Simulations of Filled Polymers on Multiple Length Scales
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Simulations of Filled Polymers on Multiple Length Scales Francis W. Starr and Sharon C. Glotzer Polymers Division and Center for Theoretical and Computational Materials Science, National Institute of Standards and Technology, Gaithersburg, MD 20899 ABSTRACT We present simulation results of the effect of nanoscopic and micron-sized fillers on the structure, dynamics and mechanical properties of polymer melts and blends. At the smallest length scales, we use molecular dynamics simulations to study the effect of a single nano-filler on the structure and dynamics of the surrounding melt. We find a tendency for polymer chains to be elongated and flattened near the filler surface. Additionally, the simulations show that the dynamics of the polymers can be dramatically altered by the choice of polymer-filler interactions. We use time-dependent Ginzburg-Landau simulations to model the mesoscale phase-separation of an ultra-thin blend film in the presence of an immobilized filler particle. These simulations show the influence of filler particles on the mesoscale blend structure when one component of the blend preferentially wets the filler. Finally, we present some preliminary finite element calculations used to predict the effect of mesoscale structure on macroscopic ultrathin film mechanical properties. INTRODUCTION Revolutionary advances in the design and fabrication of new materials that are lightweight and high strength will come from advances in the fundamental understanding of nanocomposites, in which nanoscopic fillers (“nanofillers”) are dispersed on nanometer scales within the polymer matrix [1,2,3]. Already, major enhancements in mechanical, rheological, dielectric, optical, and other properties of polymer materials have been achieved by adding fillers such as carbon black, talc, silica, and other inexpensive, inorganic materials. Nanofillers such as nanotubes, silica beads and cages, and clays, offer phenomenal advantages over these more traditional fillers because greater property improvement is achieved with far less material (see Figure 1 for examples of filler and nanofiller geometries). For example, adding 1% by weight of ultra-fine, synthetic mica (30-nm diameter disks) to nylon gives super-tough nylon, while adding the same amount of traditional mica (micron-sized talc) gives only a slight improvement in toughness over the unfilled polymer. The growing ability to design customized nanofillers of arbitrary shape and functionality provides an enormous variety of possible property modifications by introducing specific heterogeneity at the nanoscale [2,4,5]. However, little is known about the specific influence of nanofillers on the polymers surrounding them, and thus the development of highly designed, nanostructured materials for specific applications is currently limited. Future breakthroughs in the development of organic/inorganic hybrid nanocomposites will be possible by manipulating the inorganic phase on nanometer scales in order to achieve specific properties. Achieving such capability will require ins
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