Effect of Freeze/Thaw Process on Mechanical Behavior of Double-Network Hydrogels in Finite Tensile Deformation

Tensile mechanics of double-network (DN) hydrogels synthesized from 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylamide (AAm) with different cross-link density of the first networks was studied after applying the freeze/thaw (F/T) process. When a DN hydrogel which exhibits necking upon applying a tensile load undergoes F/T process, necking is suppressed and strain hardening is observed in a tensile deformation. The area under the stress–strain curve which measures the work of deformation and is a criterion of toughness also is reduced after the F/T process. The reduction of toughness in a DN hydrogel with more brittle first network is more pronounced. The toughness of samples reduced very markedly after the first F/T cycle; however, the toughness of the samples was very close after the second and third F/T cycles. The reduction of mechanical properties of DN hydrogels upon applying the F/T process is attributed to the damage induced by freezing of water to the internal structure of hydrogel by...