Fabrication of PDMS lenses with precisely controlled curvatures by confined sessile drop technique

This research presented a novel approach for forming lens form elastomeric polydimethylsiloxane (ePDMS) with precisely controlled properties such as curvature, focal length, and magnification via the confined sessile drop technique. This technique is simple, rapid, and cost effective for mass-scale production. The ePDMS lens with plano-convex shape can be directly attached onto a smartphone camera and transform into portable smartphone digital microscope. The fabrication procedure of ePDMS plano-convex lens involved an injection of liquid PDMS (lPDMS) 3-100 µL onto a circular disk with the diameter in the range 2-10 mm. The resistances to spreading by sharp enabled the reproducibility of spherical cap of lPDMS. The lPDMS axisymmetrically spread under the balance between the gravitational force and interfacial tension force for precisely controlled spherical cap. A thermal treatment at 80 oC for 30 min cured the spherical caps lPDMS into a bubble-free solid ePDMS plano-convex lens. The ePDMS plano-convex lens with focal lengths of 3.4-55.2 mm and magnifications of 4.5X-73.5X could be repeatedly reproduced. Portable smartphone digital microscope can be used to capture small objects that cannot be seen with the naked eye such as micro-printing, and gun shoot residue. High-resolution panorama microscope images without distortion were also demonstrated.