Effects of coating composition and thickness on thermochromic performance and application in earplugs for swine fever

Thermochromic coatings have been widely investigated, with most studies focusing on novel microcapsule systems. However, the thermochromic performance of coatings under a spatially separated heat source, as well as the influence of coating parameters on thermochromic behavior, remains insufficiently explored. In this study, an earplug structure embedded with a thermochromic coating was prepared, and the effects of coating filler content, coating thickness, and dye concentration on thermochromic behavior were systematically investigated. A distinct color transition was successfully achieved even when the coating was positioned away from the heat source. Simulation results indicate that, under a 40 °C heat source, the effective color‑transition temperature of the coating within the earplug structure should be maintained at approximately 34 °C. The incorporation of HBN accelerates the transition process and narrows the color-transition temperature range, enabling complete color change at around 34 °C. In addition, the effective color-changing distance is extended from 2.2 cm to 3.7 cm; however, a high HBN content reduces the ΔE color difference. Increasing coating thickness prolongs the transition time and darkens both the initial and final colors, with a thickness of 30 μm yielding the maximum ΔE value. The addition of blue dye generates visually distinguishable pre-transition and post-transition states. Although increasing blue dye concentration decreases the ΔE value between pre-transition and post-transition colors, it increases the ΔE* value between the post-transition color and pig skin color. Under a 40 °C heat source, the thermochromic coating in the earplug rapidly changes from light purple to blue. These results suggest that thermochromic coatings hold potential for low-cost, visually intuitive earplugs for fever detection in swine, although further validation is required.