Levich Institute Seminar Announcement, 03/01/2005

Tuesday, 03/01/2005
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Amir Hirsa
Rensselaer Polytechnic Institute
Department of Mechanical, Aerospace & Nuclear Engineering

"Low-Dissipation Capillary Switches at Small Scales"


A capillary surface is a gas/liquid or immiscible liquid/liquid interface whose shape is determined by surface tension. For typical liquids against gas, capillary surfaces occur on the millimeter-scale and smaller. Manipulating capillary surfaces has emerged as a useful strategy for moving liquids on the micro-scale. However, practitioners have yet to take advantage of capillary instability to design energy efficient devices. Through an understanding of capillary instability, natural tendencies of a system to assume distinct shapes may be utilized to generate force and to effect motion in an efficient manner. Here we demonstrate a system of two coupled capillary surfaces that is made to switch between its stable states via mechanical and electrochemical disturbances. Requirements for capillary switches to avoid viscous dissipation are described. Addressability of individual switches is achieved using electrochemical activation via a redox surfactant, where surface tension of one element of the switch is changed relative to the other. Strategies for utilizing capillary switches for transporting other liquids or solids are discussed. Aside from actuation, another application of such capillary systems is in optics, where a high-quality lens with adjustable focal length is demonstrated.



Research interests are on intrinsic interfacial properties of mono-molecular films on liquid surfaces, surface tension dominated systems, flow stability, non-invasive measurement techniques for interfacial flows.