Department of Mechanical engineering

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    Anisotropic Stick-Slip Behavior of Aqueous Drops on Lubricated Chemically Heterogeneous Slippery Surfaces
    (ARXIV, 2020-08) Bhatt, Geeta
    Conventional slippery surfaces show isotropic drop mobility in all directions, but many applications require directional drop motion along a particular path only. In previous studies, researchers used topographic substrates, together with different external stimuli, to demonstrate anisotropic drop motion, which is not very efficient and cost-effective. Herein, we report a novel approach to smartly control drop motion on lubricating fluid-coated chemically heterogeneous surfaces composed of alternating hydrophobic and hydrophilic stripes. Upon depositing an aqueous drop on such a surface, the underneath lubricating fluid dewets from the hydrophilic regions but remains intact on the hydrophobic ones, providing sticky and slippery areas for the drop. This results in remarkable anisotropic drop sliding behavior, from uniform motion along parallel to stripes to stick-slip motion along the perpendicular to them. Furthermore, we also demonstrate a phase diagram summarizing different dynamic situations exhibited by drops, sticking, or moving in one or both directions.
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    Anisotropic Motion of Aqueous Drops on Lubricated Chemically Heterogenous Slippery Surfaces
    (Wiley, 2020-12) Bhatt, Geeta
    Conventional slippery surfaces show isotropic drop mobility in all directions, whereas anisotropic drop motion may often be required to guide drops in a particular direction. In most cases, topographically structured substrates are employed to provide anisotropic drop motion, but this technique is neither efficient nor cost-effective. Current findings elucidate a novel approach to control the drop motion by virtue of designing lubricated chemically heterogenous (LCHet) surfaces. Upon depositing aqueous drops on such surfaces, the underneath lubricating film dewets only from the hydrophilic regions but remains intact on the hydrophobic ones. This results in the formation of lubricated microchannels, which subsequently provides sticky and slippery regions for the drops. Fabricated surfaces show remarkable anisotropic drop sliding behavior, from uniform motion along parallel to stripes to stick–slip motion along perpendicular to them. Drop motion on such LCHet surfaces can be easily controlled and tuned in the desired direction by tuning the area fraction of hydrophobic region. Furthermore, a phase diagram is presented to summarize different dynamic situations exhibited by drops; sticking or moving in one or both directions. This approach can be easily adapted to different systems to produce multiranging applications from liquid micropatterning to anisotropic drop mobility.