Hydrogen Bonding Enables Polymer Hydrogels with pH‐Induced Reversible Dynamic Responsive Behaviors

Abstract

AbstractPoly(acrylic acid‐co‐N‐vinylcaprolactam) (PAN) hydrogels containing multiple hydrogen bonds can exhibit pH‐induced reversible dynamic responsive behaviors. When placing a transparent hydrogel in an acid bath, as hydrogen bonds between comonomer units involving protonated COOH groups are formed faster than water diffusion, a nonequilibrium light‐scattering state is formed to turn the hydrogel opaque, while as the swelling equilibrium is reached over time, the hydrogel regains its transparency. Likewise, when the transparent, hydrogen‐bonded hydrogel is subsequently immersed in DI water, faster water absorption occurs in where more COOH groups are deprotonated, which also generates a light‐scattering state leading to opacity, while the transparency is slowly recovered after equilibrium. Using such two‐way dynamic transparency evolution, a PAN‐based hydrogel material is prepared to demonstrate a dynamic memory system for information memorizing‐forgetting and recalling‐forgetting.