Thermodynamic properties of sodium deoxycholate at the gel-sol transition

Sodium deoxycholate forms supramolecular aggregates in aqueous solution that are strongly dependent on temperature and pH. Upon fine tuning of these physicochemical parameters, two supramolecular aggregates can be achieved: a nanotubular phase having viscoelastic, gel-like, behavior and a sponge liquid phase. In this work, the thermodynamics of the transition between the two phases is characterized. Temperatures, volumes, and enthalpies of such transition have been experimentally determined using vibrating tube densitometry and differential scanning calorimetry. In addition, electron microscopy is used to follow the morphological transition between the two supramolecular structures. The dependencies of the thermodynamic properties with the pH and surfactant concentration of the solution are characterized, and the micrographs obtained from electron microscopy is used to explain the thermodynamics of the system. (C) 2022 The Authors. Published by Elsevier B.V.