Molecular rods in a zinc(II) porphyrin/cyclohexane physical gel: Neutron and X-ray scattering characterizations

Aggregation of some low-molecular weight compounds in organic liquids is known to result in the formation of rod-shaped colloidal particles.(1) Beyond the overlap concentration of the aggregates, the systems usually exhibit remarkable viscoelastic features which account for their description as gel-like materials. In particular, their typical consistency results from the development of a three-dimensional network made of interconnected colloidal aggregates. The sensitivity of the aggregation process to parameters such as temperature, concentration, and impurities, the fragility of the resulting network, and its thermal reversibility characterize such systems whose structural study raises specific problems.(1) By contrast to the commonly used electron microscopy technique, the small-angle scattering techniques enable a nondestructive investigation of these materials swollen by their solvents. Furthermore, comparative X-ray and neutron studies can provide complementary information concerning the internal structure of the aggregates, such as their cross-sectional heterogeneity or contrast profile.(2)