Spinodals in a Polymer-Dispersed Liquid-Crystal

Thermodynamic phase equilibria of a polymer dispersed liquid crystal (PDLC) consisting ofmonomeric 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 werecalculated by taking into consideration the Flory–Huggins (FH) theory for the free energy of mixingof isotropic phases in conjunction with the Maier–Saupe ~MS! theory for phase transition of anematic liquid crystal. The correspondence between the Landau–de Gennes expansion and theMaier–Saupe theory was found and the coefficients were evaluated. The calculation based on thecombined FH-MS theory predicted a spinodal line within the coexistence of the nematic–isotropicregion in addition to the conventional liquid–liquid spinodals. The cloud point phase diagram wasdetermined by means of polarized optical microscopy and light scattering for a polybenzylmethacrylate/E7 (PBMA/E7) PDLC system. The calculated phase diagrams were tested with theexperimental cloud points, assuming the Flory–Huggins interaction parameter simply to be afunction of temperature