Ballistically controlled nonpolar droplet dispensing method and apparatus

A process and apparatus for accurately dispensing individual droplets of nonpolar liquid is described. Monodispersed streams of polar and nonpolar liquid droplets are coordinated to intersect and collide at an intersection point. The precollision course of selected polar liquid droplets is altered so as to permit unaltered passage of a corresponding number of nonpolar liquid droplets to continue on their precollision path past the collision point. The process and apparatus has particular utility in such areas as ink jet printing, automatic titration, pharmaceutical and chemical mixing, the study of combustion dynamics, and the dispensing of fusion materials into a nuclear fusion reactor.

TECHNICAL FIELD 
The field of art to which this invention pertains is fluid dispensing and 
particularly droplet dispensing and control. 
BACKGROUND ART 
In many areas of dispensing, but in particular in the fuel combustion 
research area, it is necessary to finely control minute quantities of 
liquids in order to both obtain meaningful test data and permit analysis 
of the results. 
A currently used conventional method of generating a continuous 
monodispersed stream of liquid droplets consists of the periodic vibration 
of a capillary fluid jet. The periodic disturbance of the jet surface at a 
precise frequency causes the jet to break up into uniformly sized and 
spaced droplets with one droplet being produced for each vibration cycle. 
To further accurately dispense a selected number of these liquid droplets, 
droplet dispensing has been modified to include electrostatic charging and 
deflection of the monodispersed droplet stream to adapt the dispensing to 
a particular purpose. However, in order to effect a charge on such 
droplets and thereby alter their flight it is necessary to use polar 
liquids with a high dielectric constant, such as alcohols, as the droplet 
source. Being limited to the use of polar liquids under these droplet 
formation and path control conditions severely restricts the utility of 
such systems. Accordingly, what is needed in the art is a system for 
accurately dispensing droplets of nonpolar liquids with a degree of 
control similar to that attainable with polar liquids. 
DISCLOSURE OF INVENTION 
Accordingly, a process of accurately controlling the dispensing of 
individual droplets of a nonpolar liquid is described comprising 
generating a continuous monodispersed stream of liquid droplets of 
nonpolar liquid and utilizing the controlled trajectory of a second 
intersecting stream of polar liquid droplets to selectively remove 
droplets of said nonpolar liquid resulting in controlled nonpolar liquid 
droplet dispensing. Another aspect of the invention comprises a nonpolar 
liquid droplet dispensing apparatus with a high degree of accurate droplet 
dispensing control comprising monodispersing nonpolar liquid droplet 
dispenser and a monodispersing polar liquid droplet dispenser, the droplet 
dispensers positioned so as to produce an intersection of their respective 
droplet dispensing paths, means to coordinate the paths of the dispensed 
droplets to result in substantially complete collision of the polar and 
nonpolar droplets at their points of intersection, and means to 
selectively alter the paths of individual polar droplets to result in 
noncollision passage of selected droplets of the nonpolar liquid along its 
droplet dispensing path.

BEST MODE FOR CARRYING OUT THE INVENTION 
A matched pair of vibrated capillary jets are utilized to provide two 
streams of polar and nonpolar liquid droplets according to the present 
invention. In this manner two monodispersed droplet streams are generated 
at the same frequency and with essentially the same droplet velocity and 
droplet diameter. Alignment of the two streams can be made with polar 
droplet charging and deflection apparatus either operative or inoperative 
as long as the two droplet streams are made to miss each other at their 
point of intersection as shown in FIG. 3. 
If the polar droplets are charged either by fluid friction within the 
capillary orifice or by a low voltage DC potential applied to the orifice 
the trajectory of polar droplets can be altered by the electrostatic field 
produced between the pairs of deflection plates so as to cause each of the 
polar droplets to collide with a corresponding nonpolar droplet. 
