Dispensing device

A device for comminuting liquid has a liquid supply with first and second outlets, a first electrohydrodynamic comminuter for subjecting liquid issuing from the first outlet to an electrical potential to cause the liquid to be commrinuted to form a comminution of one polarity and a second electrohydrodynamic comminuter for subjecting liquid issuing from the second outlet to an electrical potential to cause liquid to be commninuted to form a comminution of the opposite polarity. The first and second electrohydrodynamic comminuters are arranged so as to cause substantial admixing of two opposite polarity comminutions.

The invention relates to a dispensing device for comnminuting a liquid, 
means for supplying liquid for use in such device and the use of such a 
device, in particular, in medicine. 
Dispensing devices are known which produce a finely divided spray of liquid 
droplets by electrostatic means(more properly referred to as 
`electrohydrodynamic` means). Electrohydrodynamic sprayers have found use 
in many areas of industry, especially in agriculture for crop spraying, 
paint spraying in the automotive industry and also in medicine for the 
administration of medicaments by inhalation. 
The droplet spray in such devices is generated by applying an electric 
field to a liquid located at a spray head or spray edge. The potential of 
the electric field is sufficiently high to provide comminution of 
electrically charged liquid droplets from the spray head. The electrical 
charge on the droplets prevents them from coagulating via mutual 
repulsion. 
United Kingdom patent number 1569707 describes an electrohydrodynamic spray 
device principally for use in crop spraying. An stated essential component 
of the GB 1569707 spray device is a field intensifying electrode, cited 
adjacent the spray head and maintained at the same potential as the spray 
head. The field intensifying electrode is not supplied with liquid. In use 
it is stated to reduce the incidence of corona discharge which interfere 
with spray production and thereby allows lower electric field strengths to 
be used during spray generation. 
U.S. Pat. No. 4,703,891 describes an crop spraying apparatus fi spraying 
liquids from a vehicle such as an aircraft or other airborne vehicle, 
having least two sprayheads arranged to produce spray of positive charge 
at one sprayhead and negative charge at the other. The resulting charged 
sprays are then applied to the relevant crops. 
In many circumstances it is desirable to partially or wholly remove the 
elect charge from droplet sprays produced by electrohydrodynamic 
comminution devices in a controlled manner. To date the principal method 
used to effect comminution discharge has required the use of a discharging 
electrode having a sharp or pointed edge and located downstream from the 
spray head. The discharging electrode produces a cloud of charged ions 
from the surrounding air having an opposite electrical charge of equal 
magnitude to that on the comrninuted liquid spray. In us the ion cloud is 
attracted towards, collides with and thereby neutalizes the liquid spray. 
United Kingdom patent number 2018627B discloses an electrohydrodynamic 
spray device wherein the electric charge on the droplet spray is fully or 
partially removed by means of a discharge electrode. The UK 2018627B 
device is stated to provide discharged or partially discharged sprays for 
crop spraying purposes. European Patent number 0234842 discloses an 
electrohydrodynamic inhaler wherein the spray of charged droplets is 
similarly discharged by means of a discharge electrode. The droplets are 
discharged in order to facilitate droplet deposition into the respiratory 
tract as otherwise the electrically charged droplets would deposit onto 
the mouth and throat of the user. 
A particular problem associated with the use of the sharp discharge 
electrode is that the highly mobile ion cloud from the discharge electrode 
often interferes with the comminution of the liquid spray. The inhaler 
device of EP 0234842 attempts to ameliorate the effects of the ion cloud 
at the spray head by using a neutral shield electrode located close to the 
spray head. 
It is a primary feature of the present invention that a device for 
comminuting a liquid is provided, which comminutes the liquid by 
electrohydrodynamic means and which produces a partially or fully 
electrically discharged comminution without the need for the sharp 
discharge electrode described above. The present device does not have the 
problems associated with the discharge electrode and hence it does not 
require the use of a neutral shield electrode. 
