Viscosity Measurements in the Diamond-Anvil Pressure Cell

Abstract

Comparatively few experiments have been reported concerning the effects of pressure on the viscosity of liquids at pressures above 30 kbar. Bridgman measured the viscosities of several organic liquids to about 30 kbar utilizing a swinging vane apparatus [1]. More recently, Barnett and Bosco described a capillary-type viscometer for measuring viscosities between 10³ and IO¹⁰ poise up to 60 kbar [2]. We have developed a method of measuring the pressure dependence of the viscosity of liquids in the diamond-anvil cell utilizing a simple falling-sphere technique in conjunction with the ruby method of pressure measurement. In this report we describe the details of the method and include a preliminary discussion on the accuracy of the method. Viscosity data on a 4:1 methanol:ethanol mixture to 70 kbar are reported and discussed in relation to its hydrostatic properties and glass transition pressure.