Photochromic microcapsules anchored on cotton fabric by layer-by-layer self-assembly method with erasable property

Photochromic materials have great potential applications in many fields due to their reversible color change under light irradiation. Herein, a novel photochromic cotton fabric with high fatigue resistance was creatively fabricated via a facile electrostatic layer-by-layer self-assembly technology of photochromic microcapsules and sodium alginate. Chitosan was used to encapsulate photochromic dyes to form microcapsules to improve fatigue resistance, meanwhile, as the wall material of microcapsules in weak acid environment can provide the positive charge needed for electrostatic layer-by-layer self-assembly process. After the anionic modification of cotton fabric to achieve negative charge, electrostatic layer-by-layer self-assembly was taken place between -NH3+ on the wall material of microcapsules and -COO- in sodium alginate under the condition of pH = 5. For clear characterization of the regular charge changes of fabric surface during the assembly process, the methylene blue (a kind of cationic dye) dyeing of cotton fabrics was carried out, the K/S and Lab value of the dyed fabric showed a regular odd-even oscillation. The assembled five-layer microcapsules fabric can change from colorless to purple rapidly within 12 s under UV light, and reversibly return to the original state under the irradiation of green light quickly in 90 s. It can maintain excellent reusability photochromic performance (94.65%) after more than 20 reversible color-changing cycles, implying the good reusability in erasable optical data storage. Furthermore, since the photochromic dyes can absorb UV light, the as-prepared photochromic cotton fabric has excellent UV protection properties.