Emulsions stabilized with PEO-PPO-PEO block copolymers and silica

The specific behavior of poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) (PEO-PPO-PEO) tri-block copolymers in aqueous solutions was studied in the presence of vinyl acetate (VAc) and colloidal silica. Several factors controlling specific interactions were investigated, the block copolymer molecular weight and hydrophilic/hydrophobic balance (changed via the PEO/PPO ratio), temperature and silica content. Emulsion formation for water/VAc/copolymer mixtures was investigated for different water/VAc ratios, three temperatures (20, 40 and 60 degreesC) and three block copolymer concentrations. It was proven that silica addition in the VAc/water/PEO-PPO-PEO tri-block copolymer mixtures results in a synergetic effect of the (copolymer-silica) system that act as a stabilizer For the emulsion droplets. Depending on the block copolymer content and HLB as well as on the temperature, emulsion droplets with different diameters are obtained. Efficient encapsulation of VAc can be promoted using silica particles and PEO-PPO-PEO block copolymers with a proper choice of the polymer and temperature. (C) 2002 Elsevier Science B.V. All rights reserved.