Controlled drop emission by wetting properties in driven liquid filaments

Abstract

The controlled formation of micrometre-sized drops is of great importance to many technological applications. Here we present a wetting-based destabilization mechanism of forced microfilaments on either hydrophilic or hydrophobic stripes that leads to the periodic emission of droplets. The drop emission mechanism is triggered above the maximum critical forcing at which wetting, capillarity, viscous friction and gravity can balance to sustain a stable driven contact line. The corresponding critical filament velocity is predicted as a function of the static wetting angle, which can be tuned through the substrate behaviour, and shows a strong dependence on the filament size. This sensitivity explains the qualitative difference in the critical velocity between hydrophilic and hydrophobic stripes, and accounts for previous experimental results of splashing solids. We demonstrate that this mechanism can be used to control independently the drop size and emission period, opening the possibility of highly monodisperse and flexible drop production techniques in open microfluidic geometries.

Optimal Design of Permeable Fiber Network Structures for Fog Harvesting

“…As the small deposited water droplets coalesce, the growing droplets are influenced by the competition between aerodynamic drag forces ( F drag ) and surface adhesion forces ( F adhesion ). [28][29][30] When the drag force overwhelms the adhesion force, the droplets are re-entrained in the fog flow, leading to a decrease in the fog collection efficiency (Figure 3a). …”

Unique fingering instabilities and soliton-like wave propagation in thin acoustowetting films

“…T here has long been substantial interest in the wetting of thin liquid films given the rich diversity of phenomena associated with non-linear spreading dynamics, including self-similar fractal assembly, finger patterning and self-organisation [1][2][3][4][5][6] . In addition to their prevalence in nature, their relevance to micro-and nano-scale processes have led to closer scrutiny of such phenomena in the context of microfluidic research [7][8][9][10] .…”

Measurement of a Structured Backflow in an Open Small Channel Induced by Surface-Tension Gradients

“…Typical experimental arrangements involve narrow pipes carrying fluids into a mixing region where the relevant physicochemical processes take place. Recently, the prospect of designing open-channel alternatives has been explored [6][7][8][9] in order to address some of the drawbacks of the standard methods, such as increasing flow resistance and clogging of narrow pipes. Under the confined, low dimensionality conditions of open channel microfluidics, flow control might be exerted through interfacial processes arising at the open interface.…”