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Origin of Small-Angle Scattering from Contrast-Matched Nanoparticles: A Study of Chain and Filler Structure in Polymer Nanocomposites
journal contribution
posted on 2015-09-22, 00:00 authored by Amélie Banc, Anne-Caroline Genix, Christelle Dupas, Michael Sztucki, Ralf Schweins, Marie-Sousai Appavou, Julian OberdisseThe
conformation of poly(ethyl methacrylate) chains in silica–latex
nanocomposites has been studied under zero average contrast conditions
(ZAC) using small-angle neutron scattering (SANS). Samples have been
prepared by drying colloidal suspensions of silica and polymer nanoparticles
(NPs) followed by thermal annealing, for two different silica NPs
(radius of 5 and 15 nm) and two chain molecular weights (17 and 100
kg/mol). By appropriate mixing of hydrogenated and deuterated polymer,
chain scattering contrast is introduced, and in principle silica scattering
suppressed. The silica structure consisting mostly of small fractal
aggregates is characterized by transmission electron microscopy (TEM)
and small-angle X-ray scattering (SAXS) on the same samples. The measurement
of the chain structure by SANS, however, is perturbed by unwanted
silica contributions, as often reported in the literature. Here, the
contribution of contrast-matched silica is evidenced as a function
of system parameters, namely chain mass, silica size, and volume fraction,
and a model rationalizing these contributions for the first time is
proposed. On the basis of a statistical analysis, a nanometer-thick
polymer shell surrounding silica NPs is shown to create contrast,
which is presumably maintained by the reduced mobility of polymer
close to interfaces or attractive polymer–silica interactions.
This shell is proven to be quantitatively important only for the smallest
silica NPs. Finally, the pure polymer scattering can be isolated,
and the polymer radius of gyration is found to be independent of filler
content and NP size.