A hydro-metallogel of an amphiphilic l-histidine with ferric ions: shear-triggered self-healing and shrinkage

Abstract

Metallogels of an amphiphilic L-histidine derivative (LHC18) with various transition metal ions were investigated. It was found that while the amphiphile formed precipitates in aqueous solution when mixed with Cu²⁺, Zn²⁺, Ni²⁺, it formed a hydrogel with Fe³⁺. Interestingly, upon cooling the transparent solution of LHC18 with Fe³⁺ to room temperature gently without any interruption, the gel was formed. Upon further resting at room temperature, the gel underwent shrinkage and 90% of ferric water was expelled from the gel. On the other hand, if the as-formed gel was shaken or shear forces were applied, the gel would collapse into sol. The collapsed sol will recover to become the gel within one minute upon resting and the process can be repeated many times. In addition, once the gel experiences the thixotropic process, it will not shrink anymore. So far, various metallogels have been reported, and we show the first example of a metallogel that shows dual shrinkage and self-healing properties.

Our laboratory has a long history of collaboration with the European Union. Prof. T. Wang who has authored this paper has done his post-doctoral research at the Free University of Berlin in Germany with Prof. Dr J.-H. Fuhrhop. Some of our students have further fulfilled their PhD or worked as Postdoctoral Researchers in several European countries. In particular, two of them have been supported by the Humboldt Research Fellowships and have now returned to China and are actively working in the academic and industrial fields. We have collaborated with Prof. E. Benchou, Laboratoire de Spectrométrie Ionique et Moléculaire, Université Claude Bernard Lyon in France for investigation on the supramolecular chirality in monolayers at the air/water interface and co-published a paper.