Boussoualem Mourad, Roussel Frédérick, Ismaili Mimoun
Laboratoire de Thermophysique de la Matière Condensée, Equipe de l'UMR CNRS 8024, Université du Littoral-Côte d'Opale, MREI, 59140 Dunkerque, France.
Phys Rev E Stat Nonlin Soft Matter Phys. 2004 Mar;69(3 Pt 1):031702. doi: 10.1103/PhysRevE.69.031702. Epub 2004 Mar 4.
The thermophysical, dielectric and electro-optic properties of polymer-dispersed liquid crystal (PDLC) films made of monodisperse polystyrene (PS) and 4-n-pentyl-4(')-cyanobiphenyl (5CB) are investigated by polarized optical microscopy, differential scanning calorimetry, ac impedance analysis, and forward transmittance measurement technique. The PS-5CB system exhibits an upper critical solution temperature (UCST) shape phase diagram with a wide isotropic+isotropic (I+I) miscibility gap between the isotropic and nematic+isotropic (N+I) regions. An absorption domain in the dielectric spectrum of PDLC films was clearly observed at low frequency, and unambiguously assigned to the confined liquid crystalline phase in both nematic and isotropic states. The correlation between the dielectric and electro-optical results for PS-5CB (30:70) samples has shown that in the vicinity of the low frequency absorption domain ( approximately 200 Hz at T=25 degrees C), a drastic decrease in the optical transmittance of the film occurs. This phenomenon can be related to an interfacial polarization process resulting from a charge accumulation at the droplet-polymer interface (Maxwell-Wagner-Sillars effect).
通过偏振光学显微镜、差示扫描量热法、交流阻抗分析和正向透射率测量技术，研究了由单分散聚苯乙烯（PS）和4-正戊基-4'-氰基联苯（5CB）制成的聚合物分散液晶（PDLC）薄膜的热物理、介电和电光性质。PS-5CB体系呈现出具有上临界溶液温度（UCST）形状的相图，在各向同性和向列相+各向同性（N+I）区域之间存在宽的各向同性+各向同性（I+I）混溶间隙。在低频下，在PDLC薄膜的介电谱中清楚地观察到一个吸收域，并且明确地将其归因于向列相和各向同性态中的受限液晶相。PS-5CB（30:70）样品的介电和电光结果之间的相关性表明，在低频吸收域附近（在T = 25℃时约为200 Hz），薄膜的光学透射率急剧下降。这种现象可能与液滴-聚合物界面处电荷积累引起的界面极化过程有关（麦克斯韦-瓦格纳-西拉斯效应）。
