A concise analysis of the effect of temperature and propanediol-1, 2 on Pluronic F127 micellization using isothermal titration microcalorimetry

Abstract

This article aims to explore the possibility of using isothermal titration microcalorimetry (ITC) for the investigation of F127 micellization and to study the effect of temperature and addition of propanediol-1,2 on F127 micellization behavior. From this work, ITC proved efficient to be used as a tool for the determination of the critical micellization concentration (CMC) and the enthalpy of micellization (Δ H mic) of F127, from which the other thermodynamic parameters were calculated (free energy (Δ G mic), entropy (Δ S mic), and heat capacity of micellization (Δ C p,mic)). The micellization of F127 was confirmed to be a strongly endothermic process with predominance of hydrophobic interactions ( TΔ S mic > Δ H mic) and the correlation of enthalpy and entropy of micelle formation exhibits an excellent linearity. The temperature dependence of F127 micellization was revealed by using ITC, since the CMCs values were, respectively, 0.197, 0.095, 0.085, and 0.079 mM for temperatures 28, 29, 30, and 31 °C. Secondly, by the addition of propanediol-1,2 to the micellization medium containing 1.187 mM of F127, the CMC was shifted to lower values (0.095, 0.081, 0.077, 0.069 and 0.066 mM, respectively, for propanediol-1,2 concentrations of 0%, 1.4%, 2.3%, 2.8%, and 3.7% w/v in the micellization medium). Finally, ITC was used as diagnostic tool with the aim of checking the reproducibility of the experiments independently on the kinetic and the dynamic aspects related to the micelle formation breakup. However, in this work we proved that the use of ITC for the determination of the CMC and thermodynamic parameters associated with F127 micellization is limited to a range of temperatures when sigmoidal curves were obtained.