Polarized resonant soft X-ray scattering measurements in polymer-grafted nanoparticles

Orientation and conformation in nanoscale amorphous regions often dominate the properties of soft materials. Robust correlations between structure in these amorphous regions and important properties are not well developed due to a lack of measurements with high spatial resolution and a sensitivity to molecular orientation. For example, radial polymer chain orientation with significant spatial variation is typically predicted in computational models of polymer-grafted nanoparticles (PGNs), but it has not been validated due to insufficient measurements. I will describe our approach to solving this issue using polarized resonant soft X-ray scattering (P-RSoXS), which combines principles of soft X-ray spectroscopy, small-angle scattering, and data fusion with real-space imaging to produce a molecular scale structure measurement for soft materials.

I will focus on the P-RSoXS of polymer-grafted nanoparticles (PGNs). The most unique structural motif of PGNs is the high-density region in the corona where polymer chains are “stretched” under significant confinement. We apply our approach to measure the orientation of polystyrene (PS) chains grafted to gold nanoparticles. In conjunction with a pattern simulation approach, we measure the thickness of the anisotropic region of the corona and the extent of chain orientation within it. Radial chain orientation is observed that decays in magnitude away from the particle, and differences in this nanoscale orientation landscape are observed between particles of different graft density. The shape of this nanoscale orientation landscape is found to be in excellent agreement with recent computational predictions. These results demonstrate the power of P-RSoXS to quantify and discover orientational aspects of structure in PGN systems and illustrate a framework that can be applied broadly to semicrystalline or amorphous polymers with a range of chemistries and chemical heterogeneity.