Electro-optical studies on polymer dispersed liquid crystal composite films. II. Composite of PVB/E44 and PMMABA/E44
Electro-optical studies on polymer dispersed liquid crystal composite films. II. Composite of PVB/E44 and PMMABA/E44
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DOI：
10.1080/713738767
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发表时间：
2002-01-01
影响因子：
0.7
通讯作者：
Kunte, VV
中科院分区：
文献类型：
--
作者：
Kalkar, AK;Kunte, VV
利用光散射技术研究了PVB/E44和PMMABA/E44复合膜的聚集态和电光效应。采用溶剂蒸发法制备了复合薄膜。扫描电子显微镜观察表明，E44相连续嵌入海绵状PVB和PMMABA基体聚合物中。采用He-Ne（波长632.8 nm）激光器作为光源，测定了复合膜在外加交流电场（0-240 Vp-p; 50、100、500和1 KHz）、温度（28 ℃）和膜厚（10 ± 2 μ m）条件下的电光响应。具有正介电各向异性的PVB/E44和PMMABA/E44的复合膜表现出特征可逆的光散射-光透射切换，强烈依赖于复合膜中的液晶（LC）通道的尺寸和形状。两种复合体系中液晶分子的电光响应都受到液晶分子在液晶-聚合物界面的可折叠性的影响。因此，界面极化的弛豫时间的分布对应于基体聚合物和LC之间的界面处的相容性状态。采用傅里叶变换红外光谱/衰减全反射（FT-IR/ATR）分光光度法和差示扫描量热法（DSC）研究了两相界面的相容性。结果表明，在一定条件下，输出可控制，响应时间在几毫秒以内，PVB/E44复合膜具有记忆效应。在去除施加的电压之后，存储器状态的透射率保持较长时间，其可以通过将膜加热到E44清除温度而被擦除到散射OFF状态。在PMMABA/E44复合材料的情况下，这表现出电光开关滞后，一个可能的机制，即外加电场诱导的PMMABA和E44的相混合将是一个主要原因的滞后进行了讨论。
Aggregation states and electro-optical effects based on light scattering have been investigated for PVB/E44 and PMMABA/E44 composite films. The composite films were prepared by solvent-evaporation technique. Scanning electron microscopy observations showed that E44-phase is continuously embedded in a sponge-like PVB and PMMABA matrix polymers. Electro-optical responses of the composite films under the conditions of an externally applied AC electric field (0-240 Vp-p; 50, 100, 500 and 1 KHz) temperature (28degreesC) and film thickness (10 +/- 2mum) were determined using He-Ne (wavelength 632.8 nm) laser as a light source. The composite films (of both PVB/E44 and PMMABA/E44) with positive dielectric anisotropy exhibited characteristic reversible light scattering-light transmission switching, strongly dependent on the liquid crystal (LC) channel size and shape in the composite films. The electro-optical response of LC molecules in both of the composite systems is influenced by the miscibility of the LC molecules at LC-polymer interface. Thus the distribution of relaxation time for the interfacial polarization corresponds to the miscibility state at the interface between matrix polymer and LC. The miscibility between two phases at interface was investigated by employing Fourier-Transform Infrared Spectroscopy/Attenuated Total Reflectance (FT-IR/ATR) spectrophotometry and differential scanning calorimetry (DSC). The results obtained indicate that under the conditions imposed the output can be controlled and the response time is on the order of several milliseconds or less.A memory effect is observed in PVB/E44 composite films. The transmittance of the memory state is preserved for a longer time after an applied voltage is removed, which can be erased to the scattering OFF state by heating the film to the E44-clearing temperature. In the case of PMMABA/E44 composites, which exhibit electro-optical switching hysteresis, a possible mechanism that the applied electric field-induced phase-mixing of PMMABA and E44 would be a main cause of hysteresis is discussed.