EP2182212A1 - Drop-activated micro-pump - Google Patents

Abstract

The micropump has a displacement unit displacing a drop (51) of liquid (L1) by electrowetting on a hydrophobic surface till the drop is contacted with a hydrophilic wall (12) of a microchannel (10) such that the drop is introduced by wetting in the microchannel through an inlet orifice (11) to cause displacement of fluid (F1). The displacement unit has displacement electrodes (31) and a counter-electrode provided in electrical contact with the drop. The drop forms a contact angle on the hydrophilic wall, where the angle is less than an angle formed by electrowetting on the surface.

Description

TECHNICAL AREA

The present invention relates to the general field of microfluidics and, more particularly, to that of micropumps, and relates to a drop-operated micropump.

STATE OF THE PRIOR ART

Micropumps provide controlled flow of fluid, particularly in a microchannel, and are involved in many microfluidic systems.

For example, micropumps may be present in lab-on-a-chip, medical substance injection systems, or the electronic cooling circuits of electronic chips.

The micropumps can be actuated in various ways, for example using a piezoelectric, electrostatic, thermopneumatic or even electromagnetic device. A presentation of these different actuators can be found in the document DJ Laser and JG Santiago entitled "A review of micropumps", J. Micromech. Microeng., 14 (2004), R35-R64 .

However, these actuators have certain drawbacks such as the presence of deformable membranes or valves, the use of high voltages, for example for piezoelectric or electrostatic devices, or a significant electrical consumption, for example with thermopneumatic or electromagnetic devices.

Another approach, which avoids at least partly the disadvantages mentioned above, is to actuate the micropump by electrowetting, and more precisely by electrowetting on dielectric.

Thus, the patent application WO2002 / 07503A1 describes a micropump, illustrated in Fig. 1 , comprising a substrate in which is formed a microchannel 10, and an actuating device for ensuring the flow of a fluid F1 in the microchannel 10. The operating principle of the actuating device is based on the displacement by electrowetting a conductive liquid L1 in the microchannel 10 from a tank 41.

The actuating device comprises a linear array of displacement electrodes 31 (1), 31 (2), 31 (3) ... integrated in the substrate and arranged in the microchannel 10 from the tank 41. A counter-electrode 43 is disposed in the tank 41 and provides electrical contact with the conductive liquid L1. The displacement electrodes are covered with a hydrophobic dielectric layer (not shown).

A voltage generator (not shown) is connected to the displacement electrode array 31 and to the counter-electrode 43, and makes it possible to apply a voltage U between the electrodes.

The conductive liquid L1 forms with the fluid F1 filling the microchannel 10 an interface I1.

When the displacement electrode 31 (i) located opposite the interface I1 is activated, using switching means (not shown) whose closure establishes a contact between this electrode and the voltage source via a conductor common, the liquid under voltage L1, dielectric layer and activated electrode 31 (i) acts as a capacitance.

où e est l'épaisseur de la couche diélectrique, ε_r la permittivité de cette couche et σ la tension de surface de l'interface I1 du liquide L1.As stated in the article of Berge entitled "Electrocapillarity and wetting of insulating films by water", CR Acad. Sci., 317, Series 2, 1993, 157-163 , the contact angle θ of the interface I1 of the liquid is expressed according to the relation: $$\cos \left(U\right)=\cos \left(0\right)+\frac{{\mathrm{<figure-callout\; id="2"\; label="\epsilon \; r"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\epsilon \; </figure-callout>}}_r}{2e\mathrm{\sigma }}{\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">U</figure-callout>}}^2$$

where e is the thickness of the dielectric layer, ε _r the permittivity of this layer and σ the surface tension of the interface I1 of the liquid L1.

When the polarization voltage U is alternative, the liquid L1 behaves like a conductor insofar as the frequency of the bias voltage is substantially lower than a cutoff frequency. The latter, which depends in particular on the electrical conductivity of the liquid, is typically of the order of a few tens of kilohertz (see for example the article by Mugele and Baret entitled "Electrowetting: from basics to applications", J. Phys. Condens. Matter, 17 (2005), R705-R774 ). On the other hand, the frequency is preferably substantially greater than the frequency corresponding to the hydrodynamic response time of the liquid, which depends on the physical parameters such as the surface tension, the viscosity or the size of the microchannel, and which is of the order a few tens or hundreds of Hertz. The response of the liquid then depends on the rms value of the voltage, since the contact angle depends on the voltage U ² , according to the relation (1).

It then appears an electrostatic pressure acting on the interface I1, close to the contact line, as explained in the article of Bavaria et al. entitled "Dynamics of droplet transport induced by electrowetting actuation", Microfluid Nanofluid, 4, 2008, 287-294 . The liquid can then be displaced step by step, on the hydrophobic surface, by successive activation of the electrodes 31 (1), 31 (2), etc. In its displacement, the liquid L1 "pushes" the fluid F1 along the microchannel 10.

However, the micropump according to the prior art has certain disadvantages.

The pressure force exerted by the liquid on the fluid is proportional to cosθ ( U ). Thus, the smaller the angle θ ( U ), the greater the pressure force and the high flow rate. In practice, however, the contact angle decreases with the increase of the polarization voltage U to a saturation angle which is usually between about 30 ° and 80 °. The pressure force, and thus the fluid flow rate, are then limited by this saturation angle.

