing at 90 and 100 degrees C for 1 h. DSC results showed that there was a exothermic peak near Tg after annealing for 1 h at the elected temperatures below 95 degrees C; otherwise, the exothermic peak disappeared after annealing at 100 degrees C or above. The apparent density of NPS increased suddenly in the temperature range of 90-110 degrees C. The results indicated that the macromolecules are highly constrained in NPS particles, leading to higher conformational energy, with more free volume and segments less restricted, which are the driving forces for the particles sintering at a lower temperature compared to the micro-PS particles with larger diameter.     

Adsorption of polyacrylic acid and its copolymers with acrylonitrile on zinc oxide particles

Adsorption of polyacrylic acid and its copolymers with acrylonitrile, containing different quantities of carboxyl groups, on the dispersion of zinc oxide was investigated. The kinetics of polymer desorption was investigated based on data concerning the change in concentration of free carboxylic groups of polymer and zinc ions in solution. The concentration of free carboxyl groups decreases and the concentration of zinc ions in the liquid phase above the residue after separation of zinc oxide particles increases with time, reaching a constant value. The dependence of the concentration of free carboxyl groups and zinc ions in the liquid phase on the initial concentration of polymer in the plateau section of the kinetic curve was investigated. Adsorption isotherms of copolymers depend on their solubility in water and can be described by different mathematical models.     

Electroacoustic and Potentiometric Studies of the Hematite/Water Interface

The basic charging properties of nearly spherical hematite particles were studied by using potentiometric titration and the electroacoustic technique. Both the pH and the ionic strength dependence of the surface charge and the ζ-potential were studied in detail. For calculating the ζ-potential from mobility data a few different theories were used and obtained differences are discussed. At pH values higher than 7 and at high electrolyte concentrations (50 mM and 100 mM NaNO₃), it was difficult to fit the mobility data by using the full mobility spectra including both magnitude and phase angle at several frequencies. In this regime the best fits were obtained by using a theory for aggregated complexes (porous particles). From potentiometric titrations in 0.01, 0.1, and 1.0 M NaNO₃, parameters for a 1-pK Basic Stern Model were determined. The model was used to examine the possibility of correlating the experimentally determined ζ-potentials to the model-calculated potentials at the Stern plane. Qualitatively, the model predicted the correct ionic strength dependence of the ζ-potentials, and there was also a rather good quantitative agreement at high ionic strengths (50 and 100 mM NaNO₃). However, at lower ionic strengths the model predicted values up to 40% higher than those found from the electroacoustic study. Surface conduction behind the slip plane was discussed as a possible cause for this discrepancy.     

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.