Detachment of Deposited Colloids by Advancing and Receding Air–Water Interfaces

Abstract

Moving air-water interfaces can detach colloidal particles from stationary surfaces. The objective of this study was to quantify the effects of advancing and receding air-water interfaces on colloid detachment as a function of interface velocity. We deposited fluorescent, negatively charged, carboxylate-modified polystyrene colloids (diameter of 1 μm) into a cylindrical glass channel. The colloids were hydrophilic with an advancing air-water contact angle of 60° and a receding contact angle of 40°. After colloid deposition, two air bubbles were sequentially introduced into the glass channel and passed through the channel at different velocities (0.5, 7.7, 72, 982, and 10,800 cm/h). The passage of the bubbles represented a sequence of receding and advancing air-water interfaces. Colloids remaining in the glass channel after each interface passage were visualized with confocal microscopy and quantified by image analysis. The advancing air-water interface was significantly more effective in detaching colloids from the glass surface than the receding interface. Most of the colloids were detached during the first passage of the advancing air-water interface, while the subsequent interface passages did not remove significant amounts of colloids. Forces acting on the colloids calculated from theory corroborate our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface movement were stronger than during the receding movement. Theory indicates that, for hydrophilic colloids, the advancing interface movement generally exerts a stronger detachment force than the receding, except when the hysteresis of the colloid-air-water contact angle is small and that of the channel-air-water contact angle is large.

On-chip purification via liquid immersion of arc-discharge synthesized multiwalled carbon nanotubes

“…Other possible detachment forces include viscous shear (i.e. drag) forces, gravity, and buoyancy, which are however generally found negligible for small colloids [12,14].…”

“…Unless the particle itself moves as the liquid interface immerses it, the resulting surface tension force on the particle F γ will continuously change direction and magnitude. The maxima of its vertical and lateral components are expressed as [14]:…”

Experimental studies on the detachment of multi-walled carbon nanotubes by a mobile liquid interface

“…The detachment of nano-and microscale particles from solid surfaces to liquids is an intricate phenomenon when it occurs at the liquid-air-solid contact line [1,2], a.k.a. the wetting line.…”

“…This phenomenon has been relevant in a few of the applied sciences. Examples are particle separation in mining industries [3], particle transport and trapping in environmental sciences [1], and in the cleaning processes of the microelectronics industry [4][5][6]. These conventional areas of technology are being complemented by the emerging field of nanotechnology, which brings forward new nanoscale particles whose interaction with capillary forces are an important topic as well [7,8].…”

Inverse Saffman-Taylor Experiments with Particles Lead to Capillarity Driven Fingering Instabilities

“…Due to the hydrophobicity of the surface and gravity, the water drop rolls off on the slanted leaf while also removing dust particles. This self-cleaning process is referred to as the "Lotus-Effect" [17,18] and is of primary interest to a wide variety of industrial processes including tube [14,16] or microelectronic silicon wafer cleaning [19], separation of minerals in the mining industry [20], particle flotation [13], or even stabilization of bubbly liquids, foams and emulsions [15,21,22]. Once the micro-particles are removed from the surfaces, they are adsorbed and transported by the air-water interface.…”