Brush Structure of Polymer Grafted SiO₂ Nanoparticles Measured with Neutron Scattering

Polymer chains are grafted to nanoparticles (NPs) surfaces for a variety of purposes, including altering their solubility and dispersion within a polymer matrix. Here, we have grafted either poly(methyl acrylate) (PMA) or poly(N-isopropylacrylamide) to d ≈ 10 nm SiO₂ nanoparticles, and measured the structure of the brush with small-angle neutron scattering (SANS). For moderate grafting densities (σ ≈ 0.3 nm^-2), high molecular weight polymers adopt two primary conformations. Polymer chains near the NP core are stretched in the concentrated polymer brush region (CPB). Farther away from the core, polymer chains are less confined and the conformation becomes more ideal in the semi-dilute polymer brush region (SDPB). To highlight scattering from these two regions, we took advantage of selective deuteration and contrast matching. SANS measurements are analyzed using the “core-chain-chain” form factor that we recently developed. We compare and contrast the conformation of poly(methyl acrylate) in a good solvent to that of PNIPAM in both D₂O and ethanol-d_6, in which PNIPAM has LCST and UCST behavior, respectively.