Electropermanent magnet activated microfluidic droplet size modulation

Abstract

An active microfluidic droplet generation device includes a droplet generation junction joining at least one continuous phase channel for carrying a ferrofluid, and a dispersed phase channel for carrying a dispersed phase (e.g., aqueous) flow. A miniature electropermanent magnet (EPM) upstream from the junction generates a magnetic field to modulate a flow rate of a ferrofluid in the continuous phase channel so that dispersed phase droplets are generated with volumes actively controlled on-demand and under continuous flow.

The invention claimed is: 
     
       1. A method for active microfluidic dispersed phase droplet generation, the method comprising:
 positioning a miniature electropermanent magnet (EPM) such that a magnetic field of the EPM overlaps with microfluidic channels connected to a droplet generation junction upstream from the droplet generation junction; 
 controlling the magnetic field of the EPM to modulate a continuous phase ferrofluid flow rate in the microfluidic channels while a dispersed phase flows through a dispersed phase channel connected to the droplet generation junction; 
 whereby dispersed phase droplets are generated with volumes actively controlled on-demand and under continuous flow. 
 
     
     
       2. The method of  claim 1 
 wherein positioning the EMP comprises 
 aligning the EMP such that the magnetic field is substantially orthogonal to the microfluidic channels containing the ferrofluid. 
 
     
     
       3. The method of  claim 1 
 wherein controlling the magnetic field of the EPM to modulate the continuous phase ferrofluid flow rate comprises 
 controlling the magnetic field to induce a change in viscosity of the ferrofluid through the magnetoviscous effect. 
 
     
     
       4. The method of  claim 1 
 wherein controlling the magnetic field of the EPM to modulate the continuous phase ferrofluid flow rate comprises 
 generating current pulses through a coil of the EPM to activate and deactivate the magnetic field of the EPM. 
 
     
     
       5. The method of  claim 1 
 wherein controlling the magnetic field of the EPM to modulate the continuous phase ferrofluid flow rate comprises 
 controlling a magnitude of current pulses in coils of the EPM to control a magnitude of the magnetic field. 
 
     
     
       6. The method of  claim 1 
 wherein controlling the magnetic field of the EPM to modulate the continuous phase ferrofluid flow rate comprises 
 controlling a magnitude of current pulses in coils of the EPM to produce a maximum magnetic field strength of at least 200 mT at a pole of the EPM. 
 
     
     
       7. The method of  claim 1 
 wherein controlling the magnetic field of the EPM to modulate the continuous phase ferrofluid flow rate comprises 
 generating current pulses through a coil of the EPM, where widths of the current pulses are less than 100 microseconds. 
 
     
     
       8. The method of  claim 1 
 wherein controlling the magnetic field of the EPM to modulate the continuous phase ferrofluid flow rate comprises 
 maintaining the EPM activated, whereby the volume of the generated dispersed phase droplets is constant.