Effect of extreme nanoconfinement on the capillary rise of glassy polymers into densely packed nanoparticle packings*

Capillarity is a powerful driving force at the micro- and nanoscales. We show that polymers annealed above the glass transition temperature infiltrate into densely packed nanoparticle packings regardless of their degree of polymerization. Bilayers of glassy polymer film and nanoparticle packing are annealed at different temperatures and the rate of capillary rise is monitored using ellipsometry. By using the Lucas-Washburn model, we infer the effective viscosity of highly confined polymers undergoing capillary rise through nanoparticle packings. The extent of confinement is varied over a wide range by changing the size of nanoparticles and the molecular weight of the polymers. The physical confinement of the unentangled polystyrene in SiO2 nanoparticle packings results in a significant increase in the viscosity and glass transition of the polymer. The magnitude of increase is independent of the polymer-nanoparticle attraction as determined by the use of poly(2-vinyl pyridine) but varies strongly with the extent of confinement. Entangled polystyrene exhibits different trends than the unentangled counterparts under such extreme nanoconfinement.