(393h) Polymer Dynamics in Disordered Nanoparticle Packings

Infiltration of polymers into disordered nanoparticle packings has shown to be a powerful method of fabricating highly loaded nanocomposites with superb mechanical properties. Moreover, polymer-infiltrated nanoparticle packings provide a unique platform to study the dynamics of macromolecules under extreme nanoconfinement. The degree of confinement can be tuned by appropriate choice of particle size and polymer molecular weight. By using simple yet powerful tools like microscopy and ellipsometry, we investigate the dynamics of polymers in such confined environments at unprecedented levels of confinement. In capillary rise infiltration(CaRI), the polymer film-nanoparticle packing bilayer is annealed above the glass transition temperature of the polymer leading to the polymer wicking into the pores of the packing. The dynamics of rise of the polymer into the nanoparticle packing can be studied by ellipsometric front-tracking giving a measure of the chain dynamics of polymer – effective viscosity – based on the Lucas-Washburn equation. We report that while unentangled PS show slower-than-bulk chain mobility during capillary rise into 25 nm silica nanoparticle packings, entangled chains show enhancement in mobility (average pore size is 4 nm). This decrease in viscosity with increasing size of the polymer occurs despite a segmental-level slowdown, evidenced by increase in glass transition temperature (Tg). Increasing the degree of confinement by choosing even smaller particles such that the pore-size(1 nm) is comparable to the Kuhn length of the polymer leads to a constant, molecular-weight independent viscosity of polymers. Our investigations into the dynamics of high Tg, glassy polymers is complemented by studies of low Tg, mobile chains in disordered nanoparticle packings. Low Tg chains are infiltrated from an elastomer like a PDMS gel into nanoparticle packings at room temperature using leaching-enabled capillary rise infiltration (LeCaRI). Once infiltrated into a region of nanoparticle packings using LeCaRI, these mobile chains spread out into adjoining unfilled regions. This lateral motion of the front of mobile chains can be tracked by reflection microscopy as chains move from highly filled to empty pores. We will report results on the lateral motion of PDMS chains moving inside nanoparticle packings and the effect of capillary condensed water in these systems. Insights into the motion of macromolecules in confined environments will elucidate the effects of interfaces and confinement on the flow properties of polymeric fluids with practical applications in polymer processing, plastics upcycling, catalytic packings with electro-active polymer components, and synthesis of water-purification nanocomposite membranes.