HIGH-PRESSURE VISCOSITY OF GLYCEROL MEASURED BY CENTRIFUGAL-FORCE VISCOMETRY

As a liquid approaches its glass transition temperature T(g), its viscosity increases rapidly. The glass transition can be induced either by lowering the temperature through T(g) or by increasing the pressure (and thereby the density) at constant temperature. The effect of temperature on viscosity is well studied, but the density dependence of viscosity close to T(g) is less well understood. Here we report measurements of the viscosity of glycerol, one of the most widely studied glass-forming liquids, at pressures of up to 3 GPa using centrifugal-force viscometry in a diamond-anvil cell. We find that free-volume theory1,2, which ascribes an incompressible hard-sphere volume to the molecules, provides a good description of the viscosity over the entire pressure range (and by extrapolation, up to the glass transition at approximately 5 GPa). We are thus able to predict the effect of pressure on T(g) and on the glass fragility (the structural breakdown in the liquid close to the transition).