Non-swelling, super-tough, self-healing, and multi-responsive hydrogels based on micellar crosslinking for smart switch and shape memory

Abstract

Non-swelling super-tough polymer hydrogels have great potentials for stable applications in wet conditions. It has been challenging since most polymer hydrogels uptake water from the environment and swell, which deteriorates the mechanical strength and toughness. Here, we present multi-responsive non-swelling polymer hydrogels (PHFGs) by using amphiphilic triblock copolymer micelles as non-covalent crosslinkers. Pluronic F127 (or polyethylene oxide-block-polypropylene oxide-block-polyethylene oxide, PEO-PPO-PEO) (F-127) micelles are used as a prototype for the synthesis of micelle-crosslinked poly-(2-hydroxyethylene methacrylate) (PHEMA) hydrogels, without using any modification of F-127 or other crosslinkers. FT-IR and 1H NMR studies provide first evidence that F-127 micelles form extensive hydrogen bonding and hydrophobic association with PHEMA chains. The non-covalent crosslinked hydrogels show a high fracture elongation about 460 %, a fracture strength about 240 kPa, and a fracture toughness about 660 kJ/m3. Negligible swelling is observed for the polymer hydrogels in aqueous solutions. The hydrogels are self-healable, and responsive to variations in pH or water content to change volume, shape, and transparency. Such multiple-responsive polymer hydrogels are utilized as smart switches and shape memory materials that are actuated by environmental stimuli in a controllable manner.