Coupling network synthesis and modeling for microscopic understanding of strength in entangled polymer networks

Abstract

The strength of polymer networks, the maximum stress under uniaxial tension, arises from the collective loading and failure of heterogeneous polymer strands. However, its microscopic origins remain difficult to identify because network topology and strand-level forces cannot be directly resolved experimentally. Here, we combine experiments using polyacrylamide hydrogels as a model system with simulations using a mesoscale network model to determine how network structures govern strength. By varying precursor stoichiometry and degree of swelling, we systematically control the average strand length, entanglement-to-crosslink ratio, and strand prestretch. The model explicitly distinguishes crosslinks from entanglements and accounts for strand-length polydispersity, nonlinear elasticity, strand scission, and detanglement. We identify the strand density and the homogeneity of load distribution as two general descriptors of strength that apply across different network structures. Stronger networks maintain a sufficiently large population of load-bearing strands while distributing load more uniformly among them, thereby delaying localized strand scission and detanglement. Our approach combining experiments and modeling establishes a framework that relates microscopic mechanics to macroscopic fracture, which can guide a rational design of stronger polymer networks.