The lyotropic liquid-crystalline phase behavior of phytantriol is receiving increasing interest in the literature as a result of similarities with glyceryl monooleate, despite its very different molecular structure. Some differences in the phase-transition temperature for the bicontinuous cubic to reverse hexagonal phase have been reported in the literature. In this study, we have investigated the influence that the commercial source and hence the purity has on the lyotropic phase behavior of phytantriol. Suppression of the phase-transition temperatures (by up to 15 degrees C for the bicontinuous cubic to reverse hexagonal phase transition) is apparent with lower-purity phytantriol. In addition, the composition boundaries were also found to depend significantly on the source and purity of phytantriol, with the bicontinuous cubic phase + excess water boundary occurring at a water content above that reported previously (i.e., >5% higher). Both the temperature and compositional changes in phase boundaries have significant implications on the use of these materials and highlight the impact that subtle levels of impurities can play in the phase behavior of these types of materials.

Positron annihilation lifetime spectroscopy (PALS) has potential as a novel rapid characterization method for self-assembly amphiphile systems; however, a lack of systematic correlation of PALS parameters with structural attributes has limited its more widespread application. In this study, using the well-characterized phytantriol/water and the phytantriol/vitamin E acetate/water self-assembly amphiphile systems, the impact of systematic structural changes controlled by changes in composition and temperature on PALS parameters has been studied. The PALS parameters (orthopositronium (oPs) lifetime and intensity signatures) were shown to be sensitive to the molecular packing and mobility of the self-assembled lipid molecules in various lyotropic liquid crystalline phases, enabling differentiation between liquid crystalline structures. The oPs lifetime, related to the molecular packing and mobility, is correlated with rheological properties of the individual mesophases. The oPs lifetime links the lipid chain packing and mobility in the various mesophases to resultant macroscopic properties, such as permeability, which is critical for the use of these mesophase structures as diffusion-controlled release matrices for active liposoluble compounds.