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Keywords:

  • Critical aggregation concentration;
  • Enthalpy;
  • Entropy;
  • Light scattering;
  • Organogels

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 (∼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 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.