聚合体网络对铁电液晶的影响

The Effects of a Polymer Network on a Ferroelectric Liquid Crystal

关键词:  铁电液晶  聚合体网络  聚合体网络稳定铁电液晶  分子倾斜角  自发极化强度

Key words:  ferroelectric liquid crystal  polymer network  polymer network stabilised ferroelectric liquid crystal  tilt angle  spontaneous polarisation

摘要:

通过定点聚合混合在小分子铁电液晶中的可交联单体来制备高聚合体网络稳定铁电液晶(PNSFL Cs)。试验中所用单体为紫外固化光学粘合剂NOA65,其用量少于5%。铁电液晶中存在很少量的聚合体网络可以引起相变行为的显著变化。聚合体网络的存在可减小分子倾斜角和降低液晶载体的自发极化强度。分子倾斜角和自发极化强度与温度的对应关系可用指数函数来描述。但在聚合体存在的情形下,函数参数的数值不同于在均场近似下由经典朗道理论所得到的数值。对于纯铁电液晶,自发极化强度与分子倾斜角之间存在与温度无关的线性关系;在聚合体网络存在的情形下,这一线性关系的温度独立性被破坏。

Abstract:

Polymer network stabilised ferroelectric liquid crystals (PNSFLCs) have been produced by in situ polymerisation of a small amount of a cross-linkable monomer in a low molar mass ferroelectric liquid crystal.In the present studies,the amount of prepolymer,which is a UV curable optical adhesive NOA65,is less than 5%. The embedded polymer network strongly affects the properties of the liquid crystal host. A significant change in phase transition behaviour has been observed even when the amount of the polymer network is very small Both the tilt angle and the spontaneous polarisation of the liquid crystal host are reduced in the presence of the polymer network. The temperature behaviour of these two parameters can be described by an exponential function. However, the values of the parameters of the function are different from those derived using the classical Landau theory based on the mean field approximation. For the pure ferroelectric liquid crystal, the spontaneous polarisation has a linear relation with the tilt angle, and the linearity of between the two parameters is independent of temperature. However, the temperature independence of the linear relation between the two parameters is broken in the presence of the polymer network.