Back to Table of Contents

45968-AC9
Effect of Elevated Pressure on the Rheology, Vitrification, and Aging of Suspensions of Model Colloidal Spheres

Jules J. Magda, University of Utah

The objective of this research project is to study the use of pressure to vitrify hard-sphere suspensions, and to study the effect of vitrification on suspension rheological properties. This will require construction of a novel high pressure torsional rheometer that will be used to apply pressures as high as 1Kbar under isothermal conditions to  Silica/PMMA colloidal suspension samples. Prior to vitrification, the effect of hydrostatic pressure on rheological properties such as shear viscosity, first and second normal stresses N₁ and N₂ can be investigated using a novel pressure sensor plate. During the first year of this research project, we have conducted rheological experiments at ambient pressure in collaboration with a consultant of this project, Professor G.B. McKenna of Texas Tech University. In these experiments, a novel pressure sensor plate (NSS from RheoSense, Inc.) was adapted to an Advanced Rheometrics Expansion System (ARES) rheometer in order to measure the radial pressure profile for a standard viscoelastic fluid, a poly(isobutylene) solution, during cone-plate and parallel-plate shearing flows at room temperature. The aim of these experiments was to use three different methods to investigate N₁ and N₂ as a function of shear rate in steady shear flow. This work resulted in a manuscript that was submitted to the journal Rheologica Acta in March 2008.   In addition to the above work, we have worked on the design of a new high pressure rheometer to conduct rheological experiments on colloidal suspensions using the novel pressure sensor plate at elevated pressure. The rheometer will be build at the University of Utah with the collaboration of Dr. McKenna at Texas Tech University. We mention here that there is no commercial rheometer available that can be used at extreme pressures (1 kbar or above) to measure colloid linear viscoelastic  rheological properties over a wide frequency or shear rate range. In the design, the parallel plate pressure rheometer  fits within a pressure vessel with means for driving rotation and for extracting an electrical signal for the measurements of both thrust and torque using strain gages. A mechanical feed through is used to detect the strain gage signals.

The upper rotating plate of the Rheometer is supported by thrust bearings and can be driven at different rotational speed by a servo motor external to the pressure vessel. The lower disc is fastened to a two-component load cell able to measure torque and thrust. The schematic design is ready to be sent to the machine shop at the University of Utah and will take between 2 and 4 months to execute.   In order to make sure the high pressure rheometer will work properly, we will discuss our design details with Professor Scott Bair at Georgia Tech, an expert on building high pressure rheometers.  Professor Bair has expressed in interest in collaborating on the high pressure studies of this project.

This project will have a high impact on the careers of the principal investigators by enhancing their collaborations with the oil industry.   Several corporate scientists from oil industry research laboratories have expressed interest in the novel high pressure rheometer being built in this project, and its possible use to study crude oils at ultrahigh pressures.

Back to top