(361c) Polymer Nanocomposite Films with Extremely High Filler Fractions Via Capillary Rise Infiltration (CaRI)

We present a novel approach to generate polymer nanocomposite films (PNCFs) with extremely high filler fractions (> 60 vol%) via capillary rise infiltration (CaRI) of polymer into a dense nanoparticle packing The CaRI process involves first generating a bilayer film of porous nanoparticle layer on a polymer layer, followed by annealing of the bilayer above the Tg of the polymer to induce polymer infiltration into the voids of the nanoparticle layer. By tuning the amount of polymer, we demonstrate that CaRI is also capable of generating fully filled or spatially homogeneous porous PNCFs. We utilize spectroscopic ellipsometry to characterize and monitor the polystyrene infiltration process into the titania nanoparticle packing in situ. The dynamics of CaRI is consistent with the Lucas Washburn model that has been used to describe capillary rise of liquid into porous media. However, we see a significant impact of confinement on the apparent viscosity of the polymer. In undersaturated CaRI (uCaRI), the infiltration process occurs in two stages. Upon annealing, we observe that the polymer layer is depleted rapidly via capillary-induced infiltration to form a dense composite at the base of the nanoparticle packing. Eventually, the front of this composite layer propagates throughout the nanoparticle packing, just as the refractive index of the composite decreases, indicating the redistribution of polymer throughout the nanoparticle matrix. We also demonstrate that the mechanical and optical properties of the CaRI composites can be readily tuned via varying the amount of polymer in the initial bilayers.