Microfluidic manipulation of fluids and reactions

A method, comprising:

• positioning a droplet defined by a first fluid, and a first component within the droplet, in a first region of a microfluidic network, the droplet being surrounded by a second fluid immiscible with the first fluid;
• flowing a third fluid in a microfluidic channel in fluid communication with the first region and causing a portion of the second fluid to be removed from the first region;
• changing the volume of the droplet and thereby changing a concentration of the first component within the droplet;
• and
• allowing a concentration-dependent chemical process involving the first component to occur within the droplet.

A method, comprising:

• positioning a first droplet defined by a first fluid, and a first component within the droplet, in a first region of a microfluidic network;
• positioning a second droplet defined by a second fluid, and a second component within the droplet, in a second region of the microfluidic network, wherein the first and second droplets are in fluid communication with each other;
• forming a first precipitate of the first component in the first droplet while the first droplet is positioned in the first region;
• forming a second precipitate of the second component in the second droplet while the second droplet is positioned in the second region;
• simultaneously dissolving a portion of the first precipitate and a portion of the second precipitate within the first and second droplets, respectively;
• and
• re-growing the first precipitate in the first droplet and re-growing the second precipitate in the second droplet, while the first and second droplets are positioned in the first and second regions, respectively.