Accordingly, there is provided a device for comminuting a liquid, which 
comprises at least two electrohydrodynamic comminution means arranged so 
that in use comminutions of opposing polarity are formed which are 
substantially admixed after formation. 
The electrohydrodynamic comminution means may be any conventional 
electrohydrodynamic comminution means, for example those described in the 
above mentioned patent specifications. 
Suitably, each comminution means comprises a comminution site, generally 
being a surface or edge, from which the liquid comminution is produced. 
A preferred comminution surface or edge is provided by a thin capillary 
tube, a nozzle or a slot defined by two parallel plates. However any 
comminution surface or edge described in the above mentioned patent 
specifications may be used. 
The device generally comprises an even number of comminution means but this 
is not essential, the key factors are that at least two of the comminution 
means provide comminutions of opposing polarity and that the comminutions 
produced are arranged to substantially admix. 
Suitably, the device comprises 2,4 or 6 comminution means, however higher 
numbers can be used as required An example of a device is that which has 2 
comminution means. An example of a device is that which has 6 comminution 
means. 
Suitably, each comminution means comprises a means for supplying liquid to 
the comminution site. 
Appropriate means for supplying liquid to the comminution site include 
mechanical, electrical or electronic powered means such as pumps which are 
capable of providing the required flow rate of liquid to the cornminution 
site. 
The comminution means of the invention can be used with a large range of 
flow rates, but generally operates with flow rates in the range of between 
0.1 to 500 .mu.l per second, such as 0.5 to 5 .mu.L per second, especially 
for inhaled administration, or 10 to 200 .mu.L per second, especially for 
agricultural use. 
A suitable means for supplying the liquid includes a syringe pump or an 
electrically powered pump as described in EP 0029301. 
It will be appreciated from the foregoing that the comminution means 
generally comprises a comminution site, a means for supplying a liquid to 
the comminution site and a means for electrically charging the comminution 
site to an electric potential sufficient to comminute the liquid in use. 
Accordingly, in one particular aspect of the invention there is provided a 
device for comminuting a liquid, which comprises at least two 
electrohydrodynamic comminution means each comprising a comminution site, 
a means for supplying a liquid to the comminution site and a means for 
electrically charging the comminution site to an electric potential 
sufficient to comminute the liquid in use, wherein the comminution means 
are arranged so that in use comminutions of opposing polarity are formed 
which are then substantially admixed. 
Suitably, each comminution means comprises a means for electrically 
charging the said comminution site to a potential sufficient to provide 
comminution of the liquid, the potential usually being of the order of 
1-20 kilovolts. 
The means for electrically charging the said comminution site, such as a 
surface or edge, may be provided by any conventional high voltage 
generator having the appropriate output, one particularly convenient 
generator being a piezoelectric generator. 
The piezoelectric material for the generator may be chosen from several 
types, such as barium titanate ceramic, or pvdf polymers, which generate 
significant high-voltage electric charge displacement upon being 
pressurized. The choice and capacity may be so chosen as to offer control 
of the degree of pumping and/or atomization when operated. 
The required voltage for use is provided when thc piezoelectric generators 
are squeezed, and again (with opposite polarity) when the piezoelectric 
generators are released from pressure. 
The arrangement by which the comminutions are admixed enables the net 
charge on the admixed comminution to be either essentially neutral, 
positive or negative. Generally, the residual positive or negative charges 
are less than the positive or negative charge on any of the premixed 
comminutions. 
The net residual charge on the admixed comminution may be fixed for any 
given device or the arrangement may be such that the net residual charge 
on the admixed comminution may be regulated in a controlled manner. Thus 
the device of the invention optionally comprises a means for regulating 
the electrical charge on a comminution produced from any of the 
cormminution means prior to admixture. 
Suitable means for regulating the electrical charge on a comminution may be 
provided by a variety of methods, such as by incorporating a means for 
regulating the charging means so as to provide variable voltage output 
andlor a means for regulating the means for supplying a liquid to the 
comminution site so as to vary the liquid flow rate to the comminution 
site. 
