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 an d a mixture of them. The main purpose of the present study is to find a pos sible correlation between the gel stability and the aggregation structure u sing SAXS. A typical crystalline scattering is observed for the nonionic ge l at room temperature. The ionic one gives scattering from an amorphous fib er that coexists with a small amount of crystals. On the other hand, the mi xture of gels shows scattering from a completely amorphous fiber. These cha racteristic features from the fibril structures disappear upon heating (i.e . at the gel-sol transition) for all the samples. confirming that the prese nce of the fibril structure is essential for the gel state. The fiber scatt ering is well-fitted by the hollow cylinder model with a radius of 55-60 An gstrom and this model is consistent with the helical stacking model propose d by the previous study.