Crystallization from the micellar phase of imidazolium-based cationic surfactants

• Published in: Journal of colloid and interface science Vol. 374; no. 1; pp. 197 - 205
• Main Authors: Wu, Fu-Gen, Wang, Nan-Nan, Zhang, Qing-Guo, Sun, Shu-Feng, Yu, Zhi-Wu
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15.05.2012; Elsevier
• Subjects: Calorimetry, Differential Scanning; Cationic; Cationic surfactant; cationic surfactants; Chemistry; Colloidal state and disperse state; Cooling; Cryoelectron Microscopy; Crystal structure; Crystallization; differential scanning calorimetry; dispersions; electron microscopy; Exact sciences and technology; Fourier transform infrared spectroscopy; Gelation; gels; General and physical chemistry; Imidazoles - chemistry; Micelle; Micelles; Micelles. Thin films; Phase transformations; Phase Transition; rehydration; Self assembly; Solutions; Spectroscopy, Fourier Transform Infrared; Submolecular mechanism; Surface-Active Agents - chemistry; Surfactants; Temperature; Transformations; Water - chemistry; X-radiation; X-Ray Diffraction; Cationic surfactant; Micelle; Submolecular mechanism; Gelation; Crystallization; Self assembly; Differential scanning calorimetry; Crystalline phase; Surfactant; Dehydration; Electron microscopy; Ionic surfactant; Phase transitions; Mechanism; Infrared spectrometry; Optical microscopy; Alkyl; Synchrotrons; Chlorides; Ordering; Rehydration; X ray scattering; Micellar solution; Aqueous dispersion
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2012.01.054

[Display omitted] ► We study the phase behavior of the imidazolium-based surfactant C16mimCl. ► Two types of micelles form depending on the concentration of C16mimCl. ► The spherical micellar phase converts directly into a lamellar crystalline phase upon cooling. ► The cylindrical micellar phase converts to a lamellar crystalline phase via a lamellar gel phase. ► The submolecular mechanisms of the crystallization processes were studied. 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.