Resumen de Contactless electrowetting
Vito Di Virgilio
Electrowetting technology, known since more than 100 years, just recently was successfully applied for the fabrication of devices such as pixels, liquid lenses and µTas (micro total analysis systems). Some of those devices are already a market product and some others are expected to reach the maturity to be marketed in the short period, although some fundamental aspects of the electrowetting phenomenon are not yet clear, like the origin of the saturation and the driving forces that lead to a contact angle variation. In the dissertation are presented several contributions to the electrowetting technology. First, have been reported the preliminary evidences about the contactless variation of the contact angle. Furthermore, these phenomena have been studied deeply and rigorous experimental work has been performed. Experimental data have been cross checked with simulations results and theoretical calculations. Finally, the results of the contactless electrowetting experiments lead us to be able to state that the driving element of the contact angle variation is the charge. Contactless electrowetting method has also unlocked the possibility to experimentally measure the impact of surrounding humidity in electrowetting dynamics and the limitations that introduce in the saturation of contact angle. The relationship between relative humidity and saturation contact angle resulted to be directly proportional and in line with the Peek¿s law prediction, here applied to a system in the micro scale. Therefore the last part of the dissertation was dedicated to the study of the charge driving of an electrowetting device in order to be able to control and predict the contact angle dynamics. As additional results it has been found that charge injection rate affects the speed of the contact angle variation, with negligible effects on the contact angle saturation. Cross checking the experimental results with theoretical predictions it has been found that the approximation of a droplet to a spherical cap gives a very good result while no clear contributions could be given to the saturation problem, leaving it open and without any clear solution, so far. Additionally, in this work contains a comprehensive review of state of the art of electrowetting technology and a detailed description of the multiphysic simulation method used.
