Giovanni Vleminckx

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 $\dot \gamma$γ̇ = 10−3–103 s−1 and strains in the range of 10−4–102. 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.

The effects of thermally reduced graphene sheets (TRG) on the phase separation in poly[(α-methyl styrene)-co-(acrylonitrile)]/poly(methyl-methacrylate) blends were monitored using melt rheology, conductivity spectroscopy, and electron microscopic techniques. The TRG were incorporated in the single-phase material by solution mixing. The composite samples were then allowed to phase separate in situ. The thermodynamics of phase separation have been investigated by monitoring the evolution of the storage modulus (G′) as a function of temperature as the system passes through the binodal and the spinodal lines of the phase diagram. The phase separation kinetics were probed by monitoring the evolution of G′ as a function of time at a quench depth well in the spinodal region. It was observed that TRG significantly influenced the phase separation temperature, the shape of the phase diagram and the rate of phase separation. The state of dispersion of TRG in the blends was assessed using electron microscopy and conductivity spectroscopy measurements. Interestingly, the composite samples (monophasic) were virtually insulators at room temperature, whereas highly conducting materials were obtained as a result of phase separation in the biphasic materials.