Microfluidic fabrication of oil-filled polymeric microcapsules with independently controllable size and shell thickness via Janus to core–shell evolution of biphasic droplets

Abstract

We report the microfluidic fabrication of polymeric microcapsules with an oil core and a photocured acrylic shell from biphasic Janus droplets that undergo a structural transition into core–shell droplets of two immiscible phases. Using a cross-flowing droplet generator on a glass chip, we produced biphasic Janus droplets comprised of two immiscible phases in a one-step manner, which subsequently transform into monodisperse silicone-oil-in-monomer droplets with predetermined core/shell volume ratios. A photocurable acrylate monomer and a noncurable silicone oil were used as the two immiscible droplet phases, and an aqueous polyvinyl alcohol solution was used as the continuous phase. Using this process, the size and relative shell thickness of the resultant core–shell droplets could be controlled independently and consistently. The droplet size was controlled in the range of 70–150μm by keeping the coefficients of variation in the range of 1.3–3.3% by altering the flow rate of the cross-flowing aqueous stream, and the relative shell thickness was tuned in the range of 0.004–0.3 by varying the flow-rate ratio of the two droplet phases. Subsequent off-chip photopolymerization by UV light exposure yielded oil-filled acrylic microcapsules with controlled sizes and shell thickness.