Event
MSE Seminar: Dr. Dean DeLongchamp, NIST
Wednesday, April 2, 2025
3:30 p.m.
Room 2110 Chemical and Nuclear Engineering Building
Sherri Tatum
301-405-5240
statum12@umd.edu
"Reconciling chain orientation in polymer-grafted nanoparticles between coarse-grain models and resonant soft X-ray scattering"
Subhrangsu Mukherjee,† Nicholas T. Liesen,‡ Scott T. Milner,¶ Lisa M. Hall,‡ and Dean M. DeLongchamp†,
† Materials Science and Engineering Division, Materials measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899
‡ Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43221
¶ Department of Chemical Engineering, The Pennsylvania State University, University Park, PA 16802
Abstract: 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 this measurement gap. 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. Using a GPU-accelerated virtual RSoXS instrument, 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 can be reconciled with computational predictions, and quantitative agreement is possible with data fusion that incorporates experimental data from other measurements, coarse-grain simulation results, and atomistic conformation information. 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.
Bio: Dean M. DeLongchamp leads the Polymer Processing Group at the National Institute of Standards and Technology, which develops measurement methods, data, standards, and science for the processing and manufacturing of materials into functional forms that include thin films, nanostructures, and shaped bulk solids. His group provides expertise in in situ processing measurements, structure and order evolution, nanofabrication, polymer phase behavior, and polymer dynamics needed to improve the performance of materials in application areas such as energy and electronics. Dean’s scientific portfolio includes a specialization in flexible organic electronics, as well as soft X-ray spectroscopy and scattering, powerful synchrotron-based tools that measure the composition and molecular orientation of organic systems.
