SPINODALS IN A POLYMER-DISPERSED LIQUID-CRYSTAL

Thermodynamic phase equilibria of a polymer dispersed liquid crystal (PDLC) consisting of monomeric liquid crystals and a polymer have been investigated theoretically and experimentally. The equilibrium limits of phase separation as well as phase transition of a PDLC system were calculated by taking into consideration the Flory-Huggins (FH) theory for the free energy of mixing of isotropic phases in conjunction with the Maier-Saupe (MS) theory for phase transition of a nematic liquid crystal. The correspondence between the Landau-de Gennes expansion and the Maier-Saupe theory was found and the coefficients were evaluated. The calculation based on the combined FH-MS theory predicted a spinodal line within the coexistence of the nematic-isotropic region in addition to the conventional liquid-liquid spinodals. The cloud point phase diagram was determined by means of polarized optical microscopy and light scattering for a polybenzyl methacrylate/E7 (PBMA/E7) PDLC system. The calculated phase diagrams were tested with the experimental cloud points, assuming the Flory-Huggins interaction parameter simply to be a function of temperature. © 1995 American Institute of Physics.