Suitable arrangements of the comminution means which enable the 
comminutions produced to be admixed includes any arrangement wherein the 
comminution means are relatively located so as to enable the comminutions 
to substantially admix. Favourably, the comminution means are arranged so 
that the comminutions produced are directed to converge into a mixing 
zone. For example, when the device comprises two comminution means they 
may be angled towards each other so as produce comminutions which converge 
into the mixing zone. Or when the device comprises three or more 
comminution means, they may be arranged so that the comminutions are 
directed to converge radially into the mixing zone. Alternatively, the 
relative location of the comminution means may be arranged such that the 
mutual attraction of the comminutions produced is sufficient to allow 
substantial admixing, for example they may be in a mutually parallel 
manner. 
It is envisaged that a liquid supply means may supply one or more of the 
comminution means of the invention. 
Alternatively, a liquid supply means may supply only one comminution means. 
From the foregoing it will be appreciated that it is an aspect of the 
present invention that comminuted sprays from different liquids may be 
mixed as required. Such liquids may be capable of providing a new product 
on admixture or they may comprise components which are so capable. The 
device may also be used to mix two liquids which are reactive components 
of a rapid chemical reaction. In each case the mixed droplets may then be 
applied as a spray, with a charge-to-mass ratio on the droplets that will 
be the residual after the two opposing charges have been used to coalesce 
the liquids. 
Similarly, the present device may be used to mix components which are 
incompatible one with the other and which therefore are advantageously 
admixed at the point of use. 
Suitable liquids include liquids comprising components useful for human or 
animal health care, such as medicaments for pharmaceutical or public 
health care use or medically useful compounds such as anesthetics. 
Suitable liquids include liquids comprising components for agricultural use 
such as pesticides or biocides. 
Suitable liquids include liquid cosmetic formulations. 
Other suitable liquids include paints and inks. Also included are liquids 
for providing aromas. 
Preferred liquids are pharmaceutically active liquids. 
The communition means of the dispenser provides liquid droplets within the 
range of from about 0.1 to about 500 microns in diameter: More usually 
from 0.1 to 200 microns, such as 1.0 to 200 microns: Examples include 
droplets within the range of 5.0 to 100, 0.1 to 25, 0.5 to 10 or 10 to 20 
microns. A favoured range for inhaled administration is 0.1 to 25 or 0.5 
to 10 microns, especially for administration to the lower respiratory 
tract, and 10 to 25 microns, especially for administration to the upper 
respiratory tract. 
For a given liquid the diameter of the droplets can be controlled by 
varying the applied voltage and liquid flow rate using routine 
experimental procedures. Liquids having viscosities within the range of 
from 1 to 500 centipoise and resistivities in the range of from 10.sup.2 
-10.sup.8 ohm m can be comminuted by the present device. 
One favoured use of the device of the invention is for the dispensation of 
a comminuted liquid for inhalation. 
Accordingly, in one preferred aspect of the invention there is provided a 
device for comminuting a liquid for inhalation, which comprises at least 
two electrohydrodynamic comminution means each comprising a comminution 
site, a means for supplying a liquid to the comminution site and a means 
for charging the comminution site to an electric potential sufficient to 
comminute the liquid in use, wherein the comminution means are arranged so 
that in use comminutions of opposing polarity are formed which are 
substantially admixed after formation. 
The device of the invention may be adapted into any embodiment form which 
dispenses comminuted liquid for inhalation, for both medicinal and 
non-medicinal use. 
Non-medicinal inhalation uses includes dispensing perfumes and aromas. 
Preferably, the device is in the form of an inhaler, for the inhaled 
delivery of a medicament. 
A preferred liquid is therefore a liquid medicament formulation adapted for 
inhaled administration. 
Medicaments suitable for adaption for inhaled administration include those 
used for the treatment of disorders of the respiratory tract, such as 
reversible airways obstruction and asthma and those used in the treatment 
and/or prophylaxis of disorders associated with pulmonary hypertension and 
of disorders associated with right heart failure by inhaled delivery. 
