Phase Behavior of Binary Polymer Blends Doped with Salt

Binary polymer blends are predicted to demonstrate unusual phase behavior when doped with salt, after accounting for ion-induced cross-linking and self-energy effects. In this work, we present cloud point measurements on low molecular weight poly(ethylene-alt-propylene)/polyethylene oxide (PEP/PEO) binary polymer blends doped with various salts, and explore the influence of the concentration of the salt and the size of the anion on the phase diagram. The addition of salt dramatically decreases the miscibility of the binary blends and results in an asymmetric cloud point profile. The coexistence curve is found to deviate from the cloud point profile, which can be attributed to the effect of the redistribution of ions between the two coexisting phases. Experimental data are compared with the phase diagrams obtained from a recent theory of Ren, Nakamura and Wang and may serve as a benchmark for future experimental design of polyelectrolyte systems and further theoretical research.