A double network AG/P(AAm-AAc)/P2W18 hydrogel with high stretchability for flexible electrochromic device

In this study, a novel electrochromic hydrogel AG/P(AAm-AAc)/P 2 W 18 was prepared by loading polyoxometalate K 6 P 2 W 18 ·10H 2 O (P 2 W 18 ) into a double-network hydrogel formed with agar (AG) and copolymer of polyacrylamide (PAAm) and polyacrylic acid (PAAc). The mechanical properties of hydrogels can be tuned by adjusting the proportion of PAAc in the copolymer P(AAm-AAc). Electrochromic hydrogel shows the best mechanical properties when the proportion of PAAc is 10 % (AG/P(AAm-AAc)-10/P 2 W 18 ), and the maximum elongation at break and the fracture stress are about 2.0 and 2.5 times higher than that of pure PAAm. P 2 W 18 gives good electrochromic properties to the hydrogels without the addition of electrolytes. Under the external voltage, the electrochromic hydrogel changes from colorless to blue with the optical contrast up to 65.54 % at 700 nm. The electrochromic device based on this hydrogel is simple in structure, easy to manufacture and highly stretchable, which has good application potential in the field of wearable electronics.