Molecular Dynamics Simulation On Elastomers With Different Double Network Structure:Toward Improved Mechanical Properties

Focused on the topic of improving the mechanical properties of elastomers and their composites,in this paper we microscopically explored the effect of the particular double network structure on the mechanical properties of the elastomeric materials taking advantage of the molecular dynamics simulation methods.We mainly concentrated on the microstructure of the interpenetrating double-network and the pre-stretched double-network structural elastomers and their macroscopic mechanical properties,as follows:(1)The structural characteristics,the tensile and dynamic shear mechanical properties of the interpenetrating double-network structural elastomers.Through molecular dynamics simulation,the elastomeric nanocomposites with semi-interpenetrating or interpenetrating network structure,in which the NP network connected by dual-end functionalized short chains and further immersed in the polymeric matrix was successfully fabricated.A uniform dispersion of NP and the most distinct interpenetration state of interpenetrating network structure systems was gained by tuning the flexibility and density of the dual-end grafted chains.Based on the optimal structure,stronger interfacial interaction between grafted chains and matrix chains and higher NP network integrity could both improve the tensile mechanical property of the semi-interpenetrating or interpenetrating network systems.Particularly,we found that in the semi-interpenetrating network system,compared to the direct compounding system of elastomers and bare NP,the dynamic shear mechanical properties of the NP-network filled polymer matrix system exhibited less Payne effect,higher storage modulus as well as lower energy loss at large strain amplitude.This provides a new idea for the design and preparation of new high-performance tire tread rubber.(2)The microstructure and the mechanical properties of elastomers with prestretched double network structure.Through molecular dynamics simulations,we firstly validated the accuracy of the simulation method by affirming the independent network hypothesis as well as the experimental results on the tri-block copolymers with a prestretched competitive double network.Following the simulation method verified,we investigated the effect of the crosslinking network ratio on the mechanical properties of the prestretched double-network homopolymers under uniaxial tension.We found that the prestretched double network contributed greatly to the enhanced tensile stress and ultimate strength at fracture,as well as to the lower permanent set(the residual strain)and lower dynamic hysteresis loss.Interestingly,elastomers with pre-stretched double network structure showed a significant mechanical anisotropy:in the parallel direction,both the first and the second crosslinked network took effect to bear the external force;whereas in the perpendicular direction,only the second crosslinked network was relevantly effective,which were revealed through the statistical observation of the type and number of broken bonds during the tensile fracture process.Additionally,the elastomeric nanocomposites with a prestretched double network exhibited similar tensile mechanical properties to those of the studied homopolymers with prestretched double network.The microscopic study on the prestretched double-network structural elastomers provides a novel perspective to regulate the mechanical properties of elastomers and their nanocomposites,aiming toward the design of elastomers with higher performance and a desirable anisotropical behavior.