Structure and dynamics of phytantriol-glycerol mesophases: insights into the reverse micelle to lamellar phase transition.

Abstract

Lipidic mesophases (LMPs) are lyotropic liquid crystals formed by the self-assembly of lipid in water, offering diverse phase symmetries with unique physicochemical properties. However, a fundamental understanding of how the dynamics relate to the composition and structure remains limited. In this study, we substitute water with glycerol, which closely resembles the headgroup structure of phytantriol, as the solvent to explore phytantriol-based LMPs in a pure glycerol environment. The non-crystallizing nature of both phytantriol and glycerol enables phase studies at sub-zero temperatures. Combined small-angle x-ray scattering and differential scanning calorimetry analyses confirm the formation of reverse micelles (L₂), which undergo a phase transition to lamellar phase (L_α) upon cooling. Broadband dielectric spectroscopy (BDS) reveals how the dynamics of phytantriol are governed by the composition and symmetry of the LMP: increased glycerol content decreases the relaxation time of the Debye- andα-relaxation, therefore exerting a plasticizing effect. The change in long-range order of phytantriol during theL₂-L_αphase transition reveals a decrease of the conductivity relaxation time. The introduction of a net orientation of phytantriol further reveals a new relaxation process-the dipole-matrix interaction-exclusive to theL_αphase. Our results highlight the value of combining BDS with structural and thermal analyses for a deeper understanding of the dynamics in soft matter systems.