Ultrastable, stretchable, highly conductive and transparent hydrogels enabled by salt-percolation for high-performance temperature and strain sensing. Issue 39 (28th July 2021)

• Record Type: Journal Article
• Authors: Wu, Zixuan; Shi, Wenxiong; Ding, Haojun; Zhong, Bizhang; Huang, Wenxi; Zhou, Yubin; Gui, Xuchun; Xie, Xi; Wu, Jin
• Is Part Of: Journal of materials chemistry. Volume 9:Issue 39(2021)
• Page Start: 13668
• Page End: 13679
• Publication Date: 2021-07-28
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d1tc02506f
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Salt-percolated hydrogels show excellent anti-freezing and anti-drying abilities, high conductivity at ultralow temperatures (−78.5 °C), and excellent thermal and strain sensing performance, which can monitor various physiological signals. Abstract : Ionic hydrogels are promising candidates for fabricating stretchable electronics, but the deficiency in drying and freezing tolerances severely limits their application. Here, we report a facile and versatile salt-percolated strategy to fabricate hydrogels with exceptional freezing and drying tolerances, high conductivity, and anti-swelling ability for sensitive temperature and strain detection within a broad temperature range. We discovered that lithium bromide (LiBr) was the most effective drying and freezing inhibitor for hydrogels among the various salts. The 50 wt% LiBr-percolated hydrogels retained ultrahigh stretchability (625% strain) and conductivity even at −78.5 °C or in ambient air for a year. The important role of LiBr in inhibiting the drying and freezing of hydrogels was understood using density functional theory (DFT) simulations on a molecular scale, revealing the formation of stable Li + –H2 O and Br − –H2 O clusters. It was found that the introduction of LiBr enhanced the temperature and strain sensing performance, e.g., the stability and working temperature range. Multifunctional transparent sensors exhibited a high thermal sensitivity (2.54%/°C), broad temperature detection range (−78.5 to 97 °C), low detection limit (0.1% strain), and low hysteresis and baseline drift in cycling strain sensing. Attributed to the high tolerance of hydrogels to a wide range of temperatures, the strain sensing ability was maintained even at −20 °C. Various physiological signals, such as facial expressions, word pronunciation and knee bending, are real-time monitored using hydrogel-based epidermal sensors.