Abstract
Janus droplets can function as excellent templates for fabricating physically and chemically anisotropic particles. Here, we report new surfactant-laden Janus droplets with curvature controllability and enhanced stability against coalescence, suitable for fabricating shape-anisotropic polymer microparticles. Using a microfluidic flow-focusing device on a glass chip, nanoliter-sized biphasic droplets, comprising an acrylate monomer segment and a silicone-oil (SO) segment containing a surfactant, were produced in a co-flowing aqueous polyvinyl alcohol (PVA) solution. At equilibrium, the droplets formed a Janus geometry based on the minimization of interfacial energy, and each of the two Janus segments were uniform in size with coefficient-of-variation values below 3%. By varying the concentration of the surfactant in the SO phase, the curvature of the interface between the two lobes could be shifted among concave, planar, and convex shapes. In addition, the Janus droplets exhibited significantly improved stability against coalescence compared with previously reported Janus droplets carrying no surfactant that coalesced rapidly. Finally, via off-chip photopolymerization, concave-convex, planar-convex, and biconvex lens-shaped particles were fabricated.
Highlights
Janus droplets carrying no surfactant that coalesced rapidly
In this study, we found that the simple addition of the surfactant to the SO phase resulted in the Janus morphology of the droplets at equilibrium
We synthesized surfactant-laden Janus droplets comprised of two immiscible curable and non-curable segments with high stability against coalescence and tunable morphologies, suitable for the fabrication of lens-shaped microparticles
Summary
Janus droplets carrying no surfactant that coalesced rapidly. via off-chip photopolymerization, concave-convex, planar-convex, and biconvex lens-shaped particles were fabricated. Janus droplets can be used as templates in the fabrication of various functional microparticles, which are valuable for potential applications as electrically and magnetically driven actuators [1,2], interfacial stabilizers [3] and building blocks for self-assembly [4]. Monodisperse Janus droplets comprised of two miscible [7] or two immiscible segments [8] have been produced via droplet microfluidics. While the two miscible segments tend to be mutually mixed over time through convective and diffusive transport, Janus droplets of two immiscible segments can maintain their phase-separated geometry via the minimization of interfacial free energy. Monodisperse Janus droplets with mutually immiscible curable and non-curable segments have been produced as templates for fabricating lens-shaped polymer particles for use in microoptics applications [9,10,11]
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