Collaborative Research: Capillary Micro-Switches for Actuation, Photonics and Manufacturing

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Capillary surfaces are liquid/gas or liquid/liquid interfaces whose shapes are determined by surface tension. Such interfaces generally occur for liquids against gas on scales of 1000 microns or less, scales where deformation by gravity is negligible. Use of capillarity has emerged as a leading strategy for manipulating liquids at the micro-scale. However, practitioners have yet to take advantage of capillary instabilities in such strategies. Micro-switches are configurations on the sub-millimeter scale that exhibit a bi-stable behavior. Simple capillary surfaces with nonlinear response can be combined to make an "on-off" switch, as we have recently demonstrated. Moreover, capillary surfaces formed at circular openings can act as micro-lenses having essentially zero spherical aberration. Capillary micro-lenses admit a wide range of wavelengths. For example, by accommodating uv-lasers, features at 100 nm scale may readily be accessed and hence sub-micron read-write capabilities become possible. Another application is far-field photo-lithography on non-planar surfaces. Here, an array of individually addressable lenses with adjustable focal lengths are the key. Therefore, capillary switches at the micro-scale can be used to focus and manipulate light (photonics), to effect force or motion (actuation) and to implement high through-put production (manufacturing). Our objective is to use the natural tendencies of capillary systems, including capillary instabilities, to manipulate them for a wide range of applications. Specifically, we will explore ways in which the energy landscape can be tuned so that a change from configuration A to B (and back from B to A) can be triggered by low energy disturbances. In the limit, capillary switches can be designed to be nearly reversible and implementation will lead to power-efficient devices.Triggering state changes in capillary systems can occur by mechanical (pressure), electrical (redox surfactants) or thermal (thermo-pneumatic or Marangoni) means. Various stimuli will be examined at a scale of hundreds of microns and at tens of microns.