Fluidic system, use, and method for operating the same

Abstract

A fluidic system having a first volume, a second volume and a membrane geometrically separating the two volumes, which has an open-pore microstructure for the passage of a first medium and a second medium. There is a contact angle (Θ) between the interface of the media and the pore surface. A first electrical field in the region of the membrane and a first electromagnetic radiation and a first heating of the membrane define a first state (Z.sub.1), in which the membrane is not wetted or is less wetted by the first medium and is more heavily wetted by the second medium such that a first contact angle Θ.sub.1>90° is formed between the pore surface and the interface. The first medium and the second medium and the pore surface have a surface energy of which at least one surface energy can be reversibly changed in such a way that a second contact angle Θ.sub.2<Θ.sub.1 occurs between the pore surface and the interface in a second state (Z.sub.2).

Claims

1. A fluidic system comprising: a first volume, a second volume, and a membrane geometrically separating the two volumes, which provides an open-pore microstructure with a pore surface for passage of a first medium and a second medium, between which a boundary surface is formed, while a contact angle exists between the boundary surface and the pore surface, wherein there are in the fluidic system electrodes for imposing an electric field in a region of the membrane and/or an electromagnetic radiation source acting on the membrane and/or means for heating or cooling the membrane, wherein the membrane in a first state Z.sub.1 with a first electric field E.sub.1 and a first electromagnetic radiation exposure S.sub.1 and a first temperature T.sub.1 has a pore surface which is not wetted or less wetted by the first medium and more heavily wetted by the second medium so that a first contact angle Θ.sub.1>90° is formed between the pore surface and the boundary surface in the first medium, and wherein the first medium and the second medium and the pore surface have a surface energy, of which at least one surface energy can be changed reversibly in dependence on the electric field or by electromagnetic radiation exposure or temperature change so that in a second state Z.sub.2 with a second electric field E.sub.2≠E.sub.1 and/or a second electromagnetic radiation exposure S.sub.2≠S.sub.1 and/or a second temperature T.sub.2≠T.sub.1 a second contact angle Θ.sub.2<Θ.sub.1 is formed between the pore surface and the boundary surface.

2. The fluidic system according to claim 1, wherein the first state Z.sub.1 is defined by a first electric field E.sub.1=0, a first electromagnetic radiation exposure S.sub.1 in a form of daylight or room lighting or darkness, and a first temperature T.sub.1 in a range of normal room temperature.

3. The fluidic system according to claim 1, wherein the pore surface is hydrophobic in the first state and the first medium is a water-based liquid.

4. The fluidic system according to claim 3, wherein the second medium is a gas or an oil-based liquid.

5. The fluidic system according to claim 1 wherein the pore surface in the first state is lipophobic and the first medium is an oil-based liquid.

6. The fluidic system according to claim 5, wherein the second medium is a gas or alternatively a water-based liquid.

7. The fluidic system according to claim 1, further including a pump for transporting the media from the first volume through the membrane into the second volume.

8. The fluidic system according to claim 7, wherein the pump is designed to deliver a constant volume flow Vc up to a maximum delivery pressure P.sub.max.

9. The fluidic system according to claim 8, wherein the first contact angle Θ.sub.1 corresponds to a breakthrough pressure P.sub.dhi at which the boundary surface passes through the membrane and which is greater than the maximum delivery pressure P.sub.max.

10. The fluidic system according to claim 9, wherein the second contact angle Θ.sub.2 corresponds to a breakthrough pressure P.sub.dio at which the boundary surface passes through the membrane and which is smaller than the maximum delivery pressure P.sub.max.

11. The fluidic system according to claim 8, further including a pressure sensor which is arranged and designed so that a pressure change in the first or second volume is detected and a pressure change signal is put out.

12. The fluidic system according to claim 11, further including a controller which is designed, in response to the pressure change signal and upon going above a threshold pressure in the first volume or going below a threshold pressure in the second volume, to put out a switching signal to a power supply for the electrodes or to the electromagnetic radiation source or to the means of heating the membrane.

13. The fluidic system according to claim 7, wherein the pump is designed to transport with a constant delivery pressure P.sub.c.

14. The fluidic system according to claim 13, wherein the first contact angle Θ.sub.1 corresponds to a breakthrough pressure P.sub.dhi at which the boundary surface passes through the membrane and which is larger than the constant delivery pressure P.sub.c.

