Crystallization from the micellar phase of imidazolium-based cationic surfactants

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• 作者：Fu-Gen Wu^a ; Nan-Nan Wang^a ; Qing-Guo Zhang^a ; ^b ; Shu-Feng Sun^c ; Zhi-Wu Yu^a ; ^{yuzhw@tsinghua.edu.cn}
• 关键词：Cationic surfactant ; Micelle ; Crystallization ; Gelation ; Submolecular mechanism
• 刊名：Journal of Colloid and Interface Science
• 出版年：2012
• 期刊代码：125_00219797
• 类别：ch
• 出版时间：15 May, 2012
• 卷：374
• 期：1
• 页码：197-205
• 文件大小：960 K

摘要

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 (10-25 wt%), the samples change directly from a spherical micellar solution to a lamellar crystalline phase. While at high concentrations (50-67 wt%), 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.