Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
J Colloid Interface Sci. 2013 Sep 1;405:134-44. doi: 10.1016/j.jcis.2013.05.029. Epub 2013 May 24.
Thermotropic liquid crystal formation by salt-free catanionic surfactants (alkyltrimethylammonium alkylsulfonates, herein designated as TAmSon) has been investigated as a function of chain length mismatch (asymmetry). Previous studies on these compounds have revealed an unusual and rich asymmetry-dependent lyotropic phase behavior. Herein, phase transition temperatures and transition enthalpies/entropies were determined by differential scanning calorimetry, while mesophases were assigned by polarized light microscopy. Three series of compounds were investigated, namely: the TA16Son series, where n=6-10; the TAmSo8 series, where m=12-16; and a constant m+n series, TAmSon where m+n=22. Typically, several solid phases and two smectic mesophases are found prior to isotropization to the liquid phase. As asymmetry decreases, two somewhat counterintuitive tendencies emerge: a general decrease in enthalpy/entropy for solid-solid and solid-first mesophase transitions, and an increase in solid-first mesophase transition temperatures. Yet, solid phases are seen to be more stable for the most asymmetric compounds, while the second mesophase is more stable for the least asymmetric ones, in what appears to be a more complex behavior than expected. The results are globally interpreted in terms of subtle differences in chain interdigitation and packing, and odd-even chain effects.
无盐双离子表面活性剂（烷基三甲基铵烷基磺酸盐，以下简称 TAmSon）的热致液晶形成已作为链长不匹配（不对称性）的函数进行了研究。这些化合物的先前研究揭示了一种不寻常且丰富的不对称依赖性溶致相行为。本文通过差示扫描量热法确定了相变温度和相变焓/熵，而中间相则通过偏光显微镜进行了分配。研究了三个系列的化合物：TAmSo8 系列，其中 m=12-16；以及常数 m+n 系列，TAmSon 中 m+n=22。通常，在各向同性化为液相之前，会发现几个固相和两个向列中间相。随着不对称性的降低，出现了两个有点违反直觉的趋势：固相-固相和固-第一中间相转变的焓/熵普遍降低，以及固-第一中间相转变温度升高。然而，对于最不对称的化合物，固相看起来更稳定，而对于最不对称的化合物，第二中间相更稳定，这似乎是一种比预期更复杂的行为。结果从链交错和包装的细微差异以及奇偶链效应的角度进行了全面解释。