To execute the dispensing process for one or more nonpolar droplets a low 
voltage pulse is applied to a charge repulsion ring located immediately 
downstream of the polar liquid capillary during the time when a 
corresponding number of polar droplets are formed. If this low voltage 
pulse is of sufficient strength these selected polar droplets are either 
uncharged or differently charged relative to the other polar droplets. The 
resultant ballistic trajectory of these selected polar droplets is such as 
to avoid collisions with the corresponding nonpolar droplets. Hence, the 
nonpolar droplets which do not collide with polar droplets are then 
available for dispensing. The pulsing of the charge is effected according 
to how many droplets are desired to pass at what intervals. For example, 
see FIGS. 5 and 6. The path altered polar droplets can be especially well 
seen in FIG. 7. 
Referring to FIG. 1, the nonpolar liquid droplet dispenser is indicated as 
1 and the polar liquid droplet dispenser as 2. These dispensers include 
transducers 3a and 3b, liquid inlet tubes 4a and 4b and capillary droplet 
nozzles 5a and 5b. The transducers can be either of the conventional 
electromagnetic type or piezoelectric type and the capillary droplet 
nozzles can be such things as conventional hypodermic syringes or drawn 
glass capillary tubes. In this particular instance the inlet tubes are 
syringes of an inner diameter of approximately 100 .mu.m. The liquid inlet 
flow rate and transducer frequency are such as to produce droplets of a 
size approximately 200 .mu.m in diameter at a dispensing rate of 
approximately 3,000 to 4,000 drops per second. In this particular 
embodiment the droplets will leave the syringe at a speed of approximately 
2 to 3 meters per second. The polar liquid enters the apparatus at 6 and 
the nonpolar liquid at 7. The dispensing is performed at transducer 
frequencies so as to produce a continuous monodispersed stream of the 
liquid droplets (in this instance about 3 kilohertz). By monodispersed is 
meant a steady flow of droplets of substantially the same size, the same 
spherical shape and equidistant one from the other. 
Each transducer has a separate amplitude control so the dispensing rates 
can be coordinated properly. The deflection plates 8 and 9 are high 
voltage carrying plates which act on the polar liquid droplets to 
accurately adjust the course of the polar droplets to substantially 
perfectly collide with the nonpolar droplets. Such effect is made possible 
by either (1) electrostatic charge picked up frictionally by the polar 
droplets as they emerge from the capillary nozzle 5a; (2) imposed charge 
picked up by the droplets through adjustable low voltage source 10 
connected to the dispenser 4a; or (3) electrostatic charge imposed on the 
droplets by ring 11 having a low voltage charge. Both the ring and the 
deflection plates are made of high conducting metal such as stainless 
steel. In this particular instance the plates are 10 mm by 6 mm and the 
ring has an inner diameter of 4 mm and an outer diameter of about 5 mm. 
The voltage imposed across each transducer is up to 50 V and preferably 20 
to 40 V peak RMS. A steady DC voltage of up to 1000 V is imposed across 
the plates. And the voltage across the ring is up to 200 V (DC) and 
preferably 100 to 200 V. If piezoelectric transducers are utilized higher 
voltages would be required. 
In operation, both polar and nonpolar liquids are flowed into the 
respective capillary nozzles 5a and 5b at approximately the same rate and 
made to collide at point 12 by coordinating the respective frequencies and 
by adjusting separate amplitude controls on the respective transducers. 
This can be observed visually by employing a strobe light set up as 
indicated in FIG. 2. In view of their polar nature and accompanying 
propensity for picking up charges, fine control of the flight of the polar 
liquid droplets is possible through the use of the plurality of deflector 
plates 8 and 9. 