15. The fluidic system according to claim 14, wherein the second contact angle Θ.sub.2 corresponds to a breakthrough pressure P.sub.dio at which the boundary surface passes through the membrane and which is smaller than the constant delivery pressure P.sub.c.

16. The fluidic system according to claim 13, further including a volume flow sensor which is arranged and designed to detect a change in the volume flow in the second volume and put out a volume flow change signal.

17. The fluidic system according to claim 16, further including a controller which is designed, in response to the volume flow change signal and upon going below a threshold volume flow, to put out a switching signal to a power supply for the electrodes or to the electromagnetic radiation source or to the means of heating the membrane.

18. The fluidic system according to claim 1, wherein one first electrode is preferably formed by a conducting substrate of the membrane or a conducting coating of the membrane.

19. The fluidic system according to claim 18, wherein the membrane has a layer of a dielectric on top of the first electrode.

20. The fluidic system according to claim 19, wherein the dielectric forms the pore surface.

21. The fluidic system according to claim 18, wherein a second electrode is arranged each time directly adjacent to the membrane in the first and second volume.

22. The fluidic system according to claim 1, wherein the pore surface is formed on the basis of polytetrafluorethylene (PTFE), perfluorisobutene (PFIB), or Parylene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and benefits of the invention shall be explained below by means of sample embodiments. There are shown in the figures:

(2) FIGS. 1A-B, a schematic diagram to explain “electro-wetting”;

(3) FIG. 2, a diagram of the contact angle plotted against a potential difference;

(4) FIGS. 3A-C, a model of a membrane pore to describe the position of the boundary surface in dependence on the pressure in the media;

(5) FIG. 4, a diagram of the pressure variation upon the boundary surface passing through a membrane pore for different contact angles:

(6) FIG. 5, a schematic representation of the method for operating a fluidic system in a sequence of 7 consecutive snapshots;

(7) FIG. 6A-B, a pressure and volume flow curve for the sequence of FIG. 5;

(8) FIG. 7A-C, the fluidic system in schematic representation;

(9) FIG. 8A-G, a sample embodiment of the fluidic system as a valve in a sequence of different switching states.

DETAILED DESCRIPTION OF THE INVENTION

(10) By means of FIGS. 1A and 1B, the wetting behavior is described between a first medium M1, such as a liquid drop, and a second medium M2, such as a gas surrounding the liquid drop, and a surface 11 of a body which is being wetted. In order to change the wetting behavior, one makes use of the phenomenon of electro-wetting. The surface 11 of the body being wetted has, for this purpose, an electrically conducting substrate 12, forming a first electrode, on which a layer of a dielectric 14 is deposited. A second electrode 16 is dipped directly into the first medium M1. The electrodes 12 and 16 are connected to a voltage source 18.

(11) FIG. 1A shows a state Z.sub.1 in which the surface 10 is less wetted by the first medium M1, so that a first contact angle Θ.sub.1>90° is formed. Between the electrodes 12 and 16 no voltage exists. In state Z.sub.1, the electric field is therefore E.sub.1=0 V/m.

(12) FIG. 1B describes a state Z.sub.2 in which a voltage is imposed between the two electrodes 12 and 16. This produces a charge shift within the dielectric 14 forming the surface 11, so that for example the surface energy of the dielectric 14 is changed relative to the state Z.sub.1. Consequently, the surface 11 is wetted more heavily with the medium M1 in state Z.sub.2, or in other words, the contact angle Θ.sub.2 between the boundary surface 10 and the surface 11 is decreased as compared to the contact angle Θ.sub.1 in the starting state Z.sub.1. In the case depicted, it even happens that Θ.sub.2<90°.

(13) The contact angle Θ.sub.1 and Θ.sub.2 in the sense of this document is always relative to the first medium, and so it is always measured between the surface 11 and the boundary surface 10 inside the medium M1.

(14) As already mentioned elsewhere, it is not a question of the media being essentially in direct contact, as illustrated in FIG. 1. Any electrical field in the region of contact between the media and the surface of the membrane will ensure a charge shift in the case of electro-wetting and thus a manipulation of the contact angle. However, the direct contacting is very efficient, because the field is built up very locally over the dielectric whose molecular structure is responsible for the change in the contact angle.

