(224h) Two Phase Microfluidics with Molten Polymers

Drop-based methods for fabricating complex particles in microfluidic devices have been studied heavily over the past several years. Typically, a two-phase oil/water flow is set up in a microfluidic device under conditions where capillary breakup leads to controlled generation of drops. Subsequent solidification of the drops yields particles. These approaches suffer from material limitations: they rely on fluids that can be rapidly solidified, often by UV crosslinking. We seek to overcome these material limitations, specifically we aim to unite microfluidics with polymer processing to develop a process that can fabricate polymer particles out of virtually any thermoplastic polymer.

Handling molten polymers in microfluidic devices requires entirely new concepts in device design. A new high-temperature microfluidic platform based on micromachined metal foils has been developed. The flow of the molten polymer is driven by gas pressure rather than positive displacement pumps. This talk will show that – despite the high viscosity and low interfacial tension of molten polymers – capillary breakup is still a viable route to form drops in microfluidic devices. However the mode of drop breakup is quite different in polymeric systems as compared to oil/water systems. Furthermore, the parameter space (i.e. pressure ranges) in which drops can be generated is relatively narrow, and drop sizes are highly sensitive to the operating conditions. A simple “circuit” model is developed which successfully explains these latter observations and points to operating guidelines for using pressure-driven flow in two-phase microfluidics. In summary, the vast developments in drop-based microfluidics can be transplanted to molten polymers, thus permitting the fabriction of complex particles out of a variety of thermoplastic polymers.