Mixing and phase separation in liquid crystal/matrix systems: Determination of the excess specific heat of mixing

Abstract

We report the first direct measurement of Δ${\mathit{C}}_{\mathrm{mix}}$, 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 Δ${\mathit{C}}_{\mathrm{mix}}$. A plot of Δ${\mathit{C}}_{\mathrm{mix}}$ vs LC content shows a minimum, consistent with Flory-Huggin theory; the theory also gives the upper critical solution temperature phase diagram and sign of Δ${\mathit{C}}_{\mathrm{mix}}$. Partially cured samples also exhibit Δ${\mathit{C}}_{\mathrm{mix}}$ transitions which persist until cure is almost complete and demixing is essentially irreversible.