Layer-by-layer deposition of open-pore mesoporous TiO 2- Nafion® film electrodes

The formation of variable thickness TiO2 nanoparticle-Nafion® composite films with open pores is demonstrated via a layer-by-layer deposition process. Films of about 6 nm diameter TiO2 nanoparticles grow in the presence of Nafion® by “clustering” of nanoparticles into bigger aggregates, and the resulting hierarchical structure thickens with about 25 nm per deposition cycle. Film growth is characterized by electron microscopy, atomic force microscopy, and quartz crystal microbalance techniques. Simultaneous small-angle X-ray scattering and wide-angle X-ray scattering measurements for films before and after calcination demonstrate the effect of Nafion® binder causing aggregation. Electrochemical methods are employed to characterize the electrical conductivity and diffusivity of charge through the TiO2-Nafion® composite films. Characteristic electrochemical responses are observed for cationic redox systems (diheptylviologen2+/+, Ru(NH3)3+/2+6, and ferrocenylmethyl-trimethylammonium2+/+) immobilized into the TiO2-Nafion® nanocomposite material. Charge conduction is dependent on the type of redox system and is proposed to occur either via direct conduction through the TiO2 backbone (at sufficiently negative potentials) or via redox-center-based diffusion/electron hopping (at more positive potentials)

FTIR ATR study of adsorption of trisiloxanes and hydrocarbon surfactants at hydrophobic solids from aqueous solutions

Kinetics of the integrated absorbance in C−H stretch region for ethoxylated trisiloxane and alkyl polyethoxylate surfactants on low- and highly hydrophobic surfaces has been measured by Fourier-Transform Infrared spectroscopy (FTIR) in the attenuated total reflection (ATR) mode. It has been found that regardless of the surface energy of substrate the absorbance of trisiloxanes continuously increases during the experiment (characteristic time scale is ten minutes), while the absorbance of alkyl polyethoxylate surfactants reaches equilibrium for tens of seconds on low hydrophobic and for a few minutes on the highly hydrophobic surfaces. The continuous growth of absorbance with increasing bulk concentration of surfactants has been detected in the case of trisiloxanes on both substrates even at concentrations above critical wetting concentration; while hydrocarbon surfactants attained the constant values of absorbance at concentrations above critical aggregation concentration. The results for alkyl polyethoxylate surfactants obtained from FTIR-ATR spectra are consistent with the results obtained by other authors used neutron and optical reflectometry. Influence of the length of hydrophilic chains on the value of the absorbance of surfactants has been analyzed. In the case of alkyl polyethoxylate surfactants the absorbance decreases with increasing the length of hydrophilic ethoxy groups. However, in the case of trisiloxane surfactants studied the above trend cannot be clearly traced. Some aspects associated with the relationship between adsorption of trisiloxanes at hydrophobic solid/liquid interfaces and spreading kinetics are discussed

Effect of selected non-ionic surfactants on the flow behavior of aqueous veegum suspensions

The aim of this work was to investigate the influence of some non-ionic surfactants, Tween 80 and Brij 98, on the viscosity and flow behavior of a commercial montmorillonite clay, Veegum Granules. The effect of different concentrations of the surfactants on the shear stress-shear rate rheograms of hydrated concentrated clay suspensions was determined by shear viscometry. The addition of either surfactant increased the plastic viscosity and the yield stress of the suspensions. Furthermore both surfactants altered the thixotropy of the suspensions to an extent that depended on both the surfactant concentration and the time of equilibration of the surfactant and Veegum. Brij 98 had a greater and more rapid effect. It is proposed that the surfactant polar head-groups anchor at the tetrahedral sheet surface, leaving the alkyl chains extending away from the edges and faces. Consequently, the alkyl chains undergo hydrophobic interactions that facilitate the association between the platelets and increase the physical structure within the suspension. Stereochemical differences between the polar groups may lead to differences in the way the surfactants associate with the tetrahedral sheet and hence their ultimate effect on the rheological behavior. There is a significant interaction between these surfactants and montmorillonite clays, and the rheological changes that occur could have a major impact on any pharmaceutical formulation that uses these ingredients