Composite Membrane and Method for Manufacturing Such a Membrane

Abstract

The present invention relates to a composite membrane (10) comprising a fibrous fabric (1) of nanofibres (11), wherein the thickness of the fabric (1) is between 10 nm and 50 m and said fabric is impregnated with a wetting liquid (A). According to the invention, the composite membrane is immersed in a second fluid (B) which is immiscible with the wetting liquid (A), forming an A/B interface between the wetting liquid (A) and the immiscible fluid (B), and the composite membrane is capable of remaining tensioned when it is compressed from its resting state until reaching dimensions corresponding to 5% of its dimensions in the resting state, and when it is stretched from its compressed state until reaching dimensions corresponding to 2000% of the length in the compressed state. The present invention also relates to a process for manufacturing such a membrane.

Claims

1. A composite membrane comprising a fibrous fabric of nanofibers, the thickness of the fabric being between 10 nm and 50 m, said fabric being impregnated with a wetting liquid, said composite membrane being characterized: in that it is immersed in a second fluid which is immiscible with the wetting liquid, forming an A/B interface between the wetting liquid and said immiscible fluid, and in that it is capable of remaining tensioned: when it is compressed from its resting state, until reaching dimensions corresponding to 5% of its dimensions in the resting state, and when it is stretched from its compressed state until reaching dimensions corresponding to 2000% of the length of the compressed state.

2. The composite membrane as claimed in claim 1, wherein the thickness of said fibrous fabric is between 500 nm and 30 m, and preferably between 1 m and 5 m.

3. The composite membrane as claimed in claim 2, wherein said nanofibers of the fibrous fabric have a diameter of between 100 nm and 500 nm, and preferably of about 200 nm.

4. The hybrid membrane as claimed in claim 1, wherein said A/B interface is an oil/air interface, an oil/water interface, or a glycerol/air interface, or an interface of water with surfactant/air.

5. The use of the membrane as defined in claim 1, as an organ capable of developing a mechanical force in reaction to an exterior stimulus, typically an artificial muscle.

6. The use of the membrane as defined in claim 1, for constituting a stretchable electronic circuit.

7. The use of the membrane as defined in claim 1, as a smart power circuit.

8. The use of the membrane as defined in claim 1, as a SLIPS membrane.

9. A process for manufacturing a composite membrane as defined in claim 1, comprising the following steps: A. forming a solution, in a solvent medium, of a material capable of being dissolved by said solvent medium; B. injecting said solution at a flow rate Q into a capillary tube having a diameter do subjected to an electrical voltage U of between 1 kV and 100 kV, the diameter do being between 0.5 mm and 2 mm, and preferably about 1 mm; C. forming, at the outlet of said capillary tube, a drop of said solution, said drop being electrically charged so as to bring about its destabilization in the form of a cone; D. ejecting, from said cone, a liquid cylinder toward an electrically conductive target, which is electrically earthed; E. evaporating said solvent during the ejecting of said liquid cylinder, resulting in a vortex instability generating solid nanofibers of the material; F. collecting, on a face of said target oriented toward said cylinder, said solid nanofibers so as to form a mat of nanofibers forming a fibrous fabric, said target being, prior to step B, covered with a non-stick coating; said process being characterized in that it also comprises, at the end of step F, an additional step G of wetting said fibrous fabric with a wetting liquid so as to form a wetted membrane, and in that it comprises a step H of immersing the wetted membrane thus obtained in a fluid which is immiscible with the wetting liquid, so as to create an A/B interface between the wetting liquid and said immiscible fluid and thus to form the composite membrane as claimed in the invention.

10. The process as claimed in claim 9, wherein said non-stick coating is a parchment paper.

11. The process as claimed in claim 9, wherein: said face of the target is a flat face located at a distance L from the outlet of said capillary tube which is between 5 cm and 15 cm, and said capillary tube is subjected to an electrical voltage U of between 10 kV and 15 kV.

12. The process as claimed in claim 11, wherein: said flat surface of the target is located at a distance L from the outlet of said capillary tube which is about 10 cm, and said capillary tube is subjected to an electrical voltage U of about 12 kV.

13. The process as claimed in claim 9, wherein said constituent material of the fabric is a polymer material chosen from the group consisting of the following polymers: polyacrylonitrile (PAN), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene oxide (PEO), and polyvinylidene fluoride (PVDF).

14. The process as claimed in claim 9, wherein said constituent material of the fabric is a polymer-inorganic network hybrid material, wherein the inorganic network may be, for example, SiO.sub.2 (silica), TiO.sub.2 (titanium dioxide), Fe.sub.2O.sub.3(iron oxide), in the form of an amorphous network or of crystallized nanoparticles.

15. The process as claimed in claim 9, wherein said A/B interface is an oil/air interface, an oil/water interface, or a glycerol/air interface, or an interface of water with surfactant/air.

Description

[0051] Other advantages and particularities of the present invention will result from the following description, given by way of nonlimiting example and produced with reference to the examples and to the appended figures:

[0052] FIG. 1 represents a schematic view from a side-on perspective of an electrically assisted extrusion device for carrying out the process according to the invention;

[0053] FIGS. 2A and 2B schematically represents the formation of the Taylor cone at the outlet of the capillary tube of the device of FIG. 1 (cf.

