Browsing by Author "Rappolt, M"

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    Impurities in commercial phytantriol significantly alter its lyotropic liquid-crystalline phase behavior
    (American Chemical Society, 2008-07-01) Dong, YD; Dong, AW; Larson, I; Rappolt, M; Amenitsch, H; Hanley, TL; Boyd, BJ
    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. © 2008, American Chemical Society
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    Nonequilibrium effects in self-assembled mesophase materials: unexpected supercooling effects for cubosomes and hexosomes
    (American Chemical Society, 2010-06-01) Dong, YD; Tilley, AJ; Larson, I; Lawrence, MJ; Amenitsch, H; Rappolt, M; Hanley, TL; Boyd, BJ
    Polar lipids often exhibit equilibrium liquid crystalline structures in excess water, such as the bicontinuous cubic phases (QII) at low temperatures and inverse hexagonal phase (HII) at higher temperatures. In this study, the equilibrium and nonequilibrium phase behavior of glyceryl monooleate (GMO) and phytantriol (PHYT) systems in excess water were investigated using both continuous heating and cooling cycles, and rapid temperature changes. Evolution of the phase structure was followed using small-angle X-ray scattering (SAXS). During cooling, not only was supercooling of the liquid crystalline systems by up to 25 °C observed, but evidence for nonequilibrium phase structures (not present on heating; such as the gyroid cubic phase only present at low water content in equilibrium) was also apparent. The nonequilibrium phases were surprisingly stable, with return to equilibrium structure for dispersed submicrometer sized particle systems taking more than 13 h in some cases. Inhibition of phase nucleation was the key to greater supercooling effects observed for the dispersed particles compared to the bulk systems. These findings highlight the need for continued study into the nonequilibrium phase structures for these types of systems, as this may influence performance in applications such as drug delivery. © 2010, American Chemical Society