A microtensiometer capable of measuring water potentials below −10 MPa

Abstract

Tensiometers sense the chemical potential of water (or water potential, Ψ_w) in an external phase of interest by measuring the pressure in an internal volume of liquid water in equilibrium with that phase. For sub-saturated phases, the internal pressure is below atmospheric and frequently negative; the liquid is under tension. Here, we present the initial characterization of a new tensiometer based on a microelectromechanical pressure sensor and a nanoporous membrane. We explain the mechanism of operation, fabrication, and calibration of this device. We show that these microtensiometers operate stably out to water potentials below −10 MPa, a tenfold extension of the range of current tensiometers. Finally, we present use of the device to perform an accurate measurement of the equation of state of liquid water at pressures down to −14 MPa. We conclude with a discussion of outstanding design considerations, and of the opportunities opened by the extended range of stability and the small form factor in sensing applications, and in fundamental studies of the thermodynamic properties of water.