Dual Stimuli-Responsive Supramolecular Hydrogel Based on Hybrid Inclusion Complex (HIC)

Abstract

A novel dual-responsive supramolecular hydrogel composed of an azobenzene (AZO) end-functionalized block copolymer PDMA-b-PNIPAM (AZO-(PDMA-b-PNIPAM)) and β-cyclodextrin-modified CdS quantum dot (β-CD@QD) has been demonstrated. Based on the host−guest inclusion complexation of AZO of the block copolymers and CD cavities on β-CD@QD, they form a hybrid inclusion complex (HIC). The HIC contains a QD as the core and the block copolymer as the shell with the PNIPAM block as the outer layer. Dynamic light scattering (DLS) and UV−vis spectroscopy investigation proved the HIC structure in diluted solution. Hydrogel formed easily upon heating the aqueous solution of HIC at a concentration as low as 7 wt %; as a result of PNIPAM, aggregation occurred above the LCST. The inclusion complex and the domains of the collapsed PNIPAM chains serve as two distinct cross-links and render the hydrogel excellent dual sensitivity to competitive hosts/guests substitution and to temperature variation. Furthermore, rheology results quantitatively exhibit the hydrogel formation mechanism and the sol-to-gel reversibility following the two external stimuli.