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Directed drop transport rectified from orthogonal vibrations via a flat wetting barrier ratchet.

Langmuir : the ACS journal of surfaces and colloids (2012-09-01)
Todd A Duncombe, James F Parsons, Karl F Böhringer
ABSTRACT

We introduce the wetting barrier ratchet, a digital microfluidic technology for directed drop transport in an open air environment. Cyclic drop footprint oscillations initiated by orthogonal vibrations as low as 37 μm in amplitude at 82 Hz are rectified into fast (mm/s) and controlled transport along a fabricated ratchet design. The ratchet is made from a simple wettability pattern atop a microscopically flat surface consisting of periodic semi-circular hydrophilic features on a hydrophobic background. The microfluidic ratchet capitalizes on the asymmetric contact angle hysteresis induced by the curved features to drive transport. In comparison to the previously reported texture ratchets, wetting barrier ratchets require 3-fold lower actuation amplitudes for a 10 μL drop, have a simplified fabrication, and can be made optically flat for applications where transparency is paramount.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Trichloro(1H,1H,2H,2H-perfluorooctyl)silane, 97%
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Trimethylsilanol, ≥97.5% (GC)
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Potassium trimethylsilanolate, 90%, technical grade
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Tris(trimethylsilyl) phosphite, ≥95.0% (GC)
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Sodium trimethylsilanolate, 95%
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Lithium trimethylsilanolate, 95%