Carbone G, Barberi R, Musevic I, Krzic U
Licryl - Liquid Crystal Laboratory, INFM Research Unit of Calabria c/o Physics Department, University of Calabria, 87036 Rende (CS), Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 May;71(5 Pt 1):051704. doi: 10.1103/PhysRevE.71.051704. Epub 2005 May 5.
Using a temperature controlled atomic force microscope (AFM), we have studied surface induced pre-smectic order in the nematic and isotropic phases of 4-cyano- 4'-n -octylbiphenyl. A modified AFM head with piezoresitive cantilevers has been used to measure the structural force between a flat BK7 glass plate and a 10 microm glass sphere, both being treated to induce homeotropic alignment of the confined liquid crystal layer in between. We have observed surface-induced presmectic force not only in the isotropic, but also in the nematic phase. We have measured the temperature dependencies of the presmectic force, the smectic correlation length xi and the smectic order parameter psi at the surface. The correlation length xi(T) shows a power-law temperature dependence with a critical exponent of nu=0.67 +/- 0.03 and the bare correlation length of xi(0) = (0.39 +/- 0.08) nm, in good agreement with x-ray data. The smectic density at the surface is psi(2)(S) =0.4 in the nematic phase and decreases in the isotropic phase.
我们使用温度控制原子力显微镜（AFM）研究了4-氰基-4'-正辛基联苯在向列相和各向同性相中的表面诱导近晶前序。我们使用了一种带有压阻悬臂的改进型AFM探头，来测量平坦的BK7玻璃板和一个10微米玻璃球之间的结构力，这两者都经过处理，以诱导其间受限液晶层的垂直排列。我们不仅在各向同性相中，而且在向列相中都观察到了表面诱导近晶前力。我们测量了近晶前力、近晶关联长度ξ和表面近晶序参量ψ的温度依赖性。关联长度ξ(T)表现出幂律温度依赖性，临界指数ν = 0.67±0.03，裸关联长度ξ(0) = (0.39±0.08)纳米，与X射线数据吻合良好。表面近晶密度在向列相中为ψ²(S)=0.4，在各向同性相中降低。
