Design of asymmetric-adhesion lignin reinforced hydrogels with anti-interference for strain sensing and moist air induced electricity generator.

Flexible hydrogels with integration of excellent mechanical and electrical properties are well suited for applications as wearable electronic sensors, and others. Self-adhesion is an important feature of wearable sensors. However, the usual isotropic- adhesion hydrogels have the drawback of poor anti-interference, which negatively affects their applications. In this study, we developed asymmetric-adhesion and tough lignin reinforced hydrogels in a facile two-step process: 1) PAA hydrogels, with lignin as the binder and conductive filler, were first prepared; 2) the asymmetric-adhesion property was imparted to lignin reinforced hydrogel by simple soaking of the top portion of the hydrogel in CaCl2 solution. The as-obtained asymmetric-adhesion lignin reinforced hydrogel was assembled into a wearable sensor, which shows excellent anti-interference and accurate and stable collections of sensing signals, with its gauge factor (GF) of 2.51 (in the strain range of 0-51.5%). In addition, the tough hydrogel is capable of generating electricity upon moist air sweeping through it, showing excellent energy conversion capabilities, with open-circuit voltage of as high as 306.6 mV. These results provided new prospects for the application of polyelectrolyte hydrogel materials in the fields of wet-to-electric conversion and wearable electronic sensors.