FR2935763A1 - MICROFLUID MICROFLUIDIC CONTINUES - Google Patents

Abstract

The invention relates to a micropump comprising a fluid inclusion housed in a chamber of the microchannel, and means for moving a portion of said inclusion into the axial zone of said chamber and for moving said portion along the longitudinal axis of the microchannel, so as to causing the flow of a fluid of interest (F) along the longitudinal axis of the microchannel (10).

Description

TECHNICAL FIELD The present invention relates to the general field of microfluidics and relates to a micropump for continuous microfluidics. Continuous microfluidics is concerned with the flow of a continuous phase fluid, and opposes discrete microfluidics in which drops are manipulated and displaced. STATE OF THE PRIOR ART Micropumps make it possible to ensure the controlled flow of a fluid, generally in a microchannel, and are involved in many microfluidic systems. For example, micropumps may be present in lab-on-a-chip, injection systems for medical substances, or hydraulic circuits for cooling 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 D.J. Laser and J.G. Santiago entitled A review of micropumps, J. Micromech. Microeng., 14 (2004), R35-R64. However, these actuators have certain drawbacks, such as the need for deformable membranes or valves, the use of high voltages, for example for piezoelectric or electrostatic devices, or a high electrical consumption, for example with thermopneumatic or electromagnetic devices.

Another approach is to operate the micropump by electrowetting, and more precisely by electrowetting on dielectric. Thus, the patent application FR2889633 filed in the name of the applicant describes a micropump comprising a microchannel and an actuating device, the latter for causing the flow of a fluid of interest inside the microchannel following a direction given. As illustrated in Figure 1A, the actuating device comprises a chamber A40 which separates the microchannel A10 into two ducts, an inlet duct A11 and an outlet duct Al2. Each duct A11, Al2 communicates with the chamber A40 via a valve A51, A52, each being arranged to allow the flow of the fluid of interest A31 following the single direction i. In the chamber A40 is housed a piston A53 whose displacement alternately drives the suction of the fluid from the inlet duct A11, and the injection of the fluid into the outlet duct Al2.

The displacement of the piston A53 is controlled by means of a flexible membrane A54 in contact with a drop of liquid A32. The control of the shape of the drop A32 makes it possible to modulate the profile of the membrane A54 and thus to actuate the piston A53. The control of the shape of the drop is provided by electrowetting.

More specifically, the membrane A54 defines, with a substrate A21, the internal volume of an enclosure, which is filled by the drop of liquid A32 electrically conductive and by a second liquid A33 surrounding, these two liquids being immiscible.

Electrical means are provided to modify the shape of the drop by electrowetting. These means comprise an electrode A61 integrated in the substrate A21, covered with a dielectric layer A65. The drop A32 is then in contact with said dielectric layer A65 and with the membrane A54. A counter-electrode (not shown) is in contact with the drop.

When a voltage is applied between the electrode A61 and the counter-electrode, the voltage drop assembly A32, dielectric layer A65 and activated electrode A61 act as a capacitance.

As described in the article by B. Berge entitled Electrocapillarity and wetting of insulating films by water, C.R. Acad. Sci., 317, series 2, 1993, 157-163, the contact angle of the interface of the drop A32 on the dielectric layer A62 then decreases according to the relation:

cos0 (U) = cos0 (0) + U2 2e6 where e is the thickness of the dielectric layer A65, Er the permittivity of this layer and 6 the surface tension of the interface of the drop A32. This reduction in the contact angle is accompanied by a spreading of the drop and thus a modification of its shape. Thus, the activation of the electrode A61 makes it possible to control the shape of the drop A32, in order consequently to modify the profile of the membrane A54. The piston A53 can then be displaced along its longitudinal axis in both directions, which ensures the flow of the fluid A31 from the inlet duct A11 to the outlet duct A12, through the chamber A40. Figures 1A and 1B illustrate two typical operating times of the micropump. In FIG. 1A, the electrode A61 is activated, the piston A53 then moves so as to draw fluid A31 of interest from the inlet duct A11 in the chamber A50, then when the electrode A61 is deactivated ( Figure 1B), the drop A32 returns to its original shape, and pushes the piston so that the fluid A31 inside the chamber A40 is injected into the outlet duct Al2. However, the micropump according to the prior art has a number of drawbacks arising from the presence of movable or deformable mechanical elements in the actuating device. Thus, the production and assembly of mechanical elements of micrometric size are particularly difficult operations to perform, which also involve high manufacturing costs.

