Effects of Salt on the Gelation Mechanism of a D-Sorbitol-Based Hydrogelator

The effect of salt on the gelatinization of 2,443,4-dichlorobenzylidene)-D-sorbitol (DCBS), a novel low-molecular-weight gelator, was studied. DCBS showed pronounced hydrogelation and the electron micrographs indicated that the hydrogels consists of globular aggregates. Addition of NaCl to the aqueous medium accelerated the gelation process and also caused the gel's morphology to change from globular to long fibers. In addition, the thermal properties of the hydrogels were improved with the addition of NaCl. UV-vis and fluorescence emission spectra showed that extensive aggregation of the phenyl rings was responsible for the gelation. The presence of NaCl induced a red shift in the emission peaks of DCBS and a decrease of the pyrene polarity index I-1/I-3 in the gels, which indicated that there was more pi-pi stacking in the hydrogels with NaCl than in the gels without NaCl. Variable-temperature H-1 NMR spectra further demonstrated that the pi-pi interactions were enhanced by NaCl. FTIR studies showed that hydrogen bonding was also a contributing factor in the gelation process. Wide-angle X-ray diffraction (WXRD) showed that the hydrogels had a layered structure which did not change with the addition of NaCl. Density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers.