Unraveling Self-Assembly with Liquid Resonant Soft X-Ray Scattering for In Situ Measurement of Mesoscale Structure with Chemical Specificity

Resonant soft x-ray scattering (RSoXS) is a new characterization technique that offers insights into mesoscale structure with chemical specificity and the ability to probe molecular orientation. It does this by performing conventional small-angle x-ray scattering at a series of low photon energies (285 eV at the carbon K-alpha edge) as in x-ray spectroscopy. RSoXS was originally developed around and has been applied to great effect in morphological characterization thin films of organic semiconductors. Recently, our team has developed the first quantitative fitting engine for RSoXS data using GPU-accelerated forward simulation of real-space morphologies and applied this software to measure the orientation distribution in polymer-grafted nanoparticles, reverse osmosis water membranes, and several other families of industrial materials.<br/>The promise of RSoXS as a label-free alternative to SANS has not been fully realized, however, largely due to great difficulties in the study of liquid samples, or indeed practically any sample without significant structure factor contributions. This limitation arises because of the very feature that makes RSoXS unique: at the low photon energies used for organic molecules, a typical absorption length is about 500 nm. RSoXS measurements are, therefore, overwhelmingly conducted on thin films and typically on highly concentrated samples due to the extremely small probe volume. The design of the NIST RSoXS beamline at the National Synchrotron Light Source-II addresses this issue by incorporating a TEM port holder in the chamber; the sample thicknesses required for electron beam transparency are similar to those required for soft x-rays. We have procured a commercial TEM liquid cell capable of encapsulating a 500 nm film of flowing liquid between two thin silicon nitride membranes.<br/>This talk will discuss the commissioning of the cell, our first RSoXS measurements of dilute biomolecules in solution, and our recent efforts to combine solution RSoXS with solution SANS measurements to obtain a greater-than-sum-of-the-parts characterization of self-assembly processes and mechanisms in bioformulations. We will discuss the future extension of the liquid RSoXS technique to the <i>in situ </i>study of electrochemically active thin films in the hydrated state, and how measurements of pure form factor scattering enabled by the liquid sample environment and combined SANS-RSoXS experiments will enable quantitative understanding of the localization of additives during complex self-assembly processes.