Critical Contact Angle to Induce Capillary Rise of Polymers in Nanopores Does Not Depend on Chain Length.

We study the effect of physical confinement on the capillary infiltration of polymers into cylindrical nanopores using molecular dynamics simulations. In particular, we probe whether the critical contact angle (θc) above which capillary rise infiltration ceases to occur changes for long-chain polymers, possibly due to loss of conformation entropy induced by chain confinement. Surprisingly, θc does not strongly depend on the length of polymer chains and stays constant for large N. A free energy model is developed to show that θc depends strongly on the size of statistical segments rather than N, which we confirm by performing MD simulations of infiltration with semiflexible polymers. These results could provide guidelines in manufacturing polymer nanostructures and nanocomposites using capillary rise infiltration.

Nanoporous Polymer-Infiltrated Nanoparticle Films with Uniform or Graded Porosity via Undersaturated Capillary Rise Infiltration.

In this work, we present the fabrication of nanoporous polymer-infiltrated nanoparticle films (PINFs) with either uniform or graded porosity based on undersaturated capillary rise infiltration (UCaRI) and study the processing-structure-property relationship of these nanoporous PINFs. The UCaRI process involves first generating a bilayer film of a randomly packed nanoparticle layer atop a polymer layer, such that the volume of the polymer is less than the void volume in the nanoparticle packing. Subsequently, the bilayer film is annealed above the glass transition temperature of the polymer to induce polymer infiltration into the voids of the nanoparticle packing. Using in situ spectroscopic ellipsometry and molecular dynamics simulations, we observe that the polymer transport occurs in two stages: capillarity-induced infiltration, followed by gradual spreading, likely via surface diffusion. By varying the annealing time, UCaRI enables the generation of graded or uniform nanoporous PINFs. We also show that these nanoporous PINFs have tunable optical and mechanical properties, which can be tailored simply by changing the nanoparticle to polymer layer thickness ratio in the initial bilayer. The UCaRI approach is versatile and widely applicable to various polymers, which allows generation of nanoporous PINFs for multiple applications.