ES2239861A1 - Electro hydrodynamic disperser of conducting liquid in dielectric bath includes dielectric liquid and electrical charging of droplets formed by breaking of suspension - Google Patents

Abstract

An electro hydrodynamic disperser of conducting liquid in a dielectric bath has the conducting suspension or liquid located in the dielectric liquid which is barely miscible with it, if at all. An independent claim is included for a process using the disperser. The process employs e.g. hydrosol droplets charged electrically and of highly uniform size produced by breaking of the suspension through capillary instability. The diameter of the stream of suspension and of the resulting droplets ranges from tens of nanometers to hundreds of microns, depending on the operating conditions.

Description

Device and procedure to produce electrosprays of conductive liquids within liquids multi-component dielectrics and emulsions.

Object of the invention

The present invention describes a method and the device for generating a stationary capillary jet of a conductive liquid, or conductive liquid suspension, within a liquid dielectric, immiscible or poorly miscible with it, as well as drops hydrosol, of very uniform and loaded sizes electrically, which is formed from the breakage of the jet by hair instabilities. Depending on the properties of the liquids used and operating conditions, the diameter of the jet and the resulting drops may be comprised between a few tens of nanometers and hundreds of microns.

The liquid that forms the micro jet is injected into an appropriate and constant flow rate, through a metal needle connected to a high voltage source. Yes conductivity Injection of the liquid injected is high enough you can, if desired, use non-metallic needles (for example, silica); in this case the charging process must be done through of the liquid itself. At the end of the needle, which is located submerged in the dielectric liquid (receiving fluid), a Meniscus of the conductive fluid. Both liquids are immiscible or poorly miscible. The receiving fluid may or may not be in repose. The arrangement of the needle is such that the dielectric liquid  partially or completely bathe the meniscus of the conductive liquid. Opposite the end of the needle is also immersed in the receiving fluid, a reference electrode. Electrode reference may have different geometric configurations, plate, ring, etc. In addition, the reference electrode does not have what to be solid, being able to be a conductive liquid, in resting or moving, different or not from the injected liquid, which be immiscible or poorly miscible with the dielectric. If he dielectric possesses an electrical conductivity sufficiently small, you can establish an electric potential difference between the needle and the electrode. For an appropriate range in differences in electrical potential applied between the needle and the electrode, the meniscus adopts a substantially conical shape under the action of electric forces and surface tension that They act on their interphase. From the apex of the conical meniscus, called Taylor cone, a micro / nano jet is emitted, charged electrically, and whose diameter can be in a range of values ranging from hundreds of microns to a few nanometers For appropriate values of the conductive liquid flow injected through the needle, you can get the structure of cone-jet remain stationary. This phenomenon is known in electrohydrodynamic literature as electrospray in stationary jet-cone mode. The rupture of the stationary jet loaded, due to instabilities varicose, generates a colloidal dispersion of liquid drops injected into the dielectric, which are characterized by their sizes are markedly uniform (monodispersed spray), they are loaded, and the range of its average size is in the range micro / nanometric

The device and procedure, objects of the Present invention, are applicable to fields such as Science of Materials, Food Technology, Pharmaceutical Technology, Chemical Engineering, etc., where generation and handling controlled jets and drops of micro or nanometric sizes be a essential part of the process. For example, the procedure of the invention can be used to produce a hydrosol (or suspension colloidal) very monodispersed of rigid nanometric spheres if use a conductive liquid that can be polymerized. Indeed, the rupture of the stationary liquid jet by action of hair instability results in the continuous formation of a drops hydrosol that solidify under the action of a source of ultraviolet light or any other procedure polymerization.

