学术报告（4月14日）

主持人：谢汉萍 教授

报告时间：2015年4月14日（星期二）10:30

摘要： Exfoliated monolayer zirconium phosphate sheets in water form colloidal suspensions exhibiting liquid crystal (LC) ordering above a critical concentration. Studies of the phase behavior and phenomenology of such suspensions show that the LC is nematic. Coexistence of the nematic with an isotropic phase is observed at all concentrations, indicating a long range attraction between the sheets. At high concentration the coexisting LC forms lens-shaped nematic tactoids, analysis of which enables estimates of the nematic elasticity and surface tension. Transmission electron microscopy reveals the bispherical internal structure of the nematic director field in the tactoids. Nematic cells with initial homeotropic orientation exhibit a periodic instability in the director field, which is unstable against the formation of a bend undulation of the sheets. This phenomenon, which is also observed in lyotropic colloidal suspensions of graphene oxide sheets, may be attributed to phase separation and undulation instability.
Azobenzene-based molecules which form a self-assembled monolayer (SAM) tethered to a glass surface are highly photo-sensitive and dynamically orient liquid crystals in contact with them when illuminated with polarized actinic light. We probe the coupling of such monolayers to the nematic liquid crystal in a hybrid cell by studying the dynamics of liquid crystal reorientation in response to local orientational changes of the monolayer by a focused actinic laser with a rotating polarization. This locally reorients the nematic, winding up a set of nested rings of splay-bend nematic director reorientation until the required torque exceeds that of the surface coupling, after which the nematic director starts to slip. Quantitative analysis of the dynamics enables measurement of the coupling between the azo-SAM and the nematic liquid crystal.

报告人简介：

石玥，美国科罗拉多大学博尔德分校物理系液晶材料研究中心博士，从事溶致液晶氧化石墨、磷酸锆的液晶性质的研究。