Method and electro-fluidic device to produce emulsions and particle suspensions

Abstract

The invention refers to a method, and to a device to produce emulsions and particle suspensions by using electro-hydrodinamic forces and microfluidics This combined use allow the production of droplets with mean diameters which may be either smaller than those obtained in conventional microfluidic devices or larger than those obtained by electrospray, bridging the gap between the two methods acting independently.

Claims

1. A system comprising: a micro-channel having a central axis along its length; a pump for pumping a dielectric fluid in a first flow direction within the micro-channel; a first capillary tip located within the micro-channel and extending along the central axis of the micro-channel for a portion of the length of the micro-channel; a pump for pumping a first conducting fluid in the first flow direction within the first capillary tip; a second capillary tip located downstream in the first flow direction from the first capillary tip, the second capillary tip located within the micro-channel and extending along the central axis of the micro-channel for a portion of the length of the micro-channel; an annular gap extending the length of the second capillary defined by the difference between the diameters of the micro-channel and the second capillary tip; a pump for pumping a second conducting fluid in a second flow direction within the second capillary tip; and an electrical potential generator; wherein the dielectric fluid is immiscible or poorly miscible with the conducting fluids; wherein the second flow direction of the second conducting fluid flows counter with respect to the first flow direction of the dielectric fluid; wherein upon flow of the dielectric, first and second fluids a steady state interface is formed separating the dielectric fluid and the first conducting fluid; wherein upon flow of the dielectric, first and second fluids, when an electrical potential difference is applied by the electrical potential generator to the first capillary tip and the second capillary tip, a steady state capillary jet is formed, producing a stream of charged droplets which move towards the steady state interface under the combined action of the electric and hydrodynamic forces; and wherein once the droplets reach the steady state interface they discharge and form an emulsion that leaves through the annular gap.

2. The system according to claim 1, wherein upon flow of the dielectric, first and second fluids, the steady state interface is located in between the first and second capillary tips.

3. The system according to claim 1, wherein the system comprises: a number N of feeding tips with (N≧2), wherein one of the feeding tips is the first capillary tip; and N pumps, one each for each feeding tip, for pumping conducting fluid in the first flow direction within each of the N feeding tips, wherein one of the pumps is the pump for pumping the first conducting fluid, being an inner conducting fluid, in the first flow direction within the first capillary tip; wherein upon flow of the dielectric, first and second fluids, in the first capillary tip flows the inner conducting fluid at a flow rate Q.sub.1 whilst a generic conducting fluid Li-th flows at a generic flow rate Q.sub.i through the Ti-th tip (2≦i≦N); and wherein upon flow of the dielectric, first and second fluids, the N feeding tips are arranged such that the L(i−1)-th conducting fluid surrounds the Ti-th tip and the tips, that are immersed in the dielectric fluid, which is flowing at a rate Q.sub.D.

4. The system according to claim 1, wherein the diameters of the capillary tips are between 0.001 mm and 5 mm.

5. The system according to claim 1, wherein upon flow of the dielectric, first and second fluids, the first conducting fluid flows at a flow rate of Q.sub.1 in the first capillary tip, and the second conducting fluid flows at a flow rate of Q.sub.2 in the second capillary tip; wherein upon flow of the dielectric, first and second fluids, the flow rate Q.sub.1-Q.sub.2 is between 10.sup.−15 m.sup.3/s and 10.sup.−7 m.sup.3/s; and wherein upon flow of the dielectric, first and second fluids, the flow rate Q.sub.D of the dielectric fluid and the flow rate Q.sub.1 of the first conducting fluid are both between 0 and 10.sup.−1 m.sup.3/s.

6. The system according to claim 1, wherein upon flow of the dielectric, first and second fluids, the dielectric conductivity of the first and second conducting fluids is between 10.sup.−12 and 10.sup.6 S/m.

7. The system according to claim 1, wherein upon flow of the dielectric, first and second fluids, the absolute value of the electric potential difference is between 1 V and 100 kV for obtaining a separation between the first capillary tip and the steady state interface of between 0.001 mm and 10 cm.

