Stability Limit of Water by Metastable Vapor–Liquid Equilibrium with Nanoporous Silicon Membranes

Abstract

Liquid can sustain mechanical tension as its pressure drops below the vapor-liquid coexistence line and becomes less than zero, until it reaches the stability limit-the pressure at which cavitation inevitably occurs. For liquid water, its stability limit is still a subject of debate: the results obtained by researchers using a variety of techniques show discrepancies between the values of the stability limit and its temperature dependence as temperature approaches 0 °C. In this work, we present a study of the stability limit of water by the metastable vapor-liquid equilibrium (MVLE) method with nanoporous silicon membranes. We also report on an experimental system which enables tests of the temperature dependence of the stability limit with MVLE. The stability limit we found increases monotonically (larger tension) as temperature approaches 0 °C; this trend contradicts the centrifugal result of Briggs but agrees with the experiments by acoustic cavitation. This result confirms that a quasi-static method can reach stability values similar to that from the dynamic stretching technique, even close to 0 °C. Nevertheless, our results fall in the range of ∼ -20 to -30 MPa, a range that is consistent with the majority of experiments but is far less negative than the limit obtained in experiments involving quartz inclusions and that predicted for homogeneous nucleation.

Xylem Surfactants Introduce a New Element to the Cohesion-Tension Theory

“…The energy barrier required for bubble nucleation increases with surface tension cubed (Eq. 1; Blander and Katz, 1975;Khurana et al, 1998;Chen et al, 2016), which means that surface tension even slightly lower than that of pure water will increase the likelihood of nucleation enormously. Moreover, the pressure difference required for air seeding through pit membrane pores is a linear function of surface tension (Eq.…”

“…While it is clear from physical principles and experimental microfluidic systems that evaporation from nanopores can create large negative pressures (Wheeler and Stroock, 2008;Vincent et al, 2012;Lamb et al, 2015;Lee et al, 2015;Chen et al, 2016), it remains unknown how plants can use this negative pressure to transport water through their xylem without constantly creating bubbles in the system , especially considering that xylem is highly complex, with many different surfaces and containing large amounts of gas (Gartner et al, 2004). The most successful attempt to mimic this process in an engineered system under extremely controlled conditions managed to create several MPa of negative pressure in a single 3-cm-long hydrophilic microchannel (Wheeler and Stroock, 2008), but most other attempts have resulted in bubbles at much less negative pressures (Smith, 1994).…”

“…Bubbles in negative pressure systems most likely do not form through homogenous nucleation, because pure water has great tensile strength and can withstand negative pressures down to below 222 MPa under highly controlled stationary conditions (Dixon, 1914a;Briggs, 1950;Sedgewick and Trevena, 1976;Wheeler and Stroock, 2009;Chen et al, 2016). Bubbles are much more likely to form through heterogenous nucleation on particles or rough and hydrophobic surfaces (Crum, 1982;Wheeler and Stroock, 2009;Hedges and Whitelam, 2012;Rasmussen et al, 2012;Cho et al, 2015).…”

“…Bubbles are much more likely to form through heterogenous nucleation on particles or rough and hydrophobic surfaces (Crum, 1982;Wheeler and Stroock, 2009;Hedges and Whitelam, 2012;Rasmussen et al, 2012;Cho et al, 2015). The energy barrier E het that has to be overcome to create a bubble through heterogenous nucleation is largely a function of surface tension (g), which may be dynamic in the presence of surfactants and then dependent on surfactant concentrations, the contact angle between the liquid and solid phase (w), and the liquid pressure (P l ); it is given by the equation: (Blander and Katz, 1975;Khurana et al, 1998;Chen et al, 2016), where P v is the water vapor pressure at the same chemical potential as the liquid at P l . The first term on the right side of the equation is the energy barrier for homogenous nucleation, and the second term represents the effect of the contact angle on heterogenous nucleation.…”

From the sap's perspective: The nature of vessel surfaces in angiosperm xylem

“…A coating of phospholipids on hydrophobic vessel walls would render the surface hydrophilic, but it would do so while greatly lowering surface tension. The energy requirement for nucleating a bubble on a surface is a function of the surface tension cubed (Blander and Katz, 1975;Chen et al, 2016;Schenk et al, 2017). For example, the reduction of surface tension from that of pure water (72 mJ·m −2 ) to a third of that (24 mJ·m −2 ), a typical equilibrium surface tension for phospholipids (Lee et al, 2001), would reduce the energy requirement for bubble nucleation by a factor of 27.…”