Transition Mechanism from Nonlamellar to Well-Ordered Lamellar Phases: Is the Lamellar Liquid-Crystal Phase a Must?

Understanding the self-assembly mechanisms of amphiphilic molecules in solutions and regulating their phase behaviors are of primary significance for their applications. To challenge the reported direct phase transitions from nonlamellar to ordered lamellar phases, the self-assembly and phase behavior of the 1-hexadecyl-3-methylimidazolium chloride aqueous dispersions were studied using a strategy of isothermal incubation after the temperature jump. A disordered lamellar phase (identified as the lamellar liquid-crystal (Lα) phase), serving as an intermediate, was found to bridge the transition from a spherical micellar (M) phase to a lamellar-gel (Lβ) phase. Meanwhile, the nonsynchronicity in the tail and headgroup regions of the ionic liquid surfactant during the transition process was also unveiled, with the former being prior to the latter. The in-depth understanding of the self-assembly mechanisms may help push forward the related applications in the future.