Since the charge-to-mass ratio of an electrohydrodynamic comminution may 
sometimes require optimization, to a value that may lie anywhere between 
the unadjusted value at the moment of comminution, and zero, the device of 
the invention may also be used to optimize droplet charges. For example, 
in order to apply a liquid containing a therapeutic agent to specific 
airways within a human lung, by inhalation, it would be highly beneficial 
if the droplet mass and charge could be independently controlled. This 
would give an unprecedented degree of control over the zone of deposition 
of the droplets within the lung. 
For example in a two nozzle dispensing device, it can be arranged to have 
one nozzle comminuting a spray of the medicament, such as a beta-2 
agonist, for example salbutamol, where the average droplet charge+/- Qa 
could then be accurately adjusted by arranging for deionized water to be 
comminuted from the second nozzle with an average charge-/+ Qb, thus the 
desired final value on the inhaled spray of could be Qa plus or minus Qb. 
Similqrly, for example, in charged droplet spraying of crops it is 
sometimes highly beneficial if the droplet charge can be adjusted 
independently of its mass, in order to achieve penetration into dense 
foliage. 
As indicated above, various means have been used to deliver liquid to the 
comminution site prior to comminution generation. Most are mechanical in 
nature although European Patent number 0029301 discloses a spray device 
incorporating a pump wherein the hydrostatic pressure is generated by an 
electric potential between two electrodes immersed in the feeder stream of 
the liquid to be sprayed. It is a further aspect of the present invention 
that there is provided a novel electrically powered pump, suitable for 
pumping liquid to the cornminution site of an electrohydrodynamic 
comminution device. 
An important component of the dispensing devices described above is the 
means for supplying the liquid to the comminution site. Accordingly, in a 
further aspect of the present invention there is provided a pump, suitable 
for supplying liquid to the comminution site of a comminution means, which 
pump comprises an electrically insulating conduit for the liquid, the 
conduit enclosing an electrically insulating solid permeable to liquid, 
means for retaining the solid within the conduit and means for applying an 
electric field across the solid, so that in use, when the electric field 
is applied, liquid is induced to flow through the solid and hence along 
the conduit. 
The dimensions of the conduit are not considered to be limiting to the 
successful operation of the invention, the essential feature being the 
presence of an electric field across the solid. 
A suitable means for applying an electric field across the solid is 
provided by a pair of permeable electrodes, spaced apart along the 
conduit. 
It is preferred if the solid substantially fills the conduit. A suitable 
conduit is a pipe, for example a cylindrical pipe. 
Conveniently, the means for applying an electric field across the solid 
also acts as the retaining means for the solid in the conduit. 
In one suitable form of the invention a pair of permeable electrodes are 
fixed apart along the conduit and the permeable solid substantially fills 
the space defined by the electrodes and the inner wall or walls of the 
conduit. 
Preferably, the electrodes are flat plates shaped to retain the solid 
within the conduit, thus when the conduit is a pipe the electrodes are 
disc shaped. 
The permeable electrodes are conveniently constructed from wire gauze or 
from electrically conducting titanium oxide. 
Suitably, the liquid permeable solid is in powdered form. Suitable powdered 
forms include powdered ceramic, powdered silica, powdered plastic and 
clay. 
Alternatively, the liquid permeable solid may be a fibrous solid, suitably 
a fibrous ceramic or polymer fibres. 
In addition as an alternative to powdered or fibrous forms the electrically 
insulating solid may be any permeable form of ceramic, silica, plastic or 
clay. 
The relationship between flow rate, dimensions of the conduit, applied 
voltage and the nature of permeable solid riay helpfully be described by 
the equation shown in Scheme (I) which assumes that the permeable solid is 
formed by a bundle of parallel capillary fibres of radius `r`: 
##EQU1## 
wherein: n=number of capillaries of radius r, 
V=applied voltage; 
L=distance between electrodes; 
.xi.=Zeta potential; 
.epsilon..sub.r =relative permittivity; 
.epsilon..sub.o =permittivity of free space; and 
.eta.=viscosity of the liquid. 