At this point the system is in perfect synchronization. Note the 
progression of FIGS. 3 and 4. Droplets are colliding on a polar droplet 
per nonpolar droplet basis at point 12 (FIG. 1) and no nonpolar droplets 
are continuing on their precollision path past point 12. Note FIG. 4. It 
is at this point that charge pulsing is initiated. The pulsing can take 
place in a variety of ways, the goal being to disturb just the 
predetermined numbers of polar droplets from their synchronized collision 
path sufficient to allow passage of the same number of nonpolar drops on 
their precollision course past the collision point 12. The path of 
selected polar droplets can be altered by (1) charging the selected polar 
droplets at capillary nozzle 5a through a pulsed voltage source 10 during 
the formation of the droplets at the capillary nozzle, (2) by establishing 
an electrostatic field through ring 11 by a pulsed voltage source 13 again 
during a formation of the selected droplets, or (3) by deflecting the 
selected droplets as they pass through the electrostatic field of the 
deflection plates when a momentary voltage surge, or ebb is applied to a 
pair of plates. It should also be noted that the charging of the 
individual particles can take place by imposing a voltage where none 
existed before, e.g., at 10 or 11, eliminating a voltage where one 
existed, e.g., at 8, 9, 10 or 11, or surging or ebbing the voltage at 
points 8 or 9. But the function of the voltage change is the same in all 
instances--alteration of the synchronized collision path (FIG. 4) of the 
polar droplets with respect to the nonpolar droplets. Note FIGS. 5 through 
7. The preferred pulsing takes place through ring 11 because of the low 
voltages necessary to cause deflection and the speed and quickness of 
repetition with which the charging can be performed at this point because 
of the relatively small size of the ring and relative proximity of the 
ring to the point of droplet formation. 
By measuring the size of the nonpolar droplets and density of the fluid the 
exact amount of composition per droplet can be calculated. With this 
information and by being able to allow passage of precisely the number of 
droplets desired, an extremely accurate means of measuring minute 
quantities of materials is provided by the process and apparatus of the 
present invention. As such, this represents an extremely high-powered 
research tool in such areas as ink jet printing, automatic titration, 
pharmaceutical and chemical mixing and the study of combustion dynamics. 
However, its utility is limited only by the imagination of the user. 
Referring more specifically to FIG. 2 which demonstrates an exemplary 
circuit for the apparatus and process of the present invention, high 
voltage (1,000 volts to 2,000 volts and preferably 1,500 volts) power 
sources 31 and 32 provide the necessary voltage for deflector plates 8 and 
9. Audio oscillator (signal generator) 34 sets the exact frequency for 
driving transducers 3a and 3b through transducer amplifier 33 and serves 
as the clock for the entire system. The transducers can be either 
electromagnetic or piezoelectric. The transducer amplifier has separate 
amplitude controls 33a and 33b to enable accurate coordination of the 
signals passing to the transducers. A and B in FIGS. 1 and 2 indicate the 
amplified clock signal from audio oscillator 34 separately adjustable to 
provide a constant signal amplitude to each transducer. The frequency 
supplied to the transducers through the transducer amplifier from the 
signal generator depends on the fluid used and droplet size. For the 
particular system tested, a frequency of 3 kilohertz was used. And while 
the frequencies supplied to the transducers should be identical, the flow 
rates and droplet size need not be identical. Signal generator 34 is also 
connected to variable modulus counter 39 which converts the signal from 
the audio oscillator into a logic pulse with a 1.div.N pulse function to 
be processed by pulse generator 38. This performs a divide function 
providing the option of allowing the primary (clock) pulse through or 
allowing any selected fraction of the clock pulse through. The pulse 
generator can delay or advance or change the pulse width and is primarily 
used to open and close voltage gate 36. The variable modulus counter also 
coordinates strobe 41 and strobe light 42 to coincide with the droplet 
emission frequency for visual observation purposes. Pulse generator 38 as 
stated above opens and closes voltage gate 36 allowing power supplied by 
power supply 37 to pass to ring 11. The voltage of power supply 37 
provides 100 volts to 200 volts and preferably 150 volts to ring 11. Both 
power supply 37 and power supply 35 are variable voltage supplies of 0 
volts to 300 volts. 