In addition, these elements and more precisely their connecting members, pivot or slide, are particularly sensitive to the slightest manufacturing defects. The valves and the piston are then likely to become blocked, thus rendering ineffective the micropump as well as the microfluidic system in which it intervenes. DISCLOSURE OF THE INVENTION The object of the present invention is to provide an electrowinning micropump whose operating device does not comprise moving or deformable mechanical parts. To do this, the invention relates to a micropump for moving a first fluid in a microchannel. According to the invention, the microchannel comprises at least one chamber comprising an axial zone disposed substantially along the longitudinal axis of the microchannel 20 and at least one lateral zone, and the micropump comprises: an inclusion of a second fluid occupying at least partially said lateral zone of the chamber; electrical means for bringing a portion of said inclusion into said axial zone under the effect of electrical control, comprising a plurality of actuation electrodes disposed in said axial zone of the chamber, and means for sequentially activating said actuating electrodes for moving said portion of said inclusion at least partially covering at least one actuating electrode, substantially along the longitudinal axis of the microchannel, so as to cause the flow of said first fluid along the longitudinal axis of the microchannel.

Thus, the portion of the fluid inclusion, in its displacement, causes the flow of the fluid of interest in the longitudinal direction of the microchannel. It is then no longer necessary to provide moving or deformable mechanical parts of the valve, piston or membrane type. In addition, the pumped fluid is not discretized in the form of drops by the micropump. The liquid of the drop is always located in the chamber and is not drawn into the microchannel. It is indeed continuous microfluidics. The production operations are thus greatly simplified, which reduces manufacturing costs. Reliability is improved, as there is no longer a risk of blockage or seizure of the micropump. Moreover, unlike the micropump according to the prior art, it is possible to cause the flow of the fluid of interest along any one of the two directions parallel to the longitudinal axis of the microchannel. Preferably, the first fluid or the second fluid is a liquid. The successive activation means advantageously comprise electrical switching means designed to activate and deactivate each of said actuating electrodes, said switching means being controlled by a control means. According to a first preferred embodiment, said portion of said inclusion is a local deformation of said inclusion. Said portion of said inclusion can recover at least one actuating electrode along the entire cross section of said axial zone. According to a second preferred embodiment, the chamber comprises a wall disposed between the axial zone and the lateral zone, along part of the length of the chamber, so that the lateral zone forms a secondary channel communicating with the axial zone. upstream and downstream of the wall.

Said portion of said inclusion may then be a secondary inclusion separated from said inclusion by said wall. According to one embodiment, the first fluid is a dielectric fluid, the second fluid being a conductive liquid. Said electrical means for bringing said portion into said axial zone may then comprise at least one counter-electrode in electrical contact with said inclusion, and a voltage generator for applying a potential difference between one or more actuating electrodes and said counter-electrode. electrode. Said electrical means for bringing said portion into said axial zone may further comprise a so-called confinement electrode extending substantially on the surface of said lateral zone of the chamber. According to another embodiment, the first fluid is a conductive liquid, the second fluid being a dielectric fluid. Said electrical means for bringing said portion into said axial zone may then comprise at least one counter-electrode in electrical contact with said first fluid, and a voltage generator for applying a potential difference between one or more actuating electrodes and said counter-electrode. -electrode. The micropump may further comprise a second bonnet substrate. A second plurality of actuating electrodes may then be integrated in said cover and disposed in said axial zone of the chamber, facing said first plurality of electrodes for actuating said substrate. The first fluid can then have an electrical permittivity substantially lower than that of the second fluid. Said chamber may comprise two lateral parts arranged one opposite the other, each housing a drop of conductive liquid. The distance separating the first substrate and the cover in said chamber is preferably substantially smaller than the dimensions of said chamber in the median plane of said first substrate. Preferably, the axial zone has a width substantially less than the length thereof.

The inter-electrode operating gap advantageously has a curved or angular shape, so as to facilitate the passage of the portion of the inclusion of an electrode to another.

The said electrodes may be covered with a layer of hydrophobic material. The first fluid and the second fluid may be, one, a conductive liquid comprising zwitterionic species, and the other, a dielectric fluid.

A layer of dielectric material may be disposed between the hydrophobic layer and said electrodes. Said operating electrodes may be arranged in matrix form.