(15) FIG. 2 shows the behavior of the contact angle Θ, more precisely the difference (cos Θ.sub.2−cos Θ.sub.1) plotted against the voltage imposed between the electrodes 12 and 16. In the specific example, a substrate is investigated with an electrically conducting coating of chromium and gold and deposited thereon a dielectric coating of Parylene C with a thickness of 7.5±1 μm. It turns out that the contact angle varies from Θ.sub.1=89° in state Z.sub.1 to Θ.sub.2=74° in state Z.sub.2. It reaches saturation over the 7.5 μm thick dielectric at a voltage of around 100 V. A further voltage rise no longer significantly decreases the contact angle. Hence, the maximum difference (cos Θ.sub.2−cos Θ.sub.1) is 0.26.

(16) FIGS. 3A to 3C explain the changing of the position of the boundary surface in dependence on the pressure relations without manipulating the contact angle. A pore with a minimum diameter d between two membrane elements 20 which are circular in cross section is shown here as a simplified hypothesis. The circular elements represent, for example, cross sections through wires of a membrane in the form of a wire weave or the like. The two elements define a membrane plane 22.

(17) Each time there is a medium M1 essentially above the membrane plane 22. Below the plane 22 there is a medium M2. Between the two media there is formed the boundary surface 24. A pressure P1 prevails in medium M1. A pressure P.sub.2 prevails in medium M2. In the state of FIG. 3A, P.sub.1<P.sub.2. As a result, the boundary surface 24 is bowed concavely into medium M1.

(18) Above the center plane 22 at a distance a there are contact points 26 of the boundary surface 24 with the surface of the membrane elements 20. Equivalent to the distance a is an angle α between the membrane plane 22 and the line connecting the center point of the circular element 20 and the contact point 26. The distance a and the angle α have a negative sign for the pressure ratio P.sub.1<P.sub.2.

(19) The contact angle Θ results as the intermediate angle between the tangent to the surface of the membrane element 20 and the tangent T to the boundary surface 24 at the contact point 26 and it is measured inside the medium M1, as defined above.

(20) FIG. 3B shows a state with a different pressure ratio. Here, P.sub.1=P.sub.2, so that the boundary surface 24′ is flat and parallel to the membrane plane 22. The boundary surface 24 still lies above the membrane plane 22 and therefore continues to have a negative distance a′, although the magnitude is less than that of a. This is because the wettability of the media M1 and M2 is different, or in other words, the contact angle Θ is greater than 90°. However, the contact angle Θ has not changed between the state of FIG. 3A and the state of FIG. 3B.

(21) FIG. 3C, finally, shows a state in which the pressure P.sub.1″ in the first medium M1 is greater than the pressure P.sub.2″ in medium M2. The result is a boundary surface 24″ with convex curvature out from the medium M1. The contact point 26″ of the boundary surface 24″ with the surface of the membrane elements 20 now for the first time has a positive distance a″ from the membrane plane 22, which corresponds to an angle α>> with likewise positive sign. An unchanged contact angle Θ is furthermore assumed.

(22) The pressure variation, more precisely the curve of the pressure difference P.sub.1−P.sub.2=ΔP, can be described in this model as a function of the angle alpha, as follows:

(23) $\Delta p\left(\alpha \right)=-\frac{2\gamma }{0.5d}\frac{\cos \left(\Theta -\alpha \right)}{r\left(1-\cos \alpha \right)}$

(24) Here, ΔP stands for the pressure difference P.sub.1−P.sub.2, α for the angle to parametrize the position of the boundary surface relative to the membrane plane, γ for the surface tension or boundary surface tension, Θ for the contact angle, d for the minimum pore diameter and r for the radius of curvature of the simulated membrane elements.

(25) FIG. 4 shows that pressure difference ΔP as a function of the parameter a for different contact angles Θ between 180° and 50°. One sees that, at a contact angle Θ=180°, corresponding to a complete nonwettability of the membrane surface with the medium M1, a maximum pressure difference would occur if the contact points 26 were situated in the membrane plane 22. With increasing wettability and thus with decreasing contact angle Θ, the maximum pressure difference decreases. At the same time, the maximum shifts toward a positive value of a. Moreover, one observes that a negative pressure difference even occurs at small a, that is, the boundary surface tension or surface energies ensure that the medium M1 has penetrated some distance into the pore opening. This knowledge will help in understanding the following description of the process.

(26) FIGS. 5 and 6 will explain sample embodiments of the fluidic system of the invention, as well as the method of the invention for its operation. FIG. 5 shows a sequence of 7 consecutive snapshots of the fluidic system in highly simplified schematic form. The same segment is shown in all snapshots. This has essentially one fluidic line bounded by a surface 30 of a substrate and one fluidic line in a membrane 32 geometrically separating a first volume V1 and a second volume V2. The membrane 32 is represented by circular membrane elements, between which open pores 34 are formed.

