The influence of the type of oil phase on the self-assembly process of ¿-oryzanol + ß-sitosterol tubules in organogel systems

Mixtures of ¿-oryzanol and ß-sitosterol were used to structure different oils (decane, limonene, sunflower oil, castor oil and eugenol). The ¿-oryzanol and ß-sitosterol mixtures self-assemble into double-walled hollow tubules (~10 nm in diameter) in the oil phase, which aggregate to form a network resulting in firm organogels. The self-assembly of the sterol molecules into tubules was studied using light scattering and rheology. By using different oils, the influence of the polarity of the oil on the self-assembly was studied. The effects of temperature and structurant concentration on the tubular formation process were determined and the thermodynamic theory of self-assembly was applied to calculate the change in Gibbs free energy ( DG0), enthalpy (DH0) and entropy ( DS0) resulting from the aggregation of the structurants was determined. The self-assembly was found to be enthalpy-driven as characterized by a negative DH0 and DS0. A decreasing polarity of the oil promotes the self-assembly leading to formation of tubules at higher temperatures and lower structurants concentrations.