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

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of nonlimiting examples, with reference to the appended drawings, in which: FIGS. 1A and 1B, already described, are diagrammatic representations of FIG. longitudinal section of a micropump according to the prior art; FIG. 2 is a diagrammatic representation in top view of a micropump according to the first preferred embodiment of the invention, in which the first electrode is activated; Figure 3 is a schematic representation in longitudinal section of the micropump according to the first preferred embodiment of the invention, the section being taken along the axis A-A of Figure 2; FIGS. 4A to 4C are diagrammatic representations in plan view of a micropump according to the first preferred embodiment of the invention, and illustrate a mode of operation; FIGS. 5A to 5C illustrate another mode of operation of the first preferred embodiment of the invention; FIGS. 6A to 6D are diagrammatic views in plan view of a micropump according to a variant of the first preferred embodiment of the invention, in which a liquid bridge is formed; FIGS. 7A to 7D are diagrammatic representations in plan view of a micropump according to another variant of the first preferred embodiment of the invention, in which a progressive wave is generated; FIGS. 8A to 8D are diagrammatic representations in plan view of a micropump according to the second preferred embodiment of the invention, in which a secondary fluid inclusion is formed; Figure 9 is a variant of the first preferred embodiment of the invention, wherein the pumped fluid is a conductive liquid; and Figures 10 and 11 are variants of the first preferred embodiment of the invention, wherein the axial zone of the chamber has a curved or angular longitudinal axis.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The first preferred embodiment of the invention is shown diagrammatically in FIG. 2, seen from above. The micropump comprises a first substrate 21 in which a microchannel 10 is formed. A plane of the substrate substantially parallel to the plane (i, j) of the direct orthonormal coordinate system (i, j, k) is called the median plane of the first substrate 21. The longitudinal axis of the microchannel is defined as the median line of the microchannel. The longitudinal axis may be straight or curved. The microchannel 10 may have a convex polygonal cross section, for example square, rectangular, hexagonal. It is considered here that a square section is a special case of the more general rectangular shape. It can also have a circular cross section. The term microchannel is taken in a general sense and includes in particular the particular case of the microtube whose section is circular. The microchannel 10 may be filled with a fluid of interest 31 to be displaced.

A device for actuating the micropump is provided for causing and controlling the flow of the fluid of interest 31 in the microchannel 10. The actuating device comprises a chamber 40 communicating with the microchannel so as to define therein a first conduit 11 and a second conduit 12.

The chamber 40 preferably has a substantially rectangular cross-sectional shape. The chamber 40 has an axial zone 41 disposed in the continuity of the first and second conduits, that is to say located substantially along the longitudinal axis of the microchannel. The chamber 40 also comprises at least one notch forming the lateral zone 42, communicating with the axial zone 41. The lateral zone 42 extends in the median plane of the first substrate 21. According to the invention, an inclusion of a second fluid at least partially occupies said lateral zone 42 of the chamber. In the first preferred embodiment of the invention, said second fluid inclusion is a drop of an electrically conductive liquid 32. Electrical means are provided for bringing a portion 35 of the drop of liquid into said axial zone 41 of the chamber, under the effect of an electric control, by electrowetting. In particular, the drop of liquid 32 may be deformed by said electrical means. The electrical means comprise a plurality of electrodes 61 (i), where iE [1, N], and N is preferably greater than or equal to three. In the example of Figure 2, N is equal to three. The electrodes 61 (i) are integrated in the first substrate 21 and are arranged in the axial zone 41 of the chamber 40, preferably linearly. The electrode array 61 (i) may also have a square or rectangular matrix shape.

Preferably, a so-called confinement electrode 62 is integrated in the first substrate 21 and disposed substantially in the lateral zone 42 of the chamber 40. The confinement electrode 62 advantageously extends over the entire surface of the lateral zone 42. Each electrode 61 (i) may have a substantially square or rectangular shape. Alternatively, the inter-electrode actuation spacing may have a curved or angular shape. In the case of an angular shape, the edge of an actuating 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. Preferably, a layer of a hydrophobic material covers the electrodes 61 (i) and 62. Preferably, a layer of a dielectric material is disposed between the hydrophobic layer and the electrodes 61 (i) and 62. The dielectric layer and the hydrophobic layer covering the actuating electrodes 61 (i) and the confinement electrode 62 may be a single layer combining these two functions, for example a parylene or Teflon layer. Preferably, a counterelectrode 63 is disposed in electrical contact with the liquid droplet 32. This counter-electrode 63 can be either a catenary, a buried wire, or a planar electrode in the hood of the micropump (such a hood is described later). In the latter two possibilities, an electrically conductive hydrophobic layer may cover the counter-electrode 63. The electrodes 61 (i) and 62, as well as the counter-electrode 63, may be connected to a continuous voltage generator 64 or, preferably , alternative. When the bias voltage is alternating, the liquid behaves like a conductor when the frequency of the bias voltage is substantially lower than a cutoff frequency.