State of the art

Among the many procedures usually used to generate stationary liquid jets and aerosols, This invention uses electrohydrodynamic forces (EHD). Low appropriate operating conditions, a liquid flow rate is emits in the form of stationary micro jet from the tip of a Taylor cone stationary. The rupture of said jet produces a cloud of charged drops called electrospray. This configuration It is usually called electrospray in cone-jet mode stationary (M. Cloupeau and B. Prunet-Foch, J. Electrostatics, 22, 135-159, 1992). The laws of scale of the emitted current and the size of the drops of this type of electrospray are well described in the literature (J. Fernández de la Mora & I. G. Loscertales, J. Fluid Mech. 260, 155-184, 1994; A.M. Gañán-Calvo, J. Dávila & A. Barrero, J. Aerosol Sci., 28, 249-275, 1997, A. M. Gañán-Calvo, Phys. Rev. Lett. 79, 217-220, 1997; R.P.A. Hartman, D.J Brunner, D.M.A. Camelot, J.C.M. Marijnissen, & B. Scarlett, J. Aerosol Sci. 30., 823-849, 1999). In particular, the ability of this process to generate jets is well known stationary liquids and monodisperse aerosols in a range of sizes ranging from a few nanometers to hundreds of microns  (I.G. Loscertales & J. Fernández de la Mora, J. Chem. Phys. 103, 5041-5060, 1995.).

The previous results refer to the dispersion of liquids in a vacuum or in a gaseous atmosphere but not at situations in which the dispersion process takes place in the sine of other liquid. L. Oddershede & S.R. Nagel, Phys. Rev. Lett. 85, 1234-1237, 2000, have studied experimentally the development of the cusp that forms in the interphase of two immiscible liquids when a field is applied Electric large enough. In any case, in this work is neither investigated nor established, therefore, necessary conditions to form a stationary electrospray and stable, in cone-jet mode, of a liquid in The bosom of another. The electroatomization of a liquid within another in the drip regime (microdripping) has been considered applying pulsed electric fields, C. Tsouris, S.H. Neal, V.M. Shah, M.A. Spurrier, and M.K. Lee, Chemical Eng. Comm. 160, 175-197, 1997. The application of electric fields does not Stationary variable intensity is incompatible with the mode cone-stationary jet. Atomization electrostatic dielectric fluids (such as air or organic solvents) in relatively fluid fluids drivers (for example water) has been recently investigated, C. Tsouris, W.T. Shin and S. Yiacoumi, Canadian J. Chem. Eng. 76, 589-599, 1998, M. Sato, J. Colloid Interface Sci. 156,504-507, 1993; see also US Patent number 5,762,775, by D.W. DePaolli, C. Tsouris, J.Q. Feng and US Patent 4,508,265 by M. Jido. This situation, in which they occur varied electrohydrodynamic phenomena, it is also incompatible with the formation of a cone-jet structure stable and stationary like the one claimed here.

Finally, the dispersion of a conductive liquid in another dielectric applying pulsed electric fields has been considered in the following patents: US Patent 5,503,372, by W.G. Sisson ,, M.T. Harris, T.C. Scott and O.A. They will base; US Patent 5,738,821 by W.G. Sisson, O.A. Basaran and M.T. Harris; US Patent 5,759,228 by by W.G. Sisson ,, M.T. Harris, T.C. Scott and O.A. They will base. The application of a pulsed electric field is naturally incompatible with obtaining the cone structure jet, stable and stationary, which is claimed here and that It results in a monodispersed hydrosol of charged drops.

Explanation of the invention.

The novel contribution of the present invention is that the injection of a conductive liquid, or suspension conductive liquid, through a submerged electrified needle in a bath of a dielectric liquid (and not within a gas, or empty) results in an appropriate range of flow rates and field electric applied, to the formation of the stationary Taylor cone and of the stationary jet that emerges from its vertex with diameters in The micro / nanometric range. The conical shape characteristic of Meniscus is due to a balance between tension forces interfacial and the electric forces acting simultaneously on the surface of the meniscus. The movement of the liquid is caused by the electrical tangential effort acting on the surface of the meniscus, and that drives the conductive liquid towards the Taylor cone tip. At some point, the mechanical balance described above is no longer satisfied, so the Meniscus surface changes from conical to cylindrical (cone-jet). The reasons for this loss of balance may be due, depending on the regime of operation, to the importance of the kinetic energy of the liquid or to finite value of its electrical conductivity. The ejected liquid, Due to EHD forces, it must be continuously replaced by proper injection of conductive fluid through the needle in order to achieve a steady state. The stability of This state can be characterized by monitoring the stream I carried by the jet and the hydrosol, which is collected at the reference electrode.

