Theoretical Model of Droplet Wettability on a Low-Surface-Energy Solid under the Influence of Gravity

Yukihiro Yonemoto,Tomoaki Kunugi

doi:10.1155/2014/647694

Abstract

The wettability of droplets on a low surface energy solid is evaluated experimentally and theoretically. Water-ethanol binary mixture drops of several volumes are used. In the experiment, the droplet radius, height, and contact angle are measured. Analytical equations are derived that incorporate the effect of gravity for the relationships between the droplet radius and height, radius and contact angle, and radius and liquid surface energy. All the analytical equations display good agreement with the experimental data. It is found that the fundamental wetting behavior of the droplet on the low surface energy solid can be predicted by our model which gives geometrical information of the droplet such as the contact angle, droplet radius, and height from physical values of liquid and solid.

Highlights

Wetting phenomena are widely important in industrial and chemical fields
Recent research has focused on simulation of the dynamic behavior of droplets or bubbles on solid surfaces [5,6,7] using nonlinear differential equations
The contact angle is treated as a boundary condition at a three-phase line on a solid surface

Summary

Introduction

Wetting phenomena are widely important in industrial and chemical fields. For example, the wettability of droplets or bubbles on solid surface affects heat transfer, which affects efficient heat exchange [1, 2]. Both the droplet radius and the contact angle change simultaneously These processes depend on the kind of solid [11]. In their study, assuming a droplet of a spherical cap, the Gibbs free energy and volume evaporation rate were evaluated They qualitatively explain the stick-slip behavior by invoking a pinning time and a slip time and introducing the concept of free energy barriers at a contact line. The wettability of droplets on solid surfaces has been studied from various theoretical and experimental viewpoints and have revealed other droplet hystereses, such as a size dependency of the contact angle [13]. The wetting behavior of a droplet on a solid surface under the influence of gravity is considered theoretically and experimentally. Our model can give geometrical information of the droplet on the low surface energy solid surface such as R, h, and θ from the physical properties of σlg, σc and ρl

Experiment

Theory

Result and Discussion

Conclusion