Naked-Eye Visual Thermometer Based on Glycerol─Nonclose-Packed Photonic Crystals for Real-Time Temperature Sensing and Monitoring

Real-time sensing and monitoring of temperature are of great significance for assessing human health. The sensitivity and stability are inevitable issues for thermometers. In this study, a thermometer with the cylindrical thermochromic hydrogel was prepared for real-time visual monitoring of temperature, which had excellent temperature sensitivity, angle-independence axially, and environmental stability. The customization of their initial optical properties depended on the PMMA concentrations and the content of the hydrogel monomer. The glycerol introduced with solvent displacement formed hydrogen bonds with the hydrogel network, which stabilized their mechanical properties, and the reflection peak blue-shifted from 653 to 499 nm when tensile strain was 57.85%. At the same time, the environmental stability originated from the moisturizing properties of the glycerol, which enabled the hydrogel to reliably transmit the information on temperature into the air without losing moisture. The reflection peak of the cylindrical thermochromic hydrogel shifted from 657 to 455 nm when the temperature increased from 22 to 45 °C, which realized temperature visual monitoring in the full-color range. The temperature sensitivity of the glycerol─nonclose-packed photonic crystals remained stable for 1 month, which provided an optimal option for continuous visual temperature monitoring.