Droplet forming devices and system with differential surface properties

Abstract

Devices, systems, and their methods of use, for generating droplets are provided. One or more geometric parameters of a microfluidic channel can be selected to generate droplets of a desired and predictable droplet size.

What is claimed is: 
     
         1 . A device for producing droplets of a first liquid in a second liquid, the device comprising:
 a) a first channel having a first depth, a first width, a first proximal end, a first distal end, and a first surface having a first water contact angle; and   b) a droplet formation region having a second surface having a second water contact angle, wherein the droplet formation region is configured to allow the first liquid to expand in at least one dimension and has at least one inlet and at least one outlet, and wherein the second water contact angle is greater than the first water contact angle,   
       wherein the first channel and droplet formation region are configured to produce droplets of the first liquid in the second liquid. 
     
     
         2 . The device of  claim 1 , further comprising a second channel having a second depth, a second width, a second proximal end, and a second distal end, wherein the second channel intersects the first channel between the first proximal and first distal ends. 
     
     
         3 . The device of  claim 1 , wherein the droplet formation region comprises a shelf region having a third depth and a third width. 
     
     
         4 . The device of  claim 1 , wherein the droplet formation region comprises a step region having a fourth depth. 
     
     
         5 . The device of  claim 1 , wherein the second contact angle is 5° to 100° greater than the first contact angle. 
     
     
         6 . The device of  claim 1 , wherein the second water contact angle is at least 100°. 
     
     
         7 . The device of  claim 1 , further comprising a first reservoir in fluid communication with the first proximal end. 
     
     
         8 . The device of  claim 2 , further comprising a second reservoir in fluid communication with the second proximal end. 
     
     
         9 . The device of  claim 1 , further comprising a collection reservoir configured to collect droplets formed in the droplet formation region. 
     
     
         10 . The device of  claim 9 , wherein the device is configured to produce a population of droplets that are substantially stationary in the collection reservoir. 
     
     
         11 . The device of  claim 1 , wherein the first liquid comprises particles. 
     
     
         12 . The device of  claim 1 , wherein the first channel and the droplet formation region are configured to produce droplets including a single particle. 
     
     
         13 . A system for producing droplets of a first liquid in a second liquid, the system comprising:
 a) a device for producing droplets, the device comprising:
 i) a first channel having a first depth, a first width, a first proximal end, a first distal end, and a first surface having a first water contact angle; 
 ii) a droplet formation region having a second surface having a second water contact angle, wherein the droplet formation region is configured to allow the first liquid to expand in at least one dimension and has at least one inlet and at least one outlet, wherein the second water contact angle is greater than the first water contact angle; and 
 iii) a first reservoir in fluid communication with the first proximal end and comprising at least a portion of the first liquid; and 
   b) a second liquid contained in the droplet formation region, wherein the first liquid and the second liquid are immiscible,   
       wherein the system is configured to produce droplets of the first liquid in the second liquid. 
     
     
         14 . The system of  claim 13 , wherein the first reservoir further comprises particles. 
     
     
         15 . The system of  claim 13 , wherein the device further comprises a second channel having a second depth, a second width, a second proximal end, and a second distal end, wherein the second channel intersects the first channel between the first proximal and first distal ends. 
     
     
         16 . The system of  claim 15 , wherein the device further comprises a second reservoir in fluid communication with the second proximal end and comprises at least one portion of the first liquid. 
     
     
         17 . The system of  claim 15 , wherein the portion of the first liquid in the first channel and the portion of the first liquid in the second channel combine at the intersection of the first channel and second channel to form the first liquid. 
     
     
         18 . The system of  claim 13 , wherein the droplet formation region comprises a shelf region having a third depth and a third width at or distal to the at least one inlet of the droplet formation region. 
     
     
         19 . The system of  claim 13 , wherein the droplet formation region comprises a step region having a fourth depth at or distal to the at least one outlet of the droplet formation region. 
     
     
         20 . The system of  claim 13 , wherein the second contact angle is 5° to 100° greater than the first contact angle. 
     
     
         21 . The system of  claim 13 , wherein the second water contact angle is at least 100°. 
     
     
         22 . The device of  claim 13 , further comprising a collection reservoir configured to collect droplets formed in the droplet formation region. 
     
     
         23 . The device of  claim 22 , wherein the device is configured to produce a population of droplets that are substantially stationary in the collection reservoir. 
     
     
         24 . The system of  claim 15 , further comprising a controller operatively coupled to transport the portion of the first liquid in the first reservoir and the portion of first liquid in the second reservoir to the intersection. 
     
     
         25 . A method of producing a microfluidic device comprising a surface modification comprising:
 (i) providing a primed microfluidic device comprising a channel in fluid communication with a droplet formation region having a primed surface, wherein the droplet formation region is configured to allow a liquid exiting the channel to expand in at least one dimension; and   (ii) contacting the primed surface with a coating agent having affinity for the primed surface to produce a surface having a water contact angle, wherein the contact angle is greater than the water contact angle of the primed surface and greater than the water contact angle of the channel.   
     
     
         26 . The method of  claim 25 , further comprising producing the primed microfluidic device by depositing a layer of metal oxide onto an unmodified droplet formation region surface. 
     
     
         27 . The method of  claim 25 , wherein the coating agent is in a coating liquid. 
     
     
         28 . The method of  claim 27 , wherein step (ii) comprises filling the channel with a blocking liquid that is substantially immiscible with the coating liquid, and wherein filling the channel with a blocking liquid substantially prevents ingress of the coating agent into the channel. 
     
     
         29 . The method of  claim 25 , wherein step (ii) comprises supplying a gas to the channel, wherein the gas pressure substantially prevents ingress of the coating agent into the channel. 
     
     
         30 . The method of  claim 25 , wherein the microfluidic device further comprises a coating feed channel, wherein the coating feed channel is in fluid communication with the droplet formation region, and wherein the coating agent is provided to the droplet formation region through the coating feed channel.