Effect of Strain History on Stress and Permanent Set in Cross-Linking Networks:  A Molecular Dynamics Study

• Published in: Macromolecules Vol. 37; no. 14; pp. 5468 - 5473
• Main Authors: Rottach, Dana R, Curro, John G, Grest, Gary S, Thompson, Aidan P
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 13.07.2004
• Subjects: Applied sciences; Chemical reactions and properties; Crosslinking, vulcanization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Elastic modulus; Oriented polymer; Computer simulation; Crosslink density; Molecular dynamics method; Crosslinked polymer; Mechanical properties; Theoretical study; Uniaxial strain; Crosslinking; Property structure relationship
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma049723j

Polymer networks undergoing cross-linking reactions are studied using molecular dynamics simulations to investigate how the stress is influenced by the coupling between cross-linking and deformation. For networks cross-linked in the undeformed state, the modulus increases linearly with the cross-link density as expected from rubber elasticity theory. When cross-links are added to a network that was uniaxially deformed, the stress remains constant in accordance with the independent network hypothesis of Tobolsky. When the deformed network is subsequently released, permanent set is observed. Using the independent network hypothesis, together with the affine theory of rubber elasticity, a constitutive model is developed that accounts for the effect of the coupling between the cross-link density and strain histories of the network. The permanent set predictions from the affine model are higher than found from MD simulations.