Abstract
Using light to manipulate fluids has been a long-sought-after goal for lab-on-a-chip applications to address the size mismatch between bulky external fluid controllers and microfluidic devices. Yet, this goal has remained elusive due to the complexity of thermally driven fluid dynamic phenomena, and the lack of approaches that allow comprehensive multiscale and multiparameter studies. Here, we report an innovative optofluidic platform that fulfills this need by combining digital holographic microscopy with state-of-the-art thermoplasmonics, allowing us to identify the different contributions from thermophoresis, thermo-osmosis, convection, and radiation pressure. In our experiments, we demonstrate that a local thermal perturbation at the microscale can lead to mm-scale changes in both the particle and fluid dynamics, thus achieving long-range transport. Furthermore, thanks to a comprehensive parameter study involving sample geometry, temperature increase, light fluence, and size of the heat source, we showcase an integrated and reconfigurable all-optical control strategy for microfluidic devices, thereby opening new frontiers in fluid actuation technology.
Highlights
Using light to manipulate fluids has been a long-sought-after goal for lab-on-a-chip applications to address the size mismatch between bulky external fluid controllers and microfluidic devices
A considerable amount of these studies have been performed under conditions that exclusively favor thermophoresis and suppress convection-driven dynamics[17,18], which results in short-ranged control that is comparable in size with the thermal gradient
To study the non-equilibrium fluid dynamics at the micro-scale in the presence of a localized thermal gradient we use a flow cell system containing a solution of 1.0 μm polystyrene microspheres as tracer particles
Summary
Using light to manipulate fluids has been a long-sought-after goal for lab-on-a-chip applications to address the size mismatch between bulky external fluid controllers and microfluidic devices This goal has remained elusive due to the complexity of thermally driven fluid dynamic phenomena, and the lack of approaches that allow comprehensive multiscale and multiparameter studies. To enhance the range and magnitude of fluid manipulation, static or dynamic electric fields have been coupled into the system[19,20,21], the thermal gradient has been established near a liquid-gas interface leading to Marangoni convection[22,23,24], or a coating of indium-tin-oxide (ITO) has been added to the substrate containing the heat sources to increase convective flow[25] Despite these advances, a comprehensive multiscale and multiparameter characterization that addresses the complex nature of the different contributing phenomena responsible for mass and fluid transport has been lacking. We harness the results of this comprehensive study to demonstrate that a microscopic thermal perturbation of only a few degrees is enough to manipulate a fluid from the μm- to mm-scale and achieve long-range transport
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