How a water drop removes a particle from a hydrophobic surface

Abstract

Possible outcomes when a particle collides with a water drop on a hydrophobic surface.

Molecular Desorption by a Moving Contact Line

“…This rules out any temporal process, such as, for example, a diffusive desorption of species in the liquid or by viscous stress at the wall, and is consistent with the picture of a process dominated by the tension at the contact line. Note that, in the case of particle removal, no or a weak influence of the contact line velocity is also observed [19,21]. If we now consider the τ value characterizing the contamination of the needle, we find a constant value τ ¼ 7 AE 4 s, independent of the tip, liquid, and velocity used.…”

“…This mechanism may be universal since the molecules physisorption energy and the capillary energy are both of the order of a few k B T, where k B is the Boltzmann constant and T the temperature. It is known that the capillary force at the contact line can deform a soft solid [18], move particles [19][20][21], or align DNA [22], but this issue has never been addressed experimentally at the molecular scale.…”

“…The evolution of the wetting properties observed during one series of dipping events would then be associated with the desorption by the liquid of airborne contaminant molecules adsorbed on the tip surface. We perform specific additional experiments to identify whether desorption is associated with dissolution of molecules in the liquid, helped by the shear stress at the needle wall [33] or with a specific force interaction with the contact line [19,21]. This can be achieved by successive dipping of a predefined part of a needle a large number of times and compare the force curves on the whole tip before and after this particular series.…”

Enhanced Condensation on Soft Materials through Bulk Lubricant Infusion

“…Therefore, to quantify differences in the cloaking kinetics due to lubricant infusion in PDMS, we measured the change in drop‐air interfacial tension of a water drop placed into contact with P10L0, P10L5, and P10L25 as follows. [ 49 ] A glass slide with a 2 mm diameter hole was spin‐coated with the PDMS mixture [ Figure a]. A 38 μL drop of pure water was positioned in pendant configuration such that its three‐phase contact line was pinned at the edge of the hole.…”

Actuating water droplets on liquid infused surfaces: A rickshaw for droplets

“…The control and actuation of liquid droplets in contact with a substrate is fundamental to the development of milliand microfluidic devices [1] and surface cleaning technology [2,3]. Surface energy gradients [4], thermal gradients [5], chemical reactions [6] or electric fields [7,8] can displace droplets with velocities up to 1 cm.s −1 .…”