  Nanocomposite films containing a high volume fraction (> 50vol%) of
nanoparticles (NPs) in a polymer matrix are promising for their functionality
and use as structural coatings, and also provide a unique platform to
understand polymer behavior under strong confinement. Previously, we developed
a novel technique to fabricate such nanocomposites at room temperature using
solvent-driven infiltration of polymer (SIP) into NP packings. In the SIP
process, a bilayer made of an underlying polymer film and a dense packing of
NPs is exposed to solvent vapor which induces condensation of the solvent into
the voids of the packing. The condensed solvent plasticizes the underlying
polymer film, inducing polymer infiltration into the solvent-filled voids in
the NP packing. In this work, we study the effect of confinement on the
kinetics of SIP and the final partitioning of polymer into the interstices of
the NP packing. We find that, while the dynamics of infiltration during SIP are
strongly dependent on confinement, the final extent of infiltration is
independent of confinement. The time for infiltration obeys a power law with
confinement, as defined by the ratio of the chain size and the pore size.
Qualitatively, the observed time scale is attributed to changes in
concentration regimes as infiltration proceeds, which lead to shifting
characteristic length scales in the system over time. When the concentration in
the pore exceeds the critical overlap concentration, the characteristic length
scale of the polymer is no longer that of the entire chain, but rather the
correlation length, which is smaller than the pore size. Therefore, at long
times, the extent of infiltration is independent of the confinement ratio.
Furthermore, favorable surface interactions between the polymer and the
nanoparticles enhance partitioning into the NP packing.

Materials Science;Mesoscale and Nanoscale Physics;Soft Condensed Matter