A synchrotron small-angle X-ray scattering study on structures of 1,3:2,4-dibenzylidene sorbitol gels

Synchrotron small-angle X-ray scattering (SAXS) and polarized optical microscopy were used to investigate structures of 1,3:2,4-dibenzylidene sorbitol (DBS) gels in various solvents at temperatures above and below the sol–gel transition temperatures. DBS formed a transparent gel in acetophenone, while it formed a turbid gel in ionic liquids such as 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide [BMIm][TFSI] and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIm][TFSI]. Synchrotron SAXS analysis reveals that the transparent gel in acetophenone forms fibrillar aggregates composed of circular cross-section with a radius ranging from 34 to 43 Å depending upon temperature, while the turbid gels in the ionic liquids form thicker nanofibrils in comparison with the transparent gel. As temperature approached the sol–gel transition temperature, the fibrillar aggregates in both gels gradually melted. As a consequence, the cross-sectional size of the fibrillar aggregates for the transparent gel became more homogeneous due to melting of thermodynamically unstable thinner fibrils, while the spatial inhomogeneities of the aggregates for the turbid gel became remarkable near the sol–gel transition temperature.