  Here we show a folding-stretching instability in a microfluidic flow focusing
device using silicon oil (100cSt) and water. The fluid dynamics video
demonstrates an oscillating thread of oil focused by two co-flowing streams of
water. We show several high-speed sequences of these oscillations with 30,000
frames/s. Once the thread is decelerated in a slower moving pool downstream an
instability sets in and water-in-oil droplets are formed. We reveal the details
of the pinch-off with 500,000 frames/s. The pinch-off is so repeatable that
complex droplet patterns emerge. Some of droplets are below the resolution
limit, thus smaller than 1 micrometer in diameter.
