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Polymers filled with nanoscale fillers (carbon nanotubes or nanoparticles) exhibit enhanced properties compared with the neat polymer and with the polymer filled with micron-sized fillers at same volume fraction. Most interestingly, combinations of exceptional properties may be obtained as, for example, an increase in ductility without compromising strength, while insuring optical transparency as well as UV opacity.
The physical origins of this behavior are insufficiently understood and material optimization is currently performed experimentally by trial and error. This study is aimed at elucidating the main mechanisms that control the material behavior on multiple scales, and at capturing these phenomena in a macrocopic constitutive description of the composite.
The talk will begin with an overview of the mechanism of stress production in polymeric systems. The atomic-scale origins of stress in polymers will be discussed and contrasted with stress production in metals and ceramics. The mechanisms of stress relaxation will be analyzed within the stress production framework.
Then, the discussion will focus on the nanoscale structure of the nanocomposite, in particular, the structure of the polymeric material confined between fillers. The structure is analyzed as a function of filler size and curvature, chain length and the type of interaction between the chains and the filler.
Continuum models are derived based on these data. The elasticity of the composite is predicted based on the molecular scale structure using appropriate homogenization procedures. The viscoelastic behavior is captured within a network model, which is calibrated based on atomistic simulation results. The predictions of the model are compared with experimental data.
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