On the other hand, the displacement length of the liquid in the microchannel corresponds to that of the operating electrode array. Also, moving the liquid along the entire length of the microchannel requires extending the electrode array all along the microchannel. The manufacture is then made particularly complex, especially in the case where the microchannel has a non-rectangular transverse shape, for example circular, or if it has changes of direction.

STATEMENT OF THE INVENTION

The object of the present invention is to provide a micropump whose pressure force is not limited by the electrowetting saturation angle, while having a simplified manufacturing.

To do this, the invention relates to a micropump for moving a fluid in a microchannel.

According to the invention, the microchannel comprises an inlet orifice and has a hydrophilic wall extending from said inlet orifice, and the micropump comprises means for moving a drop of liquid by electrowetting on a hydrophobic surface until contacting said drop with said hydrophilic wall, whereby said drop is introduced by wetting into said microchannel through said inlet port, causing said fluid to move.

Thus, the pressure force exerted by the liquid on the fluid in the microchannel is not limited by the electrowetting saturation angle, as in the micropump according to the prior art.

Indeed, according to the present invention, electrowetting makes it possible to bring drops of liquid to the inlet orifice of the microchannel, but is not the driving phenomenon of the micropump.

Fluid flow is achieved by introducing the drop of liquid into the microchannel through the inlet port. This naturally occurs because of the difference in wettability to which the drop is subjected. Indeed, when the drop is brought into contact with the hydrophilic wall through the inlet port, it wets at the same time the hydrophobic surface and the hydrophilic wall of the microchannel. The difference in wettability between these two surfaces causes the migration of the entire drop of the hydrophobic surface towards the hydrophilic wall. The drop of liquid is then introduced into the microchannel and simultaneously "pushes" the fluid.

In addition, the realization of the micropump is simplified since it is no longer necessary to have the electrowetting electrodes along the entire length of the microchannel.

Advantageously, said drop forms a contact angle on said hydrophilic wall substantially less than that formed by electrowetting on said hydrophobic surface.

Said displacement means preferably comprise at least one displacement electrode and a counter-electrode in electrical contact with the drop, and a voltage generator for applying a potential difference between one or more displacement electrodes and said counter-electrode. .

Said displacement electrodes may be arranged along a determined path.

Among said displacement electrodes, a so-called contacting displacement electrode is advantageously arranged so that a drop of liquid covering it is in contact with said hydrophilic wall through said inlet orifice.

Said displacement means may comprise a single displacement electrode, which is then said contacting electrode.

Said hydrophilic wall may have a nanotextured or microtextured surface.

Said hydrophilic wall may be of hydrophilic material.

Said hydrophilic wall may comprise a layer of a hydrophilic material.

Advantageously, said hydrophilic wall extends over the entire length of the microchannel.

A dielectric material layer is preferably disposed between said hydrophobic surface and said electrodes.

Advantageously, the microchannel comprises a connecting portion defining an upstream portion and a downstream portion, said connecting portion having a section transversely larger than that of the upstream portion.

The size of the connecting portion is preferably between 5 and 50 times that of the upstream portion.

A second fluid may be located downstream of the first fluid so as to form therewith an interface located in said coupling portion.

The upstream portion may comprise a first upstream portion extending from the inlet orifice and a plurality of second elementary upstream portions arranged in parallel each communicating with said first upstream portion.

Each second elementary upstream portion may communicate with said connection portion.

Each second elementary upstream portion may be at least partially filled with said fluid.

The micropump advantageously comprises means for forming said droplet on said hydrophobic surface, by electrowetting.

The drop forming means may comprise a plurality of drop forming electrodes, one of which is adjacent to a displacement electrode.

A second hydrophobic surface may be arranged facing the first hydrophobic surface so as to form a closed or confined device for said drop.

Other advantages and features of the invention will become apparent in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1, déjà décrite, est une représentation schématique en vue de dessus d'une micropompe selon l'art antérieur ;
• Les figures 2A et 2B sont des représentations schématiques en vue de dessus d'une micropompe selon un premier mode de réalisation de l'invention, pour deux étapes de fonctionnement, dans lequel la configuration des moyens de formation et de déplacement de gouttes est dite ouverte ou non confinée ;
• Les figures 3A à 3C illustrent la formation de gouttes par électromouillage dans le cas d'une micropompe selon le premier mode de réalisation ;
• Les figures 4A et 4B sont des représentations schématiques d'une micropompe selon un deuxième mode de réalisation, dans lequel la configuration des moyens de formation et de déplacement de gouttes est dite confinée, la figure 4A étant une vue de dessus et la figure 4B une vue en coupe longitudinale de la figure 4A selon l'axe I-I ;
• La figure 5 est une représentation schématique en vue de dessus d'une micropompe selon un troisième mode de réalisation de l'invention, dans lequel le microcanal comprend une portion de raccord ;
• La figure 6 est une représentation schématique en coupe longitudinale d'une micropompe selon un quatrième mode de réalisation de l'invention, dans lequel le microcanal comporte une pluralité de portions élémentaires disposées en parallèle ;
• La figure 7 est une représentation schématique en coupe longitudinale d'une micropompe selon une variante du quatrième mode de réalisation représenté sur la figure 6, comprenant deux micropompes élémentaires disposées en parallèle.

