Investigation of the segregative phase separation induced by addition of polystyrene to AOT oil-continuous microemulsions

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 (R_g) and droplet radii (R_d) resulted in a broad range of size ratios (R_g/R_d = 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.