We report on the morphological and thermal properties of polymer-dispersed liquid crystals (PDLCs) fabricated with frontal-polymerization-induced phase separation (FPIPS). Frontal polymerization is characterized by a rapid-conversion, high-temperature, and large-thermal-gradient environment. A comparison is made between the morphological and thermal properties of PDLCs fabricated with FPIPS and traditional thermal-polymerization-induced phase separation. Characterization includes differential scanning calorimetry to probe the glass and nematic-to-isotropic transitions and scanning electron microscopy to evaluate the phase-separated morphology. In addition, the frontal temperatures and velocities are reported for PDLCs fabricated with frontal polymerization.
Liquid crystalline mixtures of mono-and dimethacrylates were photopolymerized after macroscopic orientation of the monomers under a relatively weak magnetic field or via interaction with a unidirectionally rubbed polyimide substrate. Polymerization kinetics was followed by a thermoanalysis technique, and the transmitted light intensity was measured in real time. The macroscopic order parameter of one of the component comonomers (bearing a cyano group) incorporated into the polymer network prepared under different conditions was evaluated using IR dichroism. The results obtained for the cross-linked polymer network produced under the low strength magnetic field are compared with those for the polymer film produced by surface orientation.
Experimental SectionAll monomers were synthesized by the method of Portugal et al.19 All products were purified by column chromatography and recrystallized from 2-propanol. 1,1-Dimethoxy-l-phenylacetophenone (Irgacure 651, Ciba Geigy) was recrystallized from
Light-scattering and transmission properties of aligned nematic droplets dispersed in a solid polymer are studied. Theoretical evaluations of the differential and total cross sections are performed in the anomalous diffraction approximation. The corresponding attenuation coefficients are calculated in a single scattering approximation. The effect of interdroplet interference is discussed as well. Theoretical calculations are in agreement with experimental data obtained from thin films of polymer dispersed nematic droplets of micron size, aligned by an applied electric field.
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