Effect of polymer-nanoparticle interactions on solvent-driven infiltration of polymer (SIP) into nanoparticle packings: a molecular dynamics study

Naturally occurring nanocomposites like nacre owe their exceptional mechanical properties to high loadings of platelets that are bridged by small volume fractions of polymers. Polymer infiltration into dense assemblies of nanoparticles provides a powerful and potentially scalable approach to manufacture bio-inspired nanocomposites that mimic nacre's architecture. Solvent-driven infiltration of polymers (SIP) into nanoparticle packings formed on top of glassy polymer films is induced via capillary condensation of a solvent in the interstitial voids between nanoparticles (NP), followed by plasticization and transport of polymers into the liquid-filled pores, leading to the formation of the nanocomposite structure. To understand the effect of polymer-nanoparticle interactions on the dynamics of polymer infiltration in SIP, we perform molecular dynamics simulations. The mechanism of polymer infiltration and the influence of interactions between polymer and NPs on the dynamics of the process are investigated. Depending on the strength of interaction, polymer infiltration either follows (a) dissolution-dominated infiltration where plasticized polymer chains remain solvated in the pores and rapidly diffuse into the packing or (b) adhesion-dominated transport where the chains adsorb onto the nanoparticle surface and move slowly through the nanoparticle film as a well-defined front. A non-monotonic trend emerges as the adhesion strength is increased; the infiltration of chains becomes faster with the co-operative effect of adhesion and dissolution as adhesion increases but eventually slows down when the polymer-nanoparticle adhesion dominates. Dynamics of polymer motion into solvent-filled interstices of nanoparticle packings can be controlled by tuning the polymer-nanoparticle interactions, whose effect on the rate of infiltration is non-monotonic as shown by MD simulations.