FLUID VISCOSITY VERIFICATION IN A DIAMOND ANVIL CELL

The rate and volume of transport of crustal fluid is dependent on the fluid viscosity. Measurements of geophysically relevant fluid viscosities are sparse at the high pressure and temperature conditions of the deep crust. The Diamond Anvil Cell (DAC) has been used for over half a century to simulate deep earth pressures. Recent experiments to measure viscosity in the DAC using Brownian motion of suspended particles in water have established the feasibility of using the DAC as a viscometer. However, this method must be verified over a large range of fluid viscosities. Polystyrene particles were suspended in five fluids composed of ethanol, isopropanol, methanol, and water with viscosities ranging from 0.4-2.0 mPa∙s at STP. Brownian motion of the particles was recorded at ambient conditions in the DAC, and the position of each particle was determined as a function of time. A best-fit slope of the mean-square displacement was used with the Stokes equation to determine viscosity of the fluid. The results showed that the measured viscosities were within a range of a factor of 2-5 of STP viscosity values of each fluid, systematically overestimating viscosities by 1.10 mPa∙s and suggesting a calibration factor to be applied to future measurements.