The effect of pressure on the liquid–liquid phase equilibrium of two polydisperse polyalkylsiloxane blends

Abstract

The effect of pressure-induced immiscibility in polymer blends is investigated by experimental and theoretical methods. Experimental data of cloud point curves and critical points are obtained by turbidity measurements. The chosen system is a mixture of polydimethylsiloxane and polyhexylmethylsiloxane which is one of the very few polymer blends exhibiting pressure-induced immiscibility. This unusual behaviour is related to a critical temperature minimum of the critical curve and cloud point isopleths at positive pressure in the temperaturepressure diagram. The effect of the chain length on the critical temperature minimum is investigated here based on theoretical models. The effect of different attraction strength between the polymer segments on the critical temperature minimum is traced in a global phase diagram. In addition, we investigate the appearance of a small closed-loop of miscibility caused by the combination of the critical temperature minimum at positive pressure with a double-humped or bimodal cloud point curve. Such miscibility window can make it possible to process composit materials from incompatible polymers.

Solvent H/D isotope effects on miscibility and Θ-temperature in the polystyrene–cyclohexane system

“…Singh and Van Hook 24 estimated this effect for small-molecule systems to be as negligible as 10 À6 bar À1 . In accordance with these results, from an empirical equation 37,38 for the pressure influence on the critical temperature and concentration one can infer that:…”

Phase behaviour of a wheat protein isolate

“…A sharp drop of the transmitted light is observed for a monomeric system whereas a broader turbidity curve is observed for polydisperse or multimodal polymer systems. 58,59 For F > 0.12, the cloud point temperature increases again with increasing F as observed by Dill and Alsberg in 1925. This increase of the cloud point for high F is associated with a structural transition that might be either an equilibrium phenomenon such as a liquid-solid transition or a non-equilibrium phenomenon such as gelation or aggregation.…”

Liquid–liquid phase equilibria in nitrobenzene–hexane critical mixture under negative pressure

“…Although the critical concentration depends on the pressure, the change can be neglected in this pressure range. 26,27 The critical temperature under atmospheric pressure and the electric conductivity (s ¼ 3 Â 10 À6 ) suggest the negligible presence of contamination in the tested mixture. Nitrobenzene (Fluka) was triply distilled before the tests.…”