METHOD FOR FORMING A COMPACT FILM OF PARTICLES ON THE SURFACE OF A CARRIER LIQUID

Abstract

A method for forming a compact film of particles on a surface of a carrier liquid, including: positioning at least one particle support in the carrier liquid, the support including at least one solidified portion in which the particles are trapped and that is made from at least one cooled liquid, melting of the support in the carrier liquid resulting in release of the particles on the surface of the carrier liquid; and organizing the released particles to obtain the compact film of particles on the surface of the carrier liquid.

Claims

1-19. (canceled)

20. A method for formation of a compact film of particles at a surface of a carrier liquid comprising: setting up at least one support for the particles in the carrier liquid, wherein the support includes at least one solidified portion wherein the particles are trapped and which is made from at least one cooled liquid, wherein the support melting into the carrier liquid leads to particles being released at the surface of this carrier liquid; and ordering the particles released to obtain the compact film of particles at the surface of the carrier liquid.

21. A method according to claim 20, wherein the particles are non-spherical in shape.

22. A method according to claim 20, wherein the particles are micrometric or nanometric size, and have a largest dimension of between 1 nm and 500 μm.

23. A method according to claim 20, wherein the carrier liquid is deionized water.

24. A method according to claim 20, wherein the solidified part of the support, wherein the particles are trapped, includes water.

25. A method according to claim 24, wherein the solidified part of the support, wherein the particles are trapped, further includes a solvent wherein the particles were initially present, in suspension.

26. A method according to claim 20, wherein the setting up the one or more particle support is carried such that the support floats on the surface of the carrier liquid.

27. A method according to claim 26, wherein the particles are grouped together at one loaded surface of the support, and the setting up the one or more particle supports is achieved such that the loaded face of the support is substantially at the carrier liquid surface level.

28. A method according to claim 20, further comprising a prior fabrication of the one or more support wherein the particles are trapped.

29. A method according to claim 28, wherein the fabrication of the support wherein the particles are trapped comprises: a) introducing a quantity of water into a container containing a solvent that is immiscible with water and whose density is less than that of water, with the particles arranged in suspension in the solvent, so that the particles migrate to an interface between the water and the solvent; b) cooling to obtain the support comprising at least one solidified part wherein the particles are trapped.

30. A method according to claim 29, further comprising extracting all or part of the solvent between a) and b).

31. A method according to claim 29, wherein the cooling operation completely or partially solidifies the solvent introduced into the container.

32. A method according to claim 28, wherein the fabrication of the support wherein the particles are trapped comprises formation of a block of solidified water.

33. A method according to claim 32, wherein the fabrication of the support wherein the particles are trapped further comprises pouring a solvent in which the particles are arranged in suspension, onto the block of solidified water.

34. A method according to claim 33, wherein an assembly formed by the block of solidified water and the solvent incorporating the particles is cooled such that the solidified part of the support comprises at least a part of the solvent.

35. A method according to claim 32, wherein the fabrication of the support wherein the particles are trapped further comprises pouring the particles in powder form directly onto the block of solidified water.

36. A method according to claim 28, wherein the fabrication of the support wherein the particles are trapped comprises: a) introducing the particles into a bottom of a container: b) introducing water into the container to keep the particles in the bottom of the container; c) cooling to obtain the support comprising at least one solidified part wherein the particles are trapped.

37. A method for deposition of a compact film of particles onto a substrate, comprising use of the method for formation of a compact film of particles at the surface of a carrier liquid according to claim 20, followed by deposition of the compact film of particles on a substrate.

38. A method for deposition according to claim 37, wherein the deposition of the compact film of particles implemented on a moving substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] This description will be made in relation to the appended drawings, wherein:

[0057] FIG. 1 shows an installation for implementation of the method according to the invention, in longitudinal section;

[0058] FIG. 2 shows a top schematic view of the installation shown in FIG. 1;

[0059] FIGS. 2a to 5b schematically show the various steps of a method for formation and for deposition of a compact film of particles according to one preferred embodiment of the inventions, implemented using the installation shown in the preceding figures; and

[0060] FIGS. 6 to 8 show different possibilities for fabrication of the particles support implemented in the method shown schematically in FIGS. 2a to 5b.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0061] With reference first of all to FIGS. 1 et 2, an installation 1 is shown for the formation of a compact film of particles and for its transfer onto a substrate which is preferably moving. The particles concerned, not shown in FIGS. 1 and 2, are envisaged as being initially placed in suspension in a solvent. These particles have a size which may be between a few nanometres and several hundred micrometres. The particles or colloids are preferably non-spherical in shape. They may take longilinear forms such as fibres, threads, tubes or rods or more complex forms such as polygons, tetrapods, cubes, prisms, polygons etc. For the purposes of simplification of the following figures, the particles are shown in them as simple tubes with dimensions greater than the actual dimensions.

