Systematic study of jumping droplets induced by electrowetting
Yap, Eugene Jia Chang
Date of Issue2017-05-12
School of Mechanical and Aerospace Engineering
Electrowetting has found to be a crucial application in the micro and nanofluids field. By applying a driving voltage to a droplet in a controlled environment, detachment of the droplet can be achieved when the internal energy is able to break the interfacial energy barrier or adhesion. This is a phenomenon where electrical energy can be converted to mechanical energy with limited moving parts. However, this process is not fully understood due to the lack of reliability in the Young’s Lippmann theory and numerous parameter that attributes to the detachment criteria. In this project, through varying the driving voltage, size and viscosity, we are able to establish a correlation with the factors that contributes to the detachment of a droplet in an oil medium. This correlation is beneficial for future works since none has observed the behaviour of the droplets in this structure. From the experimental numerical results, we are able to proceed to work on more qualitative data such as the detachment time, maximum jump height and the initial velocity of a detaching droplet. This is crucial to get a better understanding of the forces governing the use of an electrical energy to achieve a mechanical displacement. The results has shown that a larger drop size will require a smaller driving voltage and viscous flow inside a droplet will dominate the surface tension which Young’s Lippmann theory did not have a relation to it. These drop size and viscosity effects on the driving voltage could be observed clearly throughout the entire experiment and hence, achieving the primary objective of this project. Furthermore, a relation with the detachment time and jumping height could be established with the electrowetting number, !. Even though a pattern of the initial velocity of a detaching droplet with size and viscosity could not be established, it is somewhat observed to be increasing with !. Continuation of this setup for future studies should be employed to enhance on the reliability and gain a better insight of this behaviour.
Final Year Project (FYP)
Nanyang Technological University