Abstract
Droplet microfluidics has enabled the synthesis of polymeric particles with controlled sizes, shell thickness, and morphologies. Here, we report the Janus to core-shell structural evolution of biphasic droplets formed in a microfluidic flow-focusing device (MFFD) for the synthesis of polymer microcapsules with oil core/thickness-tunable shell via off-chip photo- and thermally induced polymerization. First, nanoliter-sized biphasic Janus droplets comprising an acrylate monomer and silicone oil were generated in a co-flowing aqueous polyvinyl alcohol (PVA) solution in an MFFD on a glass chip. Immediately following their break-off, the produced Janus droplets started to change their geometry from Janus to core-shell structure comprising a single silicone-oil core and an acrylate-monomer shell by the minimization of interfacial energy. Thus, we could produce monodisperse core-shell drops with average diameters of 105–325 μm, coefficient of variation (CV) values of 1.0–4.5%, and shell thickness of 1–67 μm. Subsequently, these drops were synthesized to fabricate polymeric microcapsules with tunable shell thickness via photo- and thermally induced polymerization. By increasing the concentration of the photo- and thermal initiator, we successfully produced thinner and ultra-thin shell (800 nm thickness) microcapsules. The surface structure of resulting particles was smooth in photopolymerization and porous in thermal polymerization.
Highlights
Www.nature.com/scientificreports of ethyl cellulose shell and poly(N-isopropylacrylamide) (PNIPAM) core were prepared from W/O/W28 and W/(O/W)/W29 double emulsions via solvent evaporation
We fabricated the particles from the biphasic Janus droplets generated in an microfluidic flow-focusing device (MFFD), in which droplets underwent a structural evolution from Janus to core-shell droplets comprising an oil core and a curable monomer shell at equilibrium
By observing the structure of the biphasic droplet generated right after the junction at Qm:Qs = 1:9 (Fig. 2b), we could confirm that both hexanediol diacrylate (HDDA) and silicone oil parts were partially exposed to the polyvinyl alcohol (PVA) solution
Summary
Www.nature.com/scientificreports of ethyl cellulose shell and poly(N-isopropylacrylamide) (PNIPAM) core (average diameter of 292 μm and CV of 6.3%) were prepared from W/O/W28 and W/(O/W)/W29 double emulsions via solvent evaporation. Photonic capsules composed of a water core with 100 mOsm/L and ETPTA ultra-thin shell (750 nm thickness) were fabricated via photo-induced polymerization[38]. We reported in the one-step formation of Janus droplets in a T-junction microfluidic device, the produced Janus droplets would change their structure to core-shell droplets at equilibrium due to the minimization of interfacial energy among the three liquid phases. The resultant core-shell drops can be used as templates for the fabrication of polymeric capsules with tunable shell thickness via off-chip photo-induced polymerization[31]. We report a novel microfluidic approach to synthesize polymeric microcapsules with tunable shell thickness and surface morphology via off-chip photo- and thermally induced polymerization. We demonstrated the effect of solidification methods on surface morphology of microcapsules
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