Gradient dynamic cross-linked photochromic multifunctional polyelectrolyte hydrogels for visual display and information storage application

The homogeneous distribution of organic photochromic materials in the network can endow hydrogels with excellent photochromic properties, but many weaknesses, such as the poor mechanical properties and short service life, limit their further development in the field of visual display and information storage devices. To solve this problem, a novel photochromic polyelectrolyte hydrogel with excellent mechanical, conductive, self-healing and adhesive properties has been designed and prepared based on a triple gradual ionic-hydrogen bonds network through a unique buffer band-like structural programming method. In the hydrogel system, naphthoprans was attached to the polymer chains by hydrogen bonding to achieve remarkable photochromic efficiency and color rendering (photochromic time <4.5s). The unique photochromic hydrogel network with buffer band-like structure is programmed by introducing ionic and hydrogen bonds with gradient strength between polyelectrolyte polymer chains into the structure. The specific type and strength of interactions between polymer units were evaluated via the density functional theory (DFT) calculations. Such unique network endowed the photochromic hydrogel with considerable mechanical property (tensile strength >1.00 MPa, compressive strength >17.00 MPa), superior self-healing ability (healing time <30min, healing efficiency >90%), conductivity (6.72 × 10−3 S/cm), adhesive property and pH sensitivity. These excellent characteristics of the photochromic multifunctional polyelectrolyte hydrogel make it interesting candidates for visual displays and information storage devices.