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Résumé:

Understanding the motion of nanoparticles in polymer solutionsand melts is a problem of broad importance, with applications tomany different fields, such as material science, biophysics, andmedicine. If the nanoparticles are larger than the polymer's radiusof gyration, their structure and dynamics can be well described interms of effective pair potentials. However, much remains to beunderstood in the so-called “protein limit”, where the size of thenanoparticles becomes comparable to or smaller than that ofthe polymers. Moreover, most of the previous study consideringthis size range have only focused on the dilute nanoparticleregime, which is easier to handle since inter-nanoparticleinteraction can be neglected and the properties of the polymersolution/melt are expected to be unchanged.Using molecular dynamics simulations, we study the dynamic andstructural properties of a semidilute polymer solution containingwell dispersed spherical nanoparticles of size smaller than thepolymer's radius of gyration. We consider various nanoparticlediameters and a broad range of nanoparticle volume fractions,up to values for which the inter-nanoparticle interactionbecomes important.We find that the polymers slow down when the nanoparticleconcentration is increased, in qualitative agreement with theconfinement parameter theory (Choi et al.,ACS Macro Lett.2013,2,485−490), according to which polymers slow downbecause they have to squeeze through “bottlenecks” created bythe presence of the nanoparticles. Also the nanoparticles slowdown when their concentration is increased, with the magnitudeof the slowing down depending in a non-trivial way on their size.Surprisingly, if the concentration of the nanoparticles is increasedpast the range in which the nanoparticle dispersion is good, thediffusivities of polymers and nanoparticles reach a minimum andthen start to increase.