Electro-rheology study of a series of liquid crystal cyanobiphenyls: experimental and theoretical treatment
Electro-rheology study of a series of liquid crystal cyanobiphenyls: experimental and theoretical treatment
复制标题
一系列液晶氰基联苯的电流变研究：实验和理论处理
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
M. T. Cidade
中科院分区：
文献类型：
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作者：
P. Patrício;C. Leal;L. Pinto;A. Boto;M. T. Cidade
在这项工作中，我们研究了一系列的四个液晶（LC）氰基联苯的烷基中的碳原子数，从5到8（5CB-8 CB）的电流变行为。我们给出了不同温度和外部电场影响下的流动曲线，范围从0到3 kV mm-1，以及粘度作为温度的函数，对于相同的电场值，获得不同的剪切速率。在Leslie-Ericksen连续介质理论的框架下，对低分子量聚碳酸酯的行为进行了理论解释。在我们的分析中，指向矢取向角只是剪切速率与电场平方之比的函数-边界条件被忽略。通过拟合理论模型的实验数据，我们能够确定一些粘度系数和介电各向异性作为温度的函数。为了解释向列型-各向同性转变附近的流动曲线的行为，我们应用Olmsted-Goldbart的连续理论，该理论将Leslie-Ericksen的理论扩展到LC分子的排列程度也可以变化的情况。
In this work we study the electro-rheological behaviour of a series of four liquid crystal (LC) cyanobiphenyls with a number of carbon atoms in the alkyl group, ranging from five to eight (5CB–8CB). We present the flow curves for different temperatures and under the influence of an external electric field, ranging from 0 to 3 kV mm−1, and the viscosity as a function of the temperature, for the same values of electric field, obtained for different shear rates. Theoretical interpretation of the observed behaviours is proposed in the framework of the continuum theory of Leslie–Ericksen for low molecular weight nematic LCs. In our analysis, the director alignment angle is only a function of the ratio between the shear rate and the square of the electric field – boundary conditions are neglected. By fitting the theoretical model to the experimental data, we are able to determine some viscosity coefficients and the dielectric anisotropy as a function of temperature. To interpret the behaviour of the flow curves near the nematic–isotropic transitions, we apply the continuum theory of Olmsted–Goldbart, which extends the theory of Leslie–Ericksen to the case where the degree of alignment of the LC molecules can also vary.