Rheological Properties and Structural Correlations in Molecular Organogels

Abstract

Organogels of 12-hydroxystearic acid (HSA) have been investigated to emphasize solvent-dependent relationships between rheological properties and nanostructures in this class of physical gels. Different length scales are considered: macroscopic with optical opacity, rheology, phase diagram data; nanoscopic with small-angle neutron scattering experiments and molecular with 1 H NMR data. HSA networks are shown to be rigid fibrillar networks with rigid junction zones and behave as elastoplastic materials. Shear elasticities, yield stresses, and deformation behaviors appear connected to the crystallinity of networks through the cross-sectional shapes of fibers. Kinetics of molecular aggregation and flowing properties are also used to compare three classes of HSA gels (toluene, dodecane, nitrobenzene). The melting transitions as well as the concentration dependence of yield stresses exhibit remarkable behaviors analyzed in a context of molecular nanomaterials.