A flexible, water anchoring, and colorimetric ionogel for sweat monitoring

As water-saturated polymer networks, the easy water loss of hydrogels directly affects their end-use applications. Minimizing the ratio of free water and increasing the ratio of bound water in the gel system has become key to extending the service life. In this work, an ionogel is prepared that effectively regulates the proportion of free water and bound water through the formation of wrinkle angles by the hydrophilic and hydrophobic chains in the gel system and the non-volatile nature of the ionic liquid. Acrylamide and N-acryloyl phenylalanine are used as free radical comonomers, and phenol red is used as an acid–base indicator. The ionic liquid is used as a dispersant to stabilize the whole framework. Due to the hydrogen bonding interactions, electrostatic interactions, and ion–ion interactions, the ionogel exhibits good stretchability, adhesion, pH sensitivity, and stability. The ionogel can be stretched in multiple directions without cracking and can be bent 180° after being left in air for 45 days. Assembling the ionogel into a wearable device can effectively monitor the pH value of sweat during exercise. The detection results are displayed in the form of RGB values, providing a preliminary diagnosis of the health of the human body.