(525d) Stop Flow Lithography in Perfluoropolyether (PFPE) Microfluidic Channels

Stop Flow Lithography (SFL) is a microfluidic-based particle synthesis method for creating anisotropic multifunctional particles with applications that range from MEMs to biomedical engineering. Polydimethylsiloxane (PDMS) has been typically used to construct SFL devices as the material enables rapid prototyping of channels with complex geometries, optical transparency, and large gas permeability. However, PDMS is not compatible with organic solvents which limit the current range of materials which can be synthesized with SFL. Here, we demonstrate a fluorinated elastomer, called perfluoropolyether (PFPE), can be an alternative oxygen permeable elastomer for SFL microfluidic flow channels. We fabricate PFPE microfluidic devices with soft lithography and synthesize anisotropic multifunctional particles in the devices via the SFL process - this is the first demonstration of SFL with oxygen lubrication layers in a non-PDMS channel. We benchmark the SFL performance of the PFPE devices by comparing them to PDMS. As PFPE has three times lower elastic modulus than PDMS, the PFPE channels need longer relaxation time that leads to the decrease of the particle production rates. However, the PFPE devices can exhibit similar SFL capabilities with PDMS devices except the particle throughput. We synthesized particles in both PFPE and PDMS devices under the same SFL conditions and found the difference of particle dimensions was sub-microns. PFPE devices can greatly expand the range of precursor materials which can be processed in SFL because the fluorinated devices are chemically resistant to organic solvents, an inaccessible class of reagents in PDMS-based devices. As one demonstrative application, we synthesize electrically conducting particles from organic precursors with stable dispersion of graphene.