负性向列相液晶电致缺陷的产生与湮灭过程  

Formation and annihilation of electrically driven defects in nematic liquid crystals with negative dielectric anisotropy

作　　者：王紫凌 叶家耀 黄志军 宋振鹏 李炳祥 肖瑞林 陆延青[2] Wang Zi-Ling;Ye Jia-Yao;Huang Zhi-Jun;Song Zhen-Peng;Li Bing-Xiang;Xiao Rui-Lin;Lu Yan-Qing(College of Electronic and Optical Engineering,College of Flexible Electronics(Future Technology),Nanjing University of Posts and Telecommunications,Nanjing 210023,China;College of Engineering and Applied Sciences,Nanjing University,Nanjing 210093,China;Department of Physics,Anshan Normal University,Anshan 114000,China)

机构地区：[1]南京邮电大学电子与光学工程学院,柔性电子(未来技术)学院,南京210023 [2]南京大学现代工程与应用科学学院,南京210093 [3]鞍山师范学院物理学院,鞍山114000

出　　处：《物理学报》2024年第5期257-266,共10页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2022YFA1405000);国家自然科学基金(批准号:62375141);江苏省自然科学基金(批准号:BK20212004)资助的课题.

摘　　要：取向有序的液晶材料具有丰富的物理各向异性、外场响应性、物理效应,催生了新一代的光电应用.利用电场可在液晶中产生拓扑缺陷.缺陷动态过程受材料自身特性和外界条件的影响尚未明晰.本文选用介电各向异性△ε在-1.1到-11.5之间的7种向列相液晶材料,通过施加线性增加的交流电场,研究了负性向列相液晶电致脐点缺陷产生到湮灭过程中材料特性(△ε)和外界条件(温度、外加电场参数)对脐点缺陷的标度规律及湮灭快慢的影响.结果表明:在不同的△ε、温度和电场频率下,缺陷产生过程均满足Kibble-Zurek机制,即缺陷密度与电场变化率之间存在标度关系,且标度指数约为1/2;温度越高,产生缺陷密度越大;△ε越强或电场变化越快,缺陷湮灭速度越快.本文的研究厘清了拓扑缺陷产生湮灭与材料特性和外界条件的依赖关系,有利于对软物质中拓扑缺陷动态过程的认识和理解.Orientationally ordered liquid crystals(LCs)exhibit remarkable physical anisotropy and responsiveness to external fields,which give rise to distinguished physical effects and have led to the emergence of a new generation of electric-optical applications.The LCs are also renowned for their abundance of phases and topological defects,which are of significance in studying both fundamental science and practical technology.One simple approach to generating umbilic defects involves applying an electric field to a homeotropically aligned nematic LC with negative dielectric anisotropyΔε.However,the influence of material properties and external conditions on the dynamic process of nematic LC defects remains unclear.Here,we select seven kinds of nematic LCs with negative dielectrically anisotropy,ranging from-1.1 to-11.5,to explore the dynamics of electric-field-induced umbilics.By using a linearly increasing electric field parallel to the molecular orientation of LC,we systematically investigate the effects of material property(dielectric anisotropy)and external conditions(temperature and electric field parameters)on the formation and annihilation of umbilic defects.The experimental results show that the dynamic process of forming the umbilic defects in nematic LCs is independent of dielectric anisotropy,temperature,and electric field frequency,but follows the Kibble-Zurek mechanism,in which the density of generated umbilic defects exhibits a power-law scaling with the change of the electric field ramp rate,with a scaling exponent of approximately 1/2.Interestingly,a stronger dielectric anisotropy leads to a higher density of umbilic defects.Additionally,a change in temperature has a significant influence on the density of umbilic defects,in which higher temperature leads to greater defect density under the same external electric field conditions.Furthermore,the annihilation rate of umbilic defects is closely related to the material properties and the ramp of the applied electric field.Specifically,the annihilation rate

关 键 词：向列相液晶 脐点缺陷 电场效应 介电各向异性 

分 类 号：O753.2[理学—晶体学]