Viscosity Measurements of Water at High Temperatures and Pressures Using Dynamic Light Scattering

The application of dynamic light scattering to measure viscosity of water at high temperatures and pressures
is demonstrated. Viscosity was obtained from the translational diffusion coefficient of probe particles dispersed
in the medium by the Einstein−Stokes relationship. Measurements were carried out with polystyrene latex,
colloidal silica, and colloidal gold. Under a constant pressure of 25 MPa, good agreement was found between
the measured and calculated viscosities up to 275 °C with the polystyrene latex, 200 °C with the colloidal
silica, and 297 °C with the colloidal gold. It was found that failure of the measurements at high temperatures
is ascribed to change in either the dispersion stability or chemical stability of the probe particles. The present
results indicate that the technique could also be used for other supercritical fluids having high critical
temperature and pressure, such as methanol (Tc = 239.4 °C, Pc = 8.1 MPa) and ethanol (Tc = 243.1 °C, Pc
= 6.4 MPa).