Clegg P S, Birgeneau R J, Park S, Garland C W, Iannacchione G S, Leheny R L, Neubert M E
Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Sep;68(3 Pt 1):031706. doi: 10.1103/PhysRevE.68.031706. Epub 2003 Sep 19.
The effects of dispersed aerosil nanoparticles on two of the phase transitions of the thermotropic liquid-crystal material 4-n-pentylphenylthiol-4(')-n-octyloxybenzoate (8;S5) have been studied using high-resolution x-ray diffraction techniques. The aerosils hydrogen bond together to form a gel which imposes a weak quenched disorder on the liquid crystal. The smectic-A fluctuations are well characterized by a two-component line shape representing thermal and random-field contributions. An elaboration on this line shape is required to describe the fluctuations in the smectic-C phase; specifically the effect of the tilt on the wave-vector dependence of the thermal fluctuations must be explicitly taken into account. Both the magnitude and the temperature dependence of the smectic-C tilt order parameter are observed to be unaffected by the disorder. This may be a consequence of the large bare smectic correlation length in the direction of modulation for this transition. These results show that the understanding developed for the nematic to smectic-A transition for octylcyanobiphenyl and octyloxycyanobiphenyl liquid crystals with quenched disorder can be extended to quite different materials and transitions.
利用高分辨率X射线衍射技术研究了分散的气凝胶纳米颗粒对热致液晶材料4-正戊基苯基硫醇-4('-)-正辛氧基苯甲酸酯(8;S5)的两种相变的影响。气凝胶通过氢键结合在一起形成凝胶，该凝胶对液晶施加了微弱的猝灭无序。近晶-A涨落由代表热贡献和随机场贡献的双组分线形很好地表征。需要对这种线形进行细化以描述近晶-C相中的涨落；具体而言，必须明确考虑倾斜对热涨落波矢依赖性的影响。观察到近晶-C倾斜序参量的大小和温度依赖性均不受无序影响。这可能是由于该转变在调制方向上具有较大的裸近晶关联长度所致。这些结果表明，针对具有猝灭无序的辛基氰基联苯和辛氧基氰基联苯液晶从向列相到近晶-A相转变所形成的理解可以扩展到截然不同的材料和转变。
