Gel Filtration of Solubilized Systems. VII. Temperature Effect on the Solubilization of Ethylparaben in Hexaoxyethylene Lauryl Ether Micelles

Abstract

The effect of temperature on the solubilization of ethyl p-hydroxybenzoate (ethylparaben) in hexaoxyethylene lauryl ether (C₁₂E₆) micelles was examined by the gel filtration method using Sephadex G-200. The values of standard Gibbs energy (ΔG^〓), enthalpy (ΔH^〓) and entropy (ΔS^〓) changes for the micellar solubilization of ethylparaben were calculated, together with the interaction energy parameter (ω). The negative values of ΔH^〓 and ω showed that there is an interaction between the phenolic OH group in ethylparaben and the polyoxyethylene groups in the C₁₂E₆ micellar phase. The positive values of ΔS^〓 suggest that the alkane moiety of ethylparaben is incorporated into the hydrocarbon core of C₁₂E₆ micelles. These results showed that both enthalpy and entropy effects control the micellar solubilization of ethylparaben.