Structure and Surface Polarity of Poly(vinylformamide-<i>co</i>-vinylamine) (PVFA-<i>co</i>-PVAm)/Silica Hybrid Materials

Abstract

Structure and surface polarity properties of poly(vinylformamide-co-vinylamine) (PVFA-co-PVAm)/silica hybrid materials are investigated by means of electrokinetic measurements, atomic force microscopy (AFM), and solvatochromic probes. AFM measurements show the complete covering of the silica surface with the PVFA-co-PVAm layer, which has a thickness between 0.5 and 2 nm depending on the content of the poly(vinylamine) (PVAm) component of the copolymer. The ET(30) surface polarity parameters of PVFA-co-PVAm/silica hybrid particles were investigated by two differently substituted Reichardt's dyes, 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate (1) and its lipophilic derivative 2,6-di(4-tert-butylphenyl)-4-[tris-2,4,6-(4-tert-butylphenyl-N-pyridino)]phenolate (2). Adsorption of the basic polymer PVFA-co-PVAm on silica significantly decreases the hydrogen bond donating capacity of the former silica surface, and therefore the ET(30) surface polarity decreases linearly with increasing the content of the PVAm component of the copolymer. Furthermore, it is shown that ET(30) surface polarity values of the PVAm-co-PVFA/silica particles measured with 2 in toluene correlate with the isoelectric points determined by means of electrokinetic measurements in diluted aqueous electrolyte solutions.