Acid-base interaction of probes at silica surface. Microcalorimetry and adsorption.

The interaction of four benzyl derivatives with silica surface sites in anhydrous cyclohexane is investigated. The strength and extent of adsorption is determined from the Langmuir adsorption isotherm. The enthalpy of immersion is determined microcalorimetrically, which is recalculated to the enthalpy of adsorption. The aim is to distinguish between the Lewis-type (electron exchange) and Brønsted-type (proton exchange) of interaction by selecting methanol-acetone and acetic acid-methylamine, respectively as acid-base substituent in benzene. Moreover, the experiments were performed in anhydrous cyclohexane in order to screen out hydrocarbon interactions from the energy balance. The monomolecular adsorption is also distinguished from the bulk wetting of solids. The results are evaluated in terms of possible proton exchange in anhydrous media.

Adsorption of organic probes on silica through Lewis interactions: a comparison of experimental results and quantum chemical calculations.

The adsorption of organic probe molecules on a partly dehydroxylated silica (SiO(2)) surface has been studied in a non-aquatic and non-polar environment. These results were compared to, verified and explained by quantum chemical calculations on the same systems. Since the systems are water free and since the non-polar solvent cyclohexane is used in the experiments, the quantum chemical calculations are well comparable to the experimental results without any additional terms. The characterized surface was found to contain both Lewis acid and Lewis base sites and a good agreement between the experimentally determined and the calculated data was found.

A critical evaluation of the binary and ternary solid-oil-water and solid-water-oil interaction.

When determining the surface energies of solids the most frequently utilised method is to measure contact angles for particular probe liquids. The measured contact angles (usually measured in air) are then combined with published values of surface- and interfacial tensions of the liquids to give the surface energy of the solid. It is, however, very seldom that sufficient attention is paid to the impurities, to the experimental (e.g. saturated vapour) conditions chosen and to the heterogeneities (chemical and structural) of the solid surface. In this study five typical probe liquids: octane, hexadecane, diiodomethane, alpha-bromonaphthalene and water have been used to establish the dispersion component of the surface energy of the solid and the hydrophobic interaction occurring at the interface of four solids: hydrophobic/hydrophilic SiO2 and hydrophobic/hydrophilic TiO2. Two (solid/liquid) and three (solid/liquid/liquid) component systems were investigated. The results are compared with previously published results when Alkenyl Succinic Anhydride (ASA) was brought into contact with SiO2 under water. The preferential surface vapour pressure and liquid spreading of the one liquid over the solids in the absence and presence of a saturated liquid vapour were evaluated as sources of errors.

Alternative models for determining the surface energy components in offset printing.

Different ways of calculating surface energy components for substrates used in offset printing are compared. The results of the very useful van Oss-Chaudhury-Good bi-bidentate model (vOCG) are simplified to mono-bidentate and mono-monodentate models. The unbalance in the acid-base values often obtained by the vOCG model is strongly reduced when applying the simple mono-monodentate model. Moreover, the frequently encountered problem of negative square roots of the acid and base components is removed. An attempt to describe the ink transfer during offset printing by calculating theoretical works of adhesion between ink/plate and ink/paper is also made. The effect of paper roughness on the wetting was studied with atomic force microscopy (AFM).

Comparison of long-term indwelling catheters and bed-pads in the treatment of urinary incontinence in elderly patients.

Bed-pads and long-term indwelling catheters were compared in the treatment of urinary incontinence in two groups of eight elderly bedridden women. The same silicone catheter could be left in situ on average for 2 months. A detailed description of the changes of urinary bacterial flora in patients of both experimental groups is given. At the end of the 6 months' study all of the patients in both groups had significant bacteriuria (greater than or equal to 10(8) CFU/1), Proteus species being the most common pathogen in catheterised patients. The development of multiple resistance was observed in both groups, but it was more pronounced in the catheterised group. The indwelling catheter was more economical (P less than 0.001), but carried a higher risk of infection.