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Short Description

This project is a breakthrough work of using the continuum simulations to study the wetting dynamics on micropatterned surfaces. The scientific merit of this project includes two aspects: (1) a new slip boundary model, and (2) a pseudo-line tension model

Project PIs

Dr. Ping He, Assistant Professor, Department of Mechanical Engineering

Dr. Chun-Wei Yao, Assistant Professor, Department of Mechanical Engineering

Full Description

Modeling static and dynamic contact angles is a grand challenge in studying wetting and de-wetting. We propose a new slip boundary model based on the Navier-Stokes equations, and establish a realistic continuum approach to simulate the contact line dynamics in 3D. To validate our model, a water droplet interacting with micrometer-sized patterns of a hybrid hydrophobic/-philic surface is studied numerically and compared with experimental measurements. Good agreement has been observed with four pillar spacings in the static, receding and advancing modes. Moreover, details of the droplet-surface interaction are revealed, i.e., penetrations, sagging, local and global contact angles.

Pseudo-line tensions are used in a continuum approach to simulate contact angle hysteresis. A pair of pseudo-line tensions in the receding and advancing states, respectively, are utilized to represent contact line interactions with a substrate, because of the nano-scale topological and/or chemical heterogeneity on the substrate. A water droplet sitting on a horizontal or inclined substrate, whose volume is 4—30 µL, has been studied experimentally and numerically. Our simulation model predicts consistent hysteresis at four different droplet sizes compared to experiments. Meanwhile, the critical roll-off angles captured in simulations match well with experiments. 

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Funding

This project was funded by Research Enhancement Grants, Â鶹ÊÓƵ, 2018-2019.

Publications

• P. He, C.W. Yao, Simulating contact angle hysteresis using pseudo-line tensions, MRS Communications, 2019. 
• A.Azimi, P. He, C. Rohrs, C.W. Yao, Developing a novel continuum model of static and dynamic contact angles in a case study of a water droplet on micro-patterned hybrid substrates, MRS Communications 8, 1445-1454, 2018