X-ray scattering in the vorticity direction and rheometry from confined fluids.

Abstract

An X-ray flexure-based microgap rheometer (X-FMR) has been designed for combining rheology and in situ small-angle X-ray scattering from the vorticity plane. The gap distance can be varied continuously from 500 μm down to several μm, which provides the unique possibility to generate a strong confinement for many complex fluids. A singular advantage of this setup is the possibility to directly probe the vorticity direction of the flow field with a microfocus X-ray beam and to probe the structural response of the fluid to combined shear and confinement in the vorticity plane. The sliding-plate setup operates over a wide range of shear rates of γ = 10(-3)-10(3) s(-1) and strains in the range of 10(-4)-10(2). The flexure-based bearing maintains the plate parallelism within 10(-5) rad. The X-FMR requires very small sample volumes on the order of 10 μl. The applicability of the device is demonstrated here with limited examples of a nematic suspension of fd virus (rods), and a crystalline suspension containing sterically stabilized polystyrene-butylacrylate latex particles.