Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal

Abstract

The development of new polymerizable lyotropic liquid crystals (LLCs) utilizing charged amphiphilic molecules such as those based on long chain imidazolium compounds, is a relatively new design direction for producing robust membranes with controllable nano-structures. Here we have developed a novel polymerizable ionic liquid based LLC, 1-hexadecyl-3-methylimidazolium acrylate (C₁₆mimAcr), where the acrylate anion acts as the polymerizable moiety. The phase behaviour of the C₁₆mimAcr upon the addition of water was characterized using small and wide angle X-ray scatterings, differential scanning calorimetry and polarized optical microscopy. We compare the phase behaviour of this new polymerizable LLC to that of the well known LLC chloride analogue, 1-hexadecyl-3-methylimidazolium chloride (C₁₆mimCl). We find that the C₁₆mimAcr system has a more complex phase behaviour compared to the C₁₆mimCl system. Additional lyotropic liquid crystalline mesophases such as hexagonal phase (H₁) and discontinuous cubic phase (I₁) are observed at 20 °C for the acrylate system at 50 and 65 wt% water respectively. The appearance of the hexagonal phase (H₁) and discontinuous cubic phase (I₁) for the acrylate system is likely due to the strong hydrating nature of the acrylate anion, which increases the head group area. The formation of these additional mesophases seen for the acrylate system, especially the hexagonal phase (H₁), coupled with the polymerization functionality offers great potential in the design of advanced membrane materials with selective and anisotropic transport properties.