This depends in particular on the electrical conductivity of the liquid and is typically of the order of a few tens of kilohertz (Mugele and Baret, Electrowetting: from basics to applications, J. Phys Condens Matter, 17 (2005), R705- R774). On the other hand, the frequency is substantially greater than the frequency allowing to exceed the hydrodynamic response time of the liquid, which depends on the physical parameters of the drop such as the surface tension, the viscosity or the size of the drop, and which is of the order of a few hundred hertz. Also, the frequency is preferably between 100 Hz and 10 kHz, preferably of the order of 1 kHz. Thus, the response of the liquid of the drop 32 depends on the effective value of the applied voltage since the contact angle depends on the voltage U2, according to the relationship given above. 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. According to the invention, the actuating device comprises means for successively activating the actuating electrodes 61 (i). The successive activation means may comprise a system 71 of electrical switches 72, controlled by a control means 73 of the PC type in a predetermined sequence. Each actuating electrode 61 (i) is connected to the voltage generator via a switch 72. Thus, depending on the switching state of the different switches 72, electrical control can be transmitted to one or several actuating electrodes 61 (i). In this case, these electrodes are said to be activated. More specifically, the voltage generator 64 applies a potential difference between the counter-electrode 63 and the activation electrode (s) 61 (i) activated (s). Preferably, when at least one actuation electrode 61 (i) is activated, the containment electrode 62 is also activated.

FIG. 3 is a longitudinal sectional view of the preferred embodiment of the invention along axis AA represented in FIG. 2. A second substrate 22 forming a cover can be deposited on first substrate 21, parallel to the median plane. of it. The first and second substrates 21 and 22 may be silicon or glass, polycarbonate, polymer, ceramic.

The microchannel 10 and the chamber 40 are for example made by lithography and selective etching. Depending on the desired dimensions, it is possible to use dry etching (gas attack, for example SF6, in a plasma). Engraving can be wet too. For glass (mainly SiO 2) or silicon nitrides, it is possible to 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 height of the microchannel 10 between the substrates 21 and 22 is typically between a few tens of nanometers and 200pm, and preferably between lpm and 100pm. Preferably, the height of the chamber 40, in particular of the axial zone 41 of the chamber 40 is substantially less than the height of the microchannel 10, as shown in Figure 3. This provides a drop of liquid 32 substantially flat , that is to say spread between the first substrate 21 and the cover 22, or even a portion 35 drop substantially flat. Reducing the height of the chamber 40 also makes it possible to optimize the actuation by electrowetting. Increasing the cross section of the inlet and outlet channels reduces the pressure losses upstream and downstream of the pump.

In the nonlimiting example of FIG. 3, the counter-electrode 63 is a planar electrode integrated in the cover 22 of the micropump. The actuating electrodes 61 (i) and confinement, and the counter-electrode 63, may be made by depositing a thin layer of a metal selected from Au, Al, ITO, Pt, Cu, Cr ... or an Al-Si alloy ... using conventional microtechnologies of microelectronics, for example by photolithography.

The electrodes 61 (i) and 62 are then etched in a suitable pattern, for example by wet etching. The thickness of the electrodes 61 (i), 62, and against the electrode 63 may be between 10 nm and 1 pm, preferably 300 nm.

The actuating electrodes 61 (i) are preferably square with a side whose length is between a few micrometers to a few millimeters, preferably between 50 pm and Imm. The surface of these electrodes depends on the size of the drops to be transported. The spacing between adjacent electrodes can be between lpm and 10pm. The confinement electrode 62 advantageously extends over the entire flat surface of the lateral zone of the chamber 40, along the median plane.

A dielectric layer 65 may cover the electrodes 61 (i) and 62. It may be made of Si3N4r SiO2, SiN, barium strontium titanate (EST) or other high-permittivity materials such as HFO2r Al2O3, Ta2O5, Ta2O5 -TiO2, SrTiO3 or Ba1_XSrXTiO3.

The thickness of this layer may be between 100 nm and 3 μm, generally between 100 nm and 1 μm, preferably 300 nm. A plasma enhanced chemical vapor deposition (PECVD) process is preferred to the low pressure vapor deposition (LPCVD) process for thermal reasons. 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, a hydrophobic layer 66 may be deposited on the dielectric layer 65, and on the counter-electrode 63. For this, a Teflon deposit by dipping, spray or spin coating, or SiOC deposited by plasma can be performed. Hydrophobic silane deposition in the vapor or liquid phase can be carried out. Its thickness will be between 100 nm and 5 pm, preferably lpm. This layer makes it possible in particular to reduce or even to avoid the effects of hysteresis of the wetting angle. The microchannel may be filled with a fluid of interest 31, preferably an insulator, and may be air, a mineral oil or silicone, a perfluorinated solvent, such as FC-40 or FC-70, or an alkane as undecane. The conductive liquid 32 is electrically conductive and can be an aqueous solution charged with ions, for example of Cl-, K +, Na +, Cal +, Mg2 +, Zn2 +, Mn2 +, others. The liquid 32 can also be mercury, gallium, eutectic gallium, or ionic liquids of the type bmim PF6, bmim BF4 or tmba NTf2. The fluid of interest 31 is immiscible with the conductive liquid 32.

