Fabrication and Responsive Application of Flexible Yarns with Structural Colors Based on Photonic Crystal Hydrogels

Most of the current studies on the preparation of stimulus-responsive smart hydrogel textiles are conducted at the fabric level, ignoring the direct modulation of the fabric structure and properties by the yarns. Compared with smart-responsive fabrics, smart-responsive yarns can not only be used individually but also be woven into textiles with complex structures and brilliant patterns. However, constructing hydrogel PCs to prepare smart-responsive yarns with a rough surface, hair, and large surface undulations remains a major challenge. In this study, smart hydrogel yarns that had no color in the dry state but could quickly show bright and eye-catching structural colors after coming into contact with water were prepared. Results demonstrated that the prepared P(NIPA-co-St) hydrogel microspheres exhibited good sphericity and monodispersibility. The glass-transition temperature of the P(NIPA-co-St) hydrogel microspheres increased by 6.77 °C compared with that of the pure PNIPA hydrogel microspheres. Photonic crystal hydrogel (PCH) with vibrant structured color after coming into contact with water was easily assembled on yarns when the concentration of the P(NIPA-co-St) hydrogel microspheres was about 8.5 wt % and the self-assembly temperature was 25 °C. The smart hydrogel yarns exhibited a fast response time and excellent rubbing color fastness, washing color fastness, and reusability. The prepared smart hydrogel yarns could also be blended with ordinary yarns to produce smart warning textiles. The smart warning textiles could immediately display colors in rainy or foggy weather without affecting the original pattern of the fabric in a dry climate. This research provides ideas for realizing stimulus-responsive smart hydrogel textiles made from yarns.