Controllable gelation of coordination nanocages from the physical interactions among surface grafted cholesteryl groups

Abstract

Coordination nanocage (CNC) incorporated gels have attracted enormous attention for the effective integration of micro-porosity, mechanical flexibility and processability; however, the understanding of their microscopic structure–property relationships remains unclear. Herein, CNCs with 24 surface grafted cholesterol groups are constructed precisely and their gelation can be manipulated upon the tunning of solvent polarities. Optically homogeneous organogels can be formed by introducing a certain amount of bad solvents into the solutions of hairy CNCs and the gelation can be reversed through temperature variation. Suggested from scattering and molecular dynamics studies, the solvophobic interaction-driven aggregation of cholesterol units contributes to the physical crosslinking of CNCs and finally the gelation of CNC solutions. The mechanical strength of the obtained gels is observed to be highly dependent on the flexibility of the organic linkers that bond the cholesterol units on the CNC surface. The effective interaction and dense packing of the cholesterol units in their aggregates highly rely on the degree of freedom of the cholesterol, which is controlled by the flexibility of the organic linkers that bond them on the CNC surface. The observed viscoelastic performance accompanied by the well-controlled mechanical strength of the organogels unambiguously demonstrates the potential for exploiting the synergistic physical correlations to fabricate novel functional materials from CNCs.