Avoidance of bouncing and splashing in droplet-based fluid transport

Abstract

A system for fluid transport is provided where a quantity of fluid is held in a reservoir. A droplet generator is employed to generate droplets from the fluid, for example a nozzle-based system or a nozzleless system such as an acoustic ejection system. A generated droplet has a trajectory whereby it arrives at a target. A circuit is used to modify one or more characteristics of the generated droplet in a way which increases the likelihood that the droplet will not splash or bounce when it arrives at the target. The circuit may in different embodiments control the speed of the droplet or the Weber number of the droplet. The circuit may create an electric field in an area of space where the droplet passes. The circuit may charge the droplet by causing it to contact ions.

1 . A system for fluid transport comprising: 
 a reservoir containing a quantity of fluid,    a droplet generator for generating a droplet from the fluid in the reservoir,    a controller for controlling the operation of the droplet generator,    a target where the generated droplet arrives,    a circuit for controlling one or more characteristics of the generated droplet which increases    the likelihood that the droplet will not splash or bounce on arriving at the target.    
     
     
         2 . The system of  claim 1 , wherein the circuit for controlling generates an electric field in a zone of space through which the droplet passes.  
     
     
         3 . The system of  claim 2 , wherein the generated electric field is non-negligible in a zone proximate to a free surface of the fluid in the reservoir.  
     
     
         4 . The system of  claim 3 , wherein the generated electric field has a magnitude between 1000 and 100,000 V/m in a zone of space proximate to a free surface of the fluid in the reservoir.  
     
     
         5 . The system of  claim 2 , wherein the generated electric field is produced with the assistance of an electrode proximate to the target.  
     
     
         6 . The system of  claim 2 , wherein the generated electric field causes the generated droplet to be electrically charged.  
     
     
         7 . The system of  claim 2 , wherein the circuit for controlling comprises an electrode which is held at a predetermined voltage for a predetermined period of time.  
     
     
         8 . The system of  claim 2 , wherein the generated electric field is time varying.  
     
     
         9 . The system of  claim 2 , wherein the generated electric field does not cause the generated droplet to deviate substantially from a path the droplet would travel in the absence of the generated electric field.  
     
     
         10 . The system of  claim 9 , wherein the path comprises the path traced by the generated droplet beginning with ejection and ending with impact of the droplet on the target.  
     
     
         11 . The system of  claim 2 , wherein the circuit for controlling comprises an input allowing external logic to control a magnitude of the electric field.  
     
     
         12 . The system of  claim 2 , wherein the circuit for controlling comprises an input allowing external logic to switch a magnitude of the electric field between a predetermined value and zero.  
     
     
         13 . The system of  claim 2 , wherein the circuit for controlling comprises a charging device which charges some or all of the target or an object located in the vicinity of the target.  
     
     
         14 . The system of  claim 1 , wherein the circuit for controlling causes the velocity of the droplet in the vicinity of the target to lie within a predetermined range of velocities.  
     
     
         15 . The system of  claim 14 , wherein the predetermined range of velocities lies within the range of 1.0 to 2.5 m/s.  
     
     
         16 . The system of  claim 1 , wherein the circuit for controlling causes the Weber number of the droplet in the vicinity of the target to lie within a predetermined range.  
     
     
         17 . The system of  claim 1 , wherein the droplets travel in a direction which is at an angle of 90 degrees to 180 degrees to the direction of the earth's gravitational field as the droplets arrive at the target.  
     
     
         18 . The system of  claim 1 , wherein the droplet generator is nozzleless.  
     
     
         19 . The system of  claim 1 , wherein the droplet generator does not make contact with the fluid in order to generate a droplet.  
     
     
         20 . The system of  claim 1 , wherein the droplet generator comprises an acoustic ejection system.  
     
     
         21 . The system of  claim 1 , wherein the circuit for controlling increases the likelihood of coalescence of the droplet with a second fluid.  
     
     
         22 . The system of  claim 1 , wherein the circuit increases the probability that the droplet will not splash or bounce when there is fluid present at the target which has a different composition from the fluid in the droplet.  
     
     
         23 . The system of  claim 1 , wherein the circuit increases the probability that the droplet will not splash or bounce when there is fluid present at the target which has a volume less than twice that of the droplet.  
     
     
         24 . The system of  claim 1 , wherein the circuit increases the probability that the droplet will not splash or bounce when there is fluid present at the target which has a volume more than 100 times that of the droplet.  
     
     
         25 . The system of  claim 1 , wherein the volume of the droplet is less than 100 nL.  
     
     
         26 . The system of  claim 25 , wherein the volume of the droplet is less than 5 nL.  
     
     
         27 . The system of  claim 1 , wherein the reservoir forms part of a well plate.  
     
     
         28 . The system of  claim 1 , comprising a second reservoir, wherein the droplet generator can generate a droplet from fluid in the second reservoir.  
     
     
         29 . The system of  claim 28 , comprising a mechanism for moving the droplet generator to facilitate its generation of a droplet from fluid in the second reservoir.  
     
     
         30 . The system of  claim 28 , wherein the circuit for controlling increases the likelihood that a droplet generated from fluid in the second reservoir arrives at a second target without splashing or bouncing.  
     
     
         31 . The system of  claim 28 , wherein the circuit for controlling increases the likelihood that a droplet generated by the second reservoir coalesces with a second fluid.  
     
     
         32 . A method for fluid transport comprising the steps of: 
 generating a droplet from a quantity of fluid in a reservoir,    controlling a trajectory of the droplet in such a way that it arrives at a target,    controlling one or more characteristics of the generated droplet so as to increase the likelihood that the droplet will not splash or bounce on arriving at the target.    
     
