Effect of a Semifluorinated Copolymer on the Phase Separation of a Fluorocarbon/ Hydrocarbon Mixture

Abstract

Fluorocarbons (C{sub n}F{sub 2n+2}) and hydrocarbons (C{sub n}H{sub 2n+2}) are mutually immiscible at room temperature, while they form clear and homogeneous mixtures at high temperatures. The phase separation curves of these systems show upper critical solution temperatures (UCST), which depend on the chemical formulas of the two liquids. In this paper we report the first observation of the mixing between perfluoroctane (PFO) and isooctane (FOCT) at low temperature upon addition of a semifluorinated diblock copolymer (F{sub 8}H{sub 16}). Further cooling results in phase separation or formation of solid gels, depending on the amount of copolymer added to the mixture. Phase diagrams, light-scattering, birefringence, and small-angle X-ray-scattering measurements indicate the presence of microdomains in the gel and in the liquid phase, depending on the temperature and on the copolymer volume fraction. 31 refs., 11 figs., 2 tabs.