Janus organohydrogels to realize strain sensitivity, tough adhesion, and environmental stability

Abstract

Conductive hydrogels (CHs) have been successfully applied in wearable sensors, health monitoring, and smart electronic skins. However, conventional CHs are unstable for long-term use, mainly because of the dehydration in dry environments, freezing at low temperatures, and lack of self-adhesion properties. Herein, a Janus organohydrogel was reported to address this issue, which had a porous matrix and a dense layer to maximize their functionalities. The bottom was made from polyvinyl alcohol (PVA), water, and glycerol, to fabricate an environmental stable and robust matrix; while the top was consisted of grape seed protein (GSP), tannic acid (TA), carbon nanotubes (CNTs), and water to form the conductive yet adhesive layer. Due to the strong hydrogen bonding between glycerol and water, the evaporation and freezing issues were restrained, resulting in a resilient, conductive, adhesive, and stable organohydrogel. For example, the weight loss was 14 % after storing at ambient conditions for 7 days, and the tensile strength and elastic modulus remained 790 and 360 kPa after cooling at −20 °C. Additionally, the catechol groups from TA and amino acids from GSP endowed robust adhesion to wood, cardboard, iron, rubber, plastics, glass, and pigskin (>7 days). Moreover, the introduction of CNTs within Janus structures promoted electron transportation, resulting in high sensitivity (GF = 1.4) at low content (0.02 wt%). Bearing several merits, the present strategy is expected to greatly enrich the functions and expand the applications of conductive hydrogels.