MICRO-FLUIDIC SYSTEM AND METHOD

Abstract

A micro-fluidic system, comprising at least one first nozzle (10) that releases at least one liquid jet (15) of a first liquid into a gaseous atmosphere and a second nozzle (20) that releases a liquid film jet (25) of a second liquid in said gaseous atmosphere. Said first jet (15) is directed to be incident of said liquid film (25) at an interaction area (50). Collecting means (40) are provided for receiving an interaction product (55) of said first and second liquid downstream of said interaction area. Support means (30) are provided, having a support surface (35) that receives and supports said liquid film (25) of said second liquid from said second nozzle (20). Said support surface (35) carries said liquid film to said interaction area (55) and said interaction area (55) is supported by said support surface (35).

Claims

1. A micro-fluidic system, comprising first supply means, feeding a first liquid to an interaction area, and second supply means, feeding a second liquid to said interaction area, said first liquid and said second liquid being different to one another and engaging into an interaction with one another within said interaction area, wherein said first supply means release at least one liquid jet of said first liquid into a gaseous atmosphere upstream of said interaction area, wherein said second supply means release a liquid flow of said second liquid upstream of said interaction area, wherein collecting means are provided downstream of said interaction area, wherein said second supply means comprise support means having a support surface that extends at least to below said interaction area where said at least one liquid jet of said first liquid is received in said liquid flow of said second liquid, and wherein said support surface is configured to receive and support said liquid flow of said second liquid released by said second supply means and to carry said second liquid to said interaction area, wherein said support means comprise a support body that provides said support surface, wherein said support body is coupled to drive means that subject said support surface to a movement, and wherein said drive means are controllable allowing to adjust a velocity of said surface to at least one of a velocity of said flow of said second liquid and a velocity of impact of said jet of said first liquid.

2. The micro-fluidic system according to claim 1, wherein said movement of said support surface is effected by a lateral movement of said support body parallel to said liquid film, more particularly to a reciprocal movement of said support body.

3. The micro-fluidic system according to claim 1, wherein said movement of said support surface is effected by a rotation of said support body.

4. The micro-fluidic system according to claim 3, wherein said support body is a continuous belt, a cylinder, a cone or a sphere.

5. A micro-fluidic system, comprising first supply means, feeding a first liquid to an interaction area, and second supply means, feeding a second liquid to said interaction area, said first liquid and said second liquid being different to one another and engaging into an interaction with one another within said interaction area, wherein said first supply means release at least one liquid jet of said first liquid into a gaseous atmosphere upstream of said interaction area, wherein said second supply means release a liquid flow of said second liquid upstream of said interaction area, wherein collecting means are provided downstream of said interaction area, wherein said second supply means comprise support means having a support surface that extends at least to below said interaction area where said at least one liquid jet of said first liquid is received in said liquid flow of said second liquid, and wherein said support surface is configured to receive and support said liquid flow of said second liquid released by said second supply means and to carry said second liquid to said interaction area, wherein said support means comprise a support layer that provides said support surface at a first side, wherein said support layer is permeable to an auxiliary fluid, particularly an auxiliary gas, and wherein support layer is provided with supply means that feed said auxiliary fluid trough said support layer from an opposite side across from said first side featuring said support surface.

6. A micro-fluidic system, comprising first supply means, feeding a first liquid to an interaction area, and second supply means, feeding a second liquid to said interaction area, said first liquid and said second liquid being different to one another and engaging into an interaction with one another within said interaction area, wherein said first supply means release at least one liquid jet of said first liquid into a gaseous atmosphere upstream of said interaction area, wherein said second supply means release a liquid flow of said second liquid upstream of said interaction area, wherein collecting means are provided downstream of said interaction area, wherein said second supply means comprise support means having a support surface that extends at least to below said interaction area where said at least one liquid jet of said first liquid is received in said liquid flow of said second liquid, and wherein said support surface is configured to receive and support said liquid flow of said second liquid released by said second supply means and to carry said second liquid to said interaction area, wherein said support means comprise a cylindrical or spherical support body providing said support surface, having a curvature, at a cylindrical or spherical surface thereof.

