Microfluidic devices and methods of their use

A system for performing controlled change in the continuous phase volume fraction from an emulsion, the system comprising:

• a microfluidic device comprising a microfluidic channel for moving droplets in an emulsion from an upstream location in the microfluidic channel to a downstream location in the microfluidic channel, wherein the microfluidic channel widens from the upstream location to the downstream location,
• wherein the microfluidic channel is in fluid communication with a first and second set of extraction channels configured to remove continuous phase from the microfluidic channel while not removing droplets in the microfluidic channel, wherein the first set and the second set are on opposing sides of the microfluidic channel, and wherein the microfluidic channel is controllably pressurized such that when an emulsion is introduced into the microfluidic device, a controlled volume fraction of continuous phase flows through the one or more sets of extraction channels, whereas the droplets remain in the microfluidic channel.