Polymer Dynamics In Disordered Nanoparticle Packings: Effect Of Confinement, Interfaces, And Humidity

Infiltration of polymers into disordered nanoparticle packings has shown to be a powerful method of fabricating highly loaded nanocomposites with superb mechanical properties. 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. The presence of large interfacial area between the polymer and the particle, high degree of nanoconfinement, and environmental triggers like atmospheric humidity can impact the dynamics of polymers at the segmental and the chain level. By using tools like microscopy, ellipsometry and molecular dynamic simulations, we investigate the dynamics of polymers at unprecedented levels of confinement. In solvent-driven infiltration of polymers (SIP) system, polymer chains are plasticized by capillary condensed solvent leading to capillary motion of the solvated polymer into the pores of the nanoparticle packing. We detail our investigations on the mechanism of infiltration with increasing polymer-nanoparticle interactions. 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. Our investigations into the dynamics of high Tg, glassy polymers is complemented by studies of low Tg, mobile chains in disordered nanoparticle packings. Once infiltrated into a region of nanoparticle packings, these mobile chains spread out into adjoining unfilled regions. This room temperature, spontaneous lateral motion of polymer can be tracked to understand interfacial polymer diffusion under confinement. Higher humidity, unexpectedly, leads to faster spreading of the polymers within the packings possibly due to reduced particle-polymer friction with water coverage on particle surface. Thus, this work presents the effects of confinement, interfacial interactions, and atmospheric humidity on the chain and segmental dynamics of polymers in pores of disordered nanoparticle packings