Underwater temperature monitoring is needed for marine exploration, early warning systems in aqueous environments, and temperature tracking during aquatic activities, yet it remains challenging for hydrogel-based sensors due to swelling-induced signal drift and limited underwater sensing performance. To address this, an antiswelling charge-transfer hydrogel incorporating a viologen/pyranine charge-transfer (VP-CT) complex was developed. The VP-CT complex was formed by charge-transfer interactions and equipped with a long alkyl chain, increasing the cross-linking density and hydrophobicity of the hydrogel to improve its water resistance. The charge-transfer interactions and hydrophobic interaction from VP-CT complex, along with hydrogen bonding from poly(vinyl alcohol) (PVA) and tannic acid (TA), endowed the prepared hydrogel with exceptional swelling resistance (equilibrium swelling ratios of −4.5% in water and −6.7% in artificial seawater after 15 days). The multiple ionic groups within the VP-CT complex facilitated high ionic conductivity (0.031 S cm–1 at 25 °C) of the hydrogel. Additionally, the hydrogel-based underwater temperature sensor displayed ultrahigh temperature coefficient of resistance (TCR) of −9.86% °C1– and stable underwater temperature monitoring. This sensor also successfully detected water gradient variations when attached to human skin and served as a key element in an early warning system for sudden temperature changes in aqueous environments. This work provides a robust strategy for high-performance underwater temperature sensing in marine, sports, and biomedical applications.
Luo et al. (Tue,) studied this question.