Embodiments of the invention will now be described, by way of nonlimiting examples, with reference to the accompanying drawings, in which:

• The figure 1 , already described, is a schematic representation in top view of a micropump according to the prior art;
• The Figures 2A and 2B are schematic representations in top view of a micropump according to a first embodiment of the invention, for two operating steps, wherein the configuration of the means for forming and moving drops is said to be open or uncontained;
• The FIGS. 3A to 3C illustrate the formation of drops by electrowetting in the case of a micropump according to the first embodiment;
• The Figures 4A and 4B are schematic representations of a micropump according to a second embodiment, in which the configuration of the means for forming and moving drops is said to be confined, the Figure 4A being a view from above and the Figure 4B a longitudinal sectional view of the Figure 4A along axis II;
• The figure 5 is a schematic representation in top view of a micropump according to a third embodiment of the invention, wherein the microchannel comprises a coupling portion;
• The figure 6 is a schematic representation in longitudinal section of a micropump according to a fourth embodiment of the invention, in which the microchannel comprises a plurality of elementary portions arranged in parallel;
• The figure 7 is a schematic representation in longitudinal section of a micropump according to a variant of the fourth embodiment shown in FIG. figure 6 , comprising two elementary micropumps arranged in parallel.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A first embodiment of the invention is shown schematically on the Figures 2A and 2B , in top view.

The micropump comprises a microchannel 10 at least partially filled with a fluid F1 and an actuating device for ensuring the flow of said fluid F1 in the microchannel 10.

The Figure 2A shows a direct orthonormal frame ( i , j , k ). In the first embodiment of the invention, a droplet 51 can be moved in a plane substantially parallel to the plane ( i , j ).

The longitudinal axis of the microchannel 10 is defined as being the median line of the microchannel. The longitudinal axis may be rectilinear or curved, and have changes of direction.

The microchannel 10 may have a convex polygonal cross section, for example square, rectangular, hexagonal, a square section being a particular case of the more general rectangular shape. It can also have a circular cross section. The term microchannel is taken here in a general sense and includes in particular the case particular microtube whose section is circular. The microchannel may also be the catheter of a drug delivery system.

The term "height" refers to the transverse characteristic size of the microchannel 10. In the case of a microtube, the height refers to the diameter.

According to the invention, the microchannel 10 comprises an inlet orifice 11 allowing the passage of a liquid L1 from the outside inside the microchannel 10.

Preferably, the inlet orifice 11 is located at one end of the microchannel 10.

The microchannel 10 comprises a hydrophilic wall 12 which extends from said inlet orifice 11 over a portion of the transverse contour, or preferably over the entire transverse contour.

The hydrophilic wall 12 may extend over a length defined along the longitudinal axis of the microchannel, or preferably extend over the entire length of the microchannel.

The device for actuating the micropump ensures the flow of the fluid F1 in the microchannel 10.

It comprises means for moving at least one drop 51 of liquid L1, by electrowetting, on a hydrophobic surface to the inlet orifice 11 of the microchannel 10.

The displacement means here comprise a single displacement electrode 31 integrated in or disposed on a support substrate 21, and covered with the hydrophobic surface.

The displacement electrode 31, called the contacting electrode, is arranged so that a droplet 51 of liquid L1 covering it is in contact with the hydrophilic wall 12 through said inlet orifice 11.

According to a variant not shown, a series of displacement electrodes may be arranged in a determined path ending in a contacting electrode 31 arranged to contact a drop 51 covering it with the hydrophilic wall 12 through the inlet orifice 11 of the microchannel 10.

Note that the verbs "to cover", "to be located on" and "to be disposed of" do not necessarily imply direct contact here. Thus, the droplet 51 of liquid can cover the displacement electrode 31 without direct contact, a hydrophobic surface being disposed here between the drop 51 and the electrode 31.

Furthermore, it should be noted that the means of displacement of the drops are here in a so-called open configuration, or not confined, to the extent that said drops of liquid are not confined between two support substrates, or two hydrophobic surfaces, parallel between they but rest solely on the support substrate 21.

In the Figures 2A and 2B , the inlet orifice 11 is disposed substantially opposite the displacement electrode 31. More specifically, the inlet axis through the orifice 11, here following i , is substantially parallel to the plane ( i , j ) of the displacement electrode 31. Other arrangements are possible, as shown in FIG. figure 5 (described in detail below), where the inlet port 11 is formed substantially in the same plane as the displacement electrode 31. The input axis through the orifice, here following k , is substantially perpendicular to the plane ( i , j ) of the displacement electrode 31. In this example , the inlet orifice 11 is surrounded by the displacement electrode 31, so that a drop 51 which covers the electrode 31 is brought into contact with said hydrophilic wall 12 through said inlet orifice 11.

The hydrophobic surface may be a layer of a hydrophobic material.

Preferably, a layer of a dielectric material is disposed between the displacement electrode (s) 31 and the hydrophobic surface.

The dielectric and hydrophobic layers may be a single layer combining these two functions, for example a parylene layer.

Preferably, a counter electrode (not shown) is provided to provide electrical contact with liquid drop 51. It is arranged at least facing the displacement electrode 31. This counter-electrode can be either a catenary, a wire buried between the dielectric layer and the hydrophobic layer, or a planar electrode integrated into a hood of the micropump (a such hood is described later). In the latter case, an electrically conductive hydrophobic layer may cover the counter-electrode.

The displacement electrode 31 and the counterelectrode may be connected to a continuous voltage generator (not shown) or, preferably, alternative, to move the drop 51 by electrowetting, as previously described.

