Structural Aspects of the Gelation Process Observed with Low Molecular Mass Organogelators

We present an experimental study of the mechanism of formation and the mechanical properties of an organogel, formed by the gelator compound 2,3-di- n -decyloxyanthracene (DDOA) in propylene carbonate. Using light microscopy, light and X-ray scattering, and rheological measurements, we show that gel formation is due to a precipitation process and occurs via a nucleation−growth mechanism. Depending upon the driving force of crystallization, and thus upon the cooling rate, dendritic structures leading to a gel phase or compact aggregates leading to a suspension are obtained. DDOA, a compound recognized as a very powerful organogelator, is thus a gelator only under well-defined conditions. In the gel phase, the formed fibers are connected through two types of bonds of different characteristic energies. The number density of these junctions depends on the cooling rate. The mechanical measurements are in agreement with this observation and can be described by a phenomenological model. The same results were obtained with other organogelators and other solvents.