Calix[4]arene-based supramolecular gels with unprecedented rheological properties

Abstract

A novel calix[4]arene-based dimeric-cholesteryl derivative was synthesized, and its gelation behaviour in thirty organic solvents was investigated. It has been shown that the compound cannot gel any of the pure solvents tested. However, it gels a mixture of solvents n-decane and acetonitrile efficiently, provided the volume ratio of the two solvents in a mixture is within 9 : 1 and 3 : 2. AFM and SEM measurements revealed that the molecules of the compound aggregate into micro-/nano-rods first, then fine fibers, and then thick fibers, and finally networked structures in the mixture solvents. Interestingly, the gel with a composition of 1 to 1 (V_n-Decane:V_Acetonitrile) and 2.5% (w/v) of the compound exhibits super-smart and fully reversible thixotropic properties, a phenomenon never reported before. Furthermore, the mechanical strength of the gel could be easily adjusted by altering the concentration of the gelator and the composition of the mixture solvents. Further interrogation of the gel revealed that structurally the gel is a gel-emulsion with acetonitrile dispersed in n-decane, a rarely found O/O (oil in oil) gel-emulsion which may find uses in the templated preparation of low-density materials with complicated internal structures.