Observation of Morphology and Structure Evolution during Gelation of a Bis(Anhydrazide) Derivative

A new bis(anhydrazide) derivative containing cyclohexyl terminal groups (compound 1) was synthesized, and its gelation process was investigated. Compound 1 showed both thermal-induced gelation (T-gel) and sonication-induced gelation (S-gel) in alcohols. We investigated the gelation process of compound 1 in ethanol by different techniques. It was demonstrated that gelator 1 in ethanol underwent a transition from a clear solution through a turbid suspension to an opaque gel. Scanning electron microscopy (SEM) observations indicated that the turbid suspension consisted of separated clew-like spheres, connected spheres, and short nanorods, whereas the opaque gel consisted of fibers or bundles of fiber networks. Molecules packed loosely into an unknown phase in the spheres, whereas they packed tightly into a hexagonal columnar phase with a = 1.62 nm in the fibers. Intermolecular H-bonding between -C═O and -N-H was revealed to be the driving force for gelation, and the strength of the H-bonding became stronger in the fibers than in the spheres. We propose that the gel of compound 1 in ethanol consisting of fibers is a stable phase compared to the turbid suspension consisting of spheres or short nanorods, which is considered to be metastable. The kinetics of gelation of gelator 1 in ethanol under sonication suggest that the gelation process is a two-stage kinetic pathway with fractal values of 1.27 and 0.84. Our study hence provides new insights into the formation of fibers and the structural evolution of the gelation process and can be exploited to achieve a detailed understanding of gels.