Bubble Control, Levitation, and Manipulation Using Dielectrophoresis

Abstract

Bubbles attached to surfaces are ubiquitous in nature and in industry. However, bubbles are problematic in important technologies, including causing damage to the operation of microfluidic devices and being parasitic during heat transfer processes, so considerable efforts have been made to develop mechanical and electrical methods to remove bubbles from surfaces. In this work, liquid dielectrophoresis is used to force a captive air bubble to detach away from an inverted solid surface and, crucially, the detached bubble is then held stationary in place below the surface at a distance controlled by the voltage. In this “levitated” state, the bubble is separated from the surface by liquid layer with a voltage‐selected thickness at which the dielectrophoresis force exactly counterbalances the gravitational buoyancy force. The techniques described here provide exceptional command over repeatable cycles of bubble detachment, levitation, and reattachment. A theoretical analysis is presented that explains the observed detachment–reattachment hysteresis in which bubble levitation is maintained with voltages in an order of magnitude lower than those used to create detachment. The precision surface bubble removal and control concepts are relevant to situations such as nucleate boiling and microgravity environments and offer an approach toward “wall‐less” bubble microfluidic devices.

Electromagnetic Forces and Torques: From Dielectrophoresis to Optical Tweezers

“…As opposed to standard trapping, which usually occurs around the electrodes or the sidewalls of a microfluidic architecture, here, the negative intensity-based DEP force is used to balance the gravitational pull acting on the particle, thereby granting full control on the cell’s distance above the substrate . Similar schemes, which always employ the field gradient force, have also been devised to levitate gas bubbles and liquid droplets. , To the best of our knowledge, no DEP levitation schemes exploiting phase gradient forces have been proposed, and no DEP levitation experiments have been reported that were not conducted in water or some other liquid phase. A combination of intensity and scattering forces is instead used with optical fields to levitate and provide three-dimensional confinement of colloidal particles in air. ,, The optical intensity gradient force provides additional trapping and stability in the transverse direction, which produces a full 3D trap, as opposed to the DEP case.…”

“…29 Similar schemes, which always employ the field gradient force, have also been devised to levitate gas bubbles and liquid droplets. 290,291 To the best of our knowledge, no DEP levitation schemes exploiting phase gradient forces have been proposed, and no DEP levitation experiments have been reported that were not conducted in water or some other liquid phase. A combination of intensity and scattering forces is instead used with optical fields to levitate and provide three-dimensional confinement of colloidal particles in air.…”

Electropatterning—Contemporary developments for selective particle arrangements employing electrokinetics

“…The controlled transport of electrically charged liquid droplets has important applications in controlled drug delivery and in the separation of micro/macro molecules [73][74][75][76][77]. Charged liquid droplets suspended in an immiscible fluid can be manipulated employing EFs [78].…”

“…Microfluidic systems are often prone to undesirable air bubbles being nucleated inside microchannels or inadvertently introduced when adding tubing connections to the devices [76,79]. Air bubbles are highly undesirable, as they can affect device operation and generate parasitic heat transfer processes.…”

Towards controlled bubble nucleation in microreactors for enhanced mass transport

“…[37][38][39] Alternatively, the surface chemistry can be altered locally to also change its wettability, for example via fluorocarbon deposition to create hydrophobic islands, 21,40,41 which in turns promotes bubble nucleation on those sites. 37 Finally, the bubble detachment size and time have been manipulated using dielectrophoresis, 42 by adding surfactants or polyethylene glycol (PEG) in the solution 22 to change the surface tension and preventing bubble coalescence, by promoting convection using a horizontal magnetic field, 22 by introducing a specific texture or patterning in the catalytic surface, 20 or by applying an ultrasonic field. 43 Furthermore, in a microreactor it is particularly important that the bubble departure radius, R d , remains smaller than the hydraulic diameter of the microchannel, to prevent the bubbles from significantly obstructing flow.…”