A microtensiometer capable of measuring water potentials below −10 MPa

Abstract

Tensiometers sense the chemical potential of water (or water potential, Ψw) 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.

Passive water ascent in a tall, scalable synthetic tree

“…This may lead one to expect system dryout, however, recent reports have shown that transpiration can be self-stabilizing when the menisci recede far enough within the nanopores that the local humidity is increased to a value where ≤ | | P P K L , max 34,36 . This necessary balance between the Kelvin and Laplace pressures to stabilize the free interface is well understood and has been thoroughly characterized 25,[32][33][34] . Curiously lacking in the synthetic tree literature, however, is a second pressure balance required for conservation of mass.…”

“…In the same year, Noblin et al evaporated water from PDMS to pump water across an array of microfluidic channels 26 . Several follow-up papers characterized the thermophysical properties of the negative pressure water, including its metastability 27 , cavitation dynamics [28][29][30][31] , and using nanoporous silicon (≈3 nm diameter pores) to achieve up to 100 MPa of negative Laplace pressure [32][33][34] . For all of these tree-on-a-chip devices, transpiration is no longer used to pump water against gravity, but rather to drive flows in micro-channels or as a platform for studying the fundamental properties of negative pressure water.…”

Self-Stabilizing Transpiration in Synthetic Leaves

“…38 By integrating sensors into a synthetic leaf, it can even be used as a microtensiometer for measuring the water potential of synthetic or natural plants. 39,40 However, the menisci within synthetic leaves are known to become unstable beneath a critical relative humidity. The magnitude of this critical humidity can be quite high, which poses a severe obstacle for using synthetic trees in real-life environments.…”

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…Recently, a new type of small tensiometer has been developed for the measurement of water potential in plants. The device has a microelectromechanical (MEM) pressure sensor and a nanoporous membrane [52], and it is small enough to be embedded into plant stems to directly measure plant water potentials, down to about −10 MPa. According to the developers, this new technology has potential for automatic and continuous measurement of water potential in plants under field conditions.…”