Interactions between poly(vinylpyrrolidone) and ionic surfactants at various solid/water interfaces: A calorimetric investigation

The interaction of a neutral hydrophilic polymer poly(vinylpyrrolidone) (PVP) with sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) was studied at various solid/liquid interfaces and different surfactant coverages using an essentially calorimetric method of investigation. It was observed that the differential enthalpy of dilution of PVP in the presence of the bare particles of alumina, titanium dioxide and silica is endothermic in the two first cases and exothermic in the presence of silica. An extremum of enthalpy of dilution was observed at the same polymer concentration in the presence of the three types of mineral oxide particles. The interaction between coadsorbed PVP and SDS was found to be endothermic on alumina at all surfactant coverages, whereas it was exothermic between PVP and SDS micelles in bulk aqueous solutions. This observation suggests that PVP adsorption on alumina occurs through interactions between adsorbed PVP moieties and SDS monomers and does not involve adsorbed surfactant aggregates. CTAB adsorbed strongly on silica and on titanium dioxide above their respective isoelectric points. However, the PVP enthalpy change upon addition of the polymer to the CTAB-coated mineral oxides was small, confirming the absence of strong interactions between cationic surfactants and neutral hydrosoluble polymers at solid/liquid interfaces. These results indicate that if the interaction between a surfactant and a polymer is small in the bulk aqueous solution, it will be only marginally changed by forcing both types of solute species to interact at a solid/liquid interface. (C) 1997 Elsevier Science B.V.