Furthermore, in an alternative embodiment not shown, it should be noted that a second plurality of actuating electrodes may be integrated in the cover 22, and advantageously covered with a dielectric layer. The activation of the second plurality of actuating electrodes can be advantageously controlled by the successive activation means previously described. In this case, a counter-electrode, for example in the form of a suspended wire, can be arranged in the chamber 40 so as to ensure electrical contact with the conductive liquid 32. Thus, the application of a potential difference between a a pair of actuating electrodes disposed, one in the substrate 21 and the other in the cover 22, and the counter-electrode makes it possible to move the conducting liquid 32 by electrowetting more efficiently, for the same potential difference applied.

The operation of the micropump according to the first preferred embodiment of the invention is as follows, with reference to FIGS. 4A to 4C. FIGS. 4A to 4C, in which the numerical references identical to those of FIG. 2 denote identical or similar elements, represent in a view from above the first preferred embodiment of the invention. The embodiment shown in these figures differs from that of FIG. 2 only by the number N of electrodes, here greater than three.

For the sake of clarity, the voltage generator and the successive activation means are not shown. The electrodes 61 (i), thanks to the switches, can be placed at a potential V0 or V1, indicated by the numerical references 0 or 1. In the case of an alternating voltage and as previously described, the potential V1 then corresponds to the effective value of the applied voltage. The switching of each switch is controlled by the control means. During the operation of the micropump that will be described, the confinement electrode 62 remains advantageously activated (placed at a potential V1 different from VO), so that the drop of liquid 32 remains substantially confined in the lateral zone 42 of the chamber 40, then substantially occupying the surface delimited by the confinement electrode 62. FIG. 4A shows the electrode 61 (1) activated. By electrowetting effect described above, the droplet 32 deforms locally and wets, preferably completely, the area of the hydrophobic layer 66 facing the electrode 61 (1) activated. Local deformation is here referred to as the liquid drop portion 32 which occupies an area of the hydrophobic layer facing an electrode 61 (i) activated. Also, to move the local deformation 35 of the drop 32 on the electrode line 61 (i), it is sufficient to activate successively thereof, the electrode 61 (1) to the electrode 61 (N).

More specifically, for the local deformation 35 to pass from an electrode 61 (i) to the neighboring electrode 61 (i + 1), the control means, at the same time, deactivates the electrode 61 (i) and activates the electrode 61 (i + 1), by actuation of the corresponding switches. Said local deformation 35 can then be displaced along the longitudinal axis of the microchannel, as illustrated in FIGS. 4A and 4B, from the electrode 61 (1) to 61 (N), via the electrodes 61 (i-1 ), 61 (i), 61 (i + 1) ... The local deformation 35 pushes, in its displacement, the fluid of interest 31. The flow of the fluid 31 is thus obtained. The fluid 31 is sucked from the first conduit 11 and pushed into the second conduit 12, by the displacement of the local deformation 35. This sequence is repeated until the activation of the downstream electrode 61 (N).

As shown in FIG. 4B, when the electrode 61 (N) is activated, the local deformation 35 is situated substantially at the downstream end of the axial zone 41 of the chamber 40. To continue to ensure the flow of the fluid 31, the electrode 61 (1) is activated while the electrode 61 (N) is deactivated. Local deformation of the drop at electrode 61 (N) disappears, and new local deformation is generated at electrode 61 (1). The successive activation sequence of the electrodes 61 (i) then continues as described above.

The activation frequency of the electrodes 61 (i) makes it possible to precisely control the flow rate imposed on the fluid 31 in the microchannel. As can be seen, the drop of liquid 32 remains confined in the chamber 40 during the entire activation sequence of the electrodes 61 (i). Thus, the fluid of interest 31 is not discretized in the form of drops or bubbles downstream of the chamber. The micropump according to the invention is applicable to continuous microfluidics. Furthermore, it is understood that the direction of displacement of the deformation 35 is not limited to that from the first conduit 11 to the second conduit 12, but can just as well go in the opposite direction.

FIGS. 5A to 5C, in which the numerical references identical to those of FIG. 2 denote identical or similar elements, represent an alternative embodiment of the operation of the micropump according to the first preferred embodiment of the invention. It may indeed be advantageous to control very precisely the mass flow rate of fluid of interest 31 in the microchannel.

