Multi-phase pattern evolution in gas-permeable polydimethylsiloxane (PDMS) microchannels during heating

The evolution of the multi-phase patterns in water in heated gas-permeable PDMS microchannels was investigated using a heater wire inserted through the channel in design I and embedded alongside the channel in design II. The heating methods created different multi-phase patterns. Bubbles were found in design I generated from the channel walls rather than the wire surface. Interesting droplets-in-bubble pattern, i.e. bunches of micro droplets inside bubbles, was also observed. The channel in design II had a hot side and a cool side with the droplets-in-bubble pattern observed only on the cool side. The evaporation and condensation in the channel created a distillation process that would significantly affect reactants within channel. The multi-phase regimes in the PDMS channels were all summarized with pattern maps and curves. The droplets-in-bubble formation mechanisms were described.