Snapping Surfaces for Tunable Microlenses

To accomplish fast tuning time of microlenses. Holmes et al. utilized snap transition to change the status of microlenses [17]. This snap transition was based on the onset of an elastic snap-through instability similar to 

Tunable microlenses formed by snap-through transition. Top Concave microlenses. Middle Convex microlenses. Bottom Snapping process from concave to convex. Source Holmes, D.P. and A.J. Crosby. 2007. Advanced Materials, 19(21), 3589-3593. With permission.) 

This process caused a volumetric decrease on the surface of the polymeric film, triggering the shells to snap from convex to concave to minimize the development of tensile stresses in the outer surface layer. To snap the shells from concave to convex, a triggering mechanism that caused volumetric expansion could be used. The authors demonstrated one such approach by swelling the elastic polymer network with an organic solvent to develop an 

A thin film of cross linked PDMS (15 to 60 pm thick) coated with a thin ( 1 pm) layer of uncured PDMS was placed on the surface of the strained holes. The assembly was heated to cross link the uncured PDMS and bond the film 

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