However, FIG. 4C shows a step of the activation sequence of the electrodes 61 (i) for which a free fluid flow 31 is possible. This step is where the local deformation 35 passes from the downstream electrode 61 (N) to the upstream electrode 61 (1). The mass flow rate of the fluid 31 can not be precisely controlled.

To remedy this, activation sequence shows the figure it is advantageous to have a different in this step. Like 5C, the downstream electrode 61 (N) is kept activated activated, so obstructed by when the upstream electrode 61 (1) is that the axial zone 41 remains always less one, in this case two, local deformations of the droplet. 32. When the electrode 61 (2) is activated, the upstream electrodes 61 (1) and downstream 61 (N) are deactivated at the same time. The local deformation 35 located on the electrode 61 (N) disappears while that located on the electrode 61 (1) is displaced on the neighboring electrode 61 (2). The activation sequence is then similar to that previously described.

Figures 6A to 6D show a variant of the first preferred embodiment of the invention, seen from above. The numerical references identical to those of FIG. 2 denote identical or similar elements. In this embodiment, the chamber 40 comprises two lateral portions 42A and 42B, arranged facing each other with respect to the axial zone 41 of the chamber 40. Each lateral zone 42A, 42B houses a drop of liquid 32A, 32B. Each lateral zone 42A, 42B advantageously comprises a confinement electrode (not shown).

The mode of operation shown in these figures is substantially similar to that described in Figures 5A-5C. The activation of an electrode 61 (i) generates a local deformation of the drops 32A and 32B. Each local deformation then extends substantially over an area of the hydrophobic layer located opposite the electrode 61 (i) activated. Local deformations can then wet a sufficient surface to coalesce with each other. A liquid bridge 36 is then formed, which connects the two drops of liquid 32A and 32B. The liquid bridge 36, corresponding then to the two coalesced local deformations, is then displaced by successive activation of the electrodes 61 (i). In order to form a larger liquid bridge 36 and to move it, it is advantageous to actuate two neighboring electrodes 61 (i) and 61 (i + 1) together, as illustrated in particular in FIGS. 6A to 6C.

FIG. 6D shows, moreover, a functioning identical to that described in FIG. 5C. Thus, the joint activation of the electrodes 61 (1) and 61 (N) makes it possible to form an inclusion 31I of fluid 31. The activation sequence of the electrodes 61 (i) thus makes it possible to form this inclusion, to displace it and to merging with the fluid 31 present in the second conduit 12.

FIGS. 7A to 7D illustrate an operating variant, in which the two local deformations 35A and 35B do not coalesce with each other, for example because of a V1 activation voltage that is too low or a frequency high activation of the electrodes. During the successive activation of the electrodes 61 (i), each local deformation 35A, 35B is displaced while remaining opposite one another, fluid 31 separating the two local deformations. This variant of operation corresponds to a peristaltic micropump. The different embodiments of the invention described can operate according to this variant of operation.

Figures 8A to 8D show the second preferred embodiment of the invention, seen from above.

The reference numerals identical to those of FIG. 2 denote identical or similar elements. In this embodiment, the chamber 40 comprises a wall 43 disposed between the axial zone 41 and the lateral zone 42, over part of the length of the chamber, so that the lateral zone 42 forms a secondary channel communicating with the axial zone 41 upstream and downstream of the wall 43. Preferably, the lateral zone 42 communicates upstream of the wall 43 at the upstream electrode 61 (1) and downstream of the wall 43 at the level of the downstream electrode 61 (N). Upon activation of the upstream electrode 61 (1), a portion 35 of the droplet 32 at least partially covers said activated electrode.

Then, the activation sequence of the electrodes is implemented as described above. The electrode 61 (2) is activated while the electrode 61 (1) is deactivated. The portion 35 of liquid is then displaced so as to substantially cover the new activated electrode. Then, as a result of the deactivation of the electrode 61 (i) and the activation of the electrode 61 (i + 1), the portion 35 moves in the axial zone of the chamber of the electrode 61 (1 ) to the electrode 61 (N). In doing so, it causes the fluid of interest 31 to flow into the microchannel. Since the electrodes 61 (i), with iE [2, N-1] are separated from the lateral zone of the chamber by said wall, the portion 35 forms, when it substantially covers one of these electrodes, a secondary drop separated from the main drop housed in the lateral zone of the chamber, as illustrated in FIG. 8B.

