Temperature Effect On Interfacial Structure And Dynamics Properties In Polymer/single-chain Nanoparticle Composite

The oriented design of materials has been always the direction of the modern research.It is commonly accepted that by mixing different types of materials can enhance the materials properties,such as optical,electrical,mechanical properties and others.A better understanding and investigating of the interactions between nanoparticles(NP)and polymer segments can help us control the dispersion of NPs in polymeric materials,and hence achieve better control or design of desired properties.Recently,single chain cross-linked nanoparticle(SCNP),has received considerable attention.The nanocomposites composed of linear polymers and such SCNPs have unique rheology and glass transition behavior.For instance,in linear polystyrene(PS)chain/PS SCNP composites,the nuisance enthalpic interactions can be reduced to a minimum.In addition,both pure SCNP melt and pure linear PS chain melt has the same glass transition temperature(Tg).However,the Tgof their blends is lower than that pure melt.Furthermore,the viscosity of materials decreases with the addition of SCNPs,which is contrary to theoretical prediction by Einstein.As far,a full understanding of the mechanism of the interactions in such polymer/SCNP system is lack.It is therefore necessary to investigate the interaction mechanism in such system by multiscale simulation method.However,for long polymer chain,especially for SCNP,building a well equilibrated initial configuration is hard to achieve.In the current work,to investigate the composite system consisting of linear PS chains and one single SCNP,we utilize available coarse-grained(CG)PS model to obtain the well-equilibrated configuration through long enough molecular dynamics simulation.Based on the well-equilibrated CG configuration,we develop the reverse mapping(RM)method to reconstruct the atomistic details based on the CG configuration.Interface structure and dynamics properties in an all-polystyrene composite composed of linear chains and one single-chain nanoparticle(SCNP)are investigated by using large-scale molecular dynamics simulations at both coarse-grained and full atomistic level.We demonstrate that the SCNP adopts a crumpled globular state in composite,it has layered internal structures especially at low temperatures.When temperature decreases,its interior phenyl rings(i PRs)will parallel to each other and scaffold cross-linking bonds will undergo a “loose-to-tight” transition,leading to a “soft-to-hard” transition of the SCNP.Such transition will provide more interior free volume and therefore result in faster rotational relaxation of inner layer i PRs at low temperature.It also facilitates the infiltration of the matrix monomers,resulting in an enhanced interfacial correlation and therefore a stronger deceleration effect in diffusion of matrix monomers at low temperatures.These results provide new insights into unique structure and dynamics properties at polymer/SCNP interface region.