Developing interface localized liquid dielectrophoresis for optical applications

Glen McHale; Carl V. Brown; Michael I. Newton; Gary G. Wells; Naresh Sampara

doi:10.1117/12.2001442

26 November 2012 Developing interface localized liquid dielectrophoresis for optical applications

Glen McHale, Carl V. Brown, Michael I. Newton, Gary G. Wells, Naresh Sampara

Proceedings Volume 8557, Optical Design and Testing V; 855703 (2012) https://doi.org/10.1117/12.2001442
Event: Photonics Asia, 2012, Beijing, China

Abstract

Electrowetting charges the solid-liquid interface to change the contact area of a droplet of a conducting liquid. It is a powerful technique used to create variable focus liquid lenses, electronic paper and other devices, but it depends upon ions within the liquid. Liquid dielectrophoresis (L-DEP) is a bulk force acting on the dipoles throughout a dielectric liquid and is not normally considered to be a localized effect acting at the interface between the liquid and a solid or other fluid. In this work, we show theoretically how non-uniform electric fields generated by interdigitated electrodes can effectively convert L-DEP into an interface localized form. We show that for droplets of sufficient thickness, the change in the cosine of the contact angle is proportional to the square of the applied voltage and so obeys a similar equation to that for electrowetting – this we call dielectrowetting. However, a major difference to electrowetting is that the strength of the effect is controlled by the electrode spacing and the liquid permittivity rather than the properties of an insulator in a sandwich structure. Experimentally, we show that that this dielectrowetting equation accurately describes the contact angle of a droplet of oil viewed across parallel interdigitated electrodes. Importantly, the induced spreading can be complete, such that contact angle saturation does not occur. We then show that for thin films, L-DEP can shape the liquid-air interface creating a spatially periodic wrinkle and that such a wrinkle can be used to create a voltage programmable phase diffraction grating.

Citation Download Citation

Glen McHale, Carl V. Brown, Michael I. Newton, Gary G. Wells, and Naresh Sampara "Developing interface localized liquid dielectrophoresis for optical applications", Proc. SPIE 8557, Optical Design and Testing V, 855703 (26 November 2012); https://doi.org/10.1117/12.2001442

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