Electroclinic effect in chiral SmA* liquid crystals induced by atropisomeric biphenyl dopants: amplification of the electroclinic coefficient using achiral additives
Electroclinic effect in chiral SmA* liquid crystals induced by atropisomeric biphenyl dopants: amplification of the electroclinic coefficient using achiral additives
复制标题
DOI：
10.1039/b515313a
复制
发表时间：
2006-01-01
影响因子：
--
通讯作者：
Lemieux, Robert P.
中科院分区：
文献类型：
--
作者：
Hartley, C. Scott;Kapernaum, Nadia;Lemieux, Robert P.
阻转异构体化合物（R）-2，2 '，6，6'-四甲基-3，3 '-二硝基-4，4'-二[将（4-壬氧基苯甲酰基）氧基]联苯（（R）-1）掺杂到非手性液晶主体2-（4-丁氧基苯基）-5-辛氧基嘧啶（2-PhP）和4-（4 '-庚基[1，1'-联苯]-4-基）-1-己基环己烷甲腈（NCB 76），在T-T-C = +5 K时，测得了手性SmA* 相的电倾系数e（c）随掺杂摩尔分数x（1）的变化关系.外推的e（c）值为3.07和2.28度μ m V-1的一些最高的e（c）值报告的纯SmA* 材料。（R）-1在2-PhP中的4摩尔%混合物的电斜系数被非手性2-苯基嘧啶添加剂（5摩尔%）放大，其比2-PhP长;在最好的情况下，e（c）被5-（十四烷氧基）-2-（4（十四烷氧基）苯基）嘧啶（3g）放大3.2倍，其几乎是2-PhP的两倍长。然而，使用相同系列的添加剂，在NCB 76中的（R）-1的4摩尔%混合物中没有观察到扩增。e（c）值与SmA* 相的温度范围之间的相关性表明，e（c）随（R）-1/2-PhP混合物中添加剂3的长度增加而放大主要是由于随着二级SmA*-SmC* 相变远离三临界点而倾斜磁化率系数α减小。通过小角X射线散射测量近晶层间距作为T-T-C的函数与该解释一致。结果表明，纯主体2-PhP的约化层间距d（A）/d（C）随T-T-C的变化符合平方根规律，表明SmA-C二级相变接近三临界。另一方面，对于在2-PhP中的5mol%的3g混合物，d（A）/d（C）随T-T-C的相应变化符合线性关系，这表明二级SmA-C转变接近典型的平均场行为。
The atropisomeric compound (R)-2,2',6,6'-tetramethyl-3,3'-dinitro-4,4'-bis[(4-nonyloxybenzoyl)oxy]biphenyl ((R)-1) was doped in the achiral liquid crystal hosts 2-(4-butoxyphenyl)-5-octyloxypyrimidine (2-PhP) and 4-(4'-heptyl[1,1'-biphen]-4-yl)-1-hexylcyclohexanecarbonitrile (NCB76), and electroclinic coefficients e(c) were measured as a function of the dopant mole fraction x(1) in the chiral SmA* phase at T - T-C = +5 K. The extrapolated e(c) values of 3.07 and 2.28 deg mu m V-1 are comparable to some of the highest e(c) values reported for neat SmA* materials. The electroclinic coefficient of a 4 mol% mixture of (R)-1 in 2-PhP is amplified by achiral 2-phenylpyrimidine additives (5 mol%) that are longer than 2-PhP; in the best case, e(c) is amplified by a factor of 3.2 with 5-(tetradecyloxy)-2-(4(tetradecyloxy)phenyl) pyrimidine (3g), which is almost twice as long as 2-PhP. However, no amplification is observed in a 4 mol% mixture of (R)-1 in NCB76 using the same series of additives. A correlation between e(c) values and the temperature range of the SmA* phase suggests that the amplification of e(c) with increasing length of the additive 3 in the (R)-1/2-PhP mixture is due primarily to a decrease in the tilt susceptibility coefficient alpha as the second-order SmA*-SmC* phase transition moves away from the tricritical point. Measurements of smectic layer spacing as a function of T - T-C by small-angle X-ray scattering are consistent with this explanation. The results show that the variation in reduced layer spacing d(A)/d(C) with T - T-C for the pure host 2-PhP fits to a square-root law, which indicates that the second-order SmA-C transition is nearly tricritical. On the other hand, the corresponding variation in d(A)/d(C) with T - T-C for a 5 mol% mixture of 3g in 2-PhP fits to a linear relation, which indicates that the second-order SmA-C transition approaches typical mean-field behavior.