Research On Mechanical Properties And Microscopic Mechanisms Of Elastomers With Weak Interaction

Elastomers are amorphous cross-linked polymers in the rubber state,which shows outstanding recoverability.Elastomers have been widely applied in industry and involved in life.In recent years,researchers have made progress in tuning the mechanical properties of elastomers by introducing nanofillers,sliding-rings,and sacrificial bonds.However,the mechanical properties need to be further improved to satisfy requirements in advancing applications.Elastomers have rich scales both in time and length,resulting in various interactions.The weak interaction has a significant impact on the mechanical properties of elastomers.High-performance elastomers have been prepared by adjusting the weak interaction.However,the influence of weak interaction on mechanical properties of elastomers is elusive,and the microstructural evolutions and corresponding mechanism still need to be deeply investigated.In this work,the influence of weak interaction on the mechanical behaviors of elastomers is investigated by utilizing coarse-grained molecular dynamics.Specifically,the weak interfacial interaction within the nanoparticle-reinforced elastomers and the inter-chain weak interaction in double-network elastomers are studied.The influence of weak interaction on the microstructural evolutions and mechanical properties is analyzed,and different microscopic mechanisms are proposed,which provide theoretical guidance in the preparation of advanced elastomers.Detailed work contents are as follows:1.Study on the influence of the weak interfacial interaction on mechanical properties of block copolymer based nanocomposites and microstructural evolutions.The interface between the block copolymer and spherical nanoparticles can be tailored by changing the weak interaction strength between soft(hard)segments and spherical nanoparticles.In addition,the arrangement of the hard domains embedded in the matrix can also be altered.Three different morphologies are found by tuning the weak interfacial interaction.The Payne effect observed in experiments is reproduced by conducting oscillatory shear simulations.According to the analysis of microstructural evolutions,the molecular mechanism of the Payne effect is proposed,including the looseness of hard domains and the desorption of polymer chains from the surface of nanoparticles.The effect of weak interfacial interaction on the above mechanisms is clarified based on the morphologies,which can explain the influence of the weak interfacial interaction on the Payne effect.2.Study on the influence of weak interaction on the uniaxial tensile mechanical behaviors of double-network elastomers and microstructural evolutions.The coarse-grained model is constructed to represent double-network elastomers,consisting of weak-interaction and covalently cross-linked networks.Monomers can aggregate into dense clusters,which act as physical crosslinks in the weak-interaction network,by enhancing the weak interaction between them.Based on the analysis of microstructural evolutions under tensile loads,two molecular mechanisms are proposed to explain the mechanical behavior.Microscopic mechanisms involve the dissociation of clusters in the weak-interaction network and bond elongation in the covalently cross-linked network.When increasing the weak interaction strength or the strain rate,the dissociation of clusters is inhibited,and the bond elongation is promoted,which improves the stress.3.Study on the influence of weak interaction on the fracture behavior of double-network elastomers and microstructural evolutions.The weak-interaction network is brittle and rigid.In contrast,the covalently cross-linked network is soft and ductile.According to the mechanical properties of the individual networks,the number and length of chains within the brittle network in the coarse-grained model discussed in Chapter 2 are modified.The tensile fracture behavior of double-network elastomer with the weak-interaction network is explored by analyzing the evolutions of voids and clusters.Furthermore,the influence of weak interaction strength on the toughness of double-network elastomers is studied.The resistance of clusters to dissociation is promoted by enhancing the weak interaction.In addition,more bond-breaking events are found in the covalently cross-linked network.The synergistic mechanism of the two networks leads to improving the toughness of the double-network elastomer.4.Study on the influence of weak interaction on the shock behavior of doublenetwork elastomers and microstructural evolutions.The effect of the weak interaction on the mechanical properties of double-network elastomers under the onedimensional shock wave is studied.The average size of clusters is enlarged by increasing the content of the weak-interaction network,which can improve Young’s modulus of elastomers.As a result,the Hugoniot state quantities such as the shock velocity,the shock pressure,and the shear stress are promoted.In addition,the spall strength is also improved.The increase of shock intensity can hinder the dissociation and reconstitution of clusters,which are beneficial to promote the spall strength.However,bonds in the covalently cross-linked network are broken under the extremely high shock intensity,resulting in the reduction of the number of elastic active chains.The resistance to the spallation is weakened.The spall strength is determined by both the behavior of clusters and the number of elastic active chains in the covalently crosslinked network.