Deformation Behavior of Polystyrene-Grafted Nanoparticle Assemblies with Low Grafting Density

作者：Yang Jiao, Andrew Tibbits, Andrew Gillman, Ming-Siao Hsiao, Philip R. Buskohl, Lawrence F. Drummy, Richard A. Vaia · 发表于：Macromolecules · 年份：2018 · DOI：10.1021/acs.macromol.8b01524 · 被引用次数：60 · 研究领域：Advanced Materials and Mechanics、Electrospun Nanofibers in Biomedical Applications、Advanced Sensor and Energy Harvesting Materials

Matrix-free, polymer-grafted nanoparticle (PGN) assemblies show promise for a wide array of structural, photonic, and electrical applications. We examine the modulus, yield strength, and crazing of assemblies of polystyrene grafted Fe 3 O 4 (Fe 3 O 4 -PS) at low graft density (Σ < 0.15 chains/nm 2 ) where chain entanglements are maximized. From the wrinkling–cracking method (WCM) we show that modulus ( E ) and yield stress (σ y ) are independent of nanoscale film thickness (70 < h f < 250 nm) and graft molecular weight (30 kDa < MW < 370 kDa) and in good agreement with predictions from effective medium theory. Furthermore, thin film craze observations from TEM imply two critical length scales for maximum deformability of matrix-free PGN assemblies: (1) PGN core size should be less than the critical length scale of the craze microstructure, and (2) near-neighbor entanglements are optimized for the lowest graft length ( N ) where the PGN architecture exhibit intermediate graft densities ( r 0 Σ 0.5 ∼ 3–6 and N / N e ∼ 4–6). These findings provide a foundation for optimizing designs that simultaneously maximize inorganic volume fraction, processability, and mechanical robustness for PGN thin film assemblies.