A Calorimetric Study of Phase Separation in Liquid Crystal/Matrix Systems: Determination of the Excess Specific Heat of Mixing

Abstract

Abstract The effects of concentration and state of cure on mixing and phase separation of binary systems of a low molecular weight liquid crystal (LC) and an organic matrix have been determined for the first time. We found that, as temperature is increased, mixing in uncured LC/matrix systems is accompanied by a step-like decrease in specific heat at T mix, the mixing temperature. This decrease is due, for the most part, to the (negative) excess specific heat of mixing. ΔC mix. The excess enthalpy of mixing. ΔH mix, may also contribute to the thermal effect. A plot of ΔC mix versus LC concentration exhibits a minimum, as expected from theory. Such a plot for a mixture of a specific LC (E7) with uncured matrix (NOA65) allows us to estimate the solubility limit of E7 in the matrix-rich phase (∼15%) and of NOA65 in the LC-rich phase (∼5%). Uncured E7/NOA65 mixtures exhibit phase diagrams with an upper critical solution temperature (UCST) slightly above 300 K. To avoid undesired phase separation prior to fina...