From ultrastiff to soft materials: Exploiting dynamic metal-ligand cross-links to access polymer hydrogels combining customized mechanical performance and tailorable functions by controlling hydrogel mechanics
By Dutta, Agniva; Ghosal, Krishanu; Sarkar, Kishor; Pradhan, Debabrata; Das, Rajat K.
Published in Chemical Engineering Journal
2021
Abstract
Recently hydrogels have attracted much attention due to their great potential for a wide range of applications, which require specific set of mechanical properties and customized functions for specific applications. However, traditional hydrogels with inferior mechanical properties lack the scope for wider tuneability. So it becomes a great challenge to prepare a hydrogel system which can cater to wider mechanical and functional needs. This work reports for the first time a facile one step fabrication of Poly(methacrylamide-co-vinylimidazole)-M2+ (M= Ni and Zn) fully physically cross-linked hydrogels with fixed total monomer feed concentration and co-monomer ratio, wherein by controlling the kinetics of metal-ligand interactions, the as-prepared hydrogel shows ultra wide spectrum of mechanical properties (Compressive strength ∼ 103 to 247 MPa at 96% strain and compressive stiffness of ̴ 0.434 to 8.944 MPa; elastic modulus ∼ 0.73 to 38.8 MPa; tensile strength ∼ 0.55 to 6.77 MPa; toughness ∼ 1 to 35.88 MJ m-3; strain at break ∼ 332 to 1132 %). Furthermore, the presence of pH-responsive metal-ligand cross-links along with hydrophobic methyl group in the backbone allows for pH-dependent tuning of mechanical properties at alkaline pH (Elastic modulus ∼ 155 MPa, tensile strength ∼ 7.2 MPa and compressive stiffness ∼ 36 MPa); The hydrogels demonstrate fast self-recovery, excellent fatigue resistance and efficient self-healing, along with temperature dependent shape memory behaviour. Applications of these hydrogels are demonstrated in highly sensitive flexible resistive (Gauge factor of 11 and 22 at 100 and 200% strain respectively) and capacitive sensors for motion and pressure sensing and as an electrolyte for the fabrication of a compressible supercapacitor (which could withstand ∼ 3000 fold weight of the whole supercapacitor).