Abstract
Detachment and jumping of liquid droplets over solid surfaces under electrowetting actuation are of fundamental interest in many microfluidic and heat transfer applications. In this study we demonstrate the potential capabilities of our continuum-level, sharp-interface modelling approach, which overcomes some important limitations of convectional hydrodynamic models, when simulating droplet detachment and jumping dynamics over flat and micro-structured surfaces. Preliminary calculations reveal a considerable connection between substrate micro-topography and energy efficiency of the process. The latter results could be extended to the optimal design of micro-structured solid surfaces for electrowetting-induced droplet removal in ambient conditions.
Highlights
In this work we presented the capabilities of a recently developed modelling approach by our group, in simulating, probably for the first time, electrowetting-induced droplet detachment and jumping over topographically micro-structured surfaces
We validated our model against the work of Cavali et al [18] and performed computations for two representative cases of micro-structured surfaces in order to show that we can capture, in detail, the retraction dynamics and jumping and quantify the role of adhesion and energy dissipation due to pinning on the surface asperities
The outcome of this numerical study reveals a connection between surface micro-structure and energy efficiency of the droplet detachment and jumping process
Summary
Merdasi et al [21] suggested the idea of enhancing the droplet dynamics of detachment under electrowetting actuation by introducing macroscopically a topographic heterogeneity on the solid substrate They developed a VOF-CSF (volume of fluid-continuum surface force) hydrodynamic numerical model with no-slip and contact angle boundary conditions, considering electrical, capillary and contact line friction forces. Diffuse-interface formulations, such as VOFs and phase-field method, regularize the stress singularity by using a fixed computational mesh and implicit functions to represent different phases These methods can be used successfully for simulating multiple contact lines on complex surfaces, but exhibit some drawbacks compared to sharp-interface, hydrodynamic formulations such as higher computational cost (need for denser meshes), numerical diffusion, limited accuracy for high deformations and large thickness of the diffuse interface. We demonstrate that with this modelling approach it is possible, probably for the first time, to study the effects of substrate microtopography and the resulting wetting states on critical conditions for detachment and droplet jumping dynamics in ambient conditions
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