Electrochemically Activated Adaptive Liquid Microlenses

Liquid lens showing electrode embedded at each contact circle. Photo on right was taken with thin laser light sheet illuminating liquid lens from above. For visualization, fluorescein dye at 4 ppm concentration was dissolved in double-distilled water. Illumination was from a 488 nm line of an argon ion laser. Yellow fQter was used on the camera lens. (Source Lopez, C.A., C.C. Lee, and A.H. Hirsa. 2005. Applied Physics Letters, 87(13), 134102. With permission.) 

The radius of curvature at the tip of each free surface and the maximum thickness of the liquid define the geometric properties of the lens. To calculate the equilibrium configuration of the liquid lens, the authors used the Young-Laplace equation to solve for the top and bottom capillary surfaces, coupled through the hydrostatic pressure of the liquid column with height d and constrained by a particular total volume of liquid. In non-dimensional form, the Young-Laplace equation is 

Activation of the liquid lens was achieved by using a water soluble ferro-cenyl surfactant whose surface activity could be controlled electrochemically [27]. Application of a voltage difference across the lens produced a reversible reduction-oxidation process that modified the surface activity of the surfactant. The surface tension increased where oxidation occurred and decreased where reduction occurred with a magnitude of 8 d5m/cm. The total change in surface tension (16 dyn/cm) was more than one-fifth of the surface tension of pure water. This difference in surface tension modified the response of the system, resulting in a redistribution of the liquid. 

Liquid-Crystal Lens-Cells with Variable Focal Length, Japanese Journal of Applied Physics, vol. 18, pp. 1679-1684,1979. 

Cleverly, and P. G. Komreich, Focusing by Electrical Modulation of Refraction in a Liquid-Crystal Cell, Applied Optics, vol. 23, pp. 278-289,1984. 

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