Steric-Structure-Dependent Gel Formation, Hierarchical Structures, Rheological Behavior, and Surface Wettability.

A series of bicholesteryl-based gelators with different central linker atoms C, N, and O (abbreviated to GC, GN, and GO, respectively) have been designed and synthesized. The self-assembly processes of these gelators were investigated by using gelation tests, field-emission scanning electron microscopy, field-emission transmission electron microscopy, UV/Vis absorption, IR spectroscopy, X-ray diffraction, rheology, and contact-angle experiments. The gelation ability, self-assembly morphology, rheological, and surface-wettability properties of these gelators strongly depend on the central linker atom of the gelator molecule. Specifically, GC and GN can form gels in three different solvents, whereas GO can only form a gel in N,N-dimethylformamide (DMF). Morphologies from nanofibers and nanosheets to nanospheres and nanotubes can be obtained with different central atoms. Gels of GC, GN, and GO formed in the same solvent (DMF) have different tolerances to external forces. All xerogels gave a hydrophobic surface with contact angles that ranged from 121 to 152°. Quantum-chemical calculations indicate that the GC, GN, and GO molecules have very different steric structures. The results demonstrate that the central linker atom can efficiently modulate the molecular steric structure and thus regulate the supramolecular self-assembly process and properties of gelators.