Patent Grant
7341211
The invention describes a method and device for the production of capillary micro-jets and micro-particles, with a size ranging from some hundred microns to some nanometers. The method is based on the combined effect of electro-hydrodynamic forces, fluido-dynamic forces, and a specific geometry, to give rise to micro- and nano- fluid ligaments or jets; as these disintegrate or break up, a controllable and relatively monodisperse spray is formed, with drops in the micro- or nanometric range; in addition, the spray may display specific internal structure features, such as a nucleus surrounded by a heterogeneous shell, or a plurality of nuclei or vesiculae, which may be concentrical or not, surrounded by a shell.
The electro-hydrodynamic atomization of liquids, or electrospray, has provided an essential tool for the biochemical analysis over the last decades (Electrospray Mass Spectrometry, o ESMS), following the discovery of its potential in the middle 80s. One of the advantages it presents is the small amount of analyte required for the analysis. Nevertheless, in the case of applications requiring the atomization or breakup of a sufficiently large amount of liquids per unit of time, a key limitation of electrospray is its low productivity. Some examples of these applications are to be found in the pharmaceutical industry (active principle encapsulation), food industry (encapsulation of diverse organoleptic ingredients among other), phytosanitary industry . . . In particular, some electrospray applications have arise aiming at the generation of composite jets, with concentrical arrays of diverse immiscible or hardly miscible liquids (Loscertales, Cortijo, Barrero and Gañán 2001, patent request PCT/ES02/00047); such applications are geared to the production of micro-capsules or nano-capsules; however, research is challenged by the need to increase the productivity of the electrospray technology and devices.
On the other hand, the atomization of liquids by purely fluidomechanic means, in particular by pneumatic procedures, is a capital tool in many applications and industrial, technological or scientific developments, having an impact on our daily life. The so-called “Flow Focusing” technology (Gañán-Calvo 1998, Physical Review Letters 80, 285), is based on specific flow geometries and takes the pneumatic option to generate liquid micro-jets which break up into very small drops of essentially homogeneous size. “Flow focusing” is also able to produce liquid micro-jets surrounded by another liquid—rather than by a gas—; alternatively it can produce gas micro-jets surrounded by a liquid, which may play the role of a focusing agent, analogous to the role of the gas in a standard pneumatic device; as a result, micro-bubbles of perfectly homogeneous size are produced.
There are many liquids which cannot be atomized as a result of their physical properties; sometimes, they cannot be combined to the end of forming micro-drops or capsules by electro-hydrodynamic atomization.
The flow-focusing technology, in turn, is limited in that it may require very large atomization pressure when nano-metric sizes are sought. This may prove a handicap in some applications.
Both these disadvantages are overcome by means of the invention disclosed in the Spanish patent request P2002-00286. The invention deals with a non-trivial combination of the electrospray and flow focusing technologies. The result is a procedure allowing the manipulation of a wide parametric spectrum involving diverse liquid properties, liquid flow-rates and drop sizes including combinations that cannot be handled or are hard to handle with any of the two mentioned technologies taken separately: i.e. a low reproducibility or robustness would be observed.
The present invention aims at increasing substantially the productivity of electrospray. It is based on the simultaneous effect of two principles:
For the device to work, the electric field at the extreme or tip of the injection tubes must be above a threshold which is a function of the surface tension of the liquid which is to be atomized. Were the needle to be isolated, a flat electrode facing the needle would be enough to reach the critical electric field threshold. However, when a large number of needles are brought together and their relative distance diminishes, the electric field at their tips also decreases accordingly; this sets a limit on the packaging density of the needles in the design. The present invention provides a new approach to the electrode design allowing a high packaging density; in addition, a solution is disclosed allowing the combination of electrostatic forces acting on the liquid with mechanical forces extracting the spray through the electrode.
