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Unformatted text preview: Matrix-induced nanoparticle interactions in a polymer melt: A molecular dynamics simulation study Dmitry Bedrov, Grant D. Smith, and James S. Smith Department of Materials Science & Engineering and Department of Chemical and Fuels Engineering, University of Utah, Salt Lake City, Utah 84112 ~ Received 19 May 2003; accepted 13 August 2003 ! A molecular dynamics simulation study of the influence of a polymer melt matrix consisting of bead-necklace polymers on the effective interaction between two spherical nanoparticles was performed. The potential of mean force ~ POMF ! between the two nanoparticles as well as entropy and energy contributions to the POMF was determined as a function of nanoparticle separation. The role of energy on the POMF was investigated by varying the strength of the polymernanoparticle interaction and comparing structure and POMF with those obtained for an athermal model. All features of the POMF as a function of nanoparticle separation were found to be strongly correlated with the polymer matrix density, the structure of the polymer at the nanoparticle interface, and the structure of the polymer in the interparticle region. The POMF was not found to correlate with polymer chain dimensions ~ e.g., radius of gyration ! in contrast to colloidal suspensions in dilute and semidilute solutions. Both energy and entropy effects were found to make important contributions to the POMF. For the athermal system, where all matrix-induced interactions are entropic in nature, the nanoparticle POMF was found to exhibit qualitatively different behavior from that of the energetic systems. 2003 American Institute of Physics. @ DOI: 10.1063/1.1615965 # I. INTRODUCTION AND MOTIVATION The introduction of particles into a neat polymer matrix ~ filled polymers ! is a time-established method for modifying polymer properties. 1 A well-known example is the addition of carbon black to rubbers that is responsible for increased strength and durability. 2,3 Inclusion of nanoscopic particles ~ nanoparticles ! , which have very high surface area to volume ratio, can potentially cause a much more dramatic effect on the properties of a polymer matrix and the resulting proper- ties of the polymernanoparticle composite ~ PNPC ! than is observed in conventional polymerparticle composites. Such PNPCs exhibit promising properties for a wide variety of applications. 4 8 The properties of PNPCs are strongly influ- enced by nanoparticle size and filler fraction, nanoparticle shape, nanoparticle distribution, polymer molecular weight, and the nature of the interactions between the nanoparticle and polymer matrix. In our previous study 9 we investigated the matrix- induced interaction between nanoparticles in a model PNPC by determining the matrix-induced potential of mean force ~ POMF ! between two spherical nanoparticles in a bead- necklace polymer melt matrix using molecular dynamics ~ MD ! simulations. We have concentrated on the regime where the radius of the particle, the radius of gyration of the...
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