Surface tension driven droplet transport in an open surface is increasingly becoming popular for various microfluidic applications. In this work, efficient transport of a glycerin droplet on an open wettability gradient surface with controlled wettability and confinement is numerically investigated. Nondimensional track width * (ratio of the width of the wettability gradient track and the initial droplet diameter d0) of a wettability gradient track laid on a superhydrophobic background represents wettability confinement. A lower value of * represents higher wettability confinement. Droplet behavior changes for different wettability confinements and gradients of the track. It is found that droplet velocity is a function of the wettability confinement and the gradient; droplet transport velocity is maximum for * = 0.8. Higher confinement (* < 0.8) leads to a significant reduction in droplet velocity. Droplet transport characteristics on hydrophilic–superhydrophilic, hydrophobic–superhydrophilic, and superhydrophobic–superhydrophilic tracks are studied. It is found that for a fixed length of the track, droplet velocity is maximum for the superhydrophobic–superhydrophilic track. A droplet transport regime is demonstrated for a wettability gradient track with different confinements, and it is found that the droplet is transported for wettability confinement * > 0.6 irrespective of the wettability gradient of the track. These findings provide valuable insight into efficient droplet manipulation in microfluidic devices.
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Research Article| April 29 2019
Self-driven droplet transport: Effect of wettability gradient and confinement
Imdad Uddin Chowdhury;
Pallab Sinha Mahapatra ;
Imdad Uddin Chowdhury, Pallab Sinha Mahapatra, Ashis Kumar Sen; Self-driven droplet transport: Effect of wettability gradient and confinement. Physics of Fluids 1 April 2019; 31 (4): 042111. https://doi.org/10.1063/1.5088562
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