Combined Rheo-SAXS Investigations using a Laboratory SAXS System
Rheology deals with the flow and deformation of matter, it relates a material’s molecular structure to its mechanical properties. Applying mechanical force, e.g., shear to a material can result in orientation of molecular assemblies or crystallization. Small-angle X-ray scattering (SAXS) determines structural parameters of nanostructured materials: size, shape, inner structure and orientation. Relating the nanostructure of a material to its macroscopic mechanical properties requires in-situ characterization techniques such as rheology combined with SAXS.
Understanding the flow behavior and the viscosity of complex fluids is a key factor in many fields of science and technology. The processing of many new materials has to be adapted to these properties to maximize efficiency, e. g., in extrusion processes in polymer production. But also in many other fields, ranging from nanoparticle solutions to medical applications understanding the rheological properties is crucial for both research and production.
Classical rheology can measure both the flow behavior (or deformation behavior in a solid) as well as the viscosity of materials by applying a shear force. In this way it is possible to obtain information on material properties on a macroscopic scale. The flow behavior of liquids can be classified into three different categories:
- Ideally viscous (viscosity independent of shear rate)
- Shear-thinning (viscosity decreasing with shear rate)
- Shear thickening (viscosity increasing with shear rate)
Bulk properties of complex fluids under shear often depend on the structure of the fluid at the nano- or microscopic level. Hence rheology experiments are often combined with other analytical techniques to study the macroscopic and the nano- or microscopic properties at the same time. Depending on the size range that needs to be investigated different methods based on e.g. small-angle scattering can be used.
1. Metzger, T. G., Applied Rheology. 2nd ed.; Anton Paar GmbH: Graz, Austria, 2014.
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