Browsing by Author "Tilley, AJ"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    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
  • No Thumbnail Available
    Item
    Transfer of lipid between triglyceride dispersions and lyotropic liquid crystal nanostructured particles using time-resolved SAXS
    (Royal Society of Chemistry., 2012-04-16) Tilley, AJ; Dong, YD; Chong, JYT; Hanley, TL; Kirby, N; Drummond, CJ; Boyd, BJ
    Lipid-based lyotropic liquid crystalline nanostructured phases, such as the reverse bicontinuous cubic phase (V-2) and the reverse hexagonal phase (H-2), can be dispersed into submicron sized particles with often preserved internal nanostructure, termed cubosomes and hexosomes respectively. The internal nanostructure of the particles imparts desirable characteristics such as the ability to provide sustained release of active ingredients but is susceptible to change upon the incorporation of other lipids used as an active ingredient delivery system. These are complex systems in which the direction of lipid transfer, role of the stabiliser and formation of different phase structures, such as the frustrated H-2 phase are all likely to play a role but are not yet completely understood. Consequently, we have investigated the interparticle transfer of lipids between cubosomes/hexosomes and other dispersed lipids, namely triglycerides and vitamin E acetate emulsions. Time-resolved synchrotron small angle X-ray scattering was used to follow changes to nanostructure, attributed to the transfer of lipids into or out of the cubosomes. It was found that transfer of lipid occurred due to compositional ripening via a micelle-mediated mechanism, evident from the rate of lipid transfer increasing with Pluronic concentration. The rate of transfer of alkanes between liquid crystalline particles and emulsions has been shown previously to depend inversely on chain length. However in the triglyceride systems in the current study, the rate of lipid transfer (trilaurin > tricaprylin > supercooled trimyristin >> crystallised trimyristin and tristearin) did not decrease with increase in the chain length of triglyceride as might be anticipated. The equilibrium phase diagrams of triglyceride + phytantriol in excess water were determined. These diagrams showed that the transfer of phytantriol away from cubosomes to the emulsions, which increases the local triglyceride to phytantriol concentration in the cubosomes, would require formation of H-2 phase more readily for tricaprylin than for trilaurin. Therefore, the lack of correlation of transfer rate with chain length of the triglyceride was attributed to the system seeking to avoid the unfavourable formation of the H-2 phase, competing with the driving force from the entropy of mixing, and was therefore attributed as the reason for the greater rate of transfer of trilaurin compared to the less lipophilic tricaprylin. © 2012 Royal Society of Chemistry