Differential Scanning Calorimetry Study of the Structure of Water Confined within AOT Lamellar Mesophases

We combined thermal analysis with FT-IR measurements to solve the structure of the water network confined within lamellar bilayers of AOT surfactant. Unlike previous FT-IR analyses that allowed us only to point out spectroscopic molecular components characterized by their local connectivity, differential scanning calorimetry (DSC) allowed us to identify homogeneous thermal populations listed as low, medium and high temperature. HT water was identified with bulk water, and LT water, as hydration water closely linked with surfactants heads. MT water was assigned to a disrupted network of water corresponding to a layer of 0.5 nm modified by the effect of confinement created by the vicinity of the surfactant bilayer. It appears from this study that the actual extent of confinement influence is lower than expected, at least for lamellar structures. Each thermal population was finally described by a different distribution of the spectroscopic components identified in parallel by FT-IR.