Polymer composites based on nanosized particles are experiencing a very fast growth during the last years due to their industrial applications and improved physical properties . The so-called nanocomposite materials are formed by filling a polymer matrix with inorganic particles whose typical dimensions are of the order of a few nanometers. Interest in such materials comes from the possiblity to control the effects that polymer/filler interactions have on the polymer chains, in terms of free volume, crystallinity, mobility, and conformation with the aim to improve the material properties . However, a well-defined control of the underlying interactions in nanocomposites is not a simple task, nor experimentally neither theoretically. In computer simulations, the main problem concerns the very long times usually required to get a proper relaxation of the system.
Here we present a coarse-grained model suitable for polymer nanocomposites which combines the Iterative-Boltzmann-Inversion method , the hybrid particle-field representation of non-bonded interactions , and a convenient description of a solid nanoparticle suitable for hybrid particle-field models . By means of the proposed approach we show that molecular simulations of polystyrene-silica nanocomposites can be succesfully performed. In particular, we document how the presence of a single silica nanoparticle significantly influences the structure of the polymer chains in terms of gyration radius and autocorrelation functions of the end-to-end distances. Furthemore, by grafting the nanoparticle with polystyrene chains we document a change in the swelling state of the grafted corona, such a change depending on the chain length and on the grafting density. This phenomenon, known as “wet brush to dry brush transition” has been observed also experimentally and plays a key role in determining the behavior of the nanocomposite.
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