Structure functions and interfacial mean curvatures in a ternary amphiphilic system C₁₂E₅/water/n-octane

Abstract

Partial structure functions and mean curvatures of a ternary amphiphilic system consisting of water, n-octane and nonionic amphiphile C₁₂E₅ with equal volume fraction of oil and water have been studied by means of small-angle neutron scattering (SANS). Isotopic contrast variation technique was used to obtain suitable scattering contrasts of oil and water. We observed that the cross partial structure functions, that arise from the correlation between water-surfactant or oil-surfactant, change sign when the temperature passes through the hydrophile-lipophile balance (HLB) point. It indicates that the interaction parameter C of the spin-lattice model invert on HLB line. We have calculated mean curvatures considering that water or oil molecules can partially penetrate into the surfactant film. Experimental results show that mean curvatures increase as the temperature increases at a rate of 1.5×10⁻³ (Å⁻¹ K⁻¹).