(27) In the fluidic line there is a first medium M1 situated to the left of the membrane 32 and a second medium M2 essentially to the right of the membrane 32. Between the two media M1 and M2 is formed a boundary surface 36. Furthermore, to the left of the first medium M1 is situated a third medium M3, between which and the first medium M1 is formed a second boundary surface 42. Thus, the first medium M1 has a limited volume between the boundary surfaces 36 and 42.

(28) The fluidic system furthermore has a first electrode in the form of a conducting substrate of the membrane 32 or a conducting coating of the membrane 32 (neither of them shown) and on the other hand a second electrode 38 arranged in the immediate vicinity of the membrane 32. The first and the second electrode are connected to a power source. Between the two electrodes no voltage is applied at snapshot “1”, which essentially describes a state Z.sub.1. State Z.sub.1, furthermore, is defined of course by a first electromagnetic radiation S.sub.1 and a first temperature T.sub.1, but the latter parameters play no role in the present sample embodiment, because they do not vary and are therefore not specified here. At snapshot “1”, moreover, a pressure P.sub.1 prevails in the first medium M1 and a pressure P.sub.2 in the second medium M2. The pressure difference ΔP=P.sub.1−P.sub.2 is the driving force to move the media M1 and M2 and the boundary surface 36 in the direction of the arrow 40 toward the membrane 32.

(29) The diagram of FIG. 6A shows the pressure difference ΔP as a function of time. The snapshot “1” is situated in the segment of the diagram marked “1”. The pressure difference ΔP here is constant at low level, because the driving of the boundary surface 36 in the direction of the membrane is not opposed by any substantial resistance.

(30) This changes upon reaching the membrane 32, which is shown in the snapshot “2”. The system is still in the state Z.sub.1 with no potential difference between the two electrodes. The system is configured such that the pore surface of the membrane 32 is not wetted or less wetted by the first medium and more heavily wetted by the second medium M2. Furthermore, the system strives to maintain a constant volume flow through the fluidic line, so that the pressure rises sharply just after contact of the boundary surface 36 with the membrane 32. This results, in snapshot “2”, in a strongly convex curvature of the boundary surface 36 between the membrane elements, similar to FIG. 3C, from which one can also read the contact angle Θ.sub.1>90°.

(31) Corresponding to snapshot “2”, the diagram of FIG. 6A shows in segment “2” that the pressure difference rises to a maximum P.sub.max. Upon closer scrutiny of the pressure curve, one sees that, at the instant when the front boundary surface 36 reaches the membrane, the initial wetting of the membrane results in an accelerated movement of the medium M2 in the direction of the membrane, due to the boundary surface tension, and consequently to a slight pressure drop, because the media are moving faster than the volume delivery of the system. This holds at least for all (real) contact angles <180°. Only then does the pressure rise to P.sub.max. The first medium has now penetrated to a maximum depth into the pores, yet the boundary surfaces 36 of neighboring pores do not make contact, so that the boundary surface of the liquid cannot penetrate through the membrane.

(32) The so-called maximum delivery pressure P.sub.max is dictated by the system and established by the dimensioning of the delivery pump or by pressure limiting means. Evidently, the boundary surface 36 at the maximum delivery pressure does not yet break through the pores of the membrane, because the boundary surface tension can withstand even greater pressures. The so-called pressure breakthrough is thus substantially higher in state Z.sub.1. It corresponds to the first contact angle Θ.sub.1, as illustrated approximately in the diagram of FIG. 4. If one assumes, for example, that the contact angle Θ.sub.1 in state Z.sub.1 is 130°, this corresponds to a pressure breakthrough of 2000 mbar for the pore geometry and boundary surface tension assumed there.

(33) If the system changes to state Z.sub.2, this changes at least the surface energy of the pore surface of the membrane 32, so that a second contact angle Θ.sub.2<Θ.sub.1 is formed between the pore surface and the boundary surface 36. In the sample embodiment of FIG. 5, state Z.sub.2 differs from state Z.sub.1 by an electric field E.sub.2≠E.sub.1 or by a potential difference V≠0. The instant after the switching is shown in snapshot “3”. The pore surface is now wetted more heavily with the medium M1 and the curvature of the boundary surface 36 is reduced.

