向列相液晶分子结构与黏度关系研究及BPNN-QSAR模型建立

Molecules structure and viscosity relationship of nematic liquid crystal and BPNN-QSAR model

用于光学、微波通信调谐等器件的向列相液晶材料需要具备高响应速度来实现应用需求.液晶器件响应速度与液晶的旋转黏度、液晶的双折射率等因素相关.微波器件用向列相液晶,常采用大π-电子共轭体系、大极性基团来提高液晶分子的双折射率和介电各向异性,实现宽相位调制量,也因此增大了液晶材料黏度,影响了微波器件的响应速度.本文以液晶黏度因素为主线,对本课题组设计合成的42种向列相液晶在25℃时的黏度用旋转流变仪进行测试,从液晶化合物的结构角度分析影响液晶黏度的因素.首次建立向列相液晶分子结构与黏度的BPNN-QSAR定量构效模型,模型测试组预测值跟真实值之间的相关系数q^(2)=0.607>0.5,说明模型可用于液晶化合物的黏度性能预测,并对影响黏度性能的分子结构描述符进行了探讨.从实际应用出发结合本课题研究,设计了两个系列7个大双折射率液晶分子,BPNN模型测试黏度量度小于同类型分子,实验测试值与模型测试值相近.

Nematic liquid crystal materials designed for optics,microwave communication tuning,etc.need high response speed,which is related to the rotational viscosity and the birefringent index of the liquid crystal.In order to achieve a wide tuning range of phase modulation,the nematic liquid crystals often employ largeπ-electron conjugated systems and large polar groups to enhance the birefringence and dielectric anisotropy of the liquid crystal molecule,which,however,increases the viscosity of the liquid crystal material,deteriorating the response speed of the microwave device.Herein,we explore the viscosity of the nematic liquid crystal from the perspective of liquid crystal compound structure by testing the viscosity of our designed and synthesized fortytwo different nematic liquid crystals by using a rotating rheometer at 25℃.To the best of our knowledge,the BPNN-QSAR quantitative structure-activity model between nematic liquid crystal molecular structure and viscosity is established for the first time.The correlation coefficient between the predicted value and the experimental value is q^(2)=0.607>0.5,indicating that the model can be used to predict the viscosity performances of liquid crystal compounds.Besides,the molecular structure descriptors affecting the viscosity properties are explored.Based on the practical application and this model,seven liquid crystal molecules of two series with large birefringent index are designed and tested.The viscosity predicted by the BPNN model is smaller than that of the molecules of the same type and matches with the measured viscosity.