7. The micro-fluidic system according to claim 1, wherein said support means comprise a support body having a substantially planar main surface, wherein said support body comprises said support surface at said main surface.

8. The micro-fluidic system according to claim 1, wherein said support body comprises at least one recessed channel at said main surface, receiving said liquid flow of said second liquid, said channel having a bottom that provides said support surface.

9. The micro-fluidic system according to claim 8, wherein said channel is formed in a substantially straight gutter between opposite side walls or ridges that confine said support surface on either side of said channel.

10. The micro-fluidic system according to claim 1, wherein said support surface has a micro-profile or micro-texture.

11. The micro-fluidic system according to claim 1, wherein said first supply means comprise a first nozzle that releases at least one liquid jet, and particularly a number of liquid jets, of said first liquid into said gaseous atmosphere, being directed to said interaction area.

12. The micro-fluidic system according to claim 1, wherein said first supply means comprise a plurality of first nozzles that release a plurality of liquid jets of said first liquid, particularly mutually at least substantially parallel liquid jets, into said gaseous atmosphere, being directed to said interaction area.

13. The micro-fluidic system according to claim 1, wherein said first supply means are adjustable to release said at least one first liquid jet in a propagation direction towards said support surface at an inclined jet angle that may be set between zero and 75 degrees, particularly between 0 and 60 degrees.

14. The micro-fluidic system according to claim 1, wherein said second supply means release said liquid flow to form a liquid film onto said support surface.

15. The micro-fluidic system according to claim 1, wherein said liquid flow comprises a liquid film that has a width that is wider than a multiple of a width of said at least one liquid jet.

16. The micro-fluidic system according to claim 1, wherein said support body is provided with temperature control means that provide a temperature controlled support surface.

17. The micro-fluidic system according to claim 1, wherein said support means comprise a support layer that provides said support surface and that is permeable to an auxiliary fluid, particularly an auxiliary gas, and wherein support layer is provided with supply means that feed said auxiliary fluid trough said support layer from a side across from said support surface.

18. The micro-fluidic system according to claim 5, wherein said support means comprise a support body, providing said support surface, that is coupled to drive means that subject said support surface to a movement, particularly a lateral movement parallel to said liquid film, more particularly to a reciprocal movement, even more particularly to a rotation.

19. The micro-fluidic system according to claim 1, wherein said support means comprise a cylindrical or spherical support body providing said support surface, having a curvature, at a cylindrical or spherical surface thereof.

20. A method of operating a micro-fluidic system according to claim 1, wherein said at least one liquid jet is released as a ray of consecutive, individual liquid droplets containing said first liquid, and wherein said second liquid is released on said support surface as a substantially continuous film of said second liquid.

21. The method according to claim 20, wherein said film of said second liquid is released with a substantially laminar flow of said second liquid, at least at an interface with said support surface.

22. The method according to claim 20, wherein said film of said second liquid is released with a controlled thickness on said support surface that exceeds a penetration depth of said liquid droplets in said interaction area.

23. The method according to claim 20, wherein said film of said second liquid is released with a controlled thickness on said support surface that undershoots an penetration depth of said liquid droplets at said interaction area.

24. The method according to claim 20, wherein said liquid film is released at an elevated initial velocity to reach a velocity exceeding gravitational terminal velocity and, particularly, initially exceeding gravitational terminal velocity.

25. The method according to claim 20, wherein said first liquid is released as a compound liquid jet, comprising composite liquid droplets of at least two different liquids that form a core of one liquid surrounded by a shell of the other liquid, respectively.

26. The method according to claim 20, wherein the first liquid and the second liquid comprise liquids having different surface tensions, particularly said second liquid having a lower surface tension than said first liquid.

27. The method according to claim 20, wherein the first liquid and the second liquid are, at least partly, immiscible and wherein an emulsion is formed out of the first and second liquid in or downstream of the interaction area.

