A new physicochemical characterization of sodium taurodeoxycholate/water system†
Abstract
In this paper, some new physicochemical properties of sodium taurodeoxycholate (STDC)–water system are carefully investigated using
We observed that the isotropic liquid phase (C < 30 wt% STDC) consists of a micellar solution (L1) and presents a sharp structural transition from spherical micelles to an entangled network upon increasing the concentration. Below 10 °C, the L1 phase transforms slowly into a firm, gel phase (V) which results stable in the composition interval 15 < C < 30 wt%. The linear viscoelasticity of this phase is interpreted by means of the cooperative-flow theory.
The liquid crystalline phase (36 < C < 65 wt% STDC) is unequivocally characterized as having a direct hexagonal structure (H1). Specifically, the hexagonal mixture with 45 wt% STDC presents a low thermal stability (T < 35 °C) and slow kinetics at the liquid–hexagonal transition (>5 hours). The linear viscoelasticity of this phase is interpreted by means of the generalized Maxwell model.
All these findings are confirmed by some additional measurements performed on a lyotropic mixture of