Low Molecular Weight Gelators for Organic Solvents

Everyone knows what a gel is, but from a scientific point of view the term gel encompasses chemically very diverse systems. Well known gel systems include, for instance, dilute solutions of polymers, proteins, and surfactants in water and organic solvents. These gel systems are important in medicine, biology, chemistry, and physics, and find many applications in the photographic, cosmetics, food, and petroleum industries [1]. However, as D. Jordan Lloyd already wrote in 1926: ‘The colloidal condition, the “gel”, is one which is easier to recognise than to define,…’. And although an exact definition of a gel is still a., problem, from a topological point of view gels can be defined as dilute mixtures of at least two components, in which both components form a separate continuous phase throughout the system [2]. This definition includes not only gels composed of a solid-like and a liquid phase, but also those composed of a solid and a gas phase (so called aerogels). For most gels a solid-like phase is the minor component which forms a three dimensional network structure within the fluid or gas phase. For solid-fluid gels it can be said that the network structure prevents the fluid from flowing, whereas the liquid phase prevents the network from collapsing [3]. The coexistence of a solid network structure together with a liquid phase distinguishes gels from pure solid, liquid crystalline, or fluid materials and gives gels their unique elastic properties.