title: Directed drop transport rectified from orthogonal vibrations via a flat wetting barrier ratchet.
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.
authors.affiliation: Department of Electrical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Duncombe
authors.forename: James F
authors.initials: JF
authors.lastname: Parsons
authors.forename: Karl F
authors.initials: KF
authors.lastname: Böhringer
mesh_terms: D046210:Microfluidic Analytical Techniques; D010316:Particle Size; D012821:Silanes / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties; D014297:Trimethylsilyl Compounds / Q000737:chemistry*; D014732:Vibration; D017155:Wettability
chemical_list: D012821:Silanes; D013438:Sulfhydryl Compounds; D014297:Trimethylsilyl Compounds; C055926:trimethylsilanol