Experimental investigation of the mechanical behavior of a poly(acrylamide-co-sodium acrylate) hydrogel

Stimuli-responsive hydrogels consist of a porous 3D framework that is saturated with solvent. Immersed in a solution bath, these gels can exhibit an enormous volume change due to absorption or release of solution. Depending on the type of gel, this effect can be generated for example by variation of the ion concentration in the surrounding solution bath or by an applied electrical field. The mechanical behavior of these polymers is influenced not only by the solid-state skeleton, but also by the interacting fluid. Thus, a visco-elastic behavior can be observed on the macroscopic scale. Based on the specific properties of the polymer gel and the interaction of the different phases, the determination of the mechanical properties of this material turns out to be non-trivial. In the present work, the mechanical behavior of a poly(acrylamide-co-sodium acrylate) hydrogel in the fully swollen state is investigated by a newly developed tensile test and for longtime investigations by a creep test. For this purpose, two newly developed different experimental setups based on digital image correlation are used.