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Sergei Egorov: „Effective Pair Potentials between Nanoparticles Induced by Single Monomers and Polymer Chains”
Department of Chemistry, University of Virginia, Charlottesvile, VA, USA

Using Density Functional Theory and Molecular Dynamics simulations, we systematically study the effective pair potential between two particles induced by unconnected monomers and by poly- mers at various polymer concentrations, particle sizes of nano-scale, and polymer-particle interac- tions. In the case of athermal interactions, we verify that the entropic depletion forces between two nanoparticles inside a solvent of unconnected monomers oscillate in accordance with the ra- dial distribution of monomers around one nanoparticle, and that the strength of polymer-induced entropic depletion forces raises linearly with the increase of nanoparticle size. When introducing direct attractive interactions between nanoparticles and polymers, the adsorption of polymer seg- ments on the surface of each nanoparticle induces repulsive forces between the nanoparticles which are shown to eliminate the depletion attractions. Further adsorption by enhancing the attraction strength between polymer and nanoparticle leads to the formation of thin, enthalpically stable polymer-layers on the surfaces of nanoparticles. In this way, the nanoparticle size is effectively increased and the depletion attraction reappears at a somewhat increased particle distance. The observed phenomena become increasingly pronounced at higher polymer concentrations.