The invention combines three key aspects:
(i) In order to produce a steady capillary micro-jet in the laminar regime issuing from the tip of the liquid-feeding tube, fluidic forces are used in conjunction with external electric forces (optional): the absence of any of these forces (fluidic or electrical) will lead to a radical modification in the properties of the resulting capillary micro-jet or the resulting particles; in some cases, its production becomes impossible when only fluidic or electro-hydrodynamic forces are used. The abovementioned electric forces are produced at the liquid surface once it leaves the feed tube; these forces are caused by a potential difference established between an electrode of specific shape, facing the tube, and the tube itself. The forces of a fluidic nature, in turn, are produced at the same liquid surface when a second fluid, to be referred to as “focusing fluid”, immiscible with the liquid (for instance, a gas), is forced to flow around the capillary liquid feed tube towards an orifice located in the electrode facing the outlet of the feed tube. Such fluidic force is used in the flow-focusing technology (Gañán-Calvo 1998,Physical Review Letters 80, 285) in order to give rise to steady liquid micro-jets.
(ii) The geometry of the electrode facing the feed tube is such that it is located in front of it (
(iii) The external surface of the feed tube can be treated in an adequate manner, e.g. by means of a hydrophobe, so that the liquid injected through this feed tube does not spill or migrate by capillary action along said external surface; this surface treatment constrains the liquid to the outlet of the feed tube, needle or capillary. This feature is not essential, because in many cases, the sweeping effect caused by the focusing fluid keeps the liquid anchored to the outlet of the feed tube in the form of a capillary cone, cusp-shaped, from whose tip the fluid micro-jet or micro-ligament issues.
The three features above combine to define the invention. The object of the present invention is therefore a special combination following the claims of the previous technological modes known as electrospray and “flow focusing”; the combination is non-trivial and involves a specific geometry. This non-trivial combination allows to expand the parametrical range of the fluid properties and the fluid flow-rates, including combinations that cannot be reached with Electrospray or Flow-Focusing taken separately: i.e. it would not be possible to produce steady fluid jet-emissions for some given fluids and under particular setups, while the combination in the present invention would be successful. Another object of this invention is the device and the proposed geometry as disclosed (
Thus, an object of the invention is a device for the production of steady capillary jets and liquid drops of micrometric or nanometric size characterized by:
a) a number N of capillary tubes, wherein each capillary tube transports a flow-rate Qi of a given fluid i, and i is an integer from 1 to N; each of said capillary tubes is located so that the (i−1)-fluid surrounds the i-capillary tube; each one of the capillary tubes or each fluid in the capillary tubes is connected to an electric potential Vi with respect to a ground electrode; each one of the fluids transported by said capillary tubes is immiscible or poorly miscible with the adjacent fluids;
b) an electrode, connected to an electric potential V0, facing the outlet of the most prominent capillary tube; said electrode includes an orifice whose minimal transversal dimension is D0 ranging from 10−6 to 102 times, preferably 10−3 to 10 times, the minimal transversal dimension D1 of the outlet section of the outermost capillary tube; said orifice is located facing the outlet of the most bulging capillary tube, at a distance ranging from 0.005 to 5 times D1; said electrode is shaped in such a way that each point of its inner surface or each point of its surface oriented to said capillary tubes stands at a distance from the outer surface of the outermost capillary tube which is greater than the minimal distance from the orifice of said electrode to the most bulging outlet of all capillary tubes.
Yet another object of the invention is a device for the production of steady capillary jets and liquid drops of micrometric or nanometric size according to the above paragraph, characterized in that both the electrode orifice and the outlet sections of all capillary tubes are defined by a surface limited by a closed line of arbitrary geometry, preferably a circular shape, regular or irregular polygonal shape, or ellipsoidal shape.
An object of the present invention is also a device for the production of steady capillary jets and liquid drops of micrometric or nanometric size following the above, characterized in that both the electrode orifice and the outlet sections of all capillary tubes are defined by a surface limited by two closed curves of arbitrary geometry, such that the minimal distance between the two curves is smaller than 0.1 times the total length of the longest curve.
Yet another object of the invention is a device for the production of steady capillary jets and liquid drops of micrometric or nanometric size following the above, characterized in that the potential difference ΔV between the potential of the outermost capillary tube or the outermost fluid (V1) and the potential of the electrode V0 is larger than 0.1 times the greater of the two values (γ.D0/ε0)0.5 and (γ.D1/ε0where ε is the interfacial surface tension between the fluid flowing through the interior of the outermost capillary tube and the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode, and ε0 is the permittivity of the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode.
