Study of the physicochemical properties of silica powder and the stability of organic-inorganic hybrid emulsion in the presence of ethanol

The physicochemical properties of silica powder and stability of organic-inorganic hybrid emulsion were investigated. Silica-polymer hybrid latex particles with petal-like morphology were synthesized by emulsion polymerization using a nonionic surfactant OP-10, an anionic surfactant Dowfax2A1, copolymerization of mixture monomers (MMA-St-BA-AA monomers with molar ratios of 1:1:1.2:0.1), and modified silica powder in the presence of ethanol. The influence of several parameters such as pH values of the suspension, modified silica, ethanol, and monomer on the stability of organic-inorganic hybrid emulsion, latex particle size, and silica content in hybrid polymer was investigated. The experimental results indicate that the amount of surfactant adsorption only was reduced slightly in the presence of ethanol and the displacer effect of ethanol is limited, but ethanol leads to an increase of zeta potential of silica (i.e., a decrease of negative surface charge), and strongly attracts anionic oligomer formed in water onto the surface of silica, thereby promoting the uptake of polymer and monomer from the continuous phase. Silica particles modified by gamma-methacryloxy propyl trimethoxy silane (KH-570) had a proclivity for copolymerization with acrylate monomer due to surface-unsaturated double bond, good compatibility with the polymer due to a significant carbon content that originated from KH-570, low surface silanols group and relatively high zeta potential, thereby improving the SP percentages of hybrid emulsion. Also the weak acid environment leads to an increase of zeta potential of silica and improvement in the stability of hybrid emulsion. Particle formation was predominated by the interaction of the polymer with the silica particles in the earlier stage of polymerization. Optimal conditions were found to obtain a petal-like polymer layer around silica and to preserve the stability of hybrid particles. (C) 2008 Elsevier B.V. All rights reserved.