Microfluidic doublets in aqueous samples generated by microfabricated thermal probes

This paper describes an investigation of microfluidic actuation of doublet patterns in samples of water on blank substrates, using singular and arrayed microfabricated thermal probes. A doublet is a two-dimensional flow pattern consisting of adjacent, opposing vortices with linear streamlines between them. In this work, each probe consists of a polyimide thin film cantilever with a metal heater near the tip which generates a temperature gradient up to 1 °C/μm along its length. The probes are 360 μm long, 42–120 μm wide, and 3.5 μm thick, and the tips are typically <1 mm away from the liquid surface. The velocity of the doublet flow can be controlled by adjusting the temperature of the heat source or by controlling the gap or attack angle between the heat source and the liquid surface. Linear flow velocities exceeding 5 mm/s and rotational velocities exceeding 1200 rpm are reported.