| Summary: | 碩士 === 逢甲大學 === 航太與系統工程學系 === 103 === This study is concerned with the experimental measurement of electrowetting characteristics of a droplet on PDMS film under various modes of applied field. Deionized water at room temperature was used as the working fluid. Smooth and hydrophobic PDMS films with measured surface roughness were used as solid boundary models. Aluminum, brass and copper plates were employed as the models of conductive layer, and the thicknesses of PDMS film ranging from 9.37μm to 23.75μm were considered. Three modes of applied field, i.e. linearly increasing, stepwise rising and cyclic loading, were adopted in the experiments.
Safety range of the dielectric voltage for each case was first determined for appropriate presentation of electro-wetting effect as well as to prevent the PDMS film from being damaged under an excess voltage applied. Results show that under linearly increasing mode of voltage load with the conductive layer of the same metal, the droplet contact angle goes up with an increase in dielectric layer thickness. With the voltage applied in a stepwise rising mode, energy accumulation due to time delay leads to a reduction in droplet size, which may affect the contact angle. For the cases of the same conductive layer and time delay, the contact angle rises up with increasing thickness of the dielectric layer. As the voltage applied in a mode of cyclic loading, contact angle changes as the reaction of the voltage variation. While the voltage load goes back to the initial state of 0V, the contact angle cannot fully restore to the initial contact angle for the irreversibility of ion re-distribution near the solid-liquid interface beneath the droplet. Furthermore, as the applied voltage excesses the critical value for the dielectric layer, emergence of the so-called dielectric breakdown results in an intersecting contact angle curve during voltage up and down process in high loading regime.
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