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Length Scale Selects Directionality of Droplets on Vibrating Pillar Ratchet
Author(s) -
Agapov Rebecca L.,
Boreyko Jonathan B.,
Briggs Dayrl P.,
Srijanto Bernadeta R.,
Retterer Scott T.,
Collier C. Patrick,
Lavrik Nickolay V.
Publication year - 2014
Publication title -
advanced materials interfaces
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.671
H-Index - 65
ISSN - 2196-7350
DOI - 10.1002/admi.201400337
Subject(s) - materials science , microscale chemistry , directionality , microfluidics , nanowire , nanoscopic scale , pillar , nanotechnology , hysteresis , contact angle , ratchet , tilt (camera) , optics , composite material , mechanical engineering , condensed matter physics , genetics , mathematics education , mathematics , physics , biology , work (physics) , engineering
Directional control of droplet motion at room temperature is of interest for applications such as microfluidic devices, self‐cleaning coatings, and directional adhesives. Here, arrays of tilted pillars ranging in height from the nanoscale to the microscale are used as structural ratchets to directionally transport water at room temperature. Water droplets deposited onto vibrating chips with a nanostructured ratchet move preferentially in the direction of the feature tilt while the opposite directionality is observed in the case of microstructured ratchets. This remarkable switch in directionality is consistent with changes in the contact angle hysteresis. To glean further insights into the length scale dependent asymmetric contact angle hysteresis, the contact lines formed by a nonvolatile room temperature ionic liquid placed onto the tilted pillar arrays were visualized and analyzed in situ in a scanning electron microscope. The ability to tune droplet directionality by merely changing the length scale of surface features all etched at the same tilt angle would be a versatile tool for manipulating multiphase flows and for selecting droplet directionality in other lap‐on‐chip applications.