Tough interpenetrating Pluronic F127/polyacrylic acid hydrogels

Tough interpenetrating polymer network (IPN) hydrogels with pH- and temperature sensitivity were prepared by crosslinking copolymerization of acrylic acid (AAc) and N,N'-methylenebis(acrylamide) in 20 w/v% aqueous solutions of F127 (PEO99-PPO65-PEO99). The presence of F127 within the gel network slightly decreases the elastic modulus while the loss factor significantly increases, revealing increasing energy dissipation in IPN hydrogels. Cyclic compression tests show large mechanical hysteresis in IPN hydrogels due to the reversible formation of ionic clusters and hydrophobic associations of F127 molecules. The dissipative mechanisms created by F127 lead to the improvement in the mechanical performance of IPN hydrogels when compared to the polyacrylic acid (PAAc) gel controls. PAAc hydrogel formed at 10% AAc fractures under a compression of 0.2 MPa at 78% strain, while the corresponding IPN hydrogel sustains up to 7 MPa compressions at 98% strain, leading to an increase of toughness from 31 to 335 kJ/m(3). IPN hydrogels subjected to the heating-cooling cycles between below and above the micellization temperature of F127 show characteristic features of F127 solutions, i.e., increase of the dynamic moduli on raising the temperature, and thermal hysteresis behavior. (c) 2013 Elsevier Ltd. All rights reserved.