液晶在电场和剪切耦合作用下的流变学行为

本文通过理论和实验对液晶 5CB在剪切和电场耦合作用下流变行为进行了研究. 采用液晶连续理论, 建立了包括界面锚定能, 弹性自由能, 介电自由能和流动能在内的系统 Gibbs自由能公式, 通过最小化系统自由能的方法求解液晶在剪切和电场耦合作用下的取向分布及其黏度变化, 从分子基础模型上揭示了液晶在耦合作用下的流变行为、微观机理及其影响规律, 并通过流变测试对此进行验证. 对比分析了理论和试验结果的误差和原因, 发现界面锚定效应对于液晶分子的取向和黏度具有重要影响. 理论和试验结果均表明, 液晶在电场作用下具有明显的电黏效应, 表现出非牛顿流变行为, 其黏度值由剪切和电场的竞争和耦合作用共同决定. 在外电场作用下液晶的黏度可以增加到初始值的 4倍左右, 液晶这种其自身黏度可随着外场 (例如运动速度) 改变的特性在一定的条件下可以自适应地满足不同工况对黏度的要求, 这对实现智能摩擦润滑具有重要的意义. 关键词： 液晶 流变行为 电黏效应 耦合作用

Study the coupling effect of shear and electric field on rheological behaviors of liquid crystals

The rheological behaviors of 5CB liquid crystal under the coupling effect of shear and electric field are investigated by theoretical and experimental study. Establish calculating equation of the system Gibbs free energy by adopting the continuum theory of liquid crystals which contains anchoring energy, elastic free energy, dielectric free energy and flow energy. Then the molecular orientation angle distribution and apparent viscosity of liquid crystal under the coupling effect are obtained by minimizing the Gibbs free energy, revealing the microscopic mechanism of rheological behaviors and influence rules of coupling effect from the molecular model. Meanwhile the calculated results are verified by rheological test. Comparative Analysis of the errors and reasons of theoretical and experimental results, which demonstrates that anchoring effect plays an important role in the molecular orientation and viscosity of liquid crystal. Both the theoretical and experimental results indicate that liquid crystals have electroviscous effect and behavior like non-Newtonian liquids under electric field. The viscosities of liquid crystals are determined by the coupling and competition action of shear and electric field, which can reach 4 times of its original value under electric field. This property of controllable viscosity is important in tribology, which can self-adaptively satisfy the requirement of viscosities for different working conditions as a "smart lubrication" under certain condition.
Keywords： liquid crystals rheological behavior electric-viscous effect coupling field