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.

Numerical calculations reveal that the target and spiral growth patterns in spherulites can be generated from the time-dependent Ginzburg-Landau equations (model C) by coupling a conserved compositional order parameter and a nonconserved crystal ordering parameter. Of particular interest is that the periodic concentric rings (target) or the spirals at the spherulitic core remain stationary in both the crystal (orientational) ordering field and the concentration field. Another intriguing observation is that the growth of target and spiral spherulites occurs in a stepwise fashion in synchronism with the rhythmic energy dissipation during crystallization. PACS numbers: 61.41. + e, 64.70.Dv, 81.10.AjSpiral and target patterns are commonly observed in excitable media and nonlinear dissipative systems involving chemical waves, liquid crystal ordering, and biological organization [1]. Similar spiral and target patterns have also been found experimentally during crystallization of polymers, organic, and inorganic materials [2-5]. One major difference is that the core of the spiral crystal is stationary as opposed to the excitable media where the core is constantly oscillating. Although a similarity in patterns does not automatically guarantee that the origin is the same, it is worth investigating the pattern forming aspects of polymer crystallization from a new perspective of phase transitions.In atomic crystals, crystallization phenomena have been generally analyzed in the context of the classical macroscopic models of phase transitions [6,7]. The governing equations treat thermodynamic variables, such as temperature and composition of the individual phases, independently with a discrete interface of zero thickness. The discontinuity in the thermodynamic variables and in the gradients often presents difficult mathematical formulations and numerical singularities [8]. Recently, a new microscopic theory has been proposed, often known as a phase-field model [8,9], by incorporating the free energy functional for a crystal phase transition into the time-dependent Ginzburg-Landau-equation model C (TDGL model C) [10][11][12]. This phase-field model has been employed in the growth of atomic crystals and recently extended to the phase transitions of binary metal alloys [10] and eutectic crystal growth [13].The present paper is a first attempt to analyze the pattern forming aspects of polymer crystallization in the context of the TDGL model C equations [11,12] pertaining to phase transitions. The purpose of this paper is to demonstrate that the target and spiral growth patterns in polymer spherulites can be generated from the TDGL model C equations. In this model, we consider the system as a whole by defining the crystal ordering as a phase field to characterize the phase (or state) of the system at each point in time ͑t͒ and space ͑r͒. We then couple the conserved concentration (or number density) and nonconserved orientational order parameters in the coupled TDGL model C equations in conjunction with the Landau-type double-wel...

Palffy-Muhoray, P.; Mustafa, M.; and Kyu, Thein, "Polymerization-Induced Phase-Separation in a Liquid-Crystal-Polymer Mixture" (1993). College of Polymer Science and Polymer Engineering. 68.We have used light scattering to study the kinetics of polymerization-induced phase separation in a liquid-crystal-polymer mixture. The evolution of the structure factor is compared with scaling predictions for thermally quenched systems. We have also observed a cascading phenomenon where phase separated domains become unstable and undergo phase separation for a second time.

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