Thermoreversible gelation and self-assembly behavior of dibenzylidene sorbitol in ternary solvent mixtures

Abstract

The self-assembly behavior of 1,3:2,4-dibenzylidene-D-sorbitol (DBS) in ternary solvents has been systematically investigated for the use of kerosene gel in the aerospace propulsion. DBS forms a yield viscoelastic gels in a wide range of kerosene/hexanol/DMSO solvent concentrations despite the fact that DBS is incapable of gelling kerosene fuel. The gelation behavior of DBS in the solvent mixture is predicted using the Hansen solubility parameters. The polar parameter ((P)) and hydrogen bonding ((H)) parameter lie in the range of 1.96(P)4.30J(0.5)cm(-1.5) and 3.40(H)7.30J(0.5)cm(-1.5) respectively for the formation of gelin kerosene/hexanol/DMSO system. The phase transition temperature (T-f) of DBS gel is determined using temperature sweep measurement and predicted using modified Friedrich (MF) relation which is found be in close agreement with an average deviation of +/- 10 degrees C. However, the deviation becomes larger when (P)>4.30 and (H)>7.30, in other words, with increase in the solvent polarity. As the solvent polarity or concentration of hexanol increases in the mixture, the gels exhibit a low T-f and Gmax value because of the hindrance of self-assembling ability of DBS due to the intermolecular hydrogen bonding between DBS and solvents. The viscoelastic behavior of DBS gels is investigated using the oscillation sweep measurements and the storage modulus Gis found to be higher than the loss modulus G for larger stress amplitude and frequency, indicating a solid-like nature of the gels. Furthermore, the microstructure analysis shows the presence of 3D nano-fibrillar morphology, which further depends on the solvent polarity. Microstructure changes from rope-like' fiber aggregate (Hex100;C-H=88 wt%) to a web-like' structures (Hex25; C-H=25 wt%), when the C-H is decreased in the solvent mixture.