Although Scheme (I) is considered to be useful for describing the 
theoretical basis for the pump of the present invention, the invention is 
not considered to be limited by the relationship set out in Scheme (I). 
In a preferred form, when used to supply a liquid formulation in the 
dispensing device of the invention, the pump comprises an electrically 
insulating tube, a pair of electrodes permeable to liquid and fixed apart 
along the tube and a powdered solid permeable to liquid, the solid 
substantially filling the space defined by the electrodes and the inner 
wall of the tube and means for applying an electric field to the 
electrodes, so that in use, when the field is applied, liquid is induced 
to flow through the solid and hence along the tube. 
The above described liquid supply means allows an even liquid flow at 
precise rates, using the same (electrical) energy source that is used to 
generate the droplets thus requiring no mechanical means of pressurizing 
the liquid. The entire unit may thus be powered by very small 
battery-driven voltage sources, or even by a hand-operated piezoelectric 
device such as a stack of PVdF film or barium titanate ceramic. The device 
may thus be made pocket-size. 
The invention also extends to the conduit, retaining means and means for 
applying the electric field as described above for use with the solid as 
defined above. 
When used herein `a comminution` includes a liquid droplet spray. 
When used herein `medicament` includes proprietary medicines, 
pharmaceutical medicines and veterinary medicines. 
When used herein, unless more specifically defined herein, `inhaled 
adminisaion` includes administration to and via the upper respiratory 
tract, including the nasal mucosa, and the lower respiratory tract. 
When used herein `electrically insulating` relates to a level of electrical 
insulation sufficient to allow an electric field to be applied across the 
solid, wherein the field is sufficient to induce liquid flow; preferably 
it includes semi and fully insulating materials. 
When used herein the terms `liquid permeable` or `permeable to liquid` as 
applied to, for example, the solid and electrodes relate to solid and 
electrodes which are intrinsically permeable to liquid or to solid or 
electrodes which can be rendered permeable by processes for example, in 
the case of the solid, granulation or powdering or, for the electrode, by 
forming into shapes which allow the passage of liquid, such as mesh 
shapes. 
The liquid medicinal formulations for use in the device of the invention 
may be formulated according to conventional procedures, such as those 
disclosed in the US Pharmacopoeia, the European Pharmacopoeia, 2nd 
Edition, Martindale The Extra Pharmacopoeia, 29th Edition, Pharmaceutical 
Press and the Veterinary Pharmacopoeia 
The liquid cosmetic formulations for use in the device of the invention may 
be formulated according to conventional procedures such as those disclosed 
in Harry's Cosmeticology, 9th Edition, 1982,George Goodwin, London.

COMMINUTION SITES 
FIG. 1 shows a thin-walled capillary tube (1), which may be made of 
conducting or semiconducting material and which may be electrically 
connected to a source of high-voltage direct-current, either directly or 
through the liquid. A single jet (3) is produced from a cusp (2) of 
liquid, both of which form naturally, according to the voltage and flow 
rate for a given liquid. 
FIG. 2 shows a similar tube (1) used at a lower flow rate and voltage which 
are adjusted so as to produce multiple cusps (2) and jets (3) issuing from 
the region of the ends of the thin-walled tube (1). 
FIG. 3 shows a conducting or semiconducting cylinder (1) which may have a 
larger diameter than those shown in FIGS. 1 and 2. This nozzle has an 
inner-member, (4) which is approximately coaxial with the outer tube, (1). 
FIG. 4 shows a slot nozzle, formed between two parallel plates (2) having 
conducting, or semiconducting edges electrically connected to a 
high-voltage direct-current supply, from which the liquid emerges, forming 
cusps and jets when the voltage supply and liquid flow rates are suitably 
adjusted according to the type of liquid being sprayed For a given jet 
(and thus droplet) size, and a given liquid, this nozzle may enable a 
higher flow rate to be achieved than those in which a single cusp and jet 
are used. 
