Static contact angle θ is adjusted from hydrophilic to hydrophobic with the variation of A sl . Other parameters of the DPD fluid are given in Table I .
The computational model.
A liquid droplet on a wetting gradient with θ b > θ a in two dimension.
Comparison between DPD simulations and theoretical predictions.
The variation of (a) the center-of-mass position X CM and (b) the velocity of the droplet V and the aspect ratio α with time. The droplet-substrate system is given as Fig. 2 with θ L = 150° and θ R = 40°.
The time history of the surface energy (solid line), the translation part of the kinetic energy (dashed line – red) and their sum (circles – green), as well as the dissipative energy (dashed-dotted line – blue) of the moving droplet. E S , E K , and E D are scaled by the initial surface energy E S0 .
The three-dimensional velocity field of the moving droplet. The dashed arrows on sections A and B sketch the flow direction on each section. Vector V denotes the droplet moving direction.
The three-dimensional flow structure inside the moving droplet, in which the velocity of the droplet has been subtracted. The horizontal dark shape (blue) denotes the vortex center of each section.
The structure of velocity field of the central section Y = 0, (a) droplet locates on hydrophobic surface at X CM = −27 and (b) droplet crosses hydrophobic and hydrophilic surfaces at X CM = −5.8. The velocity of droplet has been subtracted.
Effect of (a) strength of wetting gradient, (b) droplet size, and (c) thermal fluctuation on the self-transport process actuated by linear gradient of wettability.
The computational parameters used in the present simulations. All quantities are given in DPD units.
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