In the case of an alternating voltage, the frequency is advantageously between 100 Hz and 10 kHz, preferably of the order of 1 kHz, so as to maintain the conductive electrical properties of the liquid and to exceed the hydrodynamic response time of the droplet. The response of the drop 51 then depends on the rms value of the applied voltage. The rms value can vary between a few volts and a few hundred volts, for example 200V. Preferably, it is of the order of a few tens of volts.

It is particularly advantageous that the micropump has means for forming drops 51 by electrowetting from a tank 41 containing said liquid L1.

As shown in Figure 2A the drop forming means preferably comprise at least three forming electrodes 42 (1), 42 (2), 42 (3) integrated in or deposited on said support substrate 21 and covered with said hydrophobic surface.

Preferably, said dielectric layer is also disposed between the hydrophobic surface and the formation electrodes 42.

A first forming electrode 42 (1) is disposed substantially facing or near the tank 41 containing the liquid. A second forming electrode 42 (2) is adjacent to the first 42 (1) and followed by a third electrode 42 (3). The third electrode 42 (3) is preferably adjacent to the displacement electrode 31.

Advantageously, the drop forming means have in common with the displacement means against the electrode and the voltage generator described above. The counter-electrode is then arranged so as to be opposite the formation electrodes 42.

Switching means (not shown) are provided for successively activating the different electrodes 42 (1), 42 (2), 42 (3), 31 and thus ensuring, on the one hand, the formation of a drop and, on the other hand, its displacement to the inlet orifice 11 of the microchannel 10.

The FIGS. 3A to 3C illustrate an example of forming a drop by electrowetting from a tank 41 containing said liquid L1, in the case of an open configuration. The patent application W02006 / 070162 , filed in the name of the Applicant, describes in detail the principle of drop formation used herein, and also gives an example of droplet formation in confined configuration.

As shown in figure 3A said reservoir 41 may be a reservoir electrode at which a reservoir drop 53 of liquid L1 is disposed. This reservoir electrode defines a liquid holding micro-reservoir, and may be similar or identical to the reservoir electrode 46 described later with reference to the second embodiment of the invention. Said reservoir electrode 41 may have a circular shape as on the Figures 2A and 2B , square as on the Figure 4A , or any other form.

Three electrodes 42 (1), 42 (2), 42 (3) are shown on the FIGS. 3A to 3C .

Activation of this series of electrodes 42 (1), 42 (2), 42 (3) results in liquid spreading by electrowetting from the reservoir drop 53 as a liquid segment 52, as shown in FIG. figure 3B .

Then, this liquid segment 52 is cut in two parts by deactivating the electrode 42 (2). A drop 51 is thus obtained, as shown in FIG. figure 3C .

A series of electrodes 42 (1), 42 (2), 42 (3) are thus used to stretch liquid L1 from the reservoir drop 53 into a liquid segment 52 (FIG. figure 3B ) then to cut this liquid segment 52 ( figure 3C ) and form a drop 51 which can be moved by the moving means.

The operation of the micropump according to the first embodiment of the invention is as follows, with reference to Figures 2A and 2B .

The drop forming means are activated so as to electromagnetically form a drop 51 of liquid L1 on the hydrophobic surface, as described above.

Then the displacement means are activated to move the drop 51 formed by electrowetting up to the inlet orifice 11, and thus bring it into contact with the hydrophilic wall 12.

When the drop is in contact with the hydrophilic wall 12 through the inlet orifice 11, it is introduced spontaneously by wetting in the More precisely, the drop migrates from the hydrophobic surface of the actuating device to the hydrophilic wall 12 of the microchannel 10. In doing so, it "pushes" the fluid F1 contained in the microchannel 10 and thus ensures the controlled flow of the microchannel 10. this one.

When the drop 51 is fully introduced into the microchannel 10, the procedure can be repeated. A second drop 51 can be brought to the inlet port 11 by electrowetting and then introduced by wetting in the microchannel 10. More precisely, the second drop 51 coalesces with the liquid L1 already present in the microchannel 10 from the In this case, a drop of larger volume is obtained, one part wetting the hydrophobic surface and the other part wetting the hydrophilic wall 12. The phenomenon remains the same. The new drop will move to dewake the hydrophobic surface and further wet the hydrophilic wall 12 of the microchannel 10. And in doing so, it "pushes" the fluid F1 and thus ensures the flow thereof.

The micropump according to the invention therefore has the advantage of not being limited by the saturation angle of electrowetting. The driving force is then the wetting force that appears spontaneously when the liquid drop 51 is in contact with the hydrophilic wall 12 of the microchannel 10. This wetting force depends on the contact angle formed by the liquid L1 on the hydrophilic wall . This can be very small, for example of the order of, or less than, 10 °. The pressure force and therefore the fluid flow in the microchannel are then greater than in the micropump according to the prior art.

In addition, the flow of the fluid F1 is ensured as the microchannel 10 is supplied with drops of liquid 51 by the displacement means. The liquid L1 can extend in the microchannel 10 over the entire length of the hydrophilic wall 12. It is thus not necessary to have displacement electrodes 31 along the microchannel 10. The manufacture of the micropump is then particularly simplified. .

A second embodiment of the invention is shown on the Figures 4A and 4B where the first is a view from above and the second a longitudinal section of the first along an axis II.

Numerical references identical to those of the Figure 2A designate identical or similar elements.

In this embodiment, the means for forming and moving drops contain the drop of liquid.

Indeed, a second hydrophobic surface 26 is disposed facing the first hydrophobic surface 22 and substantially parallel thereto, and integrated in or disposed on an upper cover 25.

