Solvent-mediated fiber growth in organogels

Abstract

We have investigated the decisive role of the solvent type in the gelation of an oligo(p-phenylene vinylene) molecule with OH functions on the terminal groups (OPVOH). We show that gels of “hub-like” morphology are obtained with benzyl alcohol, a solvent that mimics the chemical structure of the terminal groups, whereas a “randomly dispersed” morphology is obtained with trans-decahydronaphthalene and with benzyl methyl ether, a solvent very similar to benzyl alcohol except that the hydrogen of the OH function has been replaced by a CH₃ group. Also, the thermodynamic behaviour, gel formation and gel melting are similar for benzyl methyl ether and trans-decahydronaphthalene but are significantly different in benzyl alcohol: the gel melting point is higher, and so is the melting enthalpy. Extrapolation of this parameter to 100% OPVOH gives a value significantly higher than that directly measured on pure OPVOH. Molecular organization as studied by X-ray diffraction and fluorescence properties follow the same trend. The occurrence of a molecular compound between OPVOH and benzyl alcohol is contemplated in an attempt to account for these outcomes.