Role of Polymer–Nanoparticle Interactions on the Fracture Toughness of Polymer-Infiltrated Nanoparticle Films

Polymer–nanoparticle (NP) composite films (PNCFs) with extremely high loadings of NPs (>50 vol %) have superb transport, thermal, and electrical properties. A new class of highly loaded PNCFs known as polymer-infiltrated NP films (PINFs) have been recently developed and applied as multifunctional coatings and membranes. PINFs also represent a powerful platform to study the interfacial and confinement effects on thermal, transport, and mechanical properties of polymers. In this work, we investigate the role of the polymer–NP interface on the fracture behavior of PINFs prepared by capillary rise infiltration of polymer into silica (SiO2) NP packings. We tune the polymer–NP interaction strength by using SiO2 NPs with two different surface functional groups (hydroxyl and trimethylsilyl) and two polymers [polystyrene and poly(2-vinyl-pyridine)] with different interaction strengths with SiO2 NPs. For PINFs composed of small NPs, passivation of NPs with trimethylsilyl groups significantly impacts the fracture toughness by changing the sliding shear stress at polymer–NP interface. Polystyrene and poly(2-vinyl-pyridine) show a similar level of sliding shear stress likely due to strong adsorption on hydroxylated SiO2 NPs. In contrast, for PINFs consisting of large NPs, the fracture toughness is more strongly affected by the fracture properties of the polymers than the polymer–NP interactions. Our results illustrate the importance of understanding the interplay between confinement and polymer–NP interactions in controlling and tuning the fracture properties of PINFs for a wide range of applications.