     
         33 . The method of  claim 32 , wherein the step of controlling one or more characteristics comprises generating an electric field in a zone of space through which the droplet passes.  
     
     
         34 . The method of  claim 33 , wherein the generated electric field is non-negligible in a zone proximate to a free surface of the fluid in the reservoir.  
     
     
         35 . The method of  claim 34 , wherein the generated electric field has a magnitude between 1000 and 100,000 V/m in a zone of space proximate to a free surface of the fluid in the reservoir.  
     
     
         36 . The method of  claim 33 , wherein the generated electric field is produced with the assistance of an electrode proximate to the target.  
     
     
         37 . The method of  claim 33 , wherein the generated electric field causes the generated droplet to be electrically charged.  
     
     
         38 . The method of  claim 33 , wherein the step of generating an electric field comprises holding an electrode at a predetermined voltage for a predetermined period of time.  
     
     
         39 . The method of  claim 33 , wherein the generated electric field is time varying.  
     
     
         40 . The method of  claim 33 , wherein the generated electric field does not cause the generated droplet to deviate substantially from a path the droplet would travel in the absence of the generated electric field.  
     
     
         41 . The method of  claim 40 , wherein the path comprises the path traced by the generated droplet beginning with ejection and ending with impact of the droplet on the target.  
     
     
         42 . The method of  claim 33 , wherein the step of generating an electric field comprises setting the magnitude of the electric field in response to an external input.  
     
     
         43 . The method of  claim 33 , wherein the step of generating an electric field comprises switching a magnitude of the electric field between a predetermined value and zero.  
     
     
         44 . The method of  claim 32 , wherein the step of controlling one or more characteristics comprises causing the velocity of the droplet in the vicinity of the target to lie within a predetermined range of velocities.  
     
     
         45 . The method of  claim 44 , wherein the predetermined range of velocities lies within the range of 1.0 to 2.5 m/s.  
     
     
         46 . The method of  claim 32 , wherein the step of controlling one or more characteristics comprises causing the Weber number of the droplet in the vicinity of the target to lie within a predetermined range.  
     
     
         47 . The method of  claim 32 , wherein the droplets travel in a direction which is at an angle of 90 degrees to 180 degrees to the direction of the earth's gravitational field as the droplets arrive at the target.  
     
     
         48 . The method of  claim 32 , wherein the step of generating a droplet employs a nozzleless droplet generator.  
     
     
         49 . The method of  claim 32 , wherein the step of generating a droplet does not cause an external object to contact the fluid.  
     
     
         50 . The method of  claim 32 , wherein the step of generating a droplet comprises the step of directing focused acoustic energy at a free surface of the quantity of fluid.  
     
     
         51 . The method of  claim 32 , wherein the step of controlling one or more characteristics increases the likelihood of coalescence of the droplet with a second fluid.  
     
     
         52 . The method of  claim 32 , wherein the reservoir forms part of a well plate.  
     
     
         53 . The method of  claim 32 , comprising the step of generating a droplet of fluid from a second reservoir.  
     
     
         54 . The method of  claim 53 , wherein the step of generating a droplet from a second reservoir comprises the step of moving a droplet generator.  
     
     
         55 . The method of  claim 53 , wherein the step of controlling one or more characteristics increases the likelihood that a droplet generated from fluid in the second reservoir arrives at a second target without splashing or bouncing.  
     
     
         56 . The method of  claim 53 , wherein the step of controlling one or more characteristics increases the likelihood that a droplet generated by the second reservoir coalesces with a second fluid.  
     
     
         57 . The method of  claim 32 , wherein the step of controlling one or more characteristics increases the probability that the droplet will not splash or bounce when there is fluid-present at the target which has a different composition from the fluid in the droplet.  
     
     
         58 . The method of  claim 32 , wherein the step of controlling one or more characteristics increases the probability that the droplet will not splash or bounce when there is fluid present at the target which has a volume less than twice that of the droplet.  
     
     
         59 . The method of  claim 32 , wherein the step of controlling one or more characteristics increases the probability that the droplet will not splash or bounce when there is fluid present at the target which has a volume more than 100 times that of the droplet.  
     
     
         60 . The method of  claim 32 , wherein there is fluid present at the target which has a different composition from the fluid in the droplet and the droplet contacts the fluid present at the target.  
     
     
         61 . The method of  claim 32 , wherein there is fluid present at the target which has a volume less than twice that of the droplet and the droplet contacts the fluid present at the target.  
     
     
         62 . The method of  claim 32 , wherein there is fluid present at the target which has a volume more than 100 times that of the droplet and the droplet contacts the fluid present at the target.  
     
     
         63 . The method of  claim 32 , wherein there is fluid present at the target which has a viscosity different from that of the droplet and the droplet contacts the fluid present at the target.  
     
     
         64 . The method of  claim 63 , wherein there is fluid present at the target which has a viscosity differing by at least 50% from that of the droplet and the droplet contacts the fluid present at the target.  
     
     
         65 . The method of  claim 64 , wherein there is fluid present at the target which has a viscosity at least three times that of the droplet and the droplet contacts the fluid present at the target.  
     
     
         66 . The method of  claim 63 , wherein there is fluid present at the target which has a viscosity no more than one-third that of the droplet and the droplet contacts the fluid present at the target.  
     
     
         67 . The method of  claim 33 , wherein the step of generating an electric field comprises imparting an electrostatic charge to all or some part of the target or to an object in the vicinity of the target.  
     
     
         68 . The method of  claim 32 , wherein the step of controlling one or more characteristics comprises imparting an electrostatic charge to the droplet.  
     
     
         69 . The method of  claim 65 , wherein the step of imparting an electrostatic charge to the droplet comprises contacting the droplet with ions.