Interfacial Friction Controls the Motion of Confined Polymers in the Pores of Nanoparticle Packings

The dynamics of confined polymers play a key role in determining the properties and performance of nanoscale polymeric systems such as membranes, coatings, and nanocomposites. The impact of confinement on polymer dynamics is confounded by various factors such as entanglement, interfacial friction, and environmental conditions such as relative humidity and temperature. Here, we monitor the room-temperature lateral motion of polydimethylsiloxane of varying molecular weights in the nanopores of a silica nanoparticle packing with an average pore size of 4 nm. Lateral concentration profiles obtained by ellipsometric mapping are used to extract the effective diffusivity (Deff) of the chain. Rouse-like scaling of diffusivity (Deff N-1) for polymers above the entanglement molecular weight signals the reduced role of topological entanglements in chain relaxation. An increase in effective diffusivity with humidity further indicates the dominant role of interfacial friction in the dynamics of confined polymers. This study unveils the interplay of confinement, interfacial friction, and atmospheric humidity on the motion of chains in confined porous media. The key observations of this study can be applied in the design of particle-filled membranes, functional coatings, and patterned surfaces.