Tunable and Movable Liquid Microlenses

Dong et al. presented a tunable and movable liquid microlens in situ fabricated through a relatively simple process by manipulating fluids within 

When the air pressure difference applied to the droplet equaled the internal capillary pressure caused by the difference in the curvature between the two liquid-air interfaces of the droplet, the liquid-air interface at the junction could protrude from the microchannel and be steadily piimed along the edges. The shape of the other liquid-air interface, on the other hand, depended on the static contact angle of the liquid on the channel material under homogeneous pneumatic pressure. A liquid microlens was thus formed from the droplet. 

Because of the fluidic nature of the liquid and the surface tension as a dominant force at microscale, varying the air pressure difference within a certain range could change the shape of the pinned liquid-air interface, thus tuning the focal length of the resulting microlens. With proper pneumatic controls, this microlens could be moved further within the microchannel at various predefined spots corresponding to individual junctions. 

Microfluidic setup for in situ fabrication of liquid droplet-based microlens. To realize the movement of microlens from one junction to another, a small step is produced at junction J3. (Source Dong, L. and H. Jiang. 2007. Applied Physics Letters, 91(4), 041109. With permission.) 

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