A Theoretical Study of Tethered Nanoparticles as Novel Fillers In Polymer Nanocomposites
Arthi Jayaraman, Department of Chemical and Biological Engineering, University of Colorado, Boulder, Boulder, CO 80309 and Kenneth S. Schweizer, Department of Material Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St., Urbana, IL 61801.
We have generalized the microscopic Polymer Reference Interaction Site Model (PRISM) theory to study the phase behavior of polymer-tethered spherical nanoparticles placed in a homopolymer matrix. Melts and dense solutions of polymer-tethered nanoparticles, in the absence of polymer matrix, show strong concentration fluctuations indicative of aggregate formation and/or a tendency for microphase separation, as the total packing fraction and/or particle attraction strength increase. When tethered nanoparticles are placed in a polymer matrix there is a competition between microphase separation and macrophase separation. Single-tethered nanoparticles exhibit a microphase spinodal curve that is a combination of dilution-like (as seen in copolymer–homopolymer mixture) and depletion-like (as seen in colloid-polymer mixture) behavior. The microphase spinodal temperature shows a non-monotonic dependence on matrix polymer chain length. As the number of tethers increases, the microphase spinodal curves become more dilution-like and the effect of matrix polymer length on the spinodal temperature diminishes. The effect of matrix polymer chain length, nanoparticle size, number and length of polymer tethers, position of grafting sites, total fluid packing fraction, and particle-particle attraction strength on the structure, scattering patterns, and tendency for microphase ordering will be presented.