Stress decomposition and multimeric assembly evolution of ionotropic alginate hydrogels in large amplitude...

Sodium alginate (SA) hydrogels show complex rheological behaviors, which is related to the existence of multiple junctions, trapped entanglements, and network defects. Understanding the evolution of various structural components of SA networks in large amplitude oscillatory shear (LAOS) flow remains challenging. Herein, we develop a shear cessation method on Lissajous curves and propose a double stretch-exponential (DSE) model for analyzing multiple relaxations of SA networks. The results indicate that the response of SA networks in LAOS flow is able to be decomposed into strain rate-related network defects and the strain-related surviving network. Furthermore, a strain hardening (SH) model is developed to elucidate the strain hardening behavior of surviving network. As a result, the combination of the stress decomposition with the SH model allows us to explore the evolution of various structural components of SA networks with varying association strengths and strain amplitudes. A high association strength produces a low network defect content and a dense surviving network, while an increase in strain amplitude promotes the dissociation of multimeric assembly and the liberation of trapped entanglement. This study provides us with valuable insights to understand the microstructural origin of nonlinear mechanics, which will merit the design of high-performance polysaccharide biomaterials.