Figure 35.

(a) Concept of a contactless microdroplet manipulator based upon Marangoni flows. The flow is driven by heat sources of various geometries suspended above the oil layer. The projected heat fluxes (shown in red) generate flows which emulate droplet channels, reservoirs, and mixers. (b) A microfluidic trap generated by a point heat source. Schematic is showing the suspended heat source, the projected Gaussian heat flux profile, and the toroidal flow region in the oil layer. (c) Virtual droplet channels generated by parallel linear heat sources. The channel boundaries are defined by the heat flux projected by two heated wires with separation s held parallel to the liquid surface. Target sized droplets are pulled into the channel by the subsurface flows. Orders are excluded. Marangoni flows are shown in green and with arrows. (d) Single droplet trapping with an annular heat flux. Schematic is showing the annular heat flux projected on the surface, the trapped droplet, and the exclusion of larger and smaller droplets. Reproduced with permission from [178], A.S. Basu and Y.B. Gianchandani, “Virtual microfluidic traps, filters, channels and pumps using Marangoni flows”, Journal of Micromechanics and Microengineering, vol. 18, p. 115031, 2008. Copyright 2008, IOP Publishing, all rights reserved.