Polarized X-ray scattering measures molecular orientation in polymer-grafted nanoparticles

Abstract

Polymer chains are attached to nanoparticle surfaces for many purposes, including altering solubility, influencing aggregation, dispersion, and even tailoring immune responses in drug delivery. The most unique structural motif of polymer-grafted nanoparticles (PGNs) is the high-density region in the corona where polymer chains are stretched under significant confinement, but orientation of these chains has never been measured because conventional nanoscale-resolved measurements lack sensitivity to polymer orientation in amorphous regions. Here, we directly measure local chain orientation in polystyrene grafted gold nanoparticles using polarized resonant soft X-ray scattering (P-RSoXS). Using a computational scattering pattern simulation approach, we measure the thickness of the anisotropic region of the corona and extent of chain orientation within it. These results demonstrate the power of P-RSoXS to discover and quantify orientational aspects of structure in amorphous soft materials and provide a framework for applying this emerging technique to more complex, chemically heterogeneous systems in the future.

Resonant soft X‐ray scattering in polymer science

“…Currently, the most robust modeling available is through the voxel-based forward simulation method described above. 30,180,234 Current efforts involve highperformance computing integration to enable fitting of a models' parameter space. 234 Development of optical models, however, are ongoing with several potential methods emerging.…”

“…30,180,234 Current efforts involve highperformance computing integration to enable fitting of a models' parameter space. 234 Development of optical models, however, are ongoing with several potential methods emerging. While the first used angle dependent NEXAFS spectroscopy to generate a basic uniaxial model, 179 another recently used a film with aligned polymers through bladecoating and multi-axis NEXAFS spectroscopy to reveal the full six-component optical tensor for the electron acceptor polymer P(NDI2OD-T2).…”

“…The challenge is first the inability to use the traditional contrast function approach to modeling the scattering and the second is the lack of an established, robust method to generate a molecule's optical tensor. Currently, the most robust modeling available is through the voxel‐based forward simulation method described above 30,180,234 . Current efforts involve high‐performance computing integration to enable fitting of a models' parameter space 234 .…”

Simulation-guided analysis of resonant soft X-ray scattering for determining the microstructure of triblock copolymers

“…Computational scattering simulations of polarized resonant soft X-ray scattering (P-RSoXS) have been used to characterize molecular orientation at interfaces in organic photovoltaic donor-acceptor blends and polymergrafted nanoparticles. 24,25 By combining simulations and experiments, structure models can be quantitatively evaluated against experimental data.…”

Visualizing the Orientation of Single Polymers Induced by Spin-Coating

“…Spin coating is a universal process used to prepare thin polymer films with uniform thickness. Researchers have observed anisotropic distributions in orientations of polymer chains as a result of spin-coating, which has potential implications for improving electron transport, − mechanical strength, − and thermal conductivity. , While techniques such as Fourier transformed infrared (FTIR) microscopy, birefringence, , and polarized resonant soft X-ray scattering (P-RSoXS) , have inferred chain orientation within polymeric materials by probing bulk environments and fitting data to models, they lack the specificity of studying individual molecules. Single-chain specificity is especially useful in studying orientation around defects in bulk polymeric materials, where fractures propagated by defects can additionally be affected by the orientation of chains. , In another example, liquid crystals derive optical properties from the order of their molecules, and defects within this system disrupt order as the chains orient themselves around these features .…”