Transient Phase-Induced Nucleation in Ionic Liquid Crystals and Size-Frustrated Thickening

The crystallization behavior of amphiphilic ionic imidazolium liquid crystals has been studied with in situ small- and wide-angle X-ray scattering. We found that below the melting point four crystal phases exist. Their relative stability is checked by investigating the mutual transitions and using a heating scan. The following sequence is observed: triclinic extended bilayer > triclinic double bilayer > perpendicular double bilayer. A transient phase with a low density, which may not be stable at any temperature, is observed to serve as the nucleation mechanism for all three phases. The large size of the transient crystals is found to frustrate the layer thickening, which occurs from the double bilayer to extended bilayer transition. The competition between the thermodynamic driving force and the imposed constraints leads to the formation of wrinkles. The influence of water on the crystallization behavior is demonstrated to be indirect, which reduces the size of the crystals.