Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, USA.
J Chem Phys. 2010 Nov 7;133(17):174501. doi: 10.1063/1.3502112.
The first-order transition from the isotropic (I) to smectic-A (Sm A) phase in the liquid crystal 4-cyano-4(')-decylbiphenyl (10CB) doped with the polar solvent acetone (ace) has been studied as a function of solvent concentration by high-resolution ac-calorimetry. Heating and cooling scans were performed for miscible 10CB+ace samples having acetone mole fractions from x(ace)=0.05 (1 wt %) to 0.36 (10%) over a wide temperature range from 310 to 327 K. Two distinct first-order phase transition features are observed in the mixture whereas there is only one transition (I-Sm A) in the pure 10CB for that particular temperature range. Both calorimetric features reproduce on repeated heating and cooling scans and evolve with increasing x(ace) with the high-temperature feature relatively stable in temperature but reduced in size while the low-temperature feature shifts dramatically to lower temperature and exhibits increased dispersion. The coexistence region increases for the low-temperature feature but remains fairly constant for the high-temperature feature as a function of x(ace). Polarizing optical microscopy supports the identification of a smectic phase below the high-temperature heat capacity signature indicating that the low-temperature feature represents an injected smectic-smectic phase transition. These effects may be the consequence of screening the intermolecular potential of the liquid crystals by the solvent that stabilizes a weak smectic phase intermediate of the isotropic and pure smectic-A.
通过高分辨率交流量热法研究了向列-向列 A（SmA）相一级转变随溶剂浓度的变化，所研究的液晶为 4-氰基-4'（-癸基）联苯（10CB），其中掺杂了极性溶剂丙酮（ace）。在 310 至 327 K 的宽温度范围内，对具有从 x（ace）=0.05（1wt%）至 0.36（10%）的不同丙酮摩尔分数的可混溶 10CB+ace 样品进行了加热和冷却扫描。混合物中观察到两个明显的一级相变特征，而在该特定温度范围内，纯 10CB 中只有一个转变（I-SmA）。两个热容量特征在重复加热和冷却扫描中重现，并且随着 x（ace）的增加而演变，高温特征在温度上相对稳定但尺寸减小，而低温特征显著向低温移动并表现出增加的分散性。低温特征的共存区随 x（ace）的增加而增加，而高温特征的共存区则基本保持不变。偏光显微镜支持在高温热容特征下方存在向列相的鉴定，表明低温特征代表注入的向列-向列相转变。这些效应可能是溶剂屏蔽液晶分子间势的结果，溶剂稳定了向列相和纯向列 A 之间的弱向列相中间相。