FIG. 5, shows one example of an array of six nozzles (1) in a circular 
pattern, centrally mixing the sprays. 
Liquid Supply Means 
An example of such a device is illustrated in FIG. 6 which shows an ion 
stream method, wherein a high voltage electrode (5) breaks up pairs of 
charge carriers within the liquid, thus neutralizing those of opposite 
polarity at the electrode, and leaving a large population of monionized 
like-polarity charge carriers which stream away from the high voltage 
electrode by coulombic force, thus moving the liquid in the direction of 
the counter electrode (6) by means of viscous drag. This pumping means 
requires that an electrode (5) is able to effectively inject like-polarity 
charge carriers into the liquid, close to the electrode (5). This may be 
effectively done by using a sharp-edged conducting or semiconducting 
surface, held at a sufficiently high potential to disrupt lightly bonded 
charge carriers or to ionize the liquid. Normally, it is only possible to 
establish a strong enough field for both creating unipolar charge carriers 
and pumping the liquid, when the liquid is of sufficient resistivity. 
Typically a resistivity of, say 10 (exp. 8) ohm meters, will pump at 
several millilitre per minute, with a head of up to one meter, at a 
voltage of 10 to 20 kilovolts, and a direct current of only a few 
microamperes. More conductive liquids will draw more current and will 
establish a weaker electric field. Thus highly conducting liquids, such 
as, say tap water may not establish a practicable drag pressure. 
FIG. 7 shows an example of the novel pump of the invention in which a 
plastic tube (7a), 1.0 cm long, internal diameter 1.0 cm and 0.8 mm wall 
thickness has one of a pair of disc-shaped wire gauze electrodes (8a and 
8b) bonded to each of its ends. A source of d.c. voltage is connected to 
each electrode. Liquid is supplied to and taken from tube (7a) by two 
further plastic tubes (7b and 7c) one of each being bonded to each wire 
gauze electrode (8a or 8b). Glass tube (7a) is filled with powdered silica 
(9). In operation, on applying a voltage to the electrodes (8a and 8b) a 
net forward force is exerted on the liquid which is interfaced with the 
silica (9) due to the presence of a double layer of charge at the 
solid-liquid interface. The polarity of the dc voltage is set so as to 
draw the liquid in the required direction, according to the polarity of 
the charge layer residing in the liquid at the liquid-solid interface. The 
pressure developed may be enhanced by using a solid of finer mesh size, 
thereby increasing n (see Scheme(I) above), with a maximized specific 
surface and with maximal zeta potential difference at the solid-liquid 
interface. Electrode voltages may be adjusted in accordance with the 
length of the current path between the two electrodes, so as to limit 
current flow to a desired value. 
Using the device illustrated in FIG. 6 a flow rate of 0.03 mL sec.sub.-1 
was obtained with mineral oil of resistivity 10.sup.7 ohm m, relative 
permitivity .about.2.5 and viscosity 22 centistokes with an applied 
voltage of 20 kV. 
Electrical Charging Means 
An example of this is a piezo electric generator. FIG. 8 illustrates a pair 
of piezoelectric ceramic generators (10) (11) which may be easily squeezed 
by a cam (12) operated by a trigger-shaped lever (13). The entire assembly 
may be housed in a strong steel frame, (14), and the piezoelectric pair 
may be held tight by adjustment screw (15). The voltage terminals (16) are 
the two live electrodes for connection to the pumps and nozzles, whilst 
terminal (17) is earthed, say to the steel frame. 
When the lever (13) is pulled inward, the two ceramic generators (10) and 
(11) will produce high voltages upon the terminals (16) placed at the end 
surfaces, which may be used to activate both the electrokinetic pumps and 
the nozzles 
Typical values of charge from say a barium titanate ceramic of about 1.0 cm 
length and 1.0 sq cm surface area would be 1.0 or 2.0 microcoulomb per 
squeeze, of either positive or negative polarity. Upon release of the 
squeezing pressure, a similar charge will flow in the opposite direction. 