(34) In the pressure vs. time diagram of FIG. 6A, the behavior in segment “3” is shown. The pressure difference begins to drop immediately after the electric field is turned on—the voltage curve is shown as a rectangle underneath the pressure curve. The reason for this is that, after the state Z.sub.2 is established, a different contact angle Θ.sub.2 results, corresponding to a pressure breakthrough Pdlo at which the boundary surface passes through the membrane, the breakthrough pressure P.sub.dlo now being smaller than the maximum delivery pressure P.sub.max.

(35) Under these conditions, the first medium M1 can penetrate more deeply into the pores 34 until the liquid surfaces of neighboring pores join up and form a new common front boundary surface. The membrane is entirely wetted and rinsed by the medium M1. Thus, the media are delivered onward, which is shown in snapshot “4”. The pressure difference has dropped, except for a constant value during segment “4”, which is slightly higher than the pressure difference at the time of snapshot “1”. This is due to the fact that the membrane 32 presents a greater flow resistance to the medium M1 in this example than it does to the medium M2. Therefore, in this sample embodiment, M1 has a higher viscosity than medium M2.

(36) The snapshot “5” shows the behavior of the fluidic system, which continues to be in state Z.sub.2, at the instant when the second boundary surface 42 touches the membrane 32, whereupon the delivery of the media M2, M1 and M3 through the pores of the membrane again stops. The stopping in the corresponding segment “5” of the diagram of FIG. 6 is confirmed by a pressure rise up to the maximum delivery pressure P.sub.max. The reason for this is that the third contact angle Θ.sub.3 forming between the boundary surface 42 and the pore surface corresponds to a breakthrough pressure P.sub.dhi, which is likewise greater than the maximum delivery pressure P.sub.max. Similar to segment “2”, also in segment “5” the initial wetting with the medium M3 upon reaching the membrane at first leads to a pressure drop for all contact angles >0°, as shown by the curve of the diagram in FIG. 6A.

(37) The breakthrough pressure P.sub.dhi for the boundary surface 42 is generally not the same as the breakthrough pressure for the boundary surface 36. These are only the same if Θ.sub.3=180−Θ.sub.1. Obviously, therefore, the medium M1 wets the pore surface of the membrane 32 more heavily than does the medium M3, which is consistent with a third contact angle Θ.sub.3<90°. From the standpoint of the medium M3, the situation at the boundary surface with the medium M1 is similar to that of snapshot “2” from the standpoint of the medium M1 at the boundary surface with the medium M2.

(38) In order for the rear boundary surface 42 to also become detached from the membrane 32, the fluidic system is switched to a state Z.sub.3 with an electric field E.sub.3≠E.sub.2, as shown in snapshot “6”. This again leads to an immediate pressure drop, because by changing at least one of the surface energies of the pore surface of the membrane 32 and/or the media a fourth contact angle Θ.sub.4>Θ.sub.3 is formed between the pore surface and the boundary surface 42, which corresponds to a breakthrough pressure P.sub.dlo, which is smaller than the maximum delivery pressure P.sub.max. After this, the media M3, M1 and M2 can be further transported in the direction of the arrow 40 by exerting a lower delivery pressure, see snapshot “7”, the necessary delivery pressure being dependent on the viscosity of the medium M3 and can be different than that in snapshots “1” or “4”.

(39) FIGS. 5 and 6 show that the invention makes it possible to transport the medium M1 in controlled manner through the membrane 32 by a switching of the states, here, the electric field or the voltage applied between the electrodes 38 and the membrane 32. In a typical application, the medium M1 is a drop of liquid, while media M2 and M3 are gases, preferably the same gas. Accordingly, it makes sense to choose identical states Z.sub.3 and Z.sub.1.

(40) Before the switching on or off of the voltage during the switching from state Z.sub.1 to Z.sub.2, and from Z.sub.2 to Z.sub.3, it may make sense to initially reduce the delivery pressure on account of the very fast pressure drop, in order to prevent an abrupt formation of the combined new boundary surfaces 36 and 42.

(41) The sample embodiment shown in FIG. 6 shows the case of a volume control in which the system strives to maintain the transported volume constant, and the switching of the states occurs after reaching the maximum delivery pressure. Alternatively, the system can also be set up to automatically implement the states in order to relieve the load on the system even before reaching a threshold pressure. For this purpose, the delivery pressure must be monitored by means of a pressure sensor and upon crossing the threshold pressure in the first volume M1 it must be set automatically at the second state by means of a controller. The threshold pressure can be chosen freely, but in any case it is less than the maximum delivery pressure.

