Droplet forming devices and system with differential surface properties

A method for producing droplets comprising:

• A) providing a system comprising:
• a) a device comprising:
• i) a plurality of first channels each having a first depth, a first width, a first proximal end, a first distal end, and a first surface comprising a material;
• ii) a plurality of second channels each having a second channel depth, a second channel width, a second channel proximal end, and a second channel distal end;
• iii) a plurality of shelf regions each having a second depth and a second width, wherein each of the first distal ends of the plurality of first channels is in fluid communication with a corresponding one of the plurality of shelf regions, wherein each of the second widths is greater than the corresponding first width the plurality of first channels, wherein each of the plurality of shelf regions comprises a hydrophobic coating different from the material of the first surfaces of the plurality of first channels;
• iv) a first reservoir in fluid communication with at least one of the first proximal ends of the plurality of first channels;
• and
• v) a collection reservoir configured to collect the droplets and comprising at least one wall that forms a plurality of steps each fluidically connected to a corresponding one of the plurality of shelf regions;
• wherein each of the plurality of second channels intersects a corresponding one of the plurality of first channels between the first proximal and first distal ends of the corresponding one of the plurality of first channels;
• b) a first liquid;
• c) a second liquid;
• and
• d) a third liquid;
• wherein the first liquid and the third liquid are not miscible with the second liquid;
• wherein each of the plurality of first channels comprises the first liquid, each of the plurality of second channels comprises the third liquid, and the plurality of shelf regions and the collection reservoir comprise the second liquid;
• B) combining the first liquid and the third liquid at the intersections of the at least one of the plurality of first channels and the at least one of the plurality of second channels;
• C) flowing the combined first and third liquids to the one of the plurality of shelf regions, wherein the combined first liquid and third liquid expands at the one of the plurality of shelf regions and the plurality of steps to produce droplets of the combined first liquid and third liquid, wherein the droplets are dispersed in the second liquid in the collection reservoir.