Thus, a droplet 51 may be formed by the drop forming means and displaced by the displacement means between the first and second hydrophobic surfaces 22, 26.

Preferably, the counter-electrode 43 is integrated in the cover 25 or disposed thereon, and covered by the second hydrophobic surface 26.

The means for forming a drop are advantageously similar to those described in the patent application. W02006 / 070162 filed in the name of the plaintiff.

Thus, a well 27 is formed in the upper cover 25.

This well 27 is placed at least partially in front of a transfer electrode 47, the latter being integrated with the substrate 21 or disposed thereon.

Following the transfer electrode 47, there is a reservoir electrode 46, which will allow to define a liquid holding micro-reservoir.

The drop forming electrodes 42 are then placed followed by at least one displacement electrode, here a single so-called contacting electrode 31.

Note that the dielectric layer, if it is distinct from the hydrophobic layer 22, is not represented on the Figures 4A and 4B .

As described in the patent application W02006 / 070162 , the transfer electrode 47 makes it possible to pump the liquid from the reservoir (not shown) communicating with the well, and to bring it close to the reservoir electrode 46.

On this reservoir electrode can be accumulated a certain amount of liquid. It is represented as having a square or rectangular shape on the Figure 4A but its form can be any. Of Preferably, it can accumulate at least three to four times the volume of the drops 51 to be dispensed, and preferably at least 10 times or 20 times the volume of each drop dispensed 51.

Since the distance between the two substrates 21, 25 is substantially constant (as can be seen in FIG. Figure 4B ), it is actually the surface of the electrode 46 which is at least three to four times equal, or at least 10 or 20 times equal to the area of each of the drop forming electrodes 42.

The transfer electrode, when it is activated, makes it possible to bring a portion of liquid located in the well 27 close to the reservoir electrode 46.

When the latter is also activated, the liquid is transferred to the zone situated above the reservoir electrode 46.

If it is desired to continue feeding the zone situated above the reservoir electrode 46, the transfer electrode 47 can be reactivated, and then the reservoir electrode 46, so as to continue to accumulate liquid in this reservoir zone. .

It is thus possible to accumulate a large volume of liquid 53 ( Figure 4B ). An important advantage is that the pressure in this volume of liquid accumulated above the electrode 46 is independent of the pressure of the liquid in the well 27 by deactivation of the transfer electrode 47.

As long as the transfer electrode 47 is not activated, the liquid defined by the reservoir electrode 46 is not in contact with the well 27. The formation of drops that can be made from the The liquid stored above the reservoir electrode 46 can therefore be calibrated while using a well 27, and independently of the pressure therein, to fill the component.

It should be noted that the two hydrophobic surfaces 22, 26 form two substantially parallel planes and do not constitute a microchannel. Thus, the displacement of a drop 51 does not cause overall displacement of the surrounding fluid in the same direction. This one bypasses the drop 51 in its displacement. It is thus possible to bring a drop 51 to the inlet orifice 11 without introducing the surrounding fluid into the microchannel.

This arrangement makes it possible to dispense drops 51 in a reproducible manner with great precision in volume. Volumes of variation (CV) of volume (CV = 2x standard deviation x100) of less than 3% are usually measured.

In addition, the micropump according to this embodiment of the invention makes it possible to precisely control the flow of the fluid F1 in the microchannel 10. In fact, the fluid F1 is "pushed" by the drop 51 of liquid over a distance that depends in particular the volume of the drop 51. Thus, the formation of a calibrated volume drop makes it possible to move the fluid F1 over a precise distance.

In this embodiment of the invention, the distance between the two hydrophobic surfaces 22, 26 is of the order of a few hundred micrometers, preferably 100 microns. The drops 51 obtained have a volume between a few nanoliters to a few microliters, for example 64nl.

According to variants not shown, the drop reservoir 53 located at the reservoir electrode 46 may be formed during the production of the micropump. Thus, the drop forming means do not comprise wells communicating with a reservoir, nor transfer electrode, but only a drop reservoir located at the reservoir electrode. It is then advantageous for the cover 25 to include a cavity at the reservoir electrode 46, in order to accommodate a reservoir drop of a large volume.

It is also possible for the space located at the reservoir electrode 46, or said cavity, to communicate with the outside, so that liquid can be introduced, for example manually with a pipette, to reform or replenish the droplet. tank. The space located at the reservoir electrode and said cavity, when liquid L1 is present, then form a reservoir.

The support substrate 21 and the cover 25 may be made of silicon or glass, polycarbonate, polymer or ceramic.

The microchannel 10 is, for example, produced by lithography and selective etching. Depending on the desired dimensions, it is possible to use dry etching (gas attack, for example SF ₆ , in a plasma). Engraving can be wet too. For glass (mainly SiO ₂ ) or silicon nitrides, can use hydrofluoric or phosphoric acid etchings (these etchings are selective but isotropic). Engraving can be performed by laser ablation or ultrasound. Micromachining can also be used, in particular for polycarbonate. The microchannel 10 may also be a soft fused silica capillary.

The height of the microchannel 10 is typically between a few tens of nanometers and 200 .mu.m, and preferably between 1 .mu.m and 100 .mu.m, preferably 30 .mu.m. The length of the microchannel 10 can be from a few hundred microns to a few centimeters, for example 50cm.

