We present a microfluidic platform for high-throughput moldless fabrication of biconvex polymer microlenses. Using a confined sheath-flowing geometry that is dry-etched on a glass chip, we produced compound droplets composed of a photocurable acrylate monomer and a non-curable silicone oil containing a surfactant. The droplets developed reproducibly and rapidly in a co-flowing aqueous stream (e.g., at ～200 drops/s). At equilibrium, the produced compound droplets formed a Janus geometry with photocurable segments having a biconvex shape, and they were monodispersed with coefficients of variation below 5. Subsequent off-chip photopolymerization continuously yielded biconvex acrylic microlenses of uniform sizes and shapes. By varying the flow rates we could control the production rate and the size of the Janus droplets (equivalent diameter of 120-200 μm). In addition, the shape of the Janus segments and resultant particles could be tuned by varying the flow rate ratio of the two droplet phases as well as the type of surfactant dissolved in the non-curable phase. We also confirmed that the prepared biconvex microparticles could be used as optical lenses. With flexible size and shape control, low energy input, and the rapidity and scalability of the system, this technique has considerable potential as a manufacturing process for high-throughput microlens production.
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