Ema K, Takekoshi K, Yao H, Wang S T, Huang C C
Department of Physics, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Mar;71(3 Pt 1):031706. doi: 10.1103/PhysRevE.71.031706. Epub 2005 Mar 25.
Heat-capacity measurements have been made on liquid-crystal compounds exhibiting almost no layer-shrinkage (NLS) behavior through the Sm-A-Sm- C() phase transition. The transition was found to be second order for two of the substances studied. It was found that the heat-capacity anomaly accompanying a second-order Sm-A-Sm- C() transition with NLS behavior is quite similar to that observed for typical antiferroelectric liquid crystals of the 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) group, showing three-dimensional (3D) XY behavior in the vicinity of the transition. On the other hand, for one compound which shows a weakly first-order transition, the anomaly is almost symmetric above and below T(c) , with a significant fluctuation effect in the Sm-A phase. For this compound, the critical behavior of the heat-capacity anomaly is almost tricritical in the immediate vicinity of T(c) , while away from T(c) the behavior can be explained with the 3D XY model. This suggests that the underlying transition with the 3D XY critical behavior is driven to almost being tricritical but remaining weakly first order. No indication of low-dimensional character in the critical behavior was found in both cases.
通过Sm-A-Sm-C（）相变对几乎不表现出层收缩（NLS）行为的液晶化合物进行了热容量测量。在所研究的两种物质中，该转变被发现是二级的。发现伴随着具有NLS行为的二级Sm-A-Sm-C（）转变的热容量异常与在4-（1-甲基庚氧基羰基）苯基4'-辛氧基联苯-4-羧酸酯（MHPOBC）基团的典型反铁电液晶中观察到的异常非常相似，在转变附近表现出三维（3D）XY行为。另一方面，对于一种表现出弱一级转变的化合物，异常在T（c）之上和之下几乎是对称的，在Sm-A相中具有显著的涨落效应。对于该化合物，热容量异常的临界行为在T（c）附近几乎是三临界的，而远离T（c）时，该行为可以用3D XY模型来解释。这表明具有3D XY临界行为的潜在转变被驱动到几乎是三临界的，但仍然是弱一级的。在这两种情况下，均未发现临界行为具有低维特征的迹象。
