DescriptionThe super hydrophobicity of a surface can be quantified by touching the surface with a liquid drop attached to a force sensor, and measuring the forces during the contact.  Two important forces can be identified: the snap-in force – the force when the drop has just initiated contact with the surface – and the pull-off force – the peak force before the drop loses the contact with the surface.  These two forces can be related to the advancing and receding contact angles, respectively.
In this talk, I will discuss a computational model of the snap-in and pull-off forces. The model allows studying the relations between the forces, the contact angles, the contact radii and the volume of the drop. Relevant theory – Young-Laplace equation with boundary conditions – will be outlined. Two types of hysteresis are identified: contact angle hysteresis and the hysteresis resulting from the multiple stable configurations of the drop interface. The effects of surface topography will be discussed.
In the following part of the talk, I will interpret experimental results from a recent paper  using the model. In particular, I will use the model to show that the data is consistent with some of the surfaces having advancing contact angles beyond 179°. This poses an interesting dilemma that there are currently no other methods with comparable sensitivity to validate the results.
In the final part of the talk, I will discuss alternative approaches and further developments to the model and the theory, and some potentially interesting measurements for the experimentalists.
|Period||16 May 2018|
|Event title||Superhydrophobicity and Wetting Symposium|
|Degree of Recognition||International|