MIXING AND PHASE-SEPARATION IN LIQUID-CRYSTAL MATRIX SYSTEMS - DETERMINATION OF THE EXCESS SPECIFIC-HEAT OF MIXING

We report the first direct measurement of DELTAC(mix), the excess specific heat due to mixing of a binary system, a liquid crystal (LC)/matrix mixture. Both LC concentration and matrix cross-linking (cure) affect mixing. In uncured systems we observe a steplike decrease in specific heat due to a negative value of DELTAC(mix). A plot of DELTAC(mix) vs LC content shows a minimum, consistent with Flory-Huggins theory; the theory also gives the upper critical solution temperature phase diagram and sign of DELTAC(mix). Partially cured samples also exhibit DELTAC(mix) transitions which persist until cure is almost complete and demixing is essentially irreversible.