Mechanically Robust, Stimuli-Responsive, Multi-Functional Luminescent Hydrogels Through Strategic Exfoliation of Nano-Clay and Dynamic Lanthanide Ion Complexation

Abstract

Developing multifunctional smart luminescent hydrogel materials has recently garnered tremendous interest. Nevertheless, most of the reported luminescent hydrogels fail to adequately satisfy the criteria for both robust mechanical characteristics and smart luminescence. This study reports smart luminescent hydrogels with enhanced mechanical properties through Laponite clay-incorporated in situ lanthanide ion cross-linked co-polymerization of acrylamide, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and terpyridine-based hydrophobic acrylic co-monomer as lanthanide sensitizer and to promote hydrophobic association. The addition of Laponite clay resulted in significant enhancement of luminescence within the hydrogel matrix and superior mechanical properties. A synergistic combination of electrostatic interaction, hydrophobic association, and metal-ligand interaction helped to achieve tensile strength of ≈330 kPa, high flexibility (fracture strain of 1110%), and toughness (≈1.8 MJ m^-3). The ionically conducting (4.54 mS cm^-1) hydrogel is further utilized for demonstrating a flexible human motion sensor and communicator for speech disability. The stimuli-responsive behavior and multi-color luminescence of the hydrogel are exploited to demonstrate potential application for anti-counterfeiting through ASCII Code and QR code, and to construct a logic system using single-input logic operation (NOT, PASS1) and double-input logic operation (OR, IMPLY), which may have significant potential in the field of multicolor pattern anti-counterfeiting and information encryption.

Keywords: anti‐counterfeiting; hydrophobic association; logic gate; multi‐color luminescence; multi‐stimuli responsive luminescence.