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 A and this model is consistent with the helical stacking model proposed by the previous study