Solvent effect on organogel formation by low molecular weight molecules

Solvent-gelator interactions play a key role in mediating organogel formation and ultimately determine the properties of the gel. The effect of solvent on organogel formation was investigated in selected ester, ketone, and alcoholic solvents using unique symmetrical trehalose diesters as gelators. In solvents of the same class the gelation number (defined as the ratio of solvent molecules that gel per gelator molecule) decreased for trehalose 6,6'-diacetate and 6,6'-dibutyrate as the solvent Hildebrand solubility parameter increased. The opposite was observed for trehalose 6,6'-didecanoate and 6,6'-dimyristate. In general, the gelation numbers for all the gelators studied decreased in the order of esters > ketones > alcohols. Alcohols, which are capable of hydrogen bonding and can make substantial contribution to the total solvent-gelator interaction, significantly compromise gel formation. Optical microscopy and scanning electron microscopy revealed that for systems with high gelation numbers, such as trehalose 6,6'-diacetate and 6,6'-dibutyrate in ethyl acetate and trehalose 6,6'-didecanoate and 6,6'-dimyristate in acetonitrile, thin, flexible, and highly entangled nanofibers were formed. Conversely, thick, rigid, and often highly clustered fibers accompanied systems with poor gelation, such as gels formed from trehalose 6,6'-diacetate and 6,6'-dibutyrate in acetonitrile. Understanding the role of solvent in organogel formation is crucial in designing gels with desired structure and physicochemical properties. Such designed gels may provide controlled gelation by fine-tuning the solvent or the chemical environment of the gelator.