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.

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Miscibility phase diagram and phase separation dynamics of a mixture of a flexible polymer and a monomeric liquid crystal, hereafter called a polymer dispersed liquid crystal (PDLC), have been investigated. A theoretical calculation was carried out for predicting an equilibrium phase diagram of a PDLC system by taking into consideration Flory-Huggins (FH) free energy of mixing of isotropic liquid phases in combination with Maier-Saupe (MS) free energy of nematic ordering of the liquid crystal. The combined FH-MS theory predicts a "tea-pot" phase diagram in which liquid-liquid phase separation is overlapped with an isotropic-nematic coexistence region. A temperature-composition phase diagram of a mixture of hydroxyl functionalized polymethyl methacrylate (PMMA-OH) and eutectic nematic liquid crystals (E7) was established by light scattering and differential scanning calorimetry. This phase diagram can be characterized as an upper critical solution temperature exhibiting liquid-liquid phase separation between the polymer and the isotropic phase of the liquid crystal. The nematic-isotropic transition occurs at high liquid crystal compositions. The calculated phase diagram was found to conform well with the cloud point phase diagram. The dynamics of phase separation was investigated by means of light scattering and optical microscopy. The time-evolution of structure factor was analyzed in terms of a power law.

Miscibility of segmented rigid-rod polyimide (PI), viz., biphenyl dianhydride perfluoromethylbenzidine (BPDA-PFMB), and flexible polyether imide (PEI) molecular composites was established by differential scanning calorimetry. The composite films of BPDA -PFMB/PEI were drawn at elevated temperatures above their glass transitions. Tensile moduli of the films were evaluated as a function of composition and draw ratio. Molecular orientations of polyimide were determined by birefringence and wide-angle X-ray diffraction. The crystal orientation behavior of the 80/20 BPDA-PFMB/PEI was analyzed in the framework of the affine deformation model.Recently, various types of rigid-rod polyimide (PI) derivatives and polyether imide (PEI) molecular composites were found to be completely miscible QJ. This miscibility has been ascribed to similarity of the imide structure between PI and PEI. The tensile modulus and strength of bulk molecular composites showed remarkable improvement with increase of the polyimide content. Although the molecular reinforcement of the flexible PEI matrix via incorporation of the PI rigid-rod molecules appears unequivocal, the molecular weight of the above rigid-rod polyimide derivatives was rather low as exemplified by their low inherent viscosity (2.2-2.63 dl/g ) (1). Such low molecular weight systems tend to favor miscibility. Hence, we have selected a segmented rigid-rod polyimide, viz., biphenyldianhydride perfluoromethylbenzidine (BPDA-PFMB) having a higher molecular weight, (i.e., inherent viscosity of 4.9 dl/g) and a high aspect ratio to ascertain the concept of molecular composites. It is promising to achieve true miscibility between the segmented rigid-rod BPDA-PFMB and the flexible PEI because of their similar imide structure.The highly drawn rigid-rod polymers generally show extremely high modulus and high strength close to their theoretical values. However, the compressive strength of these rigid materials is rather poor, thereby prohibiting their applications as a