Interaction of poly(vinyl pyrrolidone) with fumed silica in dry and wet powders and aqueous suspensions

Abstract

Abstract Interaction of poly(vinyl pyrrolidone) (PVP) with fumed silica is of interest because of possible medicinal applications of their appropriate mixtures. The PVP/silica blends were studied in the form of dry and wet powders and aqueous suspensions by means of the adsorption, 1 H NMR, infrared spectroscopy, thermally stimulated depolarisation (TSD), electrophoresis, photon correlation spectroscopy, and rheology methods. Mechanical mixing of dry polymer and dry silica powder does not lead to the distribution of PVP on the silica surface. However, the diffusion of PVP molecules at a wet silica surface is promoted by water or ethanol adsorbed from saturated vapour. The polymer forms relatively uniform and dense adsorption layer with no the use of the solution, which is of importance from the practical point of view. Adsorbed PVP adds the effective hydrodynamic diameter of small particles and reduces the size of large swarms of silica particles, affects their ζ potential, modifies the hydrogen bond network in the interfacial water and its Gibbs free energy. These effects appear in the thermally stimulated depolarisation and 1 H NMR spectra. The viscosity (η) increases with increasing concentrations of oxide and polymer at their constant ratio γ=CPVP/CSiO2, but at a constant CSiO2, η depends nonlinearly on CPVP. Dried PVP/silica powders possess the pore size distribution depending on a treatment technique. Obtained results are useful for deeper understanding of regularities in the system PVP/fumed silica in liquids and dried powders.