Molecular dynamics simulations informed hyperelastic constitutive model with insights into entangled free chains

J Liu and S Liang and YX Zhu and L Zhao and MS Huang and ZH Li, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, 280, 109542 (2024).

DOI: 10.1016/j.ijmecsci.2024.109542

Due to the complexities of microstructure of molecular chains and their interactions, it has been a great challenge to quantify the correlation between physicochemical components and hyperelastic behavior of polymers through constitutive model. In the present work, molecular dynamics (MD) simulations are first performed to capture the evolutions of cross- linked and free chains under various deformation states. Following MD results, the conformations of entangled free chains are studied from two perspectives, one is the passive elongation induced by entanglement points and the other is the change in topological constraint. These conformations are then incorporated into a revised three-chain model to capture the enhancement in modulus and stretchability of highly entangled hydrogels. Accordingly, the Helmholtz free energy of polymers due to entangled free chains is divided into two parts, accounting for passive elongation and topological constraint, respectively. Based on this free energy decomposition and the revised three-chain model, a physics-based hyperelastic constitutive model is developed. This model is demonstrated to present an excellent capability to depict the behavior of a wide range of polymers under different deformation states. It can be used to decipher new enhancement mechanisms and map physicochemical components to mechanical behavior of polymers. The present model holds significant potential for optimal design of future polymeric materials.

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