Self-assembly behavior of gels composed of dibenzylidene sorbitol derivatives and poly(ethylene glycol)

Abstract

The molecular interactions, self-assembly mechanism, rheological properties and microstructure characteristics of the gels obtained from three different dibenzylidene sorbitol derivatives [1,3:2,4-dibenzylidene-D-sorbitol (DBS), 1,3:2,4-di(3,4-dimethylbenzylidene)sorbitol (DMDBS) and 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol (TBPMN)] and low-molecular-weight poly(ethylene glycol) (PEG) were investigated in this study. Ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy and molecular simulation calculation results demonstrated that the DBS/PEG systems had the strongest intermolecular hydrogen bonds and the most stable CH–π interactions, which exhibited T-shaped (point-to-face) orientations between DBS molecules; however, these strongest hydrogen bonds between DBS molecules did not improve the gel formation. We assume the interactions between DBS and PEG played an important role on the formation of the gels and influenced the gel formation time and gel formation/dissolution temperatures, as measured by dynamic rheological instruments. DMDBS and TBPMN have more alkyl groups that increased the steric hindrance to block the hydrogen bonding with PEG, which facilitated the self-assembly in comparison with DBS and led to larger diameters of the nanofibrils, as observed using scanning electron microscopy and transmission electron microscopy. In addition, the strongest intermolecular interactions between DBS molecules for the DBS/PEG systems led to the most regular structures of all the systems studied. This structure exhibited birefringent spherulitic-like textures under polarizing optical microscopy; the small-angle X-ray scattering results indicated a lamellar packing in these spherulitic-like morphologies.