Thermoreversible gelation of organic liquids by arylcyclohexanol derivatives: a structural study

Physical organogels of a 4-tert-butyl-1-arylcyclohexanol derivative (BACOI) are investigated. The small-angle scattering (SAS) technique (neutrons and X-rays) demonstrates that gel networks result from the entanglement of long,solidlike, and rigid fibers. The related cross-sections are shown to be circular (r approximate to 38 +/- 2 Angstrom) with a density comparable to that of the crystalline state and are rather monodisperse. Upon a concentration increase, the fibers merge into crystalline-like heterogeneities; (junction zones) which are randomly dispersed in the mesh. The kinetics of BACOI molecular aggregation, during which physical gelation occurs, is studied by SAS, and the typical kinetical times of the supersaturated system are evaluated. Anisotropic scatterings reveal orientational effects in the gel which are sensitive to the solvent type. Electron microscopy (SEM) confirms the fibrillar random texture of the xerogels while it demonstrates that the phase-separated solids from metastable gels present oriented microdomains of bundles of fibers. The calorimetry and scattering techniques indicate that colloids in BACOI gels exhibit complex solvent-dependent mesomorphic relationships involving the basic BACOI bimolecular units (d approximate to 14.2 Angstrom).