Dynamics of Capillary Rise Infiltration(CaRI) of entangled polymers into nanoparticle packings

Annealing a bilayer of a glassy polymer film and a nanoparticle packing above the glass transition temperature (T_g) of the polymer induces infiltration of the polymer into the interstices of the nanoparticle packing by capillary action. Ellipsometric monitoring of the rising polymer front shows that the infiltration dynamics can be described using the Lucas-Washburn equation. In this work, we probe the effect of extreme nanoconfinement on the infiltration dynamics of entangled polystyrene (molecular weight = 80k – 4M g/mol) into random packings of silica nanoparticles (diameter = 7 and 25 nm). The extent of confinement as given by the ratio of the radius of gyration of polymer to the characteristic pore size in the nanoparticle packing is varied between 2.5 and 50. We show that effective viscosity inferred from the Lucas-Washburn equation is lower than the bulk viscosity in nanoparticle packings with an average pore size of 4 nm; however, we also observe molecular-weight independent viscosity for high molecular weight polystyrene in silica packings with smaller void size (R_pore = 1 nm). We also observe that increasing confinement leads to a significant decrease in the segmental mobility as evidenced by an increase in Tg of polystyrene over 60 K higher than the bulk value.