Crystallization from the micellar phase of imidazolium-based cationic surfactants.
Crystallization from the micellar phase of imidazolium-based cationic surfactants.
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DOI：
10.1016/j.jcis.2012.01.054
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发表时间：
2012-05
影响因子：
9.9
通讯作者：
Fulin Wu;Nannan Wang;Qing-guo Zhang;Shu-Feng Sun;Zhi‐Wu Yu
中科院分区：
文献类型：
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作者：
Fulin Wu;Nannan Wang;Qing-guo Zhang;Shu-Feng Sun;Zhi‐Wu Yu
采用差示扫描量热法、同步辐射小角和广角X射线散射、冷冻断裂电子显微镜、偏光显微镜和傅里叶变换红外光谱研究了阳离子表面活性剂氯化1-十六烷基-3-甲基咪唑（C16 mimCl）的水分散体系的自组装和相行为。我们发现，C16 mimCl冷却后的结晶是强烈的浓度依赖性。在低浓度（10-25wt%）下，样品直接从球形胶束溶液变为层状结晶相。在高浓度（50-67wt%）时，初始的圆柱形胶束首先转变为层状凝胶相，然后转变为层状结晶相。特别的努力已经致力于揭示的相变过程的亚分子机制。从初始胶束相到冷却后的最终结晶相的转变涉及烷基尾部的有序重排和头部区域的脱水过程。在高浓度下，转化分为两个步骤，即，凝胶化和随后的结晶过程，都涉及表面活性剂尾部的明显重排。此外，在凝胶化步骤中发生表面活性剂头部的显著脱水，并且在结晶步骤中发生部分再水化。
The self-assembly and phase behavior of the aqueous dispersions consisting of the cationic surfactant, 1-hexadecyl-3-methylimidazolium chloride (C16mimCl), were studied by differential scanning calorimetry, synchrotron small- and wide-angle X-ray scattering, freeze-fracture electron microscopy, polarizing optical microscopy, and Fourier transform infrared spectroscopy. We found that the crystallization of C16mimCl upon cooling is strongly concentration-dependent. At low concentrations (10–25wt%), the samples change directly from a spherical micellar solution to a lamellar crystalline phase. While at high concentrations (50–67wt%), the initial cylindrical micelles first convert to the lamellar gel phase and then to the lamellar crystalline phase. Particular efforts have been devoted to unveiling the submolecular mechanisms of the phase transition processes. The transformation from the initial micellar phase to the final crystalline phase upon cooling involves both an ordering rearrangement in the alkyl tails and a dehydrating process in the head region. At high concentrations, the transformation is divided into two steps, i.e., the gelation and subsequent crystallization processes, both involving evident rearrangements of the surfactant tails. Moreover, a significant dehydration of the surfactant head part takes place in the gelation step and a partial rehydration occurs in the crystallization step.