Scanning-SAXS of microfluidic flows: nanostructural mapping of soft matter.

The determination of in situ structural information of soft matter under flow is challenging, as it depends on many factors, such as temperature, concentration, confinement, channel geometry, and type of imposed flow. Here, we combine microfluidics and scanning small-angle X-ray scattering (scanning-SAXS) to create a two-dimensional spatially resolved map, which represents quantitatively the variation of molecular properties under flow. As application examples, mappings of confined amyloid fibrils and wormlike micelles under flow into various channel geometries are compared. A simple process to fabricate X-rays resistant chips, based on polyimide and UV-curing resin, is discussed. During experiments, these chips remained in high-energy synchrotron radiation for more than 24 hours, causing constant low background scattering. Thus, sufficient statistics were obtained from sample scattering at exposure times as low as 0.1 s, even with the small scattering volumes in microfluidic channels. Scanning-SAXS of microfluidic flows has many potential applications from biology to fundamental soft matter physics. In general, any fluid which has enough contrast for X-ray scattering can be measured to obtain the dependence of molecular shape, conformation, alignment and size on the flow field. Besides, dynamic processes of soft matter caused by flow, temperature, concentration gradient, and confinement, for example self-assembling, aggregation, mixing, diffusion, and disintegration of macromolecules, can be quantified and visualized on a single image by this mapping technique.