(406g) Water-Oil Janus Emulsions: Microfluidic Synthesis and Morphology Design

Janus emulsions and particles have been widely studied because of their asymmetry and corresponding applications in different fields. There are trials using in situ microfluidic methods to prepare water-oil Janus emulsions, However, the expansion of the range was still limited. Furthermore, even the theory of crucial factors for the formation of Janus morphologies has been described, convenient and systematic experiments for adjusting the morphologies have not been done.

In this work we propose a method to design the morphology of waterâ??oil Janus emulsions. By using a double-bore capillary microfluidic device, we in-situ form the water-oil Janus droplets with the flow ratio of water and oil phases in wide range. Then we built a model to guide our experiments to realize the morphology design. The model is based on the lowest interfacial energy theory and the geometry. Moreover, by combining the lowest interfacial energy theory and our fluids properties, we could adjust the Janus morphology by simply adjusting the mass fraction of the surfactants in continuous phase and the flow rates ratio. According to our model guidance, we customize the emulsion morphologies to designed ideas with chosen surfactant mass fraction and flow ratio. Moreover, we achieve the methodology of designing Janus morphologies and first in-situ prepare water-oil Janus droplets with controlled structure. We successfully prepared Janus emulsions with gradual morphology changes, which would be meaningful in fields that have a high demand for morphology designing of amphiphilic Janus particles.

The materials we used were deionized water as the inner water phase, ethoxylated trimethylolpropane triacrylate monomer (ETPTA) as the inner oil phase, and liquid paraffin with various mass fractions of Span 80 (surfactant) as the outer oil phase. In experiments, we adjust the mass fraction of Span 80 to adjust the interfacial tension between these liquids. Another independent variable is the flow ratio of ETPTA to water phase. With clear understanding of the lowest energy theory and the geometry of Janus, we find the mass fraction of surfactant and the flow ratio are the only two variables that influence the Janus morphology. As long as they are fixed, the morphology is determined. Here in our work, we build Matlab code to predict the morphologies. When inputting the interfacial tension of liquids(which is decided by the mass fraction of surfactant) and the flow ratio of ETPTA to water, the Janus morphology could be simulated and shown as a figure. Thus we could know the Janus morphology before we do experiments. The experiment conditions(the mass fraction and the flow ratio) according to the targeted Janus morphology.

In conclusion, by combining the geometry theory, numerical modelling and experimental properties we obtained a succinct method to design the Janus morphologies and prepare specific Janus morphologies by adjusting the flow rates ratio and the mass fractions of the surfactant in the outer phase. With the clear understanding of the formation mechanism and the succinct and useful microfluidic technology and working systems, we achieved a method to design Janus morphologies with high efficiency, that would be meaningful in fields like catalysis with expensive materials.