Janus Particles Templated from Double Emulsion Droplets Generated Using Microfluidics
This paper describes a microfluidic technique to fabricate Janus particles, specifically hydrophilic-organophilic particles. Janus particles are small spherical droplets which have different properties on opposite sides. For example, half of the particle might be hydrophobic, and the other half hydrophilic.
The microfluidic device consists of one central channel with an organophilic monomer flowing through it, as seen in figure 1. This channel flows into a junction where two other channels flow in at 90 degree angles, from opposite sides. These two channels contain a hydrophilic monomer. At this junction, the organophilic monomer stops flowing in a continuous stream and forms droplets within the hydrophilic monomer.
A second junction then introduces an oil solution flowing in from opposite sides, as seen in figure 1. The hydrophilic monomer breaks up into droplets. Each of these droplets contains another droplet of organophilic monomer. These droplets-within-droplets are known as double emulsions. The relative sizes of the hydrophilic and organophilic portions can be controlled by adjusting the flow rates.
The double emulsions flow to a storage area where they are irradiated with UV light. This polymerizes the monomers and locks in the structure of the Janus particles. Once irradiated, the Janus particles are rigid and can be dried or dispersed into a variety of solvents. This microfluidic method produces Janus particles with superb control over size, shape and monodispersity.