Strain-triggered acidification in a double-network hydrogel enabled by multi-functional transduction of molecular mechanochemistry. Issue 2 (9th December 2022)

• Record Type: Journal Article
• Authors: Ouchi, Tetsu; Bowser, Brandon H.; Kouznetsova, Tatiana B.; Zheng, Xujun; Craig, Stephen L.
• Is Part Of: Materials horizons. Volume 10:Issue 2(2023)
• Page Start: 585
• Page End: 593
• Publication Date: 2022-12-09
• Subjects: Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d2mh01105k
• Languages: English
• ISSNs: 2051-6347

Abstract

Abstract : Stretching or striking a hydrogel results in its acidification by up to 2 pH units. The mechanically robust hydrogel offers promise as a synthetic platform for mechanically adaptive aqueous systems. Abstract : Recent work has demonstrated that force-triggered mechanochemical reactions within a polymeric material are capable of inducing measurable changes in macroscopic material properties, but examples of bulk property changes without irreversible changes in shape or structure are rare. Here, we report a double-network hydrogel that undergoes order-of-magnitude increases in acidity when strained, while recovering its initial shape after large deformation. The enabling mechanophore design is a 2-methoxy- gem -dichlorocyclopropane mechanoacid that is gated within a fused methyl methoxycyclobutene carboxylate mechanophore structure. This gated mechanoacid is incorporated via radical co-polymerization into linear and network polymers. Sonication experiments confirm the mechanical release of HCl, and single-molecule force spectroscopy reveals enhanced single-molecular toughness in the covalent strand. These mechanochemical functions are incorporated into a double-network hydrogel, leading to mechanically robust and thermally stable materials that undergo strain-triggered acid release. Both quasi-static stretching and high strain rate uniaxial compression result in substantial acidification of the hydrogel, from pH ∼ 7 to ∼5.