Manipulation of microscopic gas bubbles by using surface tension: Capturing, venting and pumping

Microscopic gas bubbles have recently been recognized as powerful tools for a variety of applications, such as micro-lenses, visualization particles, spacers, actuation pistons and pressure sensors. However, reliable manipulation of these marvelous bubbles is still challenging, hindering their employment in the real-world devices. In this study, surface tension force is exploited to manipulate gas bubbles, because it is inherently dominant over other forces in submillimeter scale.; Bubble capturing potential is first introduced to quantify the immobilization of a gas bubble on a solid surface. Reliable formation of bubble arrays in a liquid environment is demonstrated. A universal gas removal approach termed "hydrophobic nanoporous venting" is developed, which can promptly breathe out virtually any kind of gas bubbles. The leakage onset pressure of up to ∼35psi ensures its applications in practical microfluidic devices.; Bubble actuations in closed-loop microfluidics were traditionally restricted to thermal bubbles using the energy-hungry boiling process and limited by their slow condensation. The two basic manipulations, capturing and venting, have enabled new bubble generation approaches, such as electrolysis, injection and chemical reactions, for microactuations. The comparative study shows that electrolysis improves actuation power efficiency by 2--3 orders of magnitude while exhibiting better controllability, bio-compatibility and miniaturization potential, compared with traditional boiling actuation in a similar setup. By combining a virtual check valve with bubble capturing and venting, a new paradigm of micropumps is developed. Fluid circulation in a closed-loop is achieved by using electrolytic gas bubbles (H2 and O2) with 10--100 times higher power efficiency over traditional thermal-bubble-driven micropumps. The flexibility of the bubble source provides an opportunity to optimize the micropumping mechanism for a particular application and address its specific concerns.; Active manipulation of microscopic gas bubble is promising, considering the recent progresses in the electrical control of surface tension by electrowetting-on-dielectric (EWOD). The reliable manipulation of microscopic gas bubbles is expected to contribute greatly to the research on micro total analysis systems (muTAS) and micro power generators (e.g. micro direct methanol fuel cell or muDMFC), and facilitate their contribution to the field of MEMS and nanotechnologies.