Numerical simulations reveal 3D structure of liquid while dip-coating a plate

Rain dripping down a windshield, dipping a solid in paint or a coating, even dipping a cookie in milk are all examples of a moving line of fluid in contact with an object or surface. Understanding the wetting dynamics in these situations is important for applications in industry and manufacturing.

Gao et al. studied the wetting dynamics of moving fluid on a plate with chemical stripes that provided alternating wettabilities.

Through numerical simulations, they discovered that wetting dynamics depend greatly on the width of the wettable stripes.

They learned that the width of the stripe affects the position of the contact line instability (which leads to the entrainment of droplets) and the onset of the film deposition. Their results indicate that the wetting transition is associated with contact line curvature and theories based on straight contact lines do not apply. For wider stripes, a trapezoidal film would form, resembling the wetting transition on a homogeneous plate of finite width.

“Our paper demonstrates a connection between the dip coating of a homogeneous plate with finite widths and that of a striped plate, which were both investigated separately in previous work,” said author Peng Gao.

According to Gao, their simulations were also the first to numerically produce the 3D structure of the entrained film. The authors hope that more extensive experimental work will clarify the 3D behavior of the fluid entrainment.

To further this research, the authors suggest research focusing on the interface slope near the plate edges or the stripe boundaries.

Source: “Dynamical wetting transition on a chemically striped incline,” by Yuting Xia, Jian Qin, and Peng Gao, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5135641 .