Thermoresponsive Structural Coloration of Hydrogel Fibers

Intelligent fibers with a structural color have wide applications in many cutting-edge fields and have attracted significant attention in recent years. However, most reported optical fibers have a fixed structural color because hard colloids were used as blocks of photonic crystals. Herein, we developed a simple and scalable method to realize hydrogel fibers with a dynamic structural color using soft and thermoresponsive microgels as photonic blocks. A full interpenetrated sodium alginate-polyacrylamide hydrogel fiber was prepared through an exclusion process, which is facile for scaled-up and continuous preparation of hydrogel fibers by controlling the injection speed. Amino group-doped poly(N-Isopropylacrylamide) microgels were attached to the surface of hydrogel fibers by the Schiff-base bonds and resulted in amorphous arrays, exhibiting angle-independent colors. Under temperature stimuli, the tunable structural color could be easily displayed through the shrinkage of the microgels. Moreover, the soft microgels could also be attached to the commercial wood fabrics easily, endowing the fabrics with thermochromic properties. Besides temperature, the microgels are also sensitive to humidity and ionic strength; therefore, the fabrics can simultaneously provide measurements of humidity and sweat amount for wireless monitoring. This versatile tunable structural color coating approach shows great potential for smart fibers and clothing fabrics and tracking for changes in environmental factors.