(42) FIG. 6B shows a pressure-controlled fluidic system as an alternative. This system strives to maintain a constant pressure difference. This occurs by means of a monitoring of the volume flow V. In segment “1” of FIG. 5 the volume flow is constant. If the front boundary surface 36 between the medium M1 and medium M2 reaches the pore surface of the membrane 32, this results in an initial transient rise in the volume flow and then a very rapid decline, down to total stoppage of the transport in segment 2 of the diagram, because the delivery pressure is not enough to overcome the boundary surface tension.

(43) The constant delivery pressure P.sub.c, once more, is dictated by the system and established by the dimensioning of the delivery pump or by pressure limiting means.

(44) After switching from state Z.sub.1 to Z.sub.2, as shown by the broken line 44 of the voltage, the volume flow again rises in segment “3”, until a volume flow corresponding to the constant delivery pressure P.sub.c is reached, which is less than that in segment “1” on account of the different flow resistance of the medium M1. If the rear boundary surface 42 between the medium M1 and the adjacent medium M3 reaches the membrane, the volume flow after a transient initial rise again collapses because the constant delivery pressure P.sub.c is once more smaller than the breakthrough pressure P.sub.dhi corresponding to the contact angle Θ.sub.3. This configuration is maintained in segment “5” until the voltage, or the electric field, is again switched off and a state Z.sub.3 is produced, in which the rear boundary surface 42 can also become detached from the membrane 32, see segment “6” in the diagram of FIG. 6B. The volume flow now rises again. If the media M2 and M3 are identical or have at least the same viscosity, the volume flow in segment “7” will be equal to that in segment “1”.

(45) In FIGS. 7A to 7C the fluidic system is again shown schematically, but in somewhat more detail. The surface of the fluidic line 50 is formed in a substrate of an essentially flat microfluidic chip 52, as shown, for example as a channel in the plane of the substrate 52. It is also possible, in a departure from this, to arrange the membrane in a segment of the fluidic line in which it changes sides perpendicular to the plane of the substrate. A membrane 54 is preferably introduced perpendicular to the direction of the line, geometrically separating the fluidic line 50 into a first volume V1 and a second volume V2. The membrane 54, or more precisely the core of the membrane, not shown here explicitly, or a deeper lying layer of the membrane 54, is electrically conductive and connected to a voltage source. The surface of the fluidic line 50 is provided with a second electrode in the immediate vicinity of the membrane 54. This second electrode can surround the membrane 54, for example, as a ring. It can be vaporized or otherwise deposited as a layer on the inner surface of the fluidic line 50. The precondition for this second electrode 56 is that it protrudes into the first volume V1 and into the second volume V2 and can produce a contact here with the media situated in these volumes. If a voltage difference is imposed between the first electrode in the membrane 54 and the second electrode 56, an electric field will form in the region of the membrane 54. This electric field is used in the above described manner to manipulate the contact angle between the pore surface of the membrane 54 and a boundary surface 58 between a first medium M1 and a second medium M2 between the pore surface of the membrane 54 or a second boundary surface 60 between the first medium M1 and a third medium M3.

(46) FIGS. 8A to 8G show a sample use of the fluidic system of the invention, being used here as a valve without mechanically moving parts. The fluidic system in this case has four volumes V1, V2, V3 and V4. The second volume V2 is geometrically separated from the first volume V1 by means of a first membrane 80, from the third volume V3 by means of a second membrane 82 and from the fourth volume V4 by means of a third membrane 84. The first volume V1 together with the second volume V2 and the first membrane 80 is part of a first fluidic system 86 of the above-described kind, the second volume V2 together with the third volume V3 and the second membrane 82 is part of a second fluidic system 88, and the second volume V2 together with the fourth volume V4 and the third membrane 84 is part of a third fluidic system 90. All three membranes are identical in construction and therefore have the same surface energies in the same state.

(47) The first fluidic system 86 according to FIG. 8A is in a state Z.sub.2, in which a potential difference U is imposed between the first and the second electrode of the first membrane 80; the second fluidic system 88 is in a state Z.sub.1 in which no potential difference U is imposed between the first and the second electrode of the second membrane 82; and the third fluidic system 90 is in a state Z.sub.1 in which no potential difference U is imposed between the first and the second electrode of the third membrane 84. If a first medium M1 is under pressure in the first volume V1, thanks to the wettability of the first membrane 80 it can pass through the latter and penetrate to the second and third membrane. In the third volume V3 and the fourth volume V4 there is a second medium M2 and this forms a boundary surface with the first medium M1 at the second and third membrane 82, 84. It is assumed that the medium M1 wets the pore surface of the second and third membranes in state Z.sub.1 less than the medium M2, so that a contact angle Θ.sub.1>90° is formed here from the standpoint of the medium M1. The transporting of the media from the volume V2 into the volumes V3 and V4 stops under the condition that the delivery pressure does not exceed the breakthrough pressure at the membrane 82. The same holds at the third membrane 84.

