Moldable Perfluoropolyether–Polyethylene Glycol Networks with Tunable Wettability and Solvent Resistance for Rapid Prototyping of Droplet Microfluidics

Soft lithography-based droplet microfluidics has enabled production of highly uniform and complex emulsions. Although there is a significant potential to use these emulsions as templates for functional materials syntheses, conventional elastomers that are used for microfluidic device preparation are significantly deformed and swollen by various organic solvents, limiting the types of materials that can be processed using conventional soft lithography-based droplet microfluidics. In this report, we demonstrate that both water-in-oil and oil-in-water emulsion with organic solvents can be produced by using microfluidic devices that are prepared using cross-linked networks of perfluoropolyether (PFPE) and poly(ethylene glycol) diacrylate (PEGDA). We show that these PFPE–PEG networks are transparent and maintain excellent compatibility with various organic solvents. Importantly, the wettability of these devices can be systematically controlled by changing the ratio of the two macromonomers. By taking advantage of rapid prototyping and controlled surface wettability afforded by the PFPE–PEG network, we prepare three-dimensional monolithic elastomer devices for the parallel generation of oil-in-water and water-in-oil droplets. We also show that, using these devices, solid microparticles with high uniformity can be produced by using an organic solvent-based emulsion as a template. We believe the PFPE–PEG network will have broad impacts in the application of soft lithography-based elastomer microfluidic devices to a wide range of applications, including drug screening and solvent-based separation processes.