Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly(methyl methacrylate)
Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly(methyl methacrylate)
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DOI：
10.1016/j.jnoncrysol.2012.06.034
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发表时间：
2012-09
影响因子：
3.5
通讯作者：
S. Parab;M. Malik;R. Deshmukh
中科院分区：
文献类型：
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作者：
S. Parab;M. Malik;R. Deshmukh
以聚甲基丙烯酸甲酯和向列型液晶E44为原料，采用溶剂诱导相分离法制备了聚合物分散液晶复合膜。在本研究中，我们报道了液晶浓度对复合薄膜的电光和介电性能的影响。从液晶与聚合物的相分离、液晶液滴的形状和大小、界面电荷层效应、液晶负载量以及液晶在聚合物基质中的相容性等方面对实验结果进行了解释。用傅里叶变换红外光谱和差示扫描量热法研究了界面两相的相容性。形态研究表明，液晶相嵌入在海绵状的聚甲基丙烯酸甲酯基质中，且随着E44含量的增加，液晶相的分布更加均匀。用He-Ne激光器(波长632.8 nm)作为光源，测量了这些复合薄膜在外加交流电场(0-200Vp，50-1000 Hz)和宽温度范围内的电光行为。结果表明，聚甲基丙烯酸甲酯/E44(30/70)wt.%的复合材料比其他浓度的复合材料具有更显著的性能。所有复合材料的性能都随着施加电压和温度的不同而不同。在20~20 MHz的频率范围内和24~100℃的温度范围内，对聚合物分散液晶的介电性能进行了测量。观察到液晶液滴界面与聚合物基质之间由于界面电荷积累而产生的Maxwell-Wagner效应。
Polymer dispersed liquid crystal composite films were prepared from poly(methyl methacrylate) and nematic liquid crystal E44 by solvent induced phase separation method. In the present investigation we report effect of liquid crystal concentration on the electro-optical and dielectric properties of the composite films. The results were interpreted in terms of phase separation of liquid crystal and polymer, shape and size of liquid crystal droplet, interfacial charge layer effect, liquid crystal loading and miscibility of liquid crystal in the polymer matrix. The miscibility between two phases at interface was investigated by employing Fourier‐Transform Infrared Spectroscopy and differential scanning calorimetry. Morphological study showed that liquid crystal phase is embedded in a spongy poly(methyl methacrylate) matrix and homogeneous distribution increased with increasing E44 content. Electro optical behavior of these composite films under the condition of an externally applied AC electric field (0–200 Vp-p, 50–1000Hz) and wide range of temperature was determined using He–Ne laser (wave length 632.8nm) as a light source. It was found that Poly(methyl methacrylate)/E44 (30/70)wt.% composite has more significant properties than the other concentrations. The performance of all composites showed variations with respect to applied voltage as well as temperatures. Dielectric measurement of polymer dispersed liquid crystals has been carried out in the frequency range from 20Hz to 20MHz and over the temperature range from 24°C to 100°C. The Maxwell–Wagner effect due to interfacial charge accumulation between boundaries of liquid crystal droplets and surrounding of polymer matrix has been observed.