The displacement and forming electrodes 31, 42, as well as the transfer electrode 47 and the reservoir electrolyte 46, and the counter electrode 43, may be produced by depositing a thin layer of a metal chosen from Au , Al, ITO, Pt, Cu, Cr ... or an Al-Si alloy ... using conventional microtechnologies of microelectronics, for example by photolithography. The electrodes 31, 42, 46, 47 are then etched in a suitable pattern, for example by wet etching.

The thickness of the electrodes 31, 42, 46, 47 may be between 10 nm and 1 μm, and preferably be of the order of 300 nm. The length of the electrodes 31 and 42 can be between a few micrometers to a few millimeters, preferably between 50 .mu.m and 1 mm, preferably 800 .mu.m. The surface of these electrodes depends on the size of the drops to be formed and moved.

The spacing between adjacent electrodes may be between 1 μm and 20 μm.

It should be noted that in the various embodiments, the displacement and drop-forming electrodes 31 and 42 may have a substantially square or rectangular shape, as shown in the figures.

However, the inter-electrode spacing may have a curved or angular shape. In the case of an angular shape, the edge of an electrode may have a sawtooth shape substantially parallel to the edge of the neighboring electrode having a corresponding shape. This form of electrodes facilitates the passage of the drop of liquid from one electrode to another.

As described in the patent application W02006 / 07162 , the reservoir electrode 46 may have a comb or half-star shape, or even a tip, to ensure an electrode surface gradient. The transfer electrode 47 has a shape adapted to that of the reservoir electrode 46.

A dielectric layer may cover the various electrodes 31, 42, 46, 47. It may be made of Si ₃ N ₄ , SiO ₂ , SiN, barium strontium titanate (BST) or other high-permittivity materials such as HFO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ [29], Ta ₂ O ₅ -TiO ₂ , SrTiO ₃ or Ba _1-x Sr _x TiO ₃ . The thickness of this layer may be between 100 nm and 3 μm, generally between 100 nm and 1 μm, preferably 300 nm. The dielectric layer of SiO ₂ can be obtained by thermal oxidation. A chemical deposition process Plasma assisted vapor phase (PECVD) is preferred to the low pressure vapor deposition (LPCVD) process for reasons of thermal stress. Indeed, the temperature of the substrate is only brought between 150 ° C and 350 ° C (depending on the desired properties) against 750 ° C for LPCVD deposit.

Finally, the hydrophobic surface 22 may be deposited on the dielectric layer. For this, a Teflon deposit by dipping or spray or SiOC deposited by plasma can be achieved. Hydrophobic silane deposition in the vapor or liquid phase can be carried out. Its thickness will be between 100 nm and 5 μm, preferably 1 μm. This layer makes it possible in particular to reduce or even to avoid the effects of hysteresis of the wetting angle.

In the case of a confined configuration, a hydrophobic layer 26 covers the counter electrode 43.

The microchannel 10 is at least partially filled with F1 fluid, preferably insulating, which may be air, a mineral oil or silicone, a perfluorinated solvent, such as FC-40 or FC-70, or an alkane such as undecane.

The liquid L1 is electrically conductive and may be an aqueous solution loaded with ions, for example Cl ^- , K ⁺ , Na ⁺ , Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , Mn 2+. The liquid may also be mercury, gallium, eutectic gallium, or ionic liquids of the type bmim PF6, bmim BF4 or tmba NTf2.

The drops 51 of liquid have a volume between a few nanoliters and a few microliters, for example about 64nl.

The fluid F1 is immiscible with the conductive liquid L1.

The hydrophilic character of said wall 12 may be obtained by using a naturally hydrophilic material for the substrate 21 in which the microchannel 10 is formed, such as aluminum, silica or hydrogel.

The substrate may also be a hydrated porous medium, such as hydrated Nafion.

The hydrophilic wall 12 may also comprise a layer of silica. In the case of a substrate 21 made of silicon, the silica layer can be obtained by thermal oxidation of the silicon.

The surface of the hydrophilic wall 12 may also be microtextured or nanotextured, so as to amplify the wetting effects and increase the capillarity force, as described in the publication of J. Bico et al. entitled "Wetting of textured surfaces" Colloids and Surfaces A, Physicochem. Eng. Aspects, 206 (2002), 41-46 .

A surface is called nanotextured (or microtextured) when it has a relief whose characteristic scale is from a few nanometers (or micrometers) to a few hundred nanometers (or micrometers). The textured surface may have an array of roughnesses, for example nicks, pads or nanometric or micrometric grooves.

To obtain the hydrophilic or even super-hydrophilic character of the wall, a film of liquid is then present between the roughnesses. The thickness of this so-called impregnation film is comparable to the height of the roughness but remains negligible compared to the characteristic size of the drop. So, as explained P.-G. de Gennes et al. in the book entitled "Drops, bubbles, pearls and waves" 2002 , the drop is placed, in fine , on a wet substrate which is a sort of patchwork of solid and liquid. Thus, the wall has an important hydrophilic character.

Various techniques known to those skilled in the art can be used to obtain a textured surface, and are described in particular in the thesis of M. Callies Reyssat entitled "Splendor and misery of the lotus effect", 2007, University Paris VI.

Surface chemical treatment techniques may be used to render the wall 12 of the microchannel 10 hydrophilic. A layer or a chemical film is usually deposited on the wall 12, the thickness of which may vary between a few nanometers and a few hundred microns.

