Marc Lindheimer

Interfacial aggregation of nonionic surfactants onto silica gel: Calorimetric evidence

Abstract The search for the origins of the macroscopic interfacial phenomena, the adsorption layer structure, and the nature of interactions between solid and surfactant molecules and between molecules at adsorbed states has led us to a calorimetric investigation of adsorption. The adsorption of nonionic surfactants onto the hydrophilic surfaces of silica gel has been studied by batch microcalorimetry for a wide range of coverages. Differential molar enthalpies of adsorption corresponding to the adsorption processes have been obtained. The microcalorimetric method for the investigation of adsorption from solution is shown to be a very sensitive tool for the elucidation of the adsorption mechanism. The calorimetric results indicate that there are at least two kinds of interactions between nonionic surfactant molecules and the silica surface, the first one being due to a direct interaction between the polar parts of molecules and the surface (exothermic effect) and the second resulting from lateral interactions between the hydrophobic chains, leading to the formation of interfacial aggregates (endothermic effect). The principal conclusion resulting from the present investigation is that after the adsorption of individual “gaseous” surfactant molecules which probably constitute nucleation sites, there is the formation of interfacial micelles. The main driving forces for the formation of aggregates are of the same nature as those for the formation of micelles in the bulk solution.

Heat capacities and volumes of sodium alkylbenzene sulfonates in water

The densities and heat capacities per unit volume of the homologous sodium p-alkylbenzene sulfonates, for alkyl groups equal to ethyl, n-butyl, n-hexyl, n-heptyl, and n-octyl, were measured in water at 25°C and also at 40 and 55°C for n-octyl. The derived apparent molar volumes and heat capacities were fitted with a recently developed mass-action model (J. E. Desnoyers, G. Caron, R. DeLisi, D. Roberts, A. Roux, and G. Perron, J. Phys. Chem. 87, 1397, 1983) modified to take into account long-range coulombic forces between monomers and interactions between micelles. There appears to be a small change in the heat capacities at high concentrations of sodium n-octylbenzene sulfonate which is consistent with the transition observed by other authors.

Micellar Structure in Intestinal Bulk — Relations with Mucosal Uptake

From measurements of translational self-diffusion coefficients and from solubility characteristics of bile salt mixed micelles, we have investigated some molecular associations between the major lipids of the intestinal aqueous content in an attempt to correlate the cholesterol flux into the intestinal mucosal cells with the structure of micellar solutions.