In situ measurement of contact angles and surface tensions of interfacial nanobubbles in ethanol aqueous solutions

Abstract

The astonishing long lifetime and large contact angles of interfacial nanobubbles are still in hot debate despite numerous experimental and theoretical studies. One hypothesis to reconcile the two abnormalities of interfacial nanobubbles is that they have low surface tensions. However, few studies have been reported to measure the surface tensions of nanobubbles due to the lack of effective measurements. Herein, we investigate the in situ contact angles and surface tensions of individual interfacial nanobubbles immersed in different ethanol aqueous solutions using quantitative nanomechanical atomic force microscopy (AFM). The results showed that the contact angles of nanobubbles in the studied ethanol solutions were also much larger than the corresponding macroscopic counterparts on the same substrate, and they decreased with increasing ethanol concentrations. More significantly, the surface tensions calculated were much lower than those of the gas-liquid interfaces of the solutions at the macroscopic scale but have similar tendencies with increasing ethanol concentrations. Those results are expected to be helpful in further understanding the stability of interfacial nanobubbles in complex solutions.

Plasma physics of liquids—A focused review

“…178 Literature often suggests that they can only occur in supersaturated gas solutions 187 and that their cavitation is only related to pressure gradients and variations, contrary to temperature change, 192 yet this is opposed by experimental and theoretical reports. 189,193,194 While most research on this topic is performed with water, nanobubbles have also been reported for aqueous ethanol solutions 195 and protic nonaqueous solvents. 196 Bulk phase nanobubbles can be as small as 10 nm in diameter, 179 but typical sizes range between 100 and 300 nm.…”

A review of recent theoretical and computational studies on pinned surface nanobubbles

“…In most experiments, the morphology of surface nanobubbles was imaged with AFM [1,2,[6][7][8][9][10][11][12][13][14][15] . The interaction between AFM tips and the surface nanobubbles certainly will influence the final images of such bubbles.…”

Imaging of surface nanobubbles by atomic force microscopy in liquids: Influence of drive frequency on the characterization of ultrasoft matter

“…Despite the relatively extensive AFM nanobubble measurements available, there still exist crucial discrepancies among different imaging modes (Carambassis et al, ; Ishida et al, ; Lou et al, ; Tyrrell and Attard, ; Yakubov et al, ). The most commonly used AFM techniques to study nanobubbles are amplitude‐modulation AFM (AM‐AFM) and PeakForce Quantitative Nano‐Mechanics (PF‐QNM) AFM (Lohse and Zhang, ; Yang et al, ; Zhao et al, ). AM‐AFM holds the advantage of being a dynamic‐resonant mode of imaging that leads to smaller tip‐sample forces than static‐ or quasi‐static‐mode methods (Garcia and Perez, ).…”

“…Nanobubbles have been previously studied by different methods such as electrochemical characterization (Yang et al ; Zhang et al, ), optical (Chan and Ohl, ; Chan et al, ; Karpitschka et al, ; Seo et al, ), and X‐ray (Zhang et al, ) imaging, and AFM (Yang et al, ; Zhao et al, ). The key parameters in their characterization are the contact angle and the surface tension (Attard and Miklavcic, ; Attard and Miklavcic, ).…”

“…The most commonly used AFM techniques to study nanobubbles are amplitude-modulation AFM (AM-AFM) and PeakForce Quantitative Nano-Mechanics (PF-QNM) AFM (Lohse and Zhang, 2015;Yang et al, 2007;Zhao et al, 2016). AM-AFM holds the advantage of being a dynamic-resonant mode of imaging that leads to smaller tip-sample forces than static-or quasi-static-mode methods (Garcia and Perez, 2002).…”