28. The method according to claim 20, wherein the first liquid and the second liquid enter into a chemical reaction or physical interaction with one another to solidify into a suspension or dispersion at the interaction area.

29. The method according to claim 28, wherein said first liquid comprises at least one polymer, particularly a polysaccharide or protein, wherein an aqueous solution of a cross-linker and/or polyvalent metal salt is applied as said second liquid to form said liquid film on said support surface, and wherein said first liquid is allowed to cure upon a cross-linking reaction with said second liquid within said interaction area.

Description

[0037] The invention will hereinafter be described in further detail with reference to one or more exemplifying embodiments and an accompanying drawing. In the drawing:

[0038] FIG. 1 shows the basic setup of an example of an micro-fluidic system according to the invention;

[0039] FIG. 2A shows a cross section of a support body in a first alternative embodiment of a micro-fluidic system according to the invention; and

[0040] FIG. 2B shows a cross section of a support body in a second alternative embodiment of a micro-fluidic system according to the invention;

[0041] FIG. 3 shows a cross section of a support body in a third alternative embodiment of a micro-fluidic system according to the invention;

[0042] FIG. 4 shows a support body in a fourth alternative embodiment of a micro-fluidic system according to the invention; and

[0043] FIG. 5A-5C show photographic pictures of samples that were produced using a micro-fluidic system according to the invention.

[0044] Please note that the figures are purely schematic and not drawn to scale. Particularly certain dimensions may be exaggerated to greater or lesser extent in order to elucidate certain aspects of the invention. Like parts are generally designated by a same reference numeral throughout the drawing.

[0045] FIG. 1 is a schematic representation of a basic setup of a micro-fluidic system according to the invention. The system comprises a first nozzle 10 for releasing a liquid jet 15 of a first liquid. In this example this nozzle 10 is fed with a 0.5% (w/v) sodium alginate (Wako 80-120 Cp) solution is water at a flow rate of approximately 2.5 ml per minute. The nozzle has a diameter of 100 micron and is modulated at a frequency of 5 kHz by a vibrating element like an oscillator to release said liquid jet in the form of a droplet train of a series individual, consecutive alginate droplets, as shown in the figure. These droplets will have a substantially spherical shape of about 100 micron in diameter. Alternatively the liquid jet may be formed as a contiguous trail of liquid having a constant or regularly varying cross section, being modulated by a suitable modulating means connected to or integrated in the nozzle 10.

[0046] As shown in FIG. 1 the first nozzle 10 is provided with adjustment means 11 that allow to vary its orientation. Specifically a jet angle α of the emanating jet 15 may be set to a desired value between a lower and maximum value, for instance between 30 and 40 degrees, relative to a substrate surface 35 that will be described hereinafter. The nozzle may also be suspended to be displaceable laterally, being carried by appropriate displacement means. Also several first nozzles 10 may be placed next to one another to carry out the same or different processes according to the invention in parallel and to facilitate an upscaling of the process.

[0047] The system further comprises a second nozzle 20. Different to the first nozzle 10, this second nozzle 20 does not release an interrupted jet of droplets, but instead a continuous film 25. This film 25 is formed by a second liquid that is different from the first liquid. In this case said second liquid 25 comprises a 0.2 M calcium chloride solution in water to which 10% (w/v) ethanol is added. This solution is supplied to the second nozzle 20 at an inlet pressure of the order of 0.25 khPa and is released with an initial film width of the order of one to a few millimetre.

