Advancing Optical Technologies through Electrowetting Research

1. New Optical Research Opportunities in Electrowetting Jason Heikenfeld ECECS Department University of Cincinnati Abstract:Conventional photonic devices are often limited in optical-agility by their use of all solid-state materials. A possible solution might be found in liquid-state systems. Interestingly, the very first (1840’s) recordings of liquid-based photonics trace back to Swiss physicist Daniel Collodon and French physicist Jacques Babinet who utilized light-guiding within jets of water for dramatic fountain displays[1]. Regardless of an early start, the concept liquid optics has seen only intermittent activity. Just recently (~2000) an explosion of research in the nascent field of electrowetting has been seen. First attractive as an improved microfluidic ‘lab-on-chip’ technology, it is now commercially obvious that most applications for electrowetting are optical in nature. Electrowetting is a critical enabler since it allows control of contact angles in liquid/liquid and liquid/solid systems. It is well-understood that a polar liquid with high surface-tension such as water (water~73 dynes/cm) beads up (contact~1180) when placed on a Teflon or Parylene hydrophobic electrical-insulator with low surface energy (insulator<20 dynes/cm). By applying external potential the hydrophobic insulator becomes charged (~nF/cm2) and the polar liquid wets the surface (contact~750). Another way of expressing this effect is that the interfacial surface energy between the water and insulator decreases with increasing voltage. Voltage modulation of the wetting action is reversible at speeds >1 kHz. Complementary movement of two immiscible polar and non-polar (oil) liquids is also achievable in competitive electrowetting systems. Established and emerging research activities at the University of Cincinnati in electrowetting will be reviewed. Background on the basic physics behind electrowetting operation will first be provided. Application of electrowetting to light-transmissive and light-emissive display devices will then be presented. Emerging electrowetting optical applications such as laser-beam steering and agile optical fibers will also be discussed. The talk will then be concluded with very recent results at extending electrowetting to nanostructured surfaces and biological applications. [1] J. Hecht, City of Light: The Story of Fiber Optics, Oxford Univ. Press, 1999.. Wed. Nov. 30th