Measurement of the viscosity of guar gum solutions to 50,000 s⁻¹ using a parallel plate rheometer

Abstract

It is frequently necessary to measure the viscosity of polymer solutions at high shear rates to obtain data under the conditions encountered in industrial processes. Such measurements are most often made on a capillary viscometer. This paper presents a method of determining solution viscosities at shear rates up to 50,000 s-' in a rotational rheometer using a parallel plate geometry. The two keys to performing these measurements are very small gaps between the parallel plates (on the order of 50 microns) to eliminate inertial secondary flows, and the ability to increase and decrease the shear rate quickly to minimize viscous heating. A technique for setting and measuring small gaps is presented. Possible sources of error including inertia, axial compliance, and viscous heating are analyzed. A comparison is made between the viscosity of a 0.7 percent hydroxypropyl guar (HPG) solution measured on the parallel plate rheometer and the viscosity measured in a capillary viscometer. Viscosities of HPG solutions having concentrations of 0.25, 0.50, 1.00, and 1.45 percent are presented over the shear rate range 100 to 50,000 s-'.

The flexure-based microgap rheometer (FMR)

“…The gap offset error of the plate-and-plate configuration was determined following the procedure described by Kramer et al (Connelly and Greener 1985;Kramer et al 1987), by measuring the zero-shear viscosity of a 1 mPas PDMS oil at 16 different separation spanning the range from 1 to 500 µm and a linear regression of the inverse apparent zero-shear viscosity as a function of the inverse gap. The gap error of the plate-and-plate configuration was thus determined to be 35.7 ± 0.1 µm.…”

Rheology and processability of multi-walled carbon nanotubes—ABSE polycarbosilazane composites

“…The rheometer was carefully calibrated with a Newtonian calibration liquid in consideration of the known fact that a change in the gap (from the standard width of 1-0.5 mm) influences the viscosity measurement, especially for gaps of less than 1 mm. [20][21][22] A preheating period of at least 30 min was necessary in order to avoid changes of the gap during the measurements caused by thermal expansion of the upper part of the measuring geometry.…”

High-shear rate rheometry of micro-nanofibrillated cellulose (CMF/CNF) suspensions using rotational rheometer

“…It is therefore essential to determine the gap error in the present study in which gaps much lower than 200 lm are to be used. The method to determine the gap error has been reported earlier (Kramer et al 1987;Davies and Stokes 2008;Pipe et al 2008) which involves measuring the viscosity of an apparently Newtonian fluid such as silicone oil (polydimethylsiloxane).…”

“…(2) is valid only for Newtonian fluids which exhibit linear relationship between shear rate and shear stress. The shear stress versus shear rate data for nonNewtonian fluids obtained using parallel plate must be corrected for the heterogeneity of shear stress in the parallel plate geometry by the expression below, which is widely known as Weissenberg-Rabinowitsch correction (Kramer et al 1987;Davies and Stokes 2008;Pipe et al 2008;De Souza Mendes et al 2014):…”