(48) This changes, according to FIG. 8B, when the system is switched to a state Z.sub.2 by changing the potential difference at the second membrane 82. Hereupon, the medium M1 wets the pore surface of the membrane 80 in the manner described above and can be transported through the pores of the membrane into the volume V3 without increasing the delivery pressure. In this state according to FIG. 8B it is assumed that the relations at the third membrane 84 have not changed, so that in this regard still no transport of the medium M1 into volume V4 can occur.

(49) In FIG. 8C, the voltage in the region of the first membrane 80 is again removed, so that the transport of the medium M1 through the first membrane 80 stops. At the same time, the portion of the medium M1 already transported through the membrane 80 is further transported with the help of the medium M2 from the fourth volume V4 into the volume V3. The process stops when the boundary surface between the first and the second medium reaches the second membrane 84. By switching the system 88 at the second membrane 84 back to the state Z.sub.1, see FIG. 8D, the first medium M1 can be further transported in the third volume V3, until for example the starting state is again restored, as shown in FIG. 8A. According to FIG. 8E to 8G, the switching sequence repeats between states Z1 and Z.sub.2 with the reverse polarity at the second and third membranes 82 and 84, so that a limited volume of the medium M1 is now transported away through volume V4.

(50) In this simple design, a fluidic system can be created for separation of liquid columns without mechanical valves. The operating of such a valve by applying voltages is much more simple in design than mechanical valves, which require mechanical actuators. It is also less prone to error and wear.

(51) Another application of the fluidic system of the invention is its use as a switchable filter for separating two media which cannot dissolve into each other or mix with each other.

(52) Although only sample embodiments making use of electro-wetting are described above, it should be pointed out once more that this phenomenon is mentioned only as an example, and it can be replaced by an electromagnetic radiation or temperature increase at the membrane with identical effect.

(53) The invention further relates to the following:

(54) 1. A method for operating a fluidic system with a first volume, a second volume, and a membrane geometrically separating the two volumes, which provides an open-pore microstructure with a pore surface, comprising the steps: producing a first state Z.sub.1 with a first electric field E.sub.1 in a region of the membrane and a first electromagnetic radiation exposure S.sub.1 acting on the membrane and a first temperature T.sub.1 of the membrane, wherein the pore surface, a first medium and a second medium have surface energies and wherein the membrane has a pore surface which is not wetted or less wetted by the first medium and more heavily wetted by the second medium, transporting the first medium and the second medium, between which a boundary surface is formed, from the first volume through the membrane into the second volume until the boundary surface touches the membrane, wherein a first contact angle Θ.sub.1>90° is formed between the pore surface and the boundary surface in the first medium and the transporting is halted while the first medium is still situated mainly in the first volume and the second medium is already mainly in the second volume, producing a second state Z.sub.2 with a second electric field E.sub.2≠E.sub.1 in the region of the membrane and/or a second electromagnetic radiation exposure S.sub.2≠S.sub.1 acting on the membrane and/or a second temperature T.sub.2≠T.sub.1 of the membrane, wherein at least one surface energy is reversibly changed so that a second contact angle Θ.sub.2<Θ.sub.1 is formed between the pore surface and the boundary surface, and further transporting of the first and second medium until the first medium is also taken through the membrane and mainly into the second volume.

(55) 2. The method according to 1, wherein the second contact angle in the second state is Θ.sub.2<90°.

(56) 3. The method according to one of 1 or 2, wherein the first state Z.sub.1 is defined by a first electric field E.sub.1=0, a first electromagnetic radiation exposure S.sub.1 in a form of daylight or room lighting or darkness, and a first temperature T.sub.1 in the range of normal room temperature.

(57) 4. The method according to one of 1 to 3, wherein the transporting occurs with a constant volume flow Vc up to a maximum delivery pressure P.sub.max.

(58) 5. The method according to 4, wherein the first contact angle Θ.sub.1 corresponds to a breakthrough pressure P.sub.dhi at which the boundary surface passes through the membrane and which is greater than the maximum delivery pressure P.sub.max.

