Patterning Wettability on Solvent-Resistant Elastomers with High Spatial Resolution for Replica Mold Fabrication of Droplet Microfluidics

Controlling the surface wetting properties of channels is crucial to the robust and reliable performance of microfluidic devices. Spatially patterned hydrophobic/hydrophilic microchannels have found utility across various applications, notably in the generation of higher-order emulsions. Unfortunately, the patterning of surface wettability currently requires multistep processes with limited spatial resolution, making it impractical for many applications. In this work, we take inspiration from soft lithography and have developed a new replica mold fabrication technique wherein both the channel geometry and surface wettability are transferred from the mold to the replica. In this approach, the mold is a silicon wafer with lithographically defined features etched into its surface to define the channel geometry and lithographically defined patterns of hydrophobic silanes to define surface wetting properties. The replica is a co-polymer network of PFPE-PEG, for which PFPE can be locally enriched by the mold's patterned silanes to define the spatially patterned wetting properties. We demonstrated the utility of this approach by fabricating a PFPE-PEG-based microfluidic chip, with hydrophobic/hydrophilic patterned microchannels, to generate double emulsions.

Automated summary

Controlling surface wetting properties of microfluidic channels is essential for reliable performance. Current patterning methods have limited spatial resolution, making them impractical. In this study, a replica mold fabrication technique inspired by soft lithography was developed to transfer channel geometry and surface wettability from a silicon wafer mold to a co-polymer network replica. This technique was successfully demonstrated in the fabrication of a PFPE-PEG-based microfluidic chip with patterned microchannels for double emulsion generation.