Can morphological transitions in fibrils drive stiffness of gels formed by discotic liquid crystal organogelators?

Abstract

Organogels formed by a new thermotropic discotic liquid crystal in water/ethanol mixtures show two types of gel with very different levels of elastic modulus depending on the gelation temperature. In the pure material, transitions from a discotic columnar (Col_h) to a plastic crystal (PK) to a crystalline (K) phase were observed. The same kinds of transitions seem to take place within the gel fibrils driving the gel’s stiffness. A harder gel formed at lower temperatures, is composed of partly crystalline gelator fibrils, whereas scattering data of the gelator molecules in the soft gel, formed at higher temperatures, indicate a fairly low ordering, reflecting the modest mechanical properties of these gels. The precise structure of the soft gel fibril is very difficult to establish but comparison to the liquid crystal gelator in bulk and in “wet phases” suggests that they may be formed by “wet” columnar fibrils.