Wed. Nov. 30th

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 (1840s) 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 displays1.
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 (?water73 dynes/cm) beads up
(?contact1180) when placed on a Teflon or
Parylene hydrophobic electrical-insulator with
low surface energy (?insulatorlt20 dynes/cm). By
applying external potential the hydrophobic
insulator becomes charged (nF/cm2) and the polar
liquid wets the surface (?contact750). 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 gt1 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