For example, a silanization of a metal oxide or semiconductor surface (for example SiO ₂ , HfO ₂ , ITO, TiO ₂ , SnO ₂ ) or polymers (for example PDMS, COC) in the vapor phase or in the liquid phase makes it possible to render the wall of the microchannel hydrophilic. A large variety of silanes provides a hydrophilic surface. In order to be as hydrophilic as possible, the silanes preferably carry an ionic group such as, for example, a carboxylate, a phosphate, a phosphonate, an imidazolium, a protonated amine, a quaternary amine or a sulphonate. A number of these functions, the synthesis of the associated molecules and the functionalization methods of the surfaces are described in the patent application W02007 / 088187 .

For other oxide surfaces such as TiO ₂ or SnO ₂ , it is advantageous to use a grafting of the molecule by phosphatation or phosphanation, to improve the resistance of the layer. In this case, the group conferring the hydrophilic property may be of the same type as that described above. The preparation of such compounds and their use on surfaces are described in particular in the publication of F. Durmaz et al. entitled "New phosphates / phosphonates; A modular approach to functional sams, European Cells and Materials, Vol. 6, Suppl. 1, 2003, 55 .

These two methods described above can be implemented in different ways depending on the thickness of the layer that is desired. Thus, in an anhydrous and slightly concentrated medium, a thin layer of a few nanometers is thus obtained. In the presence of water and alcohol (for example ethanol), a thicker layer of a few hundred nanometers to a hundred microns is obtained by sol-gel type processes.

It should be noted that the grafting of molecules of the polysaccharide family also makes it possible to obtain a hydrophilic surface, as described in the patent application. W02002 / 100559 .

Polymer families make it possible to obtain a hydrophilic and resistant layer of a few hundred nanometers, such as polyhydroxystyrenes.

The patent application W02007 / 053326 also describes hydrophilic groups, for example silanols, introduced into a polymer matrix to be deposited to form the hydrophilic layer.

All the techniques mentioned above, known to those skilled in the art, make it possible to render the wall of the microchannel hydrophilic from the inlet orifice.

A third embodiment of the invention is shown on the figure 5 in top view.

Numerical references identical to those of the Figure 4A designate identical or similar elements.

In this embodiment, the microchannel 10 may comprise a second fluid F2 disposed downstream of the first fluid F1 so as to form therewith an interface 12. Preferably, the first and second fluids F1, F2 are immiscible between them.

Preferably, the interface I2 is located in a connection portion 17.

The connecting portion 17 defines an upstream portion 13 extending from the inlet orifice 11 to the connecting portion 17, and a downstream portion 16 extending downstream of the connecting portion 17.

The height of the connecting portion 17 is substantially greater than that of the upstream portion 13 of the microchannel. Preferably, the height is of the order of 5 to 50 times the height of the upstream portion 13, preferably 10 times. Preferably, the height of the upstream 13 and downstream 16 portions is constant.

The downstream portion 16 may have an identical height, greater or less than that of the connecting portion 17. In the example of the figure 4 , the downstream portion 16 has a height substantially identical to that of the upstream portion 13.

The presence of the connecting portion 17 reduces the effects of the hysteresis of the contact angle that oppose the flow of fluids. Indeed, these are inversely proportional to the height of the connecting portion 17.

The means for forming and moving the drops are here in confined configuration, as described in the second embodiment and as shown in FIG. figure 5 . Alternatively, they may be in an open configuration, as described in the first embodiment.

This third embodiment of the invention has the advantage of delivering a calibrated flow rate of fluid F2 at the outlet of the downstream portion 16 of the microchannel.

A fourth embodiment of the invention is shown on the figure 6 in longitudinal section.

Numerical references identical to those of the Figure 4A designate identical or similar elements.

In this embodiment of the invention, the inlet orifice 11 is disposed in the same plane as the displacement electrode 31 and surrounded by it. The input axis of the orifice, here following k, is substantially orthogonal to the plane of the electrode of displacement, here (i, j). Thus, a drop 51 which covers the displacement electrode is brought into contact with the hydrophilic wall 12 through the inlet orifice 11.

In this embodiment, a connecting portion 17 is disposed between an upstream portion 13 and a downstream portion 16 of the microchannel.

In addition, the upstream portion 13 comprises a first upstream portion 14 and a second upstream portion 15. The first upstream portion 14 extends from the inlet port 11. The second upstream portion 15 extends from the first upstream portion 14 to the connecting portion 17. The downstream portion 16 corresponds to a third portion 16 of the microchannel.

More specifically, the second upstream portion 15 comprises a plurality of second upstream channel elemental upstream portions 15 'arranged in parallel, each communicating with the first upstream portion 14 and with the connecting portion 17.

The second elementary portions 15 'may be arranged in a hexagonal network and have a diameter of the order of a few tens of microns, preferably 30 microns. Preferably, each second elementary portion 15 'has a circular cross section, hexagonal or having a shape of the same type. The second elementary portions 15 'can be obtained by plasma etching of the RIE type of the substrate 21.

Preferably, the second elementary portions 15 'are filled with liquid L1 and / or first fluid F1.

The second elementary portions 15 'may be of a number of hundreds, and have a height (diameter) of a few tens of microns, preferably 30 microns, and a length of a few hundred microns, preferably 700 microns.

This parallel arrangement of the second elementary portions 15 'makes it possible to obtain a large flow rate of second fluid F2 in the downstream portion 16.

The means for forming and moving the drops are here in confined configuration, as described in the second embodiment and as shown in FIG. figure 6 . Alternatively, they may be in an open configuration, as described in the first embodiment.