A typical voltage would be say 5,000 to 10,000 volts. Thus, pumping and 
atomizing may both be achieved by hand operation of a single pair of 
piezoelectric generators at appropriate voltages, say 5,000 volts, and 
sufficient currents, say 2.0 microcoulombs per second (2.0 microamperes). 
The piezoelectric material may be chosen from several types, such as barium 
titanate ceramic, or pvdf polymers, which generate significant 
high-voltage electric charge displacement upon being pressurized. The 
choice and capacity may be so chosen as to offer control of the degree of 
pumping and/or atomization when operated. The liquid flow induction, and 
the nozzle atomization will occur when the piezo electric generators are 
squeezed, and again (with opposite polarity) when the piezo electric 
generators are released from pressure. The device is arranged so that when 
squeezed, and when released the pumps and nozzles will operate without 
alteration of flow rate or droplet size. Only polarity will change 
(reverse) in the two modes of operation arising from pressure and release 
of pressure. This will maintain constant flow and droplet generation, and 
mixing of species and/or charge-to-mass ratio adjustment of the sprays, 
during the active modes of pressure, and release of pressure. 
Particular examples of the dispenser of the invention are illustrated 
below: 
FIG. 9 shows a dispenser of the invention, in which liquid in each of two 
reservoirs (20) is caused to flow along suitable conduit, say polyethelene 
tubing (21) into two electrokinetic pumps (22), say by gravity feed. The 
two piezoelectic generators (23) are then squeezed so that a high voltage 
charge is induced at the two faces of the piezoelectric materials. These 
high voltages will then appear at the terminals of the pumps (22), which 
are electrically connected to the piezoelectric material by wire 
conductors. 
At the same time, these high voltages will appear at the two conducting, or 
semi-conducting, capillary-tube nozzles (24). Thus, when the two liquids 
reach the two nozzles, the liquids will emerge from the nozzles as 
comminuted droplets with electrical charges of opposing polarity. The 
droplets will then be attracted to each other by electric field forces, 
and will tend to mix vigorously. 
The value of droplet charge on each of the two streams of droplets may be 
independently adjusted to produce the optimum residual value by one or 
more of several means: the size, shape, ancvor materials of the two 
piezoclectrc materials may be set to give differing values of voltage and 
charge; the two liquid flow rates may also be adjusted, either by suitable 
design of the two electrokinetic pumps, or by differing values of 
piezoelectric voltage applied to the two pumps thus directly influencing 
droplet charge for a given voltage and nozzle design; and the droplet size 
and charge of the two liquids may be independently adjusted by the 
formulations of the two liquids, especially by adjustment of the liquid 
resistivities. 
A second example of the dispenser of the invention is illustrated in FIG. 
10: Two identical syringes (30a and 30b) are actuated by a rigid plate 
(31), the plate being attached to a motor drive unit. Two identical 
capillary nozzles (32a and 32b) each with internal diameters of 05 mm are 
each interconnected with one of the syringes (30a or 30b) by one of a pair 
of flexible tubes (33a and 33b). Each nozzle (32a and 32b) is fixed in a 
non-conducting mounting (34a or 34b respectively) so as to define an angle 
of approximately 90.degree. with each other. One nozzle (32a) is attached 
to a high voltage source (35a) of (+) 6.7 kilovolts and the other nozzle 
(32b) is attached to a high voltage source (35b) of (-) 6.7 kilovolts. 
In one particular experiment using the above described device, the flow 
rates of liquid (a mixture of 80% ethanol and 20% polyethylene glycol) 
from each syringe was adjusted to 1.0 .mu.L/sec. The nozzles were attached 
to the high voltage sources of (+) and (-) 6.7 kVolts respectively. The 
two spray clouds were observed to mix virtually completely to provide an 
clectricay neutral spray.