A practical guide to acquisition, treatment and model-free analysis of SAXS/SANS data: methodologies and pitfalls

Small-angle X-ray and neutron scattering (SAXS and SANS) are widely used tools for probing the nanoscale structures in soft materials like polymers, colloids, proteins, etc. Data interpretation is often based on the fitting of a physical model to the scattering data. However, there are methods for model-free data analysis that offer valuable insights in the form of physical parameters while avoiding potential artifacts introduced by incorrect model assumptions. Herein, these methods of analysis are systematically discussed in detail, starting with the key considerations for scattering experimentation and data treatment. Stepwise descriptions of the invariant calculation for quantifying volume fraction, Guinier analysis for estimating the radius of gyration, and Porod analysis for determining the specific surface area of the scatterer are provided. Appropriate examples from diverse systems in literature, such as polymers, fibers, microemulsions, and nanoparticles, are discussed for illustration. Special emphasis has been placed on the common pitfalls encountered during data analysis, including the effects of polydispersity, background scattering and deviations from the ideal Porod behaviour. By explaining the useful protocols of data acquisition, treatment, analysis and corrections for deviations, this tutorial aims to support new and experienced users in obtaining reliable structural insights into materials from SAXS and SANS.