Rheology is the study of flow properties of materials. Flow properties tell about internal structure, because internal structure governs flow properties. I like the book by Mewis and Wagner on Colloidal Suspension Rheology.
During my time in Leuven, I helped build a flexure-based rheometer for use in small-angle x-ray scattering setups. It shears the sample while x-rays reveal internal structure.
It was put to use at the European Synchrotron Radiation Facility, ESRF.