Molecular Dynamics Simulation Resrarch On The Structural Design And Service Performance Of High-performance Elastomers

With the rapid development of national economy and science and technology,elastomer materials play an irreplaceable role by virtue of their unique performance characteristics.In order to manufacture high-performance elastomers,establishing a link between microstructure and macroscopic properties is the key to achieving performance controllability.In this paper,molecular dynamics simulation is used to systematically investigate the service performance of elastomer materials from the perspective of mechanics and aging.The main contents are as follows:(1)Through coarse-grained molecular dynamics simulation,we successfully fabricated a heterogeneous network structure,which was divided into several regions with different crosslink densities.Firstly,we found that there is an optimal crosslink density ratio between high and low crosslink density regions to obtain the greater mechanical strength.Secondly,the effect of the regularity of the network topology(by changing the distribution of different regions)on mechanical properties was also studied.It was clearly observed that the polymer network showed better elastic response and mechanical properties as the distribution of two-phase regions became uniform.Finally,we investigated the effect of the selective distribution of nanoparticles(NPs)on mechanical properties by introducing NPs into a pre-designed heterogeneous network.Results showed that the selective distribution of NPs in the high crosslink density region had a more significant effect on the mechanical reinforcement.By characterizing the mean square displacement of molecular chains and NPs,we attribute this phenomenon to the movement restriction effect of the extremely small mesh size in the high crosslink density region on the nanoparticles.(2)Through all-atom molecular dynamics simulation and using ethylenepropylene-diene monomer(EPDM)copolymer as the research object,the mechanism underlying the influence of the harsh environment that may cause accelerated aging(high temperature,humidity,and salt spray)on the static and dynamics characteristics of EPDM is investigated.First,evidence shows that the glass transition temperature(Tg)obtained by fitting mean square displacement does not rely on the selection of the equilibrium time.Second,radial distribution function,chain configuration,and nonbonding interaction were analyzed and it is inferred that the ambient humidity and temperature show a significant synergy on the EPDM system,which is attributed to the aggregation state transition and diffusion behavior of partial water at high temperatures.Finally,water and salt were considered as two factors to explore the influence on the Tg and the mobility of the molecular chain.It is concluded that the existence of water molecules significantly affects the chain dynamic behavior of EPDM,while salt is not regarded as an influencing factor.Deeply,aimed at improving the durability of a marine material such as EPDM,compared to salt spray atmosphere,the hot and humid environment should be more focused in the future.Generally,our simulated results may provide some guidelines and insights for fabricating elastomer materials with excellent service performance.