(59) 6. The method according to 5, wherein the second contact angle Θ.sub.2 corresponds to a breakthrough pressure P.sub.dlo at which the boundary surface passes through the membrane and which is smaller than the maximum delivery pressure P.sub.max.

(60) 7. A method according to one of 4 to 6, further including detecting a pressure change in the first or second volume and putting out a pressure change signal.

(61) 8. The method according to 7, wherein a second state Z.sub.2 is produced in response to the pressure change signal and upon going above a threshold pressure in the first volume or going below a threshold pressure in the second volume.

(62) 9. The method according to one of 1 to 3, wherein the transporting occurs with a constant delivery pressure P.sub.c.

(63) 10. The method according to 9, wherein the first contact angle Θ.sub.1 corresponds to a breakthrough pressure P.sub.dhi at which the boundary surface passes through the membrane and which is larger than the constant delivery pressure P.sub.c.

(64) 11. The method according to 10, wherein the second contact angle Θ.sub.2 corresponds to a breakthrough pressure P.sub.dlo at which the boundary surface passes through the membrane and which is smaller than the constant delivery pressure P.sub.c.

(65) 12. The method according to one of 9 to 12, further including detecting a volume flow change in the second volume and putting out a volume flow change signal.

(66) 13. The method according to 12, wherein an electric field is applied in the region of the membrane or electromagnetic radiation is beamed onto the membrane or the membrane is heated in response to the volume flow change signal and crossing below a threshold volume flow.

(67) 14. The method according to one of 1 to 13, wherein the first medium has a limited volume with a second boundary surface to a third medium formed at its end in the delivery direction, while the further transporting of the first medium through the membrane into the second volume stops when the second boundary surface touches the membrane and a third contact angle Θ.sub.3 arises between the second boundary surface and the pore surface.

(68) 15. The method according to 14, with the additional steps: producing a third state Z.sub.3 with a third electric field E.sub.3≠E.sub.2 in the region of the membrane and/or a third electromagnetic radiation S.sub.3≠S.sub.2 acting on the membrane and/or a third temperature T.sub.3≠T.sub.2 of the membrane, wherein by changing at least one surface energy a fourth contact angle Θ.sub.4<Θ.sub.3 is formed between the pore surface and the boundary surface, further transporting of the first medium in the second volume.

(69) 16. The method according to 15, wherein the third contact angle is Θ.sub.3<90° in the second state Z.sub.2 and the fourth contact angle is Θ.sub.4>90° in the third state Z.sub.3.

(70) 17. The method according to one of 14 to 16, wherein the second medium and the third medium are the same.

(71) 18. The method according to one of 15 to 17, wherein the first state Z.sub.1 and the third state Z.sub.3 are the same.

(72) 19. The method according to one of 1 to 18, wherein the second electric field E.sub.2 is applied in the region of the membrane with a field strength of 1 V/m to 10 kV/m.

(73) 20. The method according to one of 1 to 19, wherein light of a wavelength between 0.1 μm and 3 μm is beamed onto the membrane.

(74) 21. The method according to one of 1 to 20, wherein the membrane is heated to a temperature T.sub.2 between 10° C. and 100° C.

LIST OF REFERENCE SYMBOLS

(75) 10 boundary surface 11 substrate surface 12 substrate electrode/first electrode 14 dielectric layer 16 second electrode 18 voltage source 20 membrane element 22 membrane plane 24, 24′, 24″ boundary surface 26, 26′, 26″ contact point 30 fluidic line 32 membrane 34 membrane pore 36 first boundary surface 38 second electrode 40 transport direction 42 second boundary surface 44 voltage signal 50 fluidic line 52 substrate of a microfluidic chip 54 membrane 56 second electrode 58 first boundary surface 60 second boundary surface 80 first membrane 82 second membrane 84 third membrane 86 first fluidic system 88 second fluidic system 90 third fluidic system M1 first medium M2 second medium M3 third medium V1 first volume V2 second volume V3 third volume V4 fourth volume Z.sub.1 first state Z.sub.2 second state Z.sub.3 third state Θ.sub.1, Θ.sub.2, Θ.sub.3 contact angle P.sub.1, P.sub.1′, P.sub.1″ pressure in first medium P.sub.2, P.sub.2′, P.sub.2″ pressure in second medium α, α′, α″ distance of contact points from the membrane plane α, α′, α″ angle of contact points to the membrane plane r radius of the membrane element d minimum pore diameter P.sub.max maximum delivery pressure