Application of Solubility Parameters in 1,3:2,4-Bis(3,4-dimethylbenzylidene)sorbitol Organogel in Binary Organic Mixtures

The gelation behavior of 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) in binary solvents has been systematically investigated. DMDBS is soluble in DMSO and insoluble in toluene (apolar) or 1-propanol (polar). When DMSO is added to a poor solvent at a certain volume fraction, DMDBS forms an organogel in the mixed solvent. With increasing DMSO content, the minimum gelation concentration increases and the gel-to-sol transition temperature decreases in both systems. However, compared with those in toluene-DMSO mixtures, the gelation ability and thermal stability are better in 1-propanol-DMSO mixtures. Scanning electron microscopy images reveal that the gelators aggregate to form three-dimensional networks. X-ray diffraction shows that the gel has a lamellar structure, which is different from the structure of the precipitate. Fourier transform infrared results reveal H-bonding is the main driving force for self-aggregation and indicate that stronger H-bonding interactions exist between gelators in 1-propanol-DMSO mixtures in contrast with toluene-DMSO mixtures. Attempts have been taken to correlate solvent parameters to gelation behavior in binary solvents. A Teas plot exhibits distinctly different solvent zones in the studied mixed solvents. The polar parameter (delta(p)) indicates a narrow favorable domain for gel formation in the range of 1.64-7.99 MPa1/2 for some apolar solvent-DMSO mixtures. The hydrogen-bonding parameter (delta(h)) predicts that gelation occurs for values of 14.00-16.50 MPa1/2 for some polar solvent-DMSO mixtures. The result may have potential applications in predicting the gelation behavior of 1,3:2,4-di-O-benzylidene-D-sorbitol derivatives in mixed solvents.