Effect of the Chemical Structure of Ionic Glycolipids on Their Lyotropic Aqueous Phase Behavior

This study examines the self-assembly and lyotropic aqueous phase behavior of galactose- (GC) and rhamnose-based (RC) bioinspired glycolipids with C₁₀ and C₁₄ alkyl chains using small-angle X-ray scattering and wide-angle X-ray scattering measurements. In the isotropic micellar regime (L₁), ellipsoidal micelles were identified, with their size and aggregation number mainly controlled by the surfactant alkyl chain length. As the concentration increases, both GC and RC systems form hexagonal (H₁) mesophases, with the C₁₄ homologues exhibiting a broader stability range of H₁ and crystallizing above 80 wt %. Notably, above 95 wt % RC10 assembles into an additional bicontinuous cubic Ia3d phase, which was not observed in the GC systems. Phase boundary diagrams further indicate that the presence of rhamnose, with fewer hydroxyl groups and weaker hydrogen-bonding ability, favors mesophase ordering at lower concentrations, while galactose enhances hydration and expands the L₁ domain. At higher glycolipid concentrations, however, headgroup interactions may alter this trend, and the hydroxyl-rich galactose tends to promote crystallization, while rhamnose maintains the H₁ mesophase up to a more concentrated region. Overall, these findings demonstrate that bioinspired glycolipid self-assembly depends on a balance of contributions from their alkyl chains and sugar headgroups, transitioning from a sugar solubility-driven mechanism in L₁ to prevailing sugar-sugar interactions in the concentrated regime.