Effect of Polymer-Nanoparticle Interactions on the Fracture Toughness of Polymer-infiltrated Nanoparticle Films

Polymer-infiltrated nanoparticle films (PINFs) are a novel class of polymer nanocomposites that can have extremely high volume fractions of nanoparticles and thus unique mechanical properties. While our prior work focused on understanding the effect of confinement on the fracture toughness of these PINFs, the effect of interactions between polymer and nanoparticles has not been explored. Here we experimentally investigate the role of interfacial effects on the fracture toughness of PINFs prepared by capillary rise infiltration (CaRI) of polymer into silica (SiO₂) NP packings. We tune the polymer-NP interaction strength by using poly(styrene) which is known to have weak interactions with SiO₂, poly(2-vinyl pyridine) (P2VP) that is capable of forming hydrogen bonds with SiO₂, and trimethyl silane-passivated  SiO₂ that weakens interactions between the polymer and the nanoparticles. Interfacial effects play a role in PINFs composed of small NPs by changing the sliding friction at polymer-NP interface. In contrast, PINFs composed of large NPs are more affected by polymer-polymer interactions than polymer-NP interactions.