Gravity-Induced Cohesive Tension in Liquids

Presenter: Danielle Miller, Mechanical Engineering

Authors: D. Miller, N. Eyegheleme, A. Malakar, C. Wolfe, J. Boreyko

Abstract: Synthetic trees can spontaneously hold a continuous volume of water against gravity in vertically-oriented tubes, by virtue of the negative Laplace pressure generated by an air-water interface within an overlying nanoporous leaf. Alternative methods for generating liquid tension include hermetic heating and cooling, centrifugation, acoustic waves, or suction pumps, but these all rely on external energy inputs. Traditionally, gravity has only been shown to create positive (hydrostatic) pressures in liquids. Here, we show that when gravity acts on vertical liquid columns whose upper ends are supported by porous media, the underlying liquid is held in tension even in the complete absence of interfaces. A synthetic tree system was used in which glass tubes were embedded in a nanoporous medium with a water reservoir maintained at a height above the nanoporous leaf. This ensured a lack of interfacial tension, yet the water in the tubes remained suspended against gravity, even with open lower ends. These results show that gravity, when transmitted across a support boundary, is sufficient to passively manifest tension in liquids.