8. The system according to claim 1, wherein upon flow of the dielectric, first and second fluids, the first capillary tip is immersed in the dielectric fluid located close to the steady state interface, the dielectric fluid having a flow rate Q.sub.D; wherein the second capillary tip is located inside the first capillary tip and immersed in the dielectric fluid, such that upon flow of the dielectric, first and second fluids, the second conducting fluid flows through the second capillary against the dielectric fluid at a rate Q.sub.C, such that the steady state interface separating the dielectric fluid and the second conducting fluid is formed somewhere inside the first capillary tip; wherein upon flow of the dielectric, first and second fluids, the first conducting fluid forms a steady capillary jet when conducting fluids are connected to a reference electrode; wherein upon flow of the dielectric, first and second fluids, the spontaneous breakup of the capillary jet produces droplets of the first conducting fluid which move towards the fluid interface under the combined action of electric forces and drag exerted by the moving dielectric fluid; and wherein upon flow of the dielectric, first and second fluids, the droplets release most of their electrical charge upon reaching the steady state interface, then exit the device through the annular gap.

9. An electro-fluidic method to produce emulsions and particle suspensions comprising: immersion of a capillary in a dielectric fluid that flows along a micro-channel; said dielectric fluid being immiscible or poorly miscible with a first conducting fluid and a second conducting fluid; and wherein said second conducting fluid flows through a second capillary immersed in the dielectric fluid, an annular gap extending the length of the second capillary defined by the difference between the diameters of the micro-channel and the second capillary tip; pumping counter-flow said second conducting fluid with respect to the dielectric fluid and forming a steady state interface; and applying an appropriate electrical potential difference to said conducting fluids, producing a stream of charged droplets which move towards the steady state interface under the combined action of the electric and hydrodynamic forces; wherein once the charged droplets reach the steady state interface they give up their charge and form a neutral emulsion that leaves through the annular gap.

10. The method according to claim 9 further comprising: immersion of a number N of feeding tips (N≧1) in the first conducting fluid, such that a generic conducting fluid Li-th co-flows with the first conducting fluid at a flow rate Q.sub.i through the Ti-th tip (1≦i≦N); and arranging the feeding tips such that L(i−1)-th conducting fluid surrounds the Ti-th tip.

11. The method according to claim 10, wherein the diameters of the first and second capillary tips and the N feeding capillary tips are between 0.001 mm and 5 mm.

12. The method according to claim 10, wherein the flow rate Q.sub.i-th of the fluid Li-th conducting fluid flowing through the feeding tip Ti-th is in the range between 10.sup.−15 m.sup.3/s and 10.sup.−7 m.sup.3/s; and wherein the flow rate Q.sub.D of the dielectric fluid and the flow rate Q.sub.C of the second conducting fluid are both between 0 and 10.sup.−1 m.sup.3/s.

13. The method according to claim 9, wherein the dielectric conductivity of the first and second conducting fluids is between 10.sup.−12 and 10.sup.6 S/m.

14. The method according to claim 9 further comprising obtaining a separation between the first capillary tip and the steady state interface of between 0.001 mm and 10 cm; wherein the absolute value of the electric potential difference is between 1 V and 100 kV.

15. An electro-fluidic method to produce emulsions and particle suspensions comprising: immersion of a first capillary tip in a dielectric fluid that flows along a micro-channel in a first flow direction, wherein the dielectric fluid is immiscible or poorly miscible with a first conducting fluid and a second conducting fluid; injecting in a second flow direction the second conducting fluid through a second capillary tip and forming a steady state interface, the second capillary tip immersed in the dielectric fluid and located downstream in the first flow direction from the first capillary tip, wherein the second flow direction of the second conducting fluid flows counter with respect to the first flow direction of the dielectric fluid, an annular gap extending the length of the second capillary defined by the difference between the diameters of the micro-channel and the second capillary tip; and applying an electrical potential difference to the first and second conducting fluids, producing charged droplets that move towards the steady state interface under the combined action of the electric and hydrodynamic forces; wherein once the charged droplets reach the steady state interface, they give up their charge and form a neutral emulsion that travel through the annular gap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Shows a picture depicting the (A) dripping mode; and (B) the jetting mode described in the prior art.

(2) FIG. 2. Shows a picture depicting the selective withdrawal as it is described in the prior art.

