Temperature effects on optical parameters of liquid crystal binary mixtures exhibiting induced smectics phases
Temperature effects on optical parameters of liquid crystal binary mixtures exhibiting induced smectics phases
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DOI：
10.1016/j.molliq.2020.113251
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发表时间：
2020-08-01
影响因子：
6
通讯作者：
Devi, Thingujam Kiranmala
中科院分区：
文献类型：
--
作者：
Basumatary, Jwmwi;Nath, Aparna;Devi, Thingujam Kiranmala
研究了9种不同液晶混合物的双折射、折射率温度梯度、分子极化率、有效几何参数、有序参数和交叉温度等随温度变化的光学性质。这些混合物是通过混合两种纯向列相液晶化合物，即4-正戊基苯基-4-n‘-己氧基苯甲酸酯(ME60.5)和4-氰基苯基4’-正戊基苯甲酸酯(CPPB)制备的，其中，ME60.5是单向性化合物，CPPB是对映异构体。然而，发现混合物是诱导近晶相。用Hallers双折射外推法得到的理论拟合值与实验值吻合较好。观察到归一化极化率随温度的变化与折射率的变化规律完全一致。具有最高双折射的混合物的有效几何参数(α(Eg))在一定温度下表现出最大的AEG值。最后，用五种不同的方法计算了混合物的有序参数，所有混合物的有序参数的特征范围都在0.3-0.9之间。向列相前有序参数的突变是由于液晶混合物中诱导近晶相的存在。(C)2020爱思唯尔B.V.保留所有权利。
Temperature dependent optical properties like birefringence, temperature gradients of refractive indices, molecular polarizabilities, effective geometry parameter, order parameter and cross over temperatures have been investigated for nine different liquid crystal mixtures. These mixtures are prepared by mixing two pure nematic liquid crystal compounds, namely, 4-n-pentyl phenyl 4-n'-hexyloxybenzoate (ME6O.5) and 4-cyanophenyl 4'-n-pentyl benzoate (CPPB) where, ME6O.5 is a monotropic compound and CPPB is an enantiotropic compound. The mixtures however are found to be exhibit induced smectic phases. The theoretical fitting values obtained by using Hallers' extrapolated method of birefringence values agree quite well with the experimental values. It is observed that the normalized polarizability behaves exactly as refractive indices when it is plotted against temperature. The effective geometry parameter (alpha(eg)) of the mixture having highest birefringence shows highest value of aeg at certain temperature. Finally, order parameters of the mixtures have been calculated using five different techniques and for all mixtures the order parameters shows characteristics range from 0.3-0.9. The abrupt changes in order parameter before nematic phases are due to the existence of the induced smectic phases in the liquid crystal mixtures. (C) 2020 Elsevier B.V. All rights reserved.