On the Necking Phenomenon in Pseudo-Semi-Interpenetrating Double-Network Hydrogels

A detailed physical picture of necking phenomenon in semi-interpenetrating double-network (SIDN) hydrogels was developed using the tensile mechanics of DN hydrogels synthesized from 3-sulfopropyl acrylate potassium salt (SAPS) and acrylamide (AAm) with different molecular weights. Uniaxial tensile tests for DN hydrogels already damaged by a compression load demonstrated the necking required a first network with a brittle structure. Although necking originates from the brittle nature of the first network, the molecular weight of polymer chains of the second network is an important factor for neck propagation. The finite deformation of DN hydrogels is characterized by two regimes of deformation: one where the neck initiates and a second where it propagates.