(3) FIG. 3. Shows a picture depicting the flow focusing, as it is described in the prior art.

(4) FIG. 4. Shows a picture depicting whipping instability of an electrified jet of glycerin in a bath of hexane, as it is described in the prior art.

(5) FIG. 5. Shows a schematic view of a device for generating double emulsions from coaxial jets, as it is described in the prior art.

(6) FIG. 6. Shows a picture depicting (A) a compound Taylor cone; and (B) a detail of coaxial jet, as it is described in the prior art.

(7) FIG. 7. Shows a schematic view of the micro-fluidic device to produce emulsions and particle suspensions, object of the present invention, in its first embodiment.

(8) FIG. 8. Shows a schematic of a micro-fluidic device for the steady generation of emulsions under the simultaneous combined action of electric and hydrodynamic forces, object of the present invention in its second embodiment.

(9) FIG. 9. Shows a schematic of a third embodiment of a micro-fluidic device for the steady generation of emulsions under the simultaneous combined action of electric and hydrodynamic forces.

(10) FIG. 10. Shows a schematic of a fourth embodiment of a micro-fluidic device for the steady generation of emulsions under the simultaneous combined action of electric and hydrodynamic forces, object of the present invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(11) As can be shown in the attached figures, the invention consists on an electro-fluidic device to produce emulsions and particle suspensions comprising a capillary (1,1′,101,101′) immersed in a dielectric fluid (2,102) that flows along a micro-channel (3,103); said dielectric fluid (2,102) being immiscible or poorly miscible with a first conducting fluid (8,8′,108,108′) and a second conducting fluid (5,105,105′); wherein said second conducting fluid flows through a second capillary (4,104,104′) immersed in the dielectric fluid (1,102); said device characterized in that said second conducting fluid (5,105,105′) is pumped counter-flow with respect to the dielectric fluid (2,102) and a steady state interface (6,6′,106,106′,116,116′) is formed; and wherein a steady capillary jet is formed when an appropriate electrical potential difference (9,109) is applied to said conducting fluids, producing a stream of charged droplets (11,111) which move towards the steady state interface (6,6′,116,116′) under the combined action of the electric and hydrodynamic forces; and wherein once the droplets (11,111) reach the steady state interface (6,6′,116,116′) they discharge and form an emulsion that leaves through a gap (7,107).

(12) In a second aspect of the invention, the method to produce emulsions and particle suspensions, characterized in that it comprises the steps of: (i) immersion of a capillary (1,1′,101,101′) in a dielectric fluid (2,102) that flows along a micro-channel (3,103); said dielectric fluid (2,102) being immiscible or poorly miscible with a first conducting fluid (8,8′,108,108′) and a second conducting fluid (5,105,105′); and wherein said second conducting fluid flows through a second capillary (4,104,104′) immersed in the dielectric fluid (1,102); (ii) pumping counter-flow said second conducting fluid (5,105,105′) with respect to the dielectric fluid (2,102) and forming a steady state interface (6,6′,106,106′,116,116′); and (iii) applying an appropriate electrical potential difference (9,109) to said conducting fluids, producing a stream of charged droplets (11,111) which move towards the steady state interface (6,6′,116,116′) under the combined action of the electric and hydrodynamic forces; and wherein once the droplets (11,111) reach the steady state interface (6,6′,116,116′) they discharge and form an emulsion that leaves through a gap (7,107).

(13) Finally in other aspect of the invention, the system to produce emulsions and particle suspensions comprises the aforementioned device or means to perform the above described method.

(14) If the liquid forming the micro or nano-droplets carries material or species that may become solid upon a suitable stimulus (i.e. polymerization, phase transition, etc.), then a suspension may be formed.