More specifically, the secondary drop 35 is formed by dissociating the main drop as the portion 35 is moved from the electrode 61 (1) to the electrode 61 (2). Then, when the secondary drop is moved from the electrode 61 (N-1) to the electrode 61 (N), it coalesces with the main drop (Figure 8C). It should be noted that a counterelectrode is advantageously arranged so as to be in electrical contact on the one hand with the main drop 32, but also with the secondary droplet 35.

The activation sequence is then similar to what has been described with reference to FIGS. 4A to 4D.

Figure 9 illustrates a variant of the first preferred embodiment of the invention. The reference numerals identical to those of FIG. 2 denote identical or similar elements. In this example, the fluid of interest 31 is a conductive liquid and a liquid or gaseous dielectric fluid forms a fluid inclusion at least partially occupying said lateral zone of the chamber. A counter-electrode is advantageously arranged in the microchannel or in the axial part of the chamber so as to bring the conductive liquid to the desired potential, for example V1. The successive activation sequence is adapted insofar as all the electrodes 61 (i) are preferably activated beforehand. A local deformation 35 is then formed by deactivating an electrode, for example the upstream electrode 61 (1). The successive activation sequence then consists of activating the electrode 61 (i) and deactivating the electrode 61 (i + 1). The local deformation 35 of the fluid inclusion 32 is then displaced in the axial zone along the longitudinal axis of the microchannel, which causes the flow of the fluid of interest, here the conductive liquid, in the microchannel. Moreover, in order to improve the confinement of the fluid inclusion 32 inside the chamber 40, two confinement electrodes may be arranged in the channel, more precisely upstream and downstream of the axial zone 41 of the chamber. the chamber 40. The first electrode is thus upstream and close to the first electrode 61 (1), and the second electrode is downstream and close to the last electrode 61 (N). During operation of the micropump, these two electrodes are advantageously activated. Thus, the confinement of fluid inclusion 32 in said chamber is improved. This variant of the first preferred embodiment 10 can be adapted to the various modes described, as well as to the second preferred embodiment.

Figures 10 and 11 show geometry variants of the micropump according to the first preferred embodiment of the invention, seen from above. The reference numerals identical to those of FIG. 2 denote identical or similar elements. In FIG. 10, the axial zone 41 of the chamber 40 has a curved longitudinal axis. The lateral zone 42 has a substantially half-disk shape. In FIG. 11, the axial zone 41 is U-shaped. The lateral zone 42 then has a substantially rectangular shape. These different geometries can be used in the various embodiments described above.

Furthermore, it should be noted that in all the embodiments described above, the surface of the chamber, and more particularly at the level of the electrodes 61 (i), can be smooth, rough or micro-structured or nano-structured, in order to amplify wetting effects and increase capillary forces. The displacement of the portion 35 is then improved. It should be noted that, in the case where the dielectric layer is not present, the so-called direct electrowetting phenomenon can be realized. The capacity intervening then is not that of the dielectric layer 65 but that of a double electric layer forming in the conductive liquid 32 on the surface of the electrodes 61 (i) and 62. In this case, the applied voltages must remain low enough to avoid electrochemical phenomena such as electrolysis of water. The thickness e involved in the relationship connecting the contact angle e to the applied voltage U, described above, is that of the double layer, which is of the order of a few nanometers.

It is advantageous to add in the liquid 32 high permittivity species, such as zwitterionic species. This makes it possible to increase the permittivity Er 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.

Furthermore, in a variant of the embodiment of the invention shown in Figure 2, a plurality of electrodes can be integrated in the cover 22, and advantageously covered with a dielectric layer. The activation of any electrode 61 (i) of the first substrate 21 is then advantageously accompanied by a joint activation of the corresponding electrode of the cover at the potential -V1. Thus, the conductive liquid 32 located between the substrate 21 and the cover 22 is substantially set at potential 0V. A counter-electrode may not be present. Finally, it should be noted that, when the frequency of the bias voltage is substantially greater than a few tens of kilohertz, the liquid of a droplet 32 has a dielectric property. In the case where the permittivity of the liquid 32 is substantially greater than that of the fluid 31, the liquid 32 is displaced at the level of the electrode activated by dielectrophoresis. The pumping is then obtained by using a liquid 32 occupying at least partially the lateral zone 42 of the chamber 40 and a fluid of interest 31 immiscible and of different permittivities. In the case where the liquid 32 and the fluid 31 are electrically insulating, the micropump may not comprise a dielectric layer covering the activation electrodes integrated in the substrate 31 and those integrated in the cover 22. Furthermore, the bias voltage may be continue.30

Claims (21)

