Supramolecular polyurea hydrogels with anti-swelling capacity, reversible thermochromic properties, and tunable water content and mechanical performance

Abstract

Supramolecular polyurea (PU) hydrogels with combined anti-swelling capacity, thermochromic properties, and tunable water content and mechanical performance were obtained by immersing phase separated PU films with hydrophilic soft segments in water till swelling equilibrium. The multiple H-bonds within hard-segment domains are critical to the swelling and mechanical properties, which were rationally designed by using simultaneously two aliphatic diisocyanates with different symmetry and varying molar ratio. Consequently, the hydrogels exhibit a wide range of equilibrium water content (57–80%), elastic modulus (22–476 kPa), breaking strength (33–1720 kPa), and elongation at break (160–1460%). The hydrogels also exhibit fast recovery during cyclic loading-unloading. The incorporation of strong quadruple H-bonds into hard-segment domains endowed the hydrogels with stable anti-swelling capacity. Additionally, the hydrogels changed from transparent to opaque reversibly upon heating and cooling, originating from the phase transition of soft segments. The developed supramolecular PU hydrogels show promising potentials in many fields like smart windows.