(15) More concretely, in a first embodiment of the invention, as can be shown in FIG. 7, the electro-fluidic device to produce emulsions and particle suspensions, object of the present invention comprises a first feeding tip (the first capillary tip 1) such that, through the first feeding tip 1 flows an inner conducting liquid 8 at a flow rate Q.sub.1. Said first feeding tip 1 is immersed in a dielectric liquid 2 immiscible or poorly miscible with said inner conducting liquid 8 at a rate Q.sub.D. On the other hand, the device also comprises a second feeding capillary tip 4 located in front of the first feeding tip 1 and immersed in the dielectric liquid 2, such that a conducting liquid or liquid collector 5, immiscible or poorly miscible with the dielectric liquid 2 counter-flows through the second feeding capillary tip 4 against the dielectric liquid 2 at a rate Q.sub.C, such that a steady state interface 6 separating the dielectric liquid 2 and the inner conducting liquid 8 is formed somewhere in between the first and second capillary tips (1,4).

(16) The inner conducting liquid 8 forms an electrified capillary meniscus 10 of the inner conducting liquid 8 at the exit of the first feeding tip 1 whenever the first and second capillary tips (1,4) are both connected respectively to potential V.sub.1 and V.sub.C with respect to a reference electrode.

(17) A steady state capillary jet of inner conducting liquid 8 issues from the first capillary tip 1, such that its diameter, which can be smaller, comparable or larger than the characteristic diameter of the first capillary tip 1 has a value comprised between 10 nanometers and 100 microns. The spontaneous breakup of the capillary jet produces droplets 11 of the inner conducting liquid 8 which move towards the steady state interface 6 under the combined action of electric forces and the drag exerted by the moving dielectric liquid 2. The droplets 11 release most of their electrical charge upon reaching the steady state interface 6, then being dragged out of the device by the motion of the dielectric liquid 2 and the conducting liquid 5.

(18) The diameter of the first and second capillary tips (1,4) are preferably comprised between 0.001 mm and 5 mm in the present embodiment.

(19) The flow rate Q.sub.1 between the inner conducting liquid 8 and the first capillary feeding tip 1 is preferably comprised between 10.sup.−15 m.sup.3/s and 10.sup.−7 m.sup.3/s. Otherwise, the flow rate Q.sub.D of the dielectric liquid 2 and the flow rate Q.sub.C of the conducting fluid 5 have respectively a value between 0 and 10.sup.−1 m.sup.3/s.

(20) Also, in this embodiment of the invention, the dielectric conductivity of the inner conducting liquid 8 and the conducting liquid 5 varies between 10.sup.−12 and 10.sup.6 S/m.

(21) In this embodiment, for obtaining a separation between the first feeding tip 1 and the steady state interface 6 of a value between 0.001 mm and 10 cm, the absolute value of the electric potential difference (V.sub.1−V.sub.C) has to be comprised between 1 V and 100 kV.

(22) In this first embodiment, the dielectric liquid 2 can be substituted by a gas. Finally, the inner conducting liquid 8 is such that the droplets 11 can be post-processed to become solid.

(23) In a second embodiment of the invention, as can be shown in FIG. 8, the device comprises of a number N of feeding tips (1,1′) with (N≧2). In this embodiment, the first capillary tip 1 flows an inner conducting liquid 8 at a flow rate Q.sub.1 whilst a generic conducting liquid Li-th flows at a generic flow rate Q.sub.i through the Ti-th tip (2≦i≦N); in FIG. 8, the inner conducting liquid 8′ flows through the capillary tip 1′ at a flow rate Q.sub.1′ for N=2; and wherein the N feeding tips (1,1′) are arranged such that the L(i−1)-th conducting fluid surrounds the Ti-th tip and the tips (1,1′), that are immersed in a dielectric liquid 2 immiscible or poorly miscible with said inner conducting liquid 8, which is co-flowing with said conducting liquid 8 at a rate Q.sub.D.

(24) On the other hand, the device also comprises a second feeding capillary tip 4 located in front of the first feeding tip 1 and immersed in the dielectric liquid 2, such that a conducting liquid or liquid collector 5, immiscible or poorly miscible with the dielectric liquid 2 counter-flows through the second feeding capillary tip 4 against the dielectric liquid 2 at a rate Q.sub.C, such that a steady state interface 6′ separating the dielectric liquid 2 and the inner conducting liquid (8,8′) is formed somewhere in between the first and second capillary tips (1,4).

(25) Each of the N inner conducting liquids Li-th forms a meniscus (10,10′) at the exit of its respective feeding tip (1,1′) whenever the second capillary tip 4 and each Ti-th feeding tips are respectively connected to electrical potentials V.sub.C and V.sub.i-th with respect to a reference electrode 9.