[0054] FIG. 2A) and the behavior in compression and in extension of the composite membrane according to the invention obtained at the end of the implementation of the process according to the invention using the device of FIG. 1 (cf. FIG. 2B);

[0055] FIG. 3 shows the use of the composite membrane according to the invention as a smart power circuit;

[0056] FIG. 4 shows the use of the composite membrane according to the invention as a SLIPS membrane.

[0057] The technical characteristics common to these figures are each denoted by the same numerical reference in the figures in question.

[0058] Schematically represented in FIGS. 1, 2A, and 2B, from a side-on perspective, is an electrically assisted extrusion device for carrying out the process according to the invention. This device is operated as follows: [0059] introduced into a solvent medium is a material capable of being dissolved by this solvent medium; in the case of a polymer material, a polymer solution 2 is formed; [0060] this solution 2 is then injected, at a flow rate Q, into a capillary tube 3 subjected to an electrical voltage U of between 1 kV and 100 kV (cf. FIG. 1 and photograph A of FIG. 2A); [0061] the formation of a drop 4 of solution 2 is observed at the outlet 3a of the capillary tube 3 (cf. photographs A and B of FIG. 2A); [0062] this drop 4 is electrically charged, which brings about its destabilization in the form of a cone 5 (cf. photo B of FIG. 2A); [0063] then, a liquid cylinder 6 (cf. photograph B of FIG. 2A) is continuously ejected from the cone 5 toward an electrically conductive target 7 (visible in FIG. 1 and FIGS. 2A and 2B), which is electrically earthed; [0064] during the ejection of the liquid cylinder 6, the solvent evaporates, which results in a vortex instability generating solid nanofibers of the material (cf. photograph A of FIG. 2A) at a flow rate consisting of thousands of nanofibers per second, resulting in the formation of a mat of nanofibers constituting the fibrous fabric 1 (cf. photo C of FIG. 2A); [0065] then, the fibrous fabric 1 is collected on a face 7a of the target 7 oriented toward the cylinder 6, the face 7a of the target 7 being previously covered with a non-stick coating 7b such as parchment paper; [0066] then, the fibrous fabric 1 thus obtained is wetted (cf. photograph D of FIG. 2B) with a wetting liquid A (in this case water), so as to form a wetted membrane; [0067] finally, the wetted membrane thus obtained is immersed in a fluid B (in this case air), which is immiscible with the wetting liquid A, so as to create an A/B interface between the wetting liquid (A) and said immiscible fluid (B). A composite membrane 10 according to the invention is obtained (cf. photograph E of FIG. 2B).

[0068] FIGS. 1, 2A, and 2B show that the face 7a of the target 7 on which the nanofibers/fibrous fabric are collected is a flat face. However, it is possible to use a target which is not flat, for example in the shape of a sphere.

[0069] Photograph D of FIG. 2B is a photograph showing the behavior in compression of the non-wetted fibrous fabric: bending/buckling of the fabric in compression is observed.

[0070] Photograph E of FIG. 2B shows the behavior in compression of the composite membrane 10 according to the invention: it is observed that, once wetted, the membrane undergoes self-tensioning under the action of a capillary voltage. This self-tensioning is reminiscent to that of a conventional film of soap on a frame.

[0071] On photographs D and E of FIG. 2B, X.sub.0 corresponds to the distance between the two ends of the membrane (X.sub.0=6 cm for the two images).

[0072] Photograph F of FIG. 2B is a detailed view of a part of the composite membrane according to the invention, showing an excess of wrinkles inside the liquid film.

[0073] FIG. 3 shows the use of the composite membrane according to the invention as a smart power circuit, and also as a stretchable electronic circuit. In particular, this figure shows that the electrical response of a smart fabric depends on its state of extension, whereas a stretchable electronic circuit refers to an extendable fabric which can transport electronic information in any state of extension. For such uses, the composite membrane according to the invention does not undergo fatigue and, consequently, electronic information can be produced through numerous compression cycles.

[0074] FIG. 4 shows the use of the composite membrane according to the invention as a SLIPS membrane. This figure shows in particular that these membranes are interchangeable, replaceable and adaptable to several surfaces. Thus, a SLIPS membrane according to the invention made of PVDF-HFP (fabric) with an A/B interface of silicone oil/air or silicone oil/water type can be attached to any type of surface; it will adapt to its shape in order to closely cover it. It gives excellent results for self-cleaning surfaces: [0075] in photograph A, the SLIPS membrane according to the invention is placed on a self-cleaning surface: a droplet of water falling onto the glass does not attach thereto. By virtue of the SLIPS coating, it begins to slide starting from a relatively small contact angle, of about 40 (scale bar: 0.5 cm); [0076] in photograph B, the SLIPS membrane according to the invention is placed on a hydrophobic surface. By virtue of this SLIPS treatment, the drop falls back on the surface without leaving traces (scale bar 1 cm); [0077] in photograph C, the SLIPS membrane according to the invention is placed on a hemisphere of glass treated with this SLIPS membrane according to the invention; the droplets of water slide over the SLIPS coating, whereas they remain trapped on a non-treated normal glass. [0078] The same is true for paper cocktail umbrellas represented in photograph D: the droplets of water slide if a SLIPS membrane according to the invention has been placed on the umbrella.

LIST OF REFERENCES

[0079] [1] G. Taylor. Disintegration of water drops in an electric field. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 280(1382):383-397, 1964. [0080] [2] M. S. Wilm and M. Mann. Electrospray and Taylor-Cone theory, Dole's beam of macromolecules at last. International Journal of Mass Spectrometry and Ion Processes 136.2-3 (1994): 167-180.