Simulation Study On The Effect Of Nanoparticles On Conformation And Dynamics Of Polymer

The approaches of using nanoparticles to improve the properties of polymer materials have become a research hotspot in the field of polymer science.The thermal and mechanical properties of polymer nanocomposite are highly dependent on the conformational and dynamic properties of the polymer chains in the nanocomposite.Studying the effects of nanoparticles on the conformational and kinetic properties of polymer chains is helpful to understand the properties of polymer nanocomposites and to reveal the relationship between structure and activity of polymer nanocomposites In this thesis,the effects of nanoparticles on the conformational and dynamic properties of fully flexible and semi-flexible polymers are studied by performing computer simulations.Our research contents and main results are summarized as follows:(1)The conformation and dynamics of flexible polymer chains in the presence of nanoparticles are simulated using dynamic Monte Carlo method.In our simulations,nanoparticles are periodically distributed and kept stationary in the system.Several factors including the interaction between nanoparticle and polymer,the size and concentration of nanoparticles,have been investigated.The simulation results show that strongly attractive nanoparticles induce the adsorption of polymer chains,which significantly affects the conformation and dynamics of the polymer chain.The influence of nanoparticles is related to the relative size of nanoparticles(?n)and polymer chain(Rg,the radius of gyration of the polymer chain in extremely dilute solution),the relative size of the interparticle distance(d)and the end-to-end distance of polymer chain in extremely dilute solution(R),as well as the ratio of the number of polymer chains to the number of nanoparticles(Np/Nn)in the system.It is found that nanoparticles exhibit the strongest impact on the properties of polymer chain at ?n?Rg and R?2d.In this case,the size and diffusion coefficient of the polymer chain both first decrease with the increase of Np/Nn,and they reach a minimum at Np/Nn=1.Afterwards,they increase with further increase of Np/Nn.(2)The influence of nanoparticles on the structure of semi-flexible polymer solution are studied by performing molecular dynamics simulations.It shows that the structure of semi-flexible polymer solution is dependent on the concentration of polymer solution,the chain rigidity,the interaction between nanoparticle and polymer chain,as well as the concentration of nanoparticles.In terms of pure polymer solution,a transition from an isotropic phase to a nematic phase is observed with an increase in the rigidity and concentration of polymer.The critical concentration for the transition from isotropic phase to nematic phase decreases with the increase of the chain rigidity.A slow addition of strongly attractive nanoparticles into the isotropic polymer solution induces an ordered arrangement of polymer chains.And nanoparticles themselves form string-like aggregates parallel to polymer chains.