(26) A steady state compound jet, such that the liquid L(i−1)-th surrounds the Li-th one, is formed from the N jets that issue from each of the N feeding tips and such that the diameter of the compound capillary jet has a value between 10 nanometers and 100 microns. The spontaneous breakup of the compound capillary jet produces compound droplets 11 with N layers such that the L(i−1)-th liquid surrounding the Li-th one, which move under the combined action of electric forces and the drag exerted by the moving dielectric liquid 2 towards the steady state interface 6′ where the compound droplets release most of their charge, then being dragged out of the device by the motion of the dielectric liquid 2 and the conducting liquid 5.

(27) In the second embodiment, the diameter of the first feeding capillary tip 1 and the N feeding capillary tips 1′ are preferably comprised between 0.001 mm and 5 mm.

(28) The flow rate Q.sub.i-th of the liquid Li-th flowing through the feeding tip Ti-th is preferably comprised between 10.sup.−15 m.sup.3/s and 10.sup.−7 m.sup.3/s. Otherwise, the flow rate Q.sub.D of the dielectric liquid 2 and the flow rate Q.sub.C of the conducting fluid 5 have respectively a value between 0 and 10.sup.−1 m.sup.3/s.

(29) Also, in this embodiment of the invention, the dielectric conductivity of the inner conducting liquid (8,8′) and the conducting liquid 5 varies between 10.sup.−12 and 10.sup.6 S/m.

(30) In the second embodiment, for obtaining a separation between the first feeding tip 1 and the steady state interface (6,6′) of a value between 0.001 mm and 10 cm, the absolute value of the electric potential difference 9 (V.sub.1−V.sub.C) has to be comprised between 1 V and 100 kV.

(31) In the second embodiment, the dielectric liquid 2 can be substituted by a gas. Similarly, at least one of the Li-th liquids (2≦i≦N) could be substituted by a gas. Finally, the inner nature of Li-th liquids is such that the droplets 11 can be post-processed to become solid.

(32) In a third embodiment of the invention, showed in FIG. 9, the device object of the invention comprises a first conducting liquid 108 flowing at a rate Q.sub.0 and a dielectric liquid 102 that flows along a micro-channel 103, immiscible or poorly miscible with the first conducting liquid 108, which is flowing against liquid 108 at a flow rate Q.sub.D such that a steady state interface 106 separating conducting liquid 108 and dielectric liquid 102 is formed.

(33) A capillary 101 immersed in dielectric liquid 102 is located close to the steady state interface 106, sucks a flow rate Q.sub.D of dielectric liquid 102. Otherwise, a feeding capillary 104 is located inside capillary 101 and immersed in dielectric liquid 102, such that a conducting liquid 105, immiscible or poorly miscible with dielectric liquid 102, flows through the feeding capillary 104 against dielectric liquid 102 at a rate Q.sub.C, such that a steady state interface 116 separating dielectric fluid 102 and conducting fluid 105 is formed somewhere inside capillary 101.

(34) The first conducting liquid 108 forms a steady capillary jet when conducting liquids 108 and 105 are connected respectively to electrical potentials V.sub.0 and V.sub.C with respect to a reference electrode 109, such that the flow rates of liquids 108, 102 and 105 flowing through the gap 107 between capillaries 101 and 104 are Q.sub.0, Q.sub.D and Q.sub.C, respectively, such that the diameter of the jet has a value between 10 nanometers and 100 microns.

(35) The spontaneous breakup of the capillary jet produces droplets 111 of liquid 108 which move towards the liquid interface 116 under the combined action of electric forces and the drag exerted by the moving dielectric liquid 102 being. The droplets 111 release most of their electrical charge upon reaching interface 116, then being dragged out of the device by the motion of liquids 102 and 105.

(36) The diameter of the capillaries 101 and 104 are preferably comprised between 0.001 mm and mm in this fourth embodiment.

(37) The flow rate of the liquid 108 is preferably comprised between 10.sup.−15 m.sup.3/s and 10.sup.−7 m.sup.3/s. Otherwise, the flow rate Q.sub.D of the dielectric liquid 102 and the flow rate Q.sub.C of the liquid 105 have respectively a value between 0 and 10.sup.−1 m.sup.3/s.

