Gelation and gel properties of two- and three-component pyrene based low molecular weight organogelators

Abstract

The research described in this thesis covers the synthesis, characterization and the study of the gelation ability of fteen pyrene based low molecular weight organogelators (LMOGs). The gelation and gel properties were investigated by rheometry, scanning electron microscopy, di erential scanning calorimetry, UV-Vis and uorescence spectroscopy. The pyrene based LMOGs form complexes with 2,4,7-trinitro uorenone (TNF) and self-assemble non-covalently through - stacking, donor-acceptor and van der Waals interactions to form thermoreversible gels, which remain stable at least for two years. The strongest gels were obtained in primary alcohols whereas the poor solubility of TNF restricted gelation in nonpolar hydrocarbons. It was observed that the gelation behavior of the two-component gelator system can be estimated in both nonpolar and polar solvents by using the Hansen solubility parameters and distance. The unknown solubility parameters of the gelators were estimated by a group contribution method. The gelation ability of the two-component system was found to correlate with the hydrogen bonding solubility parameter of the solvent. Electron microscopy showed that the gelation occurs due to self-assembly of the gelators into long gel bers that form an entangled gel network. The solvent and the structure of the pyrene based LMOG have a large e ect on the gel structure and; consequently, the properties. The gels with less ber bundles and denser gel network were more elastic and had higher stability and viscosity. The organogels are viscoelastic soft materials showing shear thinning behavior and a yield point. The e ect of the solvent, additives like pyrene, crosslinker molecule and aluminum nanoparticles, functionality and alkyl side chain length of the pyrene based gelator on the gel properties were studied by rheometry. The results of this work indicate that two- and three-component gelator systems open wide possibilities to control the gel properties in various solvents.