REVENDICATIONS1. Micropump for moving a first fluid (31) in a microchannel (10), characterized in that the microchannel comprises at least one chamber (40) having an axial zone (41) disposed substantially along the longitudinal axis of the microchannel (10) and at least one lateral zone (42), and in that the micropump comprises: - an inclusion (32) of a second fluid occupying at least partially said lateral zone (42) of the chamber (40), - electrical means for bringing a portion (35) of said inclusion (32) into said axial zone under the effect of electrical control, comprising a plurality of actuating electrodes (61) disposed in said axial zone (41) of the chamber (40), and - means for successively activating said actuating electrodes (61) to move said portion (35) of said inclusion (32) at least partially covering at least one actuating electrode (61), substantially following the longitudinal axis of the microchannel (10), thereby e to cause the flow of said first fluid (31) along the longitudinal axis of the microchannel (10). 2. Micropump according to claim 1, characterized in that the successive activation means comprise electrical switching means (72) designed to activate and deactivate each of said actuating electrodes (61), said switching means (72). being controlled by a control means (7 3). 3. Micropump according to claim 1 or 2, characterized in that said portion (35) of said inclusion (32) is a local deformation of said inclusion (32). 4. Micropump according to any one of claims 1 to 3, characterized in that said portion (35) of said inclusion (32) covers at least one actuating electrode (61) along the entire cross section of said axial zone ( 41). 5. Micropump according to claim 1 or 2, characterized in that the chamber (40) comprises a wall (43) disposed between the axial zone (41) and the lateral zone (42), over part of the length of the chamber (40), so that the lateral zone (42) forms a secondary channel communicating with the axial zone (41) upstream and downstream of the wall (43). 6. Micropump according to claim 5, characterized in that said portion (35) of said inclusion (32) may be a secondary inclusion separated from said inclusion (32) by said wall (43). 7. Micropump according to any one of claims 1 to 6, characterized in that the first fluid (31) is a dielectric fluid, the second fluid being a conductive liquid. 8. Micropump according to claim 7, characterized in that said electrical means for bringing said portion (35) into said axial zone (41) comprise. at least one counter-electrode (63) in electrical contact with said inclusion (32), and - a voltage generator (64) for applying a potential difference between one or more actuation electrodes (61) and said counter-electrode (63). 9. Micropump according to claim 7 or 8, characterized in that said electrical means for bringing said portion (35) into said axial zone (41) further comprises a so-called confinement electrode (62) extending substantially over the surface of said lateral zone (42) of the chamber (40). 10. Micropump according to any one of claims 1 to 6, characterized in that the first fluid (31) is a conductive liquid, the second fluid being a dielectric fluid. 11. Micropump according to claim 10, characterized in that said electrical means for bringing said portion (35) into said axial zone (41) comprise. at least one counter-electrode (63) in electrical contact with said first fluid (31), and a voltage generator (64) for applying a potential difference between one or more actuating electrodes (61) and said counter-electrode electrode (63). 12. Micropump according to any one of claims 1 to 11, characterized in that it further comprises a second substrate (22) forming a cover of said micropump, and in that a second plurality of actuating electrodes is integrated in said cover (22) and disposed in said axial zone (41) of the chamber (40) facing said first plurality of actuating electrodes (61) of said substrate (21). 13. Micropump according to claim 12, characterized in that the first fluid (31) has an electrical permittivity substantially lower than that of the second fluid. 14. Micropump according to any one of claims 1 to 13, characterized in that said chamber (40) comprises two side portions (42A, 42B) arranged one facing the other, each housing a drop of conductive liquid. (32A, 32B). 15. Micropump according to any one of claims 1 to 14, characterized in that it further comprises a second substrate (22) forming a cover of said micropump, the distance separating the first substrate (21) and the cover (22). in said chamber (40) is substantially smaller than the dimensions of said chamber (40) in the median plane of said first substrate (21). 16. Micropump according to any one of claims 1 to 15, characterized in that the axial zone (41) has a width substantially less than the length thereof. 17. Micropump according to any one of claims 1 to 16, characterized in that the inter-electrodes actuating gap (61) has a curved or angular shape. 18. Micropump according to any one of claims 1 to 17, characterized in that said electrodes (61, 62) are covered with a layer of hydrophobic material (66). 20 19. Micropump according to any one of claims 1 to 18, characterized in that the first fluid (31) and the second fluid are, one, a conductive liquid comprising zwitterionic species, and the other a fluid dielectric. 20. Micropump according to claim 18, characterized in that a layer of dielectric material (65) is disposed between the hydrophobic layer (66) and said electrodes (61, 62). 10 15 5 21. Micropump according to any one of claims 1 to 20, characterized in that said actuating electrodes (61) are arranged in matrix form. 10