Abstract
We investigate the control of flow direction around a water vapor bubble using the thermoplasmonic effect of a gold nanoisland film (GNF) under laser irradiation with multiple spots. By focusing a laser spot on the GNF immersed in degassed water, a water vapor bubble with a diameter of ~10 μm is generated. Simultaneously, a sub laser spot was focused next to the bubble to yield a temperature gradient in the direction parallel to the GNF surface. Consequently, rapid flow was generated around the bubble, whose flow direction was dependent on the power of the sub laser spot. The observed flow was well-described using a stokeslet; the latter contained components normal and parallel to the GNF surface and was set to 10 μm above the GNF. This technique allows us to apply a significant force on the microfluid at the vicinity of the wall in the direction parallel to the wall surface, where the flow speed is generally suppressed by viscosity. It is expected to be useful for microfluidic pumping and microfluidic thermal management.
Highlights
During the last several decades, microfluidics has demonstrated significant impact on biological and chemical applications through the development of lab-on-a-chip devices[1,2] and micro total analysis systems[3,4]
When Psub = 0, 3, and 8 mW, a water vapor bubble of 10–12 μm diameter was generated on the primary laser spot due to the highly localized heat induced by the gold nanoisland film (GNF) and the absence of dissolved gases in water
We investigated the rapid flow generated around a water vapor microbubble using the thermoplasmonic effect of the GNF under laser irradiation with multiple spots
Summary
During the last several decades, microfluidics has demonstrated significant impact on biological and chemical applications through the development of lab-on-a-chip devices[1,2] and micro total analysis systems[3,4]. The flow field around the water vapor bubble was well described using a point force, i.e., a stokeslet that was set normal to the GNF surface, from which the flow speed was estimated to exceed 1 m/s in the vicinity of the bubble This flow speed is extremely large as compared to that can be typically achieved in conventional microfludic channels by using syringe pumps, which is of the order of 0.1–10 mm/s34–36. This technique is attractive for realization of ubiquitous microfluidic mixers and pumps because such an rapid flow can be generated at an arbitrary spot of the microchannels by focusing laser on the GNF. From the observed flow field around the bubble, we evaluate the force inducing the flow using a theoretical model and show its potential as the source of a point force in the direction parallel to the wall at the wall vicinity
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