Reports: AC9
45968-AC9 Effect of Elevated Pressure on the Rheology, Vitrification, and Aging of Suspensions of Model Colloidal Spheres
Effect of Elevated Pressure on the Rheology, Vitrification, and Aging of “Nearly Hard” Colloidal Spheres
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 last two years of this research project, we have conducted more rheological experiments at ambient pressure in collaboration with a consultant of this project, Professor G.B. McKenna of Texas Tech University. 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 three manuscripts two of which were published and one which has been submitted.
In addition to the above work, we have modified the design of the new high pressure rheometer to conduct the rheological experiments on colloidal suspensions using the novel pressure sensor plate at elevated pressure. The rheometer is in the last stage of the building process at the University of Utah and will be ready to use in two months. We note here that we have had difficulties in building the rheometer at the University of Utah and at TTU. The most difficult step has been the design of a Micrometer or (a fine pitch screw) to control the gap between the parallel plates at high pressure. We are planning on writing a manuscript on the design of the rheometer at high pressure and we will get preliminary results on measuring the shear viscosity of standard liquids (e.g. glycerin) at high pressure and under isothermal conditions. We mention here that there is no commercial rheometers 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.
