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 breaking the chemical bonds. The water content of DN hydrogels increased after the F/T process which is consistent with the hypothesis of damage induced by freezing of water. DN hydrogels immersed in liquid nitrogen for a fast freezing process shattered into small pieces, and cracks appeared on the pieces.

中文翻译：

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冻融过程对双网水凝胶有限拉伸变形力学行为的影响

在应用冻/融（F / T）后，研究了由2-丙烯酰胺基-2-甲基丙烷磺酸（AMPS）和丙烯酰胺（AAm）合成的具有不同交联密度的双网络（DN）水凝胶的拉伸力学。 ） 过程。当在施加拉伸载荷时表现出颈缩的DN水凝胶经受F / T过程时，颈缩被抑制并且在拉伸变形中观察到应变硬化。在F / T过程之后，也减小了应力-应变曲线下的面积，该面积用于测量变形的工作并作为韧性的标准。具有较脆的第一网络的DN水凝胶的韧性降低更为明显。在第一个F / T循环后，样品的韧性显着降低。然而，样品的韧性在第二和第三次F / T循环后非常接近。进行F / T工艺后，DN水凝胶的机械性能降低归因于水因冻结而破坏了化学键，从而冻结了水对水凝胶内部结构的破坏。F / T过程后，DN水凝胶的水含量增加，这与水冻结引起的损害的假设相一致。将DN水凝胶浸入液氮中进行快速冷冻，然后破碎成小块，并且在这些块上出现裂纹。