A Non-Aqueous Thermoreversible Lyotropic Gelling System: Characterization of Gels and Xerogels from Low Molecular Weight Steroid Derivatives

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Abstract
The gel to xerogel transformation of a steroid/cyclohexane gelling system is studied by optical microscopy, differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Nematic-like birefringent domains are observed for systems of increasing concentrations. It is demonstrated that the molecular organization is different in the solution, gel, xerogel and crystalline states. In particular, when the temperature is increased from the solid xerogel state, a phase transition to a crystalline state occurs before the melting to the isotropic liquid. The xerogel structure can only be obtained through a gelation route from solutions. Different behaviors for two steroid derivatives with different polarities are compared with thermoreversible polymeric gelling systems.