Investigation of the Segregative Phase Separation Induced by Addition of Polystyrene to AOT Oil-Continuous Microemulsions

Abstract

The effect of different molecular weight polystyrenes (PS) on the phase behavior of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT)/water/cyclohexane oil-continuous microemulsions was investigated. The surfactant-covered water droplets were treated as a pseudocomponent in the mixture, and ternary polymer/droplet/oil phase diagrams were established as a function of microemulsion droplet radius (2.7 or 3.8 nm), PS molecular weight (18 700, 45 730, and 700 000), and temperature. The different polymer radii of gyration (Rg) and droplet radii (Rd) resulted in a broad range of size ratios (Rg/Rd = q) being accessible: 0.9 ≤ q ≤ 8.9. The aims of this work were to study polymer−particle segregation in this well-defined system, where both polymer size, particle size, and hence size ratio could be controlled and where polymer−solvent interactions could be varied across the θ temperature, and to compare the fluid−fluid binodal phase diagrams with those predicted theoretically. It turns out that the polystyrene chains in AOT oil-continuous microemulsions behave almost as ideal chains, over all q values and temperatures investigated.