The stationary jet breaks downstream by varicose instabilities associated with surface tension. The micro / nano jet breakage results in a droplet hydrosol or conductive liquid particles within the dielectric, with very uniform sizes. The liquid to be injected flowing through the capillary is immiscible or poorly miscible with the liquid dielectric. The electrical conductivity of the receiving liquid must be low enough to apply a field Intense electrical between the collector (electrode) and the capillary. He micro / nanometric and highly charged stationary jet that emits from the apex of the Taylor cone finally breaks into a drops hydrosol, monodispersed, micro / nanometric and highly charged within the dielectric liquid. The term jet stationary micro / nanometric refers here to a jet almost cylindrical stationary, whose diameter varies between hundreds of microns and a few nanometers. The term hydrosol of highly charged micro / nanometric monodispersed drops are refers to drops, or particles, with net charge, formed by the liquid injected into the receiving fluid. The diameter of said particle can vary between hundreds of microns and about few nanometers

An advantage of this invention is that the drops, or particles, resulting from the rupture of the micro / jet
They have a uniform size, and that size can be controlled by varying the electrical conductivity of the injected liquid and the operating conditions, from tens of microns to a few nanometers.

Another advantage of the invention stems from the fact that The resulting micro / nanometric drops are loaded. Load of all the drops is always of the same sign, which avoids, by Culombian repulsion, the coagulation of them. In addition, the local electric field acts on the net charge of each drop, helping very efficiently to extract the drops from the point where they occur, also preventing coagulation. Otherwise, the resistance offered by the receiving liquid to the displacement of micro / nanometric drops would cause its accumulation at the point where they form, producing coagulation of them, and missing not only the uniformity of the average size of the drops, but also control over the size of the drops resulting.

Another important advantage of the present invention lies in the fact that the control of the dispersed phase necessary for its post-processing it is much more versatile and easy to implement (pH, temperature, ultrasound, etc.) if the Continuous phase is liquid, instead of soda.

Brief description of the figures

Figure 1 represents a scheme of the device used to produce stationary liquid jets of sizes micro and nanometric within a dielectric liquid.

Figure 2 represents a scheme of a device with renewal of the fluid bath using the present invention.

Figure 3 is a graph where the values of the current emitted through the jet as a function of the square root of the dispersed conductive fluid flow.

Detailed description of the invention

The present invention aims at the description of the device and the procedure to produce stationary liquid jets and micro-sized drops and nanometric inside another liquid, immiscible or poorly miscible with the previous one, and of low electrical conductivity (dielectric).

As shown in Figure 1, the device consists of a feeding tip 1 of a liquid conductive, or conductive liquid suspension, 2, such that by the tip of supply 1 flows a flow rate Q of the liquid 2. Said tip of power 1 is connected to an electric potential V, through of a source of electrical potential 3, with respect to an electrode of reference 4, and arranged so that a dielectric liquid 5 surrounds the feeding tip 1. The reference electrode 4, which can have varied geometric shapes; (for example ring or conductive plate), is immersed in liquid 5 and facing the feed tip 1. In addition, the liquid 2 that circulates through feed tip 1 is immiscible or poorly miscible with liquid 5. At the outlet of the feeding tip 1 an electrified capillary meniscus is formed with a shape substantially conical 6 and from whose apex a capillary stream is emitted stationary 7 of liquid 2, such that liquid 5 surrounds the liquid 2. In addition the capillary jet 7 has a diameter that is in a range between 500 microns and 15 nanometers. He diameter of the capillary stream 7 is substantially smaller than the characteristic length of the electrified meniscus 6 from which it emanates. Due to varicose instabilities, jet 7 breaks into a 8 drops charged hydrosol, with significantly average sizes uniforms, in a range that varies between 500 microns and 15 nanometers

The feeding tip 1 of the device must have a diameter between 0.01 mm and 5 mm.

