ABSTRACT:The electro-optic performance characteristic of polymer-dispersed liquid crystal (PDLC) composite films out of poly(vinyl butyral) (PVB) and nematic liquid crystal (E7) have been studied for a wide range of PVB-E7 composite compositions (20 -70 wt % of E7). Composites were prepared by solvent casting from chloroform at room temperature. A scanning electron microscopy study showed that a E7 phase is continuously embedded in chink-like structure of PVB matrix. Optical transmittance of the composite films (of 60 and 70 wt % loading of E7) under an alternating current (ac) electric field (0-250, V p-p ) and frequency (50 Hz to 1 KHz) were measured employing HeONe laser ( ϭ 632.8 nm). The results indicate that the (PVB-E7) composite exhibits a memory effect. In the memory state, higher transmittance is preserved without applying voltage. The memory state can be erased and changed to the scattering Off-state by heating the film to the clearing temperature of the liquid crystal.

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Composite films composed of poly(methyl methacrylate-co-butyl acrylate) (PMMABA) and nematic-type liquid crystals E7 and E8 (commercial products from E. Merck, Darmstadt, Germany) were prepared through solvent casting in chloroform. The morphology and electrooptic responses were studied. Scanning electron microscopy observations showed that the liquid-crystal phase (E7 or E8), as larger, elongated, interconnected cavities, was continuously embedded in a spongelike PMMABA matrix. At a specific level of the liquid-crystal (E7 or E8) loading (30/70 wt %), the effects of the voltage, temperature, and frequency of an applied alternating-current electric field on the transmittance of the composite films were measured with a He-Ne laser (wavelength 5 632.8 nm). The results were interpreted in terms of the aggregation structure, interfacial interaction, and solubility of the liquid crystal in the matrix polymer. The results indicated that, under these experimental conditions, the output could be controlled to a desired level by the selection of suitable liquid crystals to prepare polymer-dispersed liquid-crystal, electrooptic, active composite films with a response time of the order of only milliseconds or less.