A fundamental study of the molecular structure, interactions and self-organization of 1,3:2,4-dibenzylidene-D-sorbitol.

摘要

1,3:2,4-Dibenzylidene-D-sorbitol (DBS) is a low-molecular-weight amphiphile that is capable of self-organizing into a fibrilar network and promoting gelation in a wide variety of organic solvents and polymers. DBS has been shown to induce physical gelation at low concentrations (∼1 wt%), making it ideal for applications such as cosmetics, biomedical materials, and (opto)electronic devices. Despite the many uses of DBS, a comprehensive study addressing the molecular structure, intermolecular interactions, nanofibrillar morphology and macroscopic properties of DBS-containing systems remains lacking. In this work, we seek to elucidate the molecular interactions governing DBS self-assembly, the impact of molecular structure on resultant nanofibrillar morphology, and the effect of this nanostructure on macroscopic mechanical properties.; Molecular mechanics calculations performed with Cerius2 and InsightII software reveal that the pendant hydroxyl group tends to form intramolecular hydrogen bonds while the terminal hydroxyl group is quite flexible. Molecular mechanics and molecular dynamics studies of DBS dimers indicate that DBS is capable of both hydrogen bonding and pi interactions, suggesting that the mechanism of network formation is complex, involving more than one type of local interaction.; Rheology of organogels composed of poly(ethylene glycol) (PEG) and DBS reveals that the rate of gelation, the gel dissolution/formation temperatures, and the magnitude of the dynamic elastic modulus are sensitive to both DBS concentration (&phis;) and matrix polarity. Studies of DBS and amphiphilic polypropylene glycol-b-polyethylene glycol-b-polypropylene glycol (PPG-b-PEG-b-PPG) triblock copolymers indicate that the magnitude of the elastic modulus is sensitive to copolymer composition and block length at low &phis;, but becomes matrix-independent as the DBS network saturates at &phis; in excess of about 1 wt%.; Transmission electron microscopy and microtomography of DBS networks in poly(ethyl methacrylate) reveal the existence of DBS nanofibrils measuring ca. 10 nm in diameter and ranging up to several hundred nanometers in length. Dynamic mechanical property analysis reveals that, while DBS has little effect on glassy PEMA, it serves to increase the elastic modulus of molten PEMA above the glass transition temperature.