A variant of the fourth embodiment of the invention is represented on the figure 7 in longitudinal section.

Numerical references identical to those of the Figure 4A designate identical or similar elements.

According to this variant, two elementary micropumps, each of which is substantially identical to that described in the fourth embodiment, are arranged in parallel and are interconnected on the one hand by a common well 27 filled with liquid L1, and on the other hand by a junction connecting the downstream portions 16-1 and 16-2. More specifically, the two downstream portions 16-1 and 16-2 are connected by a junction 18 so as to form only a portion 19.

The two micropumps may have means for controlling the electrodes for forming and moving drops that are independent of one another.

In addition, the second fluids F2-1 and F2-2 manipulated by the two micropumps may be different.

Thus, it is possible to contact the two second fluids F2-1 and F2-2 at said junction of the downstream portions 16-1 and 16-2, and thus to achieve a mixture or a two-phase flow.

The proportions of each second fluid F2-1 and F2-2 can be controlled from the control means of the electrodes.

The first fluids F1-1 and F1-2 are advantageously identical.

Of course, several elementary micropumps can be arranged in parallel, without the number of elementary micropumps being limited to two micropumps as described above.

On the other hand, the elementary micropumps may not be interconnected at their respective downstream portion 16, to provide an independent exemption of their respective second fluid F2.

Finally, it should be noted that by associating, in the various embodiments described above, electronic programming means with the means for controlling the electrodes, it is possible to define sequences for delivering calibrated quantities of first or second fluid.

Moreover, in the case where the dielectric layer is not present, the phenomenon of direct electrowetting can be realized.

The capacity intervening then is not that of the dielectric layer but that of a double electric layer forming in the conductive liquid L1 on the surface of the electrodes 31, 41. In this case, the applied voltages must remain sufficiently low to avoid electrochemical phenomena such as the electrolysis of water.

The thickness e involved in the relationship connecting the contact angle θ to the applied voltage U, described above, is that of the double layer, which is of the order of a few nanometers.

It is then advantageous to add in the liquid L1 species with a high permittivity, such as, for example, zwitterionic species. This makes it possible to increase the permittivity ε _r of the double layer. The zwitterions used may be amine sulfonates, amine phosphates, amine carbonates, or amine carboxylates, and in particular, trialkylammonium alkane sulfonates, alkyl imidazole alkanesulfonates or alkyl alkanesulfonates pyridine.

Claims (16)

Micropump for moving a fluid (F1) in a microchannel (10), said micropump being characterized in that: the microchannel (10) has an inlet (11) and has a hydrophilic wall (12) extending from said inlet (11),
and in that it includes means for moving a droplet (51) of liquid (L1) by electrowetting on a hydrophobic surface (22) to bring said droplet (51) into contact with said hydrophilic wall (12), so that said droplet (51) is introduced by wetting into said microchannel (10) through said inlet (11), causing the displacement of said fluid (F1). Micropump according to claim 1, characterized in that said drop (51) forms a contact angle on said hydrophilic wall (12) substantially less than that formed by electrowetting on said hydrophobic surface (22). Micropump according to claim 1 or 2, characterized in that said displacement means comprise at least one displacement electrode (31) and a counter-electrode in electrical contact with the drop (51), and a voltage generator for applying a difference potential between one or more displacement electrodes (31) and said counter-electrode. Micropump according to Claim 3, characterized in that the said displacement means comprise a displacement electrode (31) arranged such that a drop (51) of liquid covering it is in contact with the said hydrophilic wall (12) through the said orifice input (11). Micropump according to any one of claims 1 to 4, characterized in that said hydrophilic wall (12) has a nanotextured or microtextured surface. Micropump according to any one of claims 1 to 5, characterized in that said hydrophilic wall (12) is of hydrophilic material or comprises a layer of a hydrophilic material. Micropump according to any one of claims 1 to 6, characterized in that said hydrophilic wall (12) extends over the entire length of the microchannel (10). Micropump according to any one of claims 1 to 7, characterized in that the microchannel (10) comprises a connecting portion (17) defining an upstream portion (13) and a downstream portion (16), said connecting portion (17 ) having a cross section substantially larger than that of the upstream portion (13). Micropump according to claim 8, characterized in that the size of the connecting portion (17) is between 5 and 50 times that of the upstream portion (13). Micropump according to claim 8 or 9, characterized in that a second fluid (F2) is located downstream of the first fluid (F1) so as to form therewith an interface (I2) located in said connection portion (17) . Micropump according to any one of claims 8 to 10, characterized in that the upstream portion (13) comprises a first upstream portion (14) extending from the inlet port (11) and a plurality of second elementary upstream portions (15 ') arranged in parallel each communicating with said first upstream portion (14). Micropump according to claim 11, characterized in that each second elementary upstream portion (15 ') communicates with said connection portion (17). Micropump according to claim 12, characterized in that each second elementary upstream portion (15 ') is at least partially filled with said fluid (F1). Micropump according to any one of Claims 1 to 13, characterized in that it further comprises means for forming said droplet (51) on said hydrophobic surface (22) by electrowetting. Micropump according to Claim 14, characterized in that , said displacement means comprising at least one displacement electrode (31), the drop forming means comprise a plurality of drop formation electrodes (42), one of which is adjacent to a displacement electrode (31). Micropump according to claim 14 or 15, characterized in that a second hydrophobic surface (26) is arranged facing the first hydrophobic surface (22) so as to form a closed or confined device for said droplet (51).

Images