The feed rate of the flowing liquid 2 by the feeding tip 1 is between 10-15 m 3 / s and 10-7 m 3 / s.

When the distance between the tip of supply 1 and reference electrode 4 is comprised between 0.01 mm and 50 cm, the applied electrical potential must be between 10V and 100KV.

Thus, the device object of the invention consists of from:

a) a feeding tip 1 through which it flows a flow rate Q of a liquid 2 and connected to an electrical potential V.

b) A liquid bath 5 arranged in such a way that the feeding tip 1 is surrounded by the liquid 5 and the potential V is a differential value with respect to an electrode 4, also immersed in liquid 5, and connected to a source of potential 3. Liquids 2 and 5 are immiscible or poorly miscible. At the outlet of the feeding tip 1 a electrically capillary meniscus of substantially conical shape 6 and of its apex emits a stationary capillary jet 7 of liquid 2, so that liquid 5 completely surrounds liquid 2. Said capillary jet 7 has a diameter between 500 microns and 15 nanometers that is smaller than the characteristic diameter of the electrified liquid meniscus 6 from which it emanates.

The object of the present invention is hydrosol 8 formed spontaneously by the rupture of the hair jet stationary 7 that is formed using the device and mentioned procedure.

Finally, it is also the subject of this invention the procedure described for the generation of jets e hydrosols when instead of a solid conductor 4 a conductive liquid, for example mercury, located in the part Bottom of the bathroom and grounded.

A possible configuration for operation continuously shown in Figure 2 where the dielectric bath 5 is continually renewed by evacuating an appropriate flow rate by the pump 14 to an outer tank 11 where the emulsion 16. The same flow rate of purified dielectric liquid 5 is pumped from another tank 10, by pump 15, to bath 9.

Example 1

The basic device used in this example It consists of: (1) a means for supplying a first liquid 2 consisting of a metal tube 1 of 0.8 mm outside diameter and 0.4 mm inside diameter. In this example, liquid 2 was a DuPont photo-polymer, called SOMOS 6120; (2) a vessel 9 to contain a volume of a second liquid 5, immiscible with liquid 2, and of low electrical conductivity; in This case heptane has been used. The end of tube 1 is immersed in liquid 5; (3) a reference electrode 4, such as a metal plate or ring, located opposite the end of 1 e immersed in the liquid 5. The end of 1 and the electrode of reference 4 was 1 cm away; (4) a high voltage source 3, with one of the poles connected to 1 and the other connected to the electrode of reference 4. The potential difference applied was in this case of 2 KV.

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For illustrative purposes, Table I gives values experimental current intensity carried by the jet as a function of ejected flow.

TABLE I

Q (m 3 / s) 1.1 x10 <-1> 2.7x10 <-1> 5.4x10 <-1> 1.4x10 <-1> 2.7x10 <10> 4.2x10 <10> 5.4x10 <10> I (nA) 5.3 8.5 10 14.8 twenty-one 25 28.7

These data are collected in Figure 3 where represents the emitted current on the ordinate axis and on the abscissa, the square root of the values of the dispersed flow. The experimental data so represented follow very roughly the experimental law I \ simQ ^ 1/2, which is common to all electrospray in stationary jet-cone mode. To the As in electrosprays in a gaseous or empty atmosphere, our experiments in dielectric liquid atmospheres indicate that the obtaining the cone-jet mode requires  operate with flows between two values. Lower one, which corresponds to the minimum ejectable from one liquid tip and another higher that is fixed by the maximum load density compatible with the existence of a stationary jet.

