Understanding of Dynamic Contacting Behaviors of Underwater Gas Bubbles on Solid Surfaces

Understanding of dynamic behaviors of gas bubbles on solid surfaces has significant impacts on gas-involving electrochemical reactions, mineral flotation, and so on in industry. Contact angle (θ) is widely employed to characterize the wetting behaviors of bubbles on solid surfaces; however, it usually fluctuates within the bubble’s advancing (θ a ) and receding (θ r ) range. Although the term of most-stable contact angle (θ ms ) was defined previously as the closest valuable approximation for thermodynamically meaningful contact angle for a droplet on a solid surface, it has not been widely studied; and the precise θ ms measurement methods are inadequate to describe bubbles’ wetting behaviors on solid surfaces. Herein, we proposed to take θ ms as the mean value of θ a and θ r, as a more accurate descriptor of gas bubbles’ dynamic behaviors on nonideal solid surfaces, similar to the definition of droplets’ θ ms on solid surfaces. The feasibility and accuracy of the proposed θ ms have been evidenced by recording the bubbles’ contacting behaviors on solid surfaces with varied wettabilities. In addition, it was found that the contact angle hysteresis (δ), as the difference between θ a and θ r, reached its maximum value when θ ms approached 90°, regardless of the roughness ( r ) of the substrates. Finally, built on the above concept, the lateral adhesion force ( f ) of the gas bubble on the solid interface, which worked on the three-phase contact line (TPCL) of an individual bubble on a solid surface against its lateral motion during the bubble advancing or receding process, was described quantitatively by combining θ a, θ r, and the liquid–gas interfacial tension (γ lg ). Experimental and theoretical data jointly confirmed that f reached its maximum value at θ ms ∼ 90°, namely, a “super-sticky” state, which described the dynamically most sluggish movement of the bubble along the solid surface.