In operation the pulse generator sends the appropriate signal to gate 36 to 
allow voltage from power supply 37 to charge ring 11. The air around the 
forming droplet being emitted from nozzle 5a acts as a capacitor directing 
the charge from the ring to the droplet. Depending on the charge 
relationship between the forming droplet and plates 8 and 9 the respective 
droplets either receive a charge greater than the remainder of the 
droplets and pass through plates 8 and 9 on a path different from the 
other droplets or more preferably the ring is maintained at a constant 
voltage such that each droplet is charged as it comes off the nozzle 5a 
and the pulse generator sends the appropriate pulse to substantially 
eliminate this charge for the specific droplets desired resulting in a 
relatively neutral droplet passing by the plates and such droplet being 
unaffected (or in actuality less affected than the other charged droplets) 
as they pass through the plates. This is sufficient to alter the path of 
the uncharged droplet so that it does not collide with the corresponding 
nonpolar droplet. 
Power supply 35 is an optional component which can be used to produce a 
specific charge on the polar droplets in excess of the frictional charge. 
Power supply 35 imparts an electrostatic charge to the polar droplets as 
they come off the nozzle and in the embodiment of FIG. 1 the ring 11 is 
utilized to alter the electrostatic charge on the droplets as they come 
off the nozzle so that they react differently as they pass through plates 
8 and 9 again varying the path of selected polar droplets from the 
collision path of the remainder of the droplets. 
In the exemplary system shown in FIG. 1, the polar droplet path from the 
end of the droplet nozzle 5a to collision point 12 is about 60 mm. The 
length of the path from nozzle 5b to collision point 12 is about 20 mm 
from the nonpolar droplets. Pulse ring 11 in this particular system was 
located approximately 8 mm from nozzle 5a and 10 mm from the closest edge 
of the closest deflection plates 8. The location of pulse ring 11 should 
be such that the polar droplets pass through the ring. The ring should be 
located close enough to nozzle 5a to establish an electrostatic field of 
sufficient magnitude to alter the charge on the droplets emitted from 
nozzle 5a as they are being formed. The nozzle should also be located 
sufficiently far from the nearest deflection plate to have no effect or at 
worst a minimal effect on the electrostatic field formed by such plates 
when they are activated. 
FIGS. 3 through 7 demonstrate actual photographs of an apparatus according 
to the present invention in use. FIG. 3 demonstrates the first stage 
according to the present invention comprising coordinating concurrent 
passage of the two streams of droplets controlled so that no collisions 
occur and both polar and nonpolar liquids after intersecting continue on 
their precollision courses. FIG. 4 demonstrates the second stage in the 
practice of the present invention where concurrent passage of the two 
streams of droplets is altered by pulsing a charge so as to change the 
course of the polar droplets such that no polar or nonpolar droplets 
continue on their precollision paths. FIGS. 5 and 6 demonstrate two 
typical operating modes for selected dispensing rates of one droplet and 
two droplets from every five precollision nonpolar droplet groups 
respectively. Several selected polar droplets not colliding with nonpolar 
droplets can be seen passing to the lower right. FIG. 7 is similar to 
FIGS. 5 and 6 with a better view of the polar droplets altered from their 
synchronized collision paths provided. 
It should be noted that the orientation of the two droplet streams is 
important only insofar as executing the necessary droplet collisions and 
locating the dispensing target, i.e., determining the postcollision course 
of the nonpolar droplets. 
The principal advantage of a droplet dispenser according to the present 
invention is its ability to dispense a very small quantity of a nonpolar 
or high dielectric fluid such as a hydrocarbon liquid with extreme 
accuracy. The normally encountered problems of fluid dispensing such as 
film-forming, capillary retention and dilution are eliminated by this 
device. The amount of fluid dispensed can be readily varied over a 
continuous range from a single droplet to an unlimited number of droplets 
with rapid and repetitive delivery times. Some polar liquids useful with 
the present invention include alcohols such as methanol, ethanol, 
isopropanol, butanol, furfuryl and water. Some nonpolar liquids include 
such things as hexane, hexadecane, isooctane and No. 2 fuel oil. Mixtures 
of these materials along with other materials in their class can also be 
used. 
Although this invention has been shown and described with respect to a 
preferred embodiment, it will be understood by those skilled in this art 
that various changes in form and detail thereof may be made without 
departing from the spirit and scope of the claimed invention.