In addition, an object of the present invention is a device for the production of steady capillary jets and liquid drops of micrometric or nanometric size following the above, characterized in that the number of capillary tubes is N=1 and the minimal transversal dimension of the electrode orifice D0 ranges between 10−2 and 5 times the minimal transversal dimension D1 of the outlet section of the outermost capillary tube, the outlet orifice of the electrode is located facing the outlet of the capillary tube at a distance ranging between 0.05 and 2 times D1, and each point of the inner surface of the electrode stands at a distance from the outer surface of the capillary tube ranging from 1 to 10 times the minimal distance from the orifice of said electrode to the outlet of the capillary tube, while the external rim of the electrode is located at a distance of 1 to 100 times D1 from said orifice.
Yet another object of this invention is a device for the production of steady capillary jets and liquid drops of micrometric or nanometric size following claims the above, characterized in that D1 ranges from 0.5 micrometers and 5 milimeters, preferably from 10 micrometers and 1 milimeter; and also characterized in that the outer surface ot at least one of the capillary tubes is covered by a hydrophobe substance, so that it stops or limits the wetting of said surface by the fluid flowing through the interior of said capillary tube.
Yet another object of this invention is a multi-device for the production of steady capillary jets and liquid drops of micrometric or nanometric size characterized in that it is made up of at least three devices following the above description, assembled in the vicinity of each other, and with relative angles ranging from −89 to 89 sexagesimal degrees, preferably −10 to 10 sexagesimal degrees, all of said devices pointing in the same direction, so that the axes of the capillary tubes form a minimal angle from 5 to 90 sexagesimal degrees, preferably 70 to 90 sexagesimal degrees, relative to the plane or virtual surface where the orifices of said electrodes are located.
In addition, an object of this invention is a procedure for the production of steady capillary jets and liquid drops of micrometric or nanometric size by means of a device as disclosed in the above paragraphs characterized by the following steps:
a) forcing N fluids to flow, with flow-rates Qi, i being an integer from 1 to N, through N capillary tubes, wherein each of said capillary tubes is located so that the (i−1)-fluid surrounds the i-capillary tube; each one of the capillary tubes or each fluid in the capillary tubes is connected to an electric potential Vi with respect to a ground electrode; each one of the fluids transported by said capillary tubes is immiscible or poorly miscible with the adjacent fluids;
b) connecting an electrode, located facing the outlet of the most prominent of the N capillary tubes at an electric potential V0, in such a way that the potential difference ΔV between the potential of the outermost capillary tube or the outermost fluid (V1) and the potential of the electrode V0 is larger than 0.1 times the greater of the two values (γ.D0/ε0)0.5 and (γ.D1/ε0)0.5, where γ is the interfacial surface tension between the fluid flowing through the interior of the outermost capillary tube and the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode, and ε0 is the permittivity of the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode.
Yet another object of the invention is a procedure for the production of steady capillary jets and liquid drops of micrometric or nanometric size by means of a device following the above characterized in that along with with connecting the outermost fluid or capillary tube at a potential V1 and connecting the electrode at a potential V0, a surrounding fluid is forced to flow between the outer surface of the electrode and the inner surface of the outermost capillary tube towards the outlet orifice of the electrode, said surrounding fluid being immiscible with the fluid forced through the outermost capillary tube, the flow-rate of said surrounding fluid being Q0, where Q0 is larger than 0.1 times the greater value of D02[γ/(D0.ρ0)]0.5 and [γ/(D1.ρ0)]0.5, where ρ0 is the density of said surrounding fluid, and γ is the interfacial surface tension between the fluid flowing through the interior of the outermost capillary tube and the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode.