[0062] The materials that may be envisaged for these particles will depend on the desired applications. They may be, for example, particles of silica, of glass fibre, carbon nanotube particles or particles of gallium nitride fibres. Other particles of interest may be made of metal or of metal oxide such as Platinum, TiO2, of polymers such as polystyrene or PMMA, of carbon fibres etc., or particles made up of several materials. More precisely, in the preferred embodiment the particles are made of glass fibre of diameter of the order of 10 μm, and whose length is of the order of 4 mm. It should be noted that the invention applies in particular to thread-like elements whose largest dimension is more than ten times greater than the smallest dimension. As will be described in detail below, the particles are intended to be placed in suspension in a solvent, here of a type such as butanol or chloroform, where the proportion of the medium is about 7 g of particles per 200 ml of solvent.

[0063] The installation also comprises a liquid conveyor 10 which receives a carrier liquid 16 upon which the particles are intended to float. The carrier liquid 16 is preferably deionised water. The conveyor 10 incorporates a zone 14 for the accumulation and transfer of the particles, whose bottom is essentially horizontal, or slightly inclined in order to favour drainage from the installation if necessary.

[0064] The zone 14 exhibits an outlet for the particles 26, defined using two lateral ledges 28 which retain the carrier liquid 16 in the zone 14. These edges 28, facing each other and set a distance apart, extend parallel to a principal direction represented schematically by the arrow 30 in FIGS. 1 and 2. This direction 30 corresponds to that of the movement of the compact film of particles during its transfer onto the substrate, as will be described in detail hereafter.

[0065] The bottom of the downstream part of the zone 14 has a plateau which is slightly inclined towards the upstream direction relative to the horizontal direction, for example with a value of the order of 5 to 10°. The downstream extremity of this same plateau, also known as the “blade” partially defines the outlet for the particles 26.

[0066] The installation 1 is also provided with a substrate conveyor 36 intended to set the substrate 38 in motion. This substrate may be rigid or flexible. In this last case, which is not shown, it may be set in motion on a roller whose axis is parallel to the outlet 26 from the zone 14 close to which it is located.

[0067] Irrespective of the envisaged configuration, the substrate 38 is intended to move in such a way that it is very close to the outlet 26, in order that the particles reaching this outlet can be easily transferred onto this substrate, via a capillary bridge 42, also known as a meniscus, which links it to the carrier liquid 16. The capillary bridge 42 is achieved between the carrier liquid 16 which is located at the outlet 26, and a part of the substrate 38 which fits against the guide/drive roller 40. Alternatively, the substrate can be in direct contact with the transfer zone, without going beyond the scope of the invention. The capillary bridge mentioned above is no longer required.

[0068] For information, in the case of the substrate being rigid and the objects to be transferred also being rigid and being unable to adapt to an angular break during transfer, it may be advantageous to immerse the substrate in the liquid of the accumulation and transfer zone 14 and to carry out the withdrawal in this configuration. This will maximise the angle formed between the horizontal plane of the liquid of the zone 14 and the plane of the substrate.

[0069] In the example shown in the figures, the width of the substrate 38 is slightly greater than the width of the zone 14 and of its outlet 26. The width of the zone 14 also corresponds to the maximum width of the film of particles that can be deposited on the substrate 38. This width may be of the order of 25 to 30 cm. The width of the substrate over which the particles must be deposited may however be less than the width of the zone 14, without going beyond the scope of the invention.

[0070] A method for formation and for deposition of a compact film of particles according to a preferred embodiment of the invention will now be described with reference to FIGS. 2a to 5b.

