Synchrotron small angle X-ray scattering from organogels. Part 1. Changes in molecular assemblies of cholesterol gelators during gel–sol transition

We examined the synchrotron small angle X-ray scattering (SAXS) from three azobenzene-appended cholesterol organogels: an ionic gel, a nonionic gel and a mixture of them. The main purpose of the present study is to find a possible correlation between the gel stability and the aggregation structure using SAXS. A typical crystalline scattering is observed for the nonionic gel at room temperature. The ionic one gives scattering from an amorphous fiber that coexists with a small amount of crystals. On the other hand, the mixture of gels shows scattering from a completely amorphous fiber. These characteristic features from the fibril structures disappear upon heating (i.e., at the gel–sol transition) for all the samples, confirming that the presence of the fibril structure is essential for the gel state. The fiber scattering is well-fitted by the hollow cylinder model with a radius of 55–60 Å and this model is consistent with the helical stacking model proposed by the previous study.