(38) Also, in this third embodiment of the invention, the dielectric conductivity of the liquids 108 and 105 varies between 10.sup.−12 and 10.sup.6 S/m.

(39) In this third embodiment, for obtaining a separation between interfaces 106 and 106′ of a value between 0.001 mm and 10 cm, the absolute value of the electric potential difference 109 (V.sub.0−V.sub.0) has to be comprised between 1 V and 100 kV.

(40) In this third embodiment, the dielectric liquid 102 can be substituted by a gas. Finally, the liquid 108 is such that the droplets can be post-processed to become solid.

(41) The fourth embodiment of the invention, that can be shown in FIG. 10, comprises a conducting liquid 108′ flowing at a flow rate Q.sub.0 and a dielectric liquid 102, immiscible or poorly miscible with liquid 108′, which is flowing against liquid 108′ at a flow rate Q.sub.D such that a steady state interface 106′ separating liquids 108′ and 102 is formed.

(42) A number N of feeding tips (N≧1), such that a Li-th liquid 108″ co-flows with liquid 108′ at a flow rate Q.sub.i through the Ti-th tip (1≦i≦N) and the feeding tips are arranged such that the L(i−1)-th liquid (108″,108′″) surrounds the Ti-th tip and the tips are immersed in liquid 108′.

(43) A capillary 101′ is immersed in liquid 102, located close to the interface 106′, sucks a flow rate Q.sub.D of dielectric liquid 102. Otherwise, a feeding capillary 104′ is located inside capillary 101′ and immersed in liquid 102, such that a conducting liquid 105′, immiscible or poorly miscible with liquid 102, flows through 104′ against liquid 102 at a rate Q.sub.C, such that a steady state interface 116′ separating fluids 102 and 105′ is formed somewhere inside capillary 101′.

(44) A steady compound capillary jet of conducting liquids (108′,108″, 108′″), such that liquid L(i−1)-th surrounds liquid Li-th, forms when liquids 108′ and 105′ are connected respectively to electrical potentials V.sub.0 and V.sub.C with respect to a reference electrode 109, such that the flow rates of liquid Li-th (0≦i≦N), 102 and 105′ flowing through the gap between capillaries 101′ and 104′ are Q.sub.i, Q.sub.D and Q.sub.C, respectively, such that the diameter of the jet has a value between 10 nanometers and 100 microns.

(45) The spontaneous breakup of the compound jet produces compound droplets 111′ with N layers such that the L(i−1)-th liquid surrounding the Li-th one, which move towards the liquid interface 116′ under the combined action of electric forces and the drag exerted by the moving dielectric liquid 102. The compound droplets 111′ release most of their electrical charge upon reaching interface 116′, then being dragged out of the device by the motion of liquids 102 and 105′.

(46) In fourth embodiment, the diameter of the 101′, 104′ and the N feeding capillary tips are preferably comprised between 0.001 mm and 5 mm.

(47) The flow rate Q.sub.i-th of the liquid Li-th flowing through the feeding tip Ti-th and the liquid 108′ is preferably comprised between 10.sup.−15 m.sup.3/s and 10.sup.−7 m.sup.3/s. Otherwise, the flow rate Q.sub.D of the dielectric liquid 102 and the flow rate Q.sub.C of the fluid 105′ have respectively a value between 0 and 10.sup.−1 m.sup.3/s.

(48) Also, in these embodiments of the invention, the dielectric conductivity of the liquids 108′ and 105′ varies between 10.sup.−12 and 10.sup.6 S/m.

(49) In these embodiments, for obtaining a separation between interfaces 106′ and 116′ of a value between 0.001 mm and 10 cm, the absolute value of the electric potential difference 109 (V.sub.0−V.sub.C) has to be comprised between 1 V and 100 kV.

(50) In these embodiments, the dielectric liquid D can be substituted by a gas. Similarly, at least one of the Li-th liquids (1≦i≦N) could be substituted by a gas. Finally, the nature of liquids Li-th is such that the droplets 111 can be post-processed to become solid.