[0071] First of all with reference to FIGS. 2a and 2b, a support 40 for the particles in said carrier liquid 16 is set up. Initially this support 40 comprising at least one solidified portion in which the particles 4 are trapped, where this solidified part is made from at least one frozen liquid. Preferably, before it is introduced into the carrier liquid 16 the support is completely solidified, and comprises a lower part 42 which corresponds to frozen pure water together with an upper part 44 which corresponds to the solidified solvent. Alternatively, the solvent may take the form of a liquid film resting on pure frozen water. Whichever is the case, the particles 4 are trapped at the interface between the upper part 44 and lower part 42. Details of the fabrication of the support 40 will be given later.

[0072] The support 40, in its initial state has, for example, a cylindrical form with a circular cross-section, with a thickness of about 5 mm and a diameter of 40 mm. Greater dimensions may be chosen however without going beyond the scope of the invention. The particles 4 are grouped together at a loaded face of the support, which corresponds to the upper surface 40′, which is substantially flat and aligned horizontally.

[0073] Because of its composition essentially based on frozen water, the support 40 floats when it is introduced into the carrier liquid 16. This introduction is achieved in such a way that the charged face 40′ of the support 40 is substantially at the level of the surface 16′ of the carrier liquid 16, or close to the latter. This aim is easily achieved when the thickness of the solidified solvent 44 is small. Nevertheless, the solvent may not be entirely solidified, but made to be in a viscous state, for example.

[0074] Once introduced into the carrier liquid 16, the support 40 undergoes fusion and gradually melts, releasing the particles 4 which may then be dispersed, also gradually, at the surface of the carrier liquid 16, as has been shown schematically in FIGS. 3a and 3b.

[0075] As a result of the temperature gradient and the phase change during melting of the support 40, the fluid is not at rest, in particular as a result of the descent of the cold fluid. The liquid motion within the zone 14 thus promotes agitation of the surface which favours the dispersion of the particles 4. Furthermore, the local drop in temperature results in an increase of the surface tension of the carrier liquid 16 located close to block of frozen material 40. This effect is beneficial since it helps to keep the particles 4 at the surface 16′ of the carrier liquid 16. Moreover, due to the difference in surface tension between the water and the solvent as fusion occurs, the interfacial tension gradient induces hydrodynamic instabilities which thus contribute to local agitation of the two liquids, favouring the dispersion of the particles at the surface 16′ of the carrier liquid.

[0076] It should be noted that several supports 40 may be introduced successively or simultaneously into the carrier liquid in order to increase the quantity of the required particles. A pumping system (not shown) can in addition regulate the total volume of the liquid in the zone 14, taking into consideration the additional water added by the supports 40 introduced into this zone.

[0077] When the total amount of particles 4 are present at the surface 16′ in the accumulation and transfer zone 14, they are pushed in the direction of the outlet 26 by a barrier 50 or a similar element. This barrier 50 is in effect moved along the direction 30 so that the particles 4 are ordered by being retained upstream by the substrate 38 forming an end stop.

[0078] This ordering by means of the barrier 50 and the substrate 38 generates a compact film 4′ of particles 4, as has been shown schematically in FIGS. 4a and 4b.

[0079] Alternatively, it is possible to set up a ramp conveyor as described earlier, in which the particles are automatically ordered, without assistance, in particular because of their kinetic energy and use made of the capillary forces at the moment of impact onto the leading edge of the particles present on the ramp. In this instance, the supports 40 are then preferably placed in the reservoir of the conveyor, upstream of the ramp.

[0080] Other means of ordering known to those skilled in the art may also be envisaged without going beyond the scope of the invention.

[0081] The ordering desired is such that the compact film obtained exhibits a structure that is similar to a “compact hexagonal” structure in the case of spheres, wherein each particle 4 is surrounded by and in contact with six other particles 4 which are in contact with each other. This may be referred to either as a compact film of particles or equally as a film of ordered particles.

[0082] Once the film 4′ has been obtained at the surface of the carrier liquid 16 in the zone 14, a step involving structuring of this film may be carried out, details of which will not be given here, but which is known to those skilled in the art. This involves, for example, placing objects on the compact film.

[0083] Then the substrate 38 is set in motion at the same time as the barrier 50 continues to undergo displacement downstream, so as to gradually deposit the film 4′ on this substrate 38 via the capillary bridge 42. This step of deposition of the film 4′, also known as the transfer step, has been shown schematically in FIGS. 5a and 5b. In effect, when the substrate 38 starts to move past, the film 4′ is deposited on it by passing through the outlet 26 and over the capillary bridge 42, in the manner described in document CA 2 695 449. A solution using direct contact rather than a capillary bridge can also be envisaged without going beyond the scope of the invention.

