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

Abstract

Mixtures of γ-oryzanol and β-sitosterol were used to structure different oils (decane, limonene, sunflower oil, castor oil, and eugenol). The γ-oryzanol and β-sitosterol mixtures self-assemble into double-walled hollow tubules (~10nm 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 tubuler formation process were determined and the thermodynamic theory of self-assembly was applied to calculate the change in Gibbs free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0) resulting from the aggregation of the structurants was determined. The self-assembly was found to be enthalpy-driven as characterized by a negative ΔH0 and ΔS0. A decreasing polarity of the oil promotes the self-assembly leading to formation of tubules at higher temperatures and lower structurant concentrations. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.