[0048] According to an aspect of the present invention the micro-fluidic provides a support body 30 having a support surface 35 that receives and support the film 25 that is released by said second nozzle 20. The support body 30 comprises a moving continuous belt, but may also be formed by a displaceable substrate of glass or a displaceable substrate of another solid material, like for instance a sheet of plastic. As shown in FIG. 1, the second nozzle 20 as well as the support body 30 are provided with adjustment means 22,33 that allow to adjust their respective orientation β, φ with respect to the horizon. This setup particularly allows to adjust their mutual angle such that thereby an angle of incidence β of the second film 25 onto said support surface 35 may be varied. Drive means (not shown) are provided that set said continuous belt or solid substrate in motion with a velocity V. These drive means allow to adjust a planar velocity V of said support surface at an interaction area where the first liquid jet 15 impinges. Particularly shear and drag forces at an interface between the second liquid and the support surface may thereby be counteracted that could other wise give rise to flow rate disturbance over en thickness of the second liquid film.

[0049] The supported film 25 of said second liquid is carried by said support body 30 to collecting means 40, like a container, in which the second liquid 45 is collected and, optionally, re-circulated back to the second nozzle 20. The first nozzle and second nozzle 20 are suspended such that the ray of droplets 15 of said first liquid will enter said film 25 of said second liquid in an interaction area 50 while said film 25 is carried and supported by said support body 30. The support surface 35 stabilizes the second liquid film 25 that will absorb said jet droplets 15.

[0050] The droplets 15 of said first liquid will interact with said second liquid 25 at said interaction area 50. In this example, the second liquid has a lower surface tension than said first liquid, which facilitates the encapsulation, coalescence or uptake of the material of said droplets 15. Due to this mutual difference in surface tension between both liquids 15,25, the droplets 15 of the first liquid are surrounded by a shell of second liquid 25 to form compound droplets 55, if the first and second liquid are mutually immiscible liquids. These droplets 55 form micro-capsules containing a core of the first liquid encapsulated by the second liquid 25 to create a suspension 45 of such micro-capsules that may be collected by the collecting means 40. If the liquids would be miscible, the same will result in a mixture or compound solution that may chemically or physically react. The droplets 15 of said first liquid may for instance solidify into particles, once they are exposed to the second liquid.

[0051] The core-shell capsules between the first and second liquid may be subjected to a solidifying agent, temperature or radiation downstream of the interaction area to harden the shell. Alternatively, the droplets 15 may be provided as core-shell droplets using, for instance, a coaxial nozzle 10 in-air micro-fluidics technology (drop-jet coalescence) to achieve core-shell compound droplets during flight, prior to impact with the liquid sheet 25 in which they may stabilize or solidify. The flowing film of said second liquid 25 will drag the droplets further downstream where they will be collected finally by the collecting means 40. The alginate capsules that are produced appear almost identical in size and shape as shown in FIG. 5A. It turns out that such micro-fluidic system allows a stable and reproducible physical interaction or chemical reaction on a millimetre to micron scale to deliver millimetre, micrometre or sub-micron sized particles and/or compound droplets, in a range between a few nanometre and the order of ten millimetre, that allows upscaling to an increased, particularly industrial scale.

[0052] FIG. 1 shows an interaction between merely two liquids. The invention, however, allows to add further liquids and/or other fluids. As an example a number of first nozzles 10 may be placed in parallel to release a number of jets of the first liquid that will enter the liquid film 25 at various interaction areas 50 substantially concurrently. But also more that two liquids may be involved by adding further jet nozzles to release continuous or dis-continuous jets of first and further liquids and also further films of further liquids may be released onto the substrate prior, past, on top or below the film of said second liquid.

[0053] Besides liquids, also gasses may be joined into the interaction. To that end a substrate 30 may be employed as support body, having a top layer that is permeable to such gas while offering the support surface to the second liquid. FIGS. 2a and 2B show examples of a support body that may be used in such embodiments.

[0054] In FIG. 2A a perforated silicon nitride layer 37 is provided on a monolithic silicon substrate 30 with an intervening silicon oxide layer 38, said nitride layer 37 and oxide layer 38 having multiple tiny pores 39 that allow a passage of a reaction gas. Said reaction gas may be supplied by suitable supply means, not shown, through cavity 31 in said support substrate 30 underneath said top layer 37,38. The pores 39 are hydrophobic such that the liquid film 25 will run over it without entering the pores 39, while gas is being fed into the liquid flow 25. Said pores may be of sub-micron to millimetre scale and may be created by etching or micro-machining techniques.

