Three dimensional flow structures in a moving droplet on substrate: A dissipative particle dynamics study

Abstract

It is of both fundamental and practical interest to study the flow physics in the manipulation of droplets. In this paper, we investigate complex flow in liquid droplets actuated by a linear gradient of wettability using dissipative particle dynamics simulation. The wetting property of the substrate ranging from hydrophilic to hydrophobic is achieved by adjusting the conservative solid-liquid interactions which results in a variation of solid-liquid surface tension. The internal three-dimensional velocity field with transverse flow in droplet is revealed and analyzed in detail. When the substrate is hydrophobic, it is found that there is slight deformation but strong flow circulation inside the droplet, and the droplet rolling is the dominant mechanism for the movement. However, large deformation of the droplet is generated after the droplet reaches the hydrophilic surface, and a mechanism combining rolling and sliding dominates the transportation of the droplet. Another interesting finding is that the thermal fluctuation can accelerate the spontaneous motion of a liquid droplet under a wetting gradient. The effects of the steepness of wetting gradient and the size of droplet on the translation speed are studied as well.

Numerical Simulations of the Digital Microfluidic Manipulation of Single Microparticles

“…It is found that there is faster transport of more hydrophilic microparticles. For A ls = −19, the travel time of droplet with a microparticle over the whole region with wettability gradient is almost same as that without the microparticle reported in our previous study 18. …”

“…This is because, for larger droplet, the difference of wettability across droplet is larger due to larger contact surface between droplet and substrate. 18 For R l ≥ 8, the effect on the manipulation of the microparticle from the droplet size becomes negligible. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 III.2.3 Effect on the transport of microparticle from the wettability of the microparticle As shown in Fig.…”

Dissipative Particle Dynamics (DPD): An Overview and Recent Developments

“…Recently the DPD method is modified to model the solid-liquid-gas co-existing systems, either by using the many body DPD approach developed by Warren [77] or by using a new conservative interaction potential with long-distance attraction and shortrange repulsion proposed by Liu et al [71], or by other approaches which are able to describe the attraction and repulsion between interacting DPD particles. For example, Li et al [91] investigated the 3D flow structures in a moving droplet on substrate by using the many body DPD, Zhang et al [92] studied the movement of a droplet in a grooved channel by using Liu's conservative interaction potential. Merabia and Pagonabarraga developed a mesoscopic model for simulating the dynamics of a non-volatile liquid on a solid substrate and they analyzed the kinetics of spreading of a liquid drop wetting a solid substrate and the dewetting of a liquid fill on a hydrophobic substrate [93].…”

A GPU-accelerated package for simulation of flow in nanoporous source rocks with many-body dissipative particle dynamics

“…These simulations are computationally demanding and require significant computing resources. In early exercises we used the DPD package [31] in LAMMPS [47]. The package takes advantage of the parallel computing readiness of LAMMPS and delivers satisfying scalability for homogeneous porous systems.…”