Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Local transient rheological behavior of concentrated suspensions

Abstract: This paper reports experiments on the shear transient response of concentrated non-Brownian suspensions. The shear viscosity of the suspensions is measured using a wide-gap Couette rheometer equipped with a particle image velocimetry device that allows measuring the velocity field. The suspensions made of PMMA particles (31 μm in diameter) suspended in a Newtonian index- and density-matched liquid are transparent enough to allow an accurate measurement of the local velocity for particle concentrations as high as 50%. In the wide-gap Couette cell, the shear induced particle migration is evidenced by the measurement of the time evolution of the flow profile. A peculiar radial zone in the gap is identified where the viscosity remains constant. At this special location, the local particle volume fraction is taken to be the mean particle concentration. The local shear transient response of the suspensions when the shear flow is reversed is measured at this point where the particle volume fraction is well defin...

Elastomer biaxial characterization using bubble inflation technique. I: Experimental investigations

Abstract: The biaxial rheological behavior of materials such as elastomers or polymers can be obtained using a bubble-inflation-technique. A circular membrane is clamped at the rim and expanded under gas pressure. The inflation of the circular membrane is recorded using a CCD video camera and the blowing pressure by a pressure sensor. Then, from elongation and curvature radius measurements at the pole of the bubble, one can deduce equibiaxial stress-strain data. This study describes the optimization of a bubble-inflation rheometer. The most sensitive point of the technique is the estimation of the elongation at the bubble pole, deduced from video camera measurements. A direct measurement of the bubble thickness was performed using a magnetic probe in order to validate rheometer results. Such a validation has evidently never been carried out before. Results of quasi-static equibiaxial characterization of elastomers are presented and analyzed.

Observations on shear-induced textures and rheology of a smectic-A phase

Abstract: Observations are reported of the behaviour of a smectic-A liquid crystal, 4-n-octyl-4’-cyanobiphenyl (8CB), as it is sheared in two geometries. In the first an initially-homeo-tropic sample is sheared in a planar shear flow cell, and it is observed that the shear creates textures which resemble those caused by dilating a smectic. The same textures are seen in the second geometry, where the sample is placed in a transparent cone-and-plate rheometer. The apparent viscosity of the smectic material measured in this geometry is found to increase with the fraction of the sample which contains a certain disordered focal conic texture induced by the shear. It appears that the presence of this texture gives the smectic a finite yield stress.

The flexure-based microgap rheometer (FMR)

Abstract: We describe the design and construction of a new microrheometer designed to facilitate the viscometric study of complex fluids with very small sample volumes (1–10μl) and gaps of micrometer dimensions. The flexure-based microgap rheometer (FMR) is a shear-rate-controlled device capable of measuring the shear stress in a plane Couette configuration with directly controlled gaps between 1 and 200μm. White light interferometry and a three-point nanopositioning stage using piezo-stepping motors are used to control the parallelism of the upper and lower shearing surfaces, which are constructed from glass optical flats. A compound flexure system is used to hold the fluid sample testing unit between a drive spring connected to an “inchworm” motor and an independent sensor spring. Displacements in the sensing flexure are detected using an inductive proximity sensor. Ready optical access to the transparent shearing surfaces enables monitoring of the structural evolution in the gap with a long working-distance vide...