Sasaki Y, Ema K, Le K V, Takezoe H, Dhara S, Sadashiva B K
Department of Physics, Tokyo Institute of Technology, O-okayama, Meguro, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Jun;83(6 Pt 1):061701. doi: 10.1103/PhysRevE.83.061701. Epub 2011 Jun 8.
We report results of calorimetric studies for the binary mixture of rodlike host n-alkyloxy-cyanobiphenyl (nOCB, n=8,9) and bent-shaped guest 1,3-phenylene-bis[4-(3-methylbenzoyloxy)]-4'-n-dodecylbiphenyl-4'-carboxylate (BC12). The effect of bent-shaped dopant molecules on the critical behavior associated with the nematic-smectic-A(d) phase transition has been studied in detail. The transition temperature for the nematic-smectic-A(d) phase sharply decreases as the increase of the mole fraction of the dopant concentration (denoted X for the BC12/9OCB mixture and Y for the BC12/8OCB mixture). The dependence of the critical exponent α on X and Y is well explained in terms of the McMillan ratio. A nearly tricritical exponent has been obtained for the X=0.01 mixture. X=0.02-0.03 mixtures, pure 8OCB, and Y=0.01-0.03 mixtures exhibit nonuniversal behaviors with effective exponents lying between the 3D-XY and tricritical exponents. The heat capacity anomaly for Y=0.05 has been well described with the 3D-XY exponent. The critical amplitude ratio A(-)/A(+) is close to 1 and insensitive to the dopant concentration. No Fisher renormalization of the critical exponent has been observed even for nearly tricritical compositions, which indicates the smallness of the concentration plays a decisive role rather than the steepness of the N-SmA(d) phase boundary.
我们报告了棒状主体正烷氧基氰基联苯（nOCB，n = 8,9）与弯曲形状客体1,3 - 亚苯基 - 双[4 - （3 - 甲基苯甲酰氧基）] - 4'- 正十二烷基联苯 - 4'- 羧酸盐（BC12）二元混合物的量热研究结果。详细研究了弯曲形状掺杂分子对与向列相 - 近晶A（d）相变相关的临界行为的影响。随着掺杂剂浓度摩尔分数的增加（BC12/9OCB混合物中用X表示，BC12/8OCB混合物中用Y表示），向列相 - 近晶A（d）相的转变温度急剧下降。根据麦克米兰比很好地解释了临界指数α对X和Y的依赖性。对于X = 0.01的混合物，获得了接近三临界指数的值。X = 0.02 - 0.03的混合物、纯8OCB以及Y = 0.01 - 0.03的混合物表现出非普适行为，有效指数介于三维XY指数和三临界指数之间。Y = 0.05时的热容异常已用三维XY指数得到很好的描述。临界振幅比A（ - ）/A（ + ）接近1且对掺杂剂浓度不敏感。即使对于接近三临界组成的情况，也未观察到临界指数的费希尔重整化，这表明浓度小起决定性作用，而不是N - SmA（d）相界的陡峭程度。
