Foam formation in microfluidic EDGE devices: tuning the bubble size

The stability and flow properties of foams crucially depend on the bubble size and its distribution. Microfluidic devices are capable of producing extremely monodisperse yet small foam bubbles at low energetic cost. Upscaling towards an array of parallelized pores allows to increase the throughput of the device, but increases complexity of bubble formation due to possible pore-pore and bubble-bubble interactions. We use so-called partitioned-EDGE microfluidic chips with which we can produce bubbles in an array of rectangular pores. Pore height is minimized to (sub)micron size in order to produce bubbles down to 20 micron in diameter. The size of a single bubble formed at a pore is independent of pressure for the lower range of applied gas pressures (spontaneous formation mechanism), followed by bubble size increase (blow-up) at higher gas pressures. Here we discuss the final bubble size obtained for high gas flow rate through an array of parallel pores, which induces additional bubble-bubble interactions that can be modified by shear flow rate and stabilizer (protein) concentration. Surprisingly, monodisperse foams with a coefficient of variation around 10% can be produced, irrespective of these additional complexities.