Claims (12)

1. Device for producing electrosprays of conductive liquids within dielectric liquids characterized in that the device consists of a feed tip through which a flow Q of a conductive liquid flows 2. The feed tip, immersed in a dielectric liquid 5, it is connected to an electrical potential V with respect to a reference electrode immersed in the dielectric liquid 5, immiscible or poorly miscible with the conductive liquid 2. For appropriate values of Q and V a capillary meniscus is formed at the outlet of the feeding tip electrified with a substantially conical shape and whose apex emits a stationary micro / nano jet and such that said micro / nano capillary jet has a diameter between 500 microns and 15 nanometers that is substantially smaller than the characteristic length of the electrified liquid meniscus of the which emanates 2. Device for producing electrosprays of conductive liquids within dielectric liquids according to claim 1, characterized in that the feeding tip has a diameter between 0.01 mm and 5 mm. 3. Device for producing electrosprays of conductive liquids within dielectric liquids according to claim 2, characterized in that the feed rate Q flowing through the feed tip is between 10-15 m3 / s 10-7 m3 / s. 4. Device for producing electrosprays of conductive liquids within dielectric liquids according to claim 3, characterized in that for a distance between the supply tip and the reference electrode between 0.01 mm and 50 cm, the applied electrical potential V It is between 10V and 100KV. 5. Devices for producing electrosprays of conductive liquids within dielectric liquids according to any of claims 1 to 4, characterized in that the reference electrode is a conductive liquid immiscible with the dielectric liquid 5 and with the dispersed liquid 2. 6. Device for producing multicomponent emulsions of conductive liquids within dielectric liquids characterized in that the device consists of at least 2 feeding tips through which flows Qi of at least 2 immiscible conductive liquids flow into each other. The supply tips, immersed in a dielectric liquid 5 immiscible in turn with the conductive liquids, are connected to potential Vi with respect to a reference electrode immersed in the immiscible liquid. For appropriate values of Qi and Vi, at the exit of each feeding tip a conical meniscus is formed from whose apex a jet that breaks into drops is emitted giving rise to the multi-component emulsion. 7. Device for producing multicomponent emulsions of conductive liquids within dielectric liquids according to claim 6 characterized in that the feeding tips have diameters between 0.01 mm and 5 mm. 8. Device for producing multicomponent emulsions of conductive liquids within dielectric liquids according to claim 7, characterized in that the flow rates Qi flowing through the feed tips are comprised between 10-15 m3 / s and 10-7 m3 / s. 9. Device for producing multicomponent emulsions of conductive liquids within dielectric liquids according to claim 8, characterized in that for distances between the supply tips and the reference electrode between 0.01 mm and 50 cm, the applied electric potential Vi It is between 10 V and 100 KV. 10. Device for producing multicomponent emulsions of conductive liquids within dielectric liquids according to any of claims 6 to 9, characterized in that the reference electrode is a conductive liquid immiscible with the dielectric liquid 5 and with the dispersed conductive liquids. 11. Method for producing electrosprays of conductive liquids within dielectric liquids according to any of claims 1 to 5 characterized by flowing a flow Q of a conductive liquid 2 through the feed tip, immersed in the dielectric liquid 5 immiscible with the conductive liquid 2 and connected to a potential V with respect to a reference electrode, and an electrified capillary meniscus having a substantially conical shape and whose apex emits a stationary micro / nano capillary liquid jet is emitted at the outlet of the feed tip conductor 2, such that the dielectric liquid 5 completely surrounds the conductive liquid and such that said capillary stream has a diameter between 500 microns and 15 nanometers that is smaller than the characteristic diameter of the electrified liquid meniscus from which it emanates, spontaneously producing the rupture of the micro / nano jet leading to the formation of p articles of the conductive liquid of size between 500 microns and 15 nanometers. 12. Method for producing multicomponent emulsions of conductive liquids within dielectric liquids according to any of claims 6 to 10 characterized by flowing Qi flows of conductive liquids through at least 2 feed points, immersed in the dielectric liquid immiscible with conductive liquids and connected to a potential Vi with respect to a reference electrode, obtaining at the exit of each feeding tip an electrified capillary meniscus with a substantially conical shape and from whose apex a stationary micro / nano capillary jet is emitted from each of the conductive liquids, such that the dielectric liquid 5 completely surrounds the conductive liquids and such that said capillary jets have a diameter between 500 microns and 15 nanometers that is smaller than the characteristic diameter of the electrified liquid meniscus from which it emanates, producing spontaneously a stream that It is broken into drops giving rise to the multi-component emulsion.