Yet another object of the present invention is a procedure for the production of bubbles of micrometric or nanometric size by means of a device as disclosed above characterized by the following steps:
a) forcing N fluids to flow, with flow-rates Qi, i being an integer from 1 to N, through N capillary tubes, wherein each of said capillary tubes is located so that the (i−1)-fluid surrounds the i-capillary tube; each one of the capillary tubes or each fluid in the capillary tubes is connected to an electric potential Vi with respect to a ground electrode; each one of the fluids transported by said capillary tubes is immiscible or poorly miscible with the adjacent fluids;
b) connecting an electrode, located facing the outlet of the most prominent of the N capillary tubes at an electric potential V0, in such a way that the potential difference ΔV between the potential of the outermost capillary tube or the outermost fluid (V1) and the potential of the electrode V0 is larger than 0.1 times the greater of the two values (γ.D0/ε0)0.5 and (γ.D1/ε0)0.5, where γ is the interfacial surface tension between the fluid flowing through the interior of the outermost capillary tube and the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode, and ε0 is the permittivity of the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode;
characterized in that the fluid forced through the innermost capillary tube is a gas.
Finally, an object of the present invention is a procedure for the production of bubbles of micrometric or nanometric size following the above, characterized in that along with connecting the outermost fluid or capillary tube at a potential V1 and connecting the electrode at a potential V0, a surrounding fluid is forced to flow between the outer surface of the electrode and the inner surface of the outermost capillary tube towards the outlet orifice of the electrode, said surrounding fluid being immiscible with the fluid forced through the outermost capillary tube, the flow-rate of said surrounding fluid being Q0, where Q0 is larger than 0.1 times the greater value of D02 [γ/(D0.ρ0)]0.5 and D12 [γ/(D1.ρ0)]0.5, where ρis the density of said surrounding fluid, and γ is the interfacial surface tension between the fluid flowing through the interior of the outermost capillary tube and the fluid or the void located in the space between the outer wall of the outermost capillary and the inner wall of the electrode.
A substantial advantage of the method here proposed with respect to the state-of-the-art is that much larger liquid flow-rates can be used (up to several hundred times larger) in each capillary tube with stable regime; such flow-rates would give rise to instability in the absence of a suction or flow-focusing effect.
Other advantage of the invention relative to the state-of-the-art is that the drops originating from the micro-jet's breakup are automatically unelectrified as they move near the edges of the orifice.
Other advantage of the invention relative to the state-of-the-art is that, since the capillary feed tube is located significantly close to the outlet orifice of the electrode, electric effects are restricted to the area next to said orifice and feed tube; and the electrostatic effect of nearby feed tubes is damped.
Other advantage of the invention relative to the state-of-the-art is that, provided the electrode has as heath-geometry, the electrode will guide the flow of the external fluid, thus increasing drag effects on the external surface of the outermost feed tube and leading to an increase in the suction or drag effect on the fluids to be atomized through said orifice.
Other advantage of the invention relative to the state-of-the-art is that, provided the electrode has a sheath-geometry, said electrode will have an increased mechanical stiffness, being more resilient—owing to its shape—against deformations caused by the pressure of the outermost fluid.
In what follows, an embodiment example is described for the present invention; it does not attempt to be exhaustive nor to limit the scope of the present invention; it is only disclosed as an illustration, while the actual protection field of the invention is to be construed from the claims.
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 200200285 | Feb 2002 | ES | national |
| 200300276 | Feb 2003 | ES | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/ES03/00065 | 2/4/2003 | WO | 00 | 1/21/2005 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO03/066231 | 8/14/2003 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4508265 | Jido | Apr 1985 | A |
| 4962885 | Coffee | Oct 1990 | A |
| 6086740 | Kennedy | Jul 2000 | A |
| 6119953 | Ganan-Calvo et al. | Sep 2000 | A |
| 6405936 | Ganan-Calvo | Jun 2002 | B1 |
| 6481648 | Zimmermann | Nov 2002 | B1 |
| 6679441 | Borra et al. | Jan 2004 | B1 |
| Number | Date | Country |
|---|---|---|
| 563807 | Jul 1975 | CH |
| 2 776 538 | Oct 1999 | FR |
| Number | Date | Country | |
|---|---|---|---|
| 20050116070 A1 | Jun 2005 | US |
