title: Independent control of drop size and velocity in microfluidic flow-focusing generators using variable temperature and flow rate.
abstract: This paper describes a method to control the volume and the velocity of drops generated in a flow-focusing device dynamically and independently. This method involves simultaneous tuning of the temperature of the nozzle of the device and of the flow rate of the continuous phase; the method requires a continuous phase liquid that has a viscosity that varies steeply with temperature. Increasing the temperature of the flow-focusing nozzle from 0 to 80 degrees C increased the volume of the drops by almost 2 orders of magnitude. Tuning both the temperature and the flow rate controlled the drop volume and the drop velocity independently; this feature is not possible in a basic flow-focusing device. This paper also demonstrates a procedure for identifying the range of possible drop volumes and drop velocities for a given flow-focusing device and shows how to generate drops with a specified volume and velocity within this range. This method is easy to implement in on-chip applications where thermal management is already incorporated in the system, such as DNA amplification using the polymerase chain reaction and nanoparticle synthesis.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 01238, USA.
authors.forename: Claudiu A
authors.initials: CA
authors.lastname: Stan
authors.forename: Sindy K Y
authors.initials: SK
authors.lastname: Tang
authors.forename: George M
authors.initials: GM
authors.lastname: Whitesides