Reversible heat-set organogel based on supramolecular interactions of beta-cyclodextrin in N,N-dimethylformamide

This paper describes the first reversible, heat-set organogel based on the supramolecular interactions of beta-cyclodextrin (beta-CD). The gel was prepared by interaction of diphenylamine (DPA) with beta-CD and lithium chloride in N,N-dimethylformamide (DMF). In this gel system, DPA could be gelated in DMF as the temperature increased and then dissolved again as the temperature decreased. In the microscopic structure of gel, beta-CDs play a key role in the formation of nanorods and microfibers. Some important features of the gel were observed. (1) The system is a multicomponent solution, in which each of the four components is required for the organogelation property. (2) The system is a reversible, thermo-responsive organogel composed of small organic molecules. When the temperature is lower than T(gel), the gel transforms back into a solution. The reversible thermo-transition was confirmed by differential scanning calorimetry (DSC). The gel system is responsive to the concentration of LiCl. No gel was formed without LiCl. The stimuli responses of the system with other salts such as KCl and NaCl were weaker than with LiCl. (4) The system is responsive to the addition of guest molecules. The structures and sizes of the guest molecules could influence the gel formation. Generally, T(gel) decreased by adding guest molecules in the gel system, but some guest molecules, whose structures are exactly fitted to the cavity of CDs, could prevent gel formation. This work may provide new avenues in delivery of functional molecules as well as design of intelligent materials and biomaterials.