[0055] Alternatively a porous, particularly a micro-porous, substrate 30 may be used as support body, as shown in FIG. 2B. This substrate 30 is for instance a foam body of a suitable polymer foam having an open cell structure that allows a passage of a gas while being hydrophobic to block a penetration of the second liquid.

[0056] Instead of having a flat, planar main surface 32, the support body 30 may also be configured to have one or more channels at a main surface. FIG. 3 shows such an embodiment in which a gutter or trench is formed by a recessed portion at said main surface 32. A bottom of said channel forms the support surface that will receive and carry the liquid film that is released from the second nozzle. The liquid film 25 will, in that case, not only be stabilized by the support surface 35 provided by the bottom of such channel, but will also be confined by both side walls 36 that further stabilize the liquid film and avoid spreading of the surface 32. Optionally, these side walls 32 may additionally be configured to have overhangs that further facilitate liquid pinning, thereby acting as ‘liquid phase guides’. FIG. 5B shows collected particles that were produced in this manner having an almost identical, mono-disperse diameter of around 1895 micron±64 micron.

[0057] The support surface may be stationary, like in the preceding examples, but may also be moving at a velocity. Particularly, the support surface may be provided by an endless conveyer belt or a rotating drum, cylinder or sphere. Providing a liquid film on a spherical surface has the advantage that no boundary interaction are to be expected alongside the interaction area. This particularly facilitates a parallel setup of several first nozzles to release several liquid jets of a first liquid to a common liquid film of a second liquid that is supported by a spherical surface.

[0058] FIG. 4 shows a typical setup of a micro-fluidic system according to the invention in which a liquid film of a second liquid is supported by a spherical support surface. The system comprises a number of first nozzles 100 arranged at regular intervals around an axis of rotation X of a spherical support body 300. Instead of jetting the first liquid with a substantial initial velocity, the nozzles of the current example release the first liquid by dripping droplets 15 with hardly any velocity. The first liquid is supplied to the nozzles 100 at a stable flow rate that allows the liquid to initially adhere to the nozzle outlet due to surface tension forces. The stable flow causes such a hanging droplet to deploy until, finally, the gravitational forces exceed said surface tension forces and the droplet 15 detaches from to nozzle 100. The nozzles 100, that are used in this example, are 150 micron precision cores by Subrex. Using these nozzles a 1% low viscosity alginate solution from Wako is ejected at a constant pressure of approximately 0.2 bar. The droplets 15 will accelerate to a terminal velocity at which they impacts an interaction area 50 at a surface of the spherical body 300.

[0059] At said interaction area 50, the spherical support body 300 carries a sheet 25 of a second liquid that has been sprayed on top of its surface by a second nozzle 200. This will create a film 25 of diminishing film thickness that spreads around the spherical support surface 300 and eventually will leave the support body 300 at its bottom to be collected by suitable collecting means 400 or to be carried further downstream. The second liquid 25 is a calcium chloride solution to produce almost identical alginate bodies 55 as shown in FIG. 5C, having a almost identical shape and size of around 3007 micron±113 micron.

[0060] Although the invention has been described with reference to merely a limited number of exemplifying embodiments, it will be appreciated that the present invention is by no means limited to those embodiments. On the contrary many more embodiments and variations are feasible within the spirit and scope of the present invention without requiring a skilled person to exercise any inventive skill. As such the liquids used in the example of FIG. 1 may be replaced by other liquids that will have an interaction with one and another. Apart from physical interactions due to a difference in surface tension, causing the first liquid to be encapsulated by the other, second liquid, or the other way around, also chemical reaction are envisaged within said interaction area, for instance a solidification of first liquid droplets to solid particles upon reaction with the second liquid. Also the dimensions that were given, are merely an indication but may be set larger or smaller in practice to serve a particular application.