Adsorption and Migration of Poly(Vinyl Pyrrolidone) at a Fumed Silica Surface

Abstract

A series of poly(vinyl pyrrolidone) (PVP)/fumed silica powder samples were studied using adsorption, FT-IR and AFM methods. Mild treatment (293 K for several hours) of PVP/A-300 powder with an added additional portion of A-300 in a glass reactor (2 dm 3 ) using a mixer (> 500 rpm which provided the powder as a pseudo-liquid state, PLS) led to the redistribution (migration) of the PVP molecules between silica particles previously covered by PVP and free of PVP. This time-dependent rearrangement of the adsorbed PVP molecules caused the formation of a denser polymer layer at the silica surface. The aggregate size of the primary silica particles with adsorbed PVP molecules decreased after treatment. The volume of macropores with a pore radius R p > 25 nm increased due to the decrease in the distances between aggregates in agglomerates because of the adhesive effect of the PVP molecules. However, the volume of micropores at R p < 1 nm decreased because of the penetration of the PVP molecules into the primary silica particle aggregates and the filling of gaps between adjacent particles. A decrease occurred in the amount of adsorbed water in the PVP layer exhibiting a maximum density.