Effect of Extra Gas Amount on Liquid Outflow from Hydrophobic Nanochannels: Enhanced Liquid–Gas Interaction and Bubble Nucleation

Abstract

Understanding liquid motion in nanoenvironment is of fundamental importance in nanofluidics-based systems. While the liquid outflow from hydrophobic nanochannels can significantly affect system performance, its underlying mechanism remains unclear so far. Here, we present an experimental study of the gas-phase effect on liquid outflow behavior from hydrophobic nanochannels in a liquid nanofoam (LN) system. Four LN samples, consisting of same liquid−solid composition but different amounts of the gas phase, are characterized by cyclic quasi-static compression tests. A remarkable difference in the LN system reusability has been observed, indicating that the liquid outflow behavior is highly sensitive to the amount of the gas phase. As the gas amount increases, the degree of liquid outflow from hydrophobic nanochannels is considerably promoted. This promotive effect is because of the suppression of gas outflow and acceleration of bubble nucleation in the nanochannels. These fundamental findings open a new perspective on liquid outflow behavior and can facilitate the design of reusable nanofluidics-based energy absorbers.

Time- and Pressure-Dependent Gas Diffusion in a Nanoconfined Liquid Phase

“…The initial pressure of the plateau, namely, the liquid infiltration pressure, is governed by the classic Laplace–Young equation as P in = 2Δγ/ r = 19 MPa, where Δγ is the excessive solid–liquid interfacial tension and r is the nanopore radius. With the increased system pressure, the gas molecules outside the nanopores are fully dissolved by the bulk liquid phase based on Henry’s law, while the gas molecules inside the nanopores are fully dissolved by the confined liquid phase based on Henry’s law and gas oversolubility. ,, When all the nanopores are filled with the liquid, the slope of the loading curve increases to a value slightly higher than its initial bulk modulus due to the reduced liquid amount outside of the nanopores. The accessible nanopore volume is determined by the width of the pressure plateau L 1 (Figure ).…”

“…When the LN system is pressurized to a critical value, the liquid molecules infiltrate into the nanopores and dissolve all the gas molecules. This liquid infiltration process is a novel energy mitigation mechanism with an unprecedented energy absorption efficiency (∼100 J/g), nearly 2 orders of magnitude higher than those of traditional materials. , As the pressure is removed, the spontaneous liquid outflow from the hydrophobic nanopores is driven by the gas–liquid interaction. , It has been demonstrated that the degree of liquid outflow reduces with the increase in the amount of gas escaped from the nanoconfined liquid to the bulk liquid phase. , Previous studies on this gas transfer from the nanophase to the bulk phase are focused on advection, while the gas diffusion is ignored due to the relatively short time duration of the liquid outflow process. In the current study, the gas diffusion from the nanophase to the bulk phase is thoroughly studied by holding the infiltrated liquid molecules in the hydrophobic nanopores at different peak pressures with variable time durations.…”

Dynamic changes in gas solubility of xylem sap reiterate the enigma of plant water transport under negative pressure

“…Nevertheless, bubble nucleation may increase with gas concentration in liquids (Mori et al ., 1976). Considering that xylem sap in pit membranes may be oversaturated with dissolved gas, rapid changes in pressure and temperature may nucleate bubbles since excessive volume and gaseous molecules dissolved in a liquid (V g ) could then be released into vapour phase, as P g V g = C s H cc V g (Li et al ., 2020), where P g is the partial pressure of a given gas. This will also depend on the solid surface hydrophobicity, which can decrease the free energy and increase bubble nucleation.…”

Anomalous solid-like necking of confined water outflow in hydrophobic nanopores

“…The hydrophilic nanopore surface was converted to hydrophobic by anchoring a thin layer of silyl groups on the nanopore wall. 51 The surface reagents, including n-Octyldimethylchlorosilane (C8), Dodecyldimethylchlorosilane (C12), and n-Octadecyldimethylchlorosilane (C18), were purchased from Gelest, Inc. Briefly, 1 g of Kiesel gel was mixed with 40 mL of anhydrous toluene for 3 h; 10 mL of surface reagent and 1 mL of pyridine were then injected into the mixture, after which the mixture was stirred at 95 C for 24 h. Finally, the treated Kiesel gel was filtered, washed, and dried.…”