Abstract
The phase diagrams and the amount of emulsion phase in water/vinyl acetate (VAc)/block copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) systems depend on temperature. In water/VAc mixtures, the PEO-PPO-PEO block copolymers exhibit a phase transition (micellisation) at ∼40°C and a conformational transition at 55°C. At the phase transition temperature, the experimental findings, which have been obtained by dynamic light scattering (DLS), evidence the formation of aggregates. In these mixtures, the onset of gel formation occurs at a lower polymer concentration than in the water. At temperatures higher than the phase transition temperature, water becomes a bad solvent for PEO and the disruption of the aggregates is produced by the contraction of PEO chains. The VAc molecules are eliminated outside the micelles. The restructuring of the solvent in the micelles proximity is followed by the increase of the emulsion percentage.
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