Simple design but marvelous performances: molecular gels of superior strength and self-healing properties

Abstract

Four nitrobenzoxadiazole (NBD)-containing cholesteryl (Chol) derivatives were prepared, and their gelation behaviors were tested. It was demonstrated that the compounds show a remarkable gelling ability. In particular, a subtle change in the length of the spacers connecting the two structural units of the compounds, which are NBD and Chol, respectively, produced a dramatic change in the gelation ability and the gel properties of the compounds. As for gelation, compound 1 is much more powerful than others, especially in the gelation of methanol-containing organic mixtures. It is to be noted that the gel of 1/pyridine–methanol exhibits superior mechanical strength with a yield stress higher than 6300 Pa at a gelator concentration of 2.5% (w/v), and the value exceeds 23 000 Pa when the gelator concentration reaches 5.0% (w/v), a result never reported before in the field of molecular gels based on low-molecular mass gelators (LMMGs). More importantly, the gel shows a rapid self-healing property as evidenced by the fact that the gel heals up immediately upon cutting, provided the segments from the cutting are squeezed together. No doubt, our findings establish a benchmark for LMMG-based molecular gels in their rheological performances. FTIR, 1H NMR and XRD studies revealed that intermolecular hydrogen bonding and π–π stacking are two of the main driving forces to promote the gelation of the system and the self-assembling of the molecules of the gelator.