[0084] In order to facilitate the deposition and the adhesion of particles 4 onto the substrate 38 made, for example, of polymer, thermal annealing subsequent to the transfer may be envisaged. This thermal annealing may be carried out, for example, at 80° C., using a polyester-based low temperature mat lamination film, for example that sold under the name PERFEX-MATT™, with a thickness of 125 μm. The advantage of such a film as a substrate is that one of its faces becomes adhesive at temperatures of the order of 80° C. This facilitates the adhesion of the particles 4 onto the film. More specifically, at this temperature the particles 4 sink into the softened film 38, enabling direct contact to be made with the film, which leads to adhesion of the particles.

[0085] Alternatively, the substrate 38 may be of the silicon, glass or even piezoelectric film type.

[0086] During transfer the linear velocity of the substrate 38, also known as the draw speed, may be of the order of 0.1 cm/min to 100 cm/min.

[0087] With reference now to FIG. 6, a first technique for fabrication of the support 40 is shown.

[0088] First of all, a container 60 is envisaged in which the solvent 3 incorporating the particles 4 in suspension is arranged. A given quantity of pure water is then introduced into the container 60. The solvent 3, butanol, is immiscible with water and has a density which is less than that of water. Thus, after the pure water is introduced, the particles 4 migrate so that they are arranged in a horizontal plane at the interface between the water 5 located above and the solvent located below. The migration can be encouraged by stirring in the container.

[0089] According to a first possibility, the assembly 60′ is then cooled directly in order to obtain the aforementioned support 40. The cooling temperature is therefore preferably below the melting point of the solvent, so that the solidified part of the support incorporates both the pure water and the solvent, with the particles trapped at the interface.

[0090] According to another possibility, an operation for extraction of the solvent is carried out such that only a very thin layer is retained above the water, or this solvent is even removed altogether. The assembly 60″ is then frozen, in order to obtain the support 40 whose solidified part made of pure water incorporates the particles 4. Any film 3′ of solvent that remains can be kept in the liquid state at a low temperature before the support 40 is introduced into the carrier liquid, or can also be solidified if the cooling temperature is sufficiently low.

[0091] According to a second technique for fabrication of the support 40 shown schematically in FIG. 7, an operation for the formation of a block of solidified pure water 70 in a container 60 is first of all carried out. Then an operation is carried out involving pouring a solvent 3, in which the particles 4 are in suspension, into the container 60, over the block of solidified water 70. This leads to the particles 4 migrating to the interface between the solvent 3 and the block of solidified water 70, so that they are trapped at the upper surface of the latter. Moving the particles to the interface can also be achieved by decantation. Then the surplus solvent is also preferably withdrawn, so that only a very thin layer of solvent remains, with the particles arranged at the interface between this layer and the ice. Removal of the solvent can be achieved by pipetting or by flowing under gravity.

[0092] The assembly then forms the support 40 which can then be introduced as it is into the carrier liquid.

[0093] According to another possibility, the assembly 60′ obtained can be cooled below the melting temperature of the solvent 3 so that the entire support 40 is solidified before it is introduced into the carrier liquid.

[0094] According to yet another possibility, after the block of solidified water 70 is obtained, an operation may be carried out involving pouring particles 4 in a powder state directly onto the upper surface of the block 70. These particles 4, when they come into contact with the upper surface of the block 70 are trapped by the latter.

[0095] Finally, with reference to FIG. 8, a third technique is shown schematically for fabrication of the support 40, which involves first of all introducing particles 4 into the bottom of a container 60. Then water 5 is poured into the container 60 so as to keep the particles 4 in the bottom of the container, by keeping the flow of water being poured low. To complete the process the assembly is cooled and solidified in order to obtain the support 40. The solidified part of the latter is then made up of a block of water wherein the particles 4 are trapped on the lower surface. When this support is introduced into the carrier liquid, it is preferably turned over so that the surface loaded with particles forms the upper surface of the support 40.

[0096] Naturally those skilled in the art may make various modifications to the invention which has just been described, solely as non-restrictive examples.