Installation and method with improved performance for forming a compact film of particles on the surface of a carrier fluid

Abstract

An installation for forming a compact film of particles on a surface of a carrier fluid, including: a zone acting as a reservoir of carrier fluid; an inclined ramp; a particle storage and transfer zone situated extending from the inclined ramp; a mechanism moving the fluid; a mechanism dispensing the particles in solution, configured to dispense the particles at the surface of the carrier on the surface of the carrier fluid in the zone acting as a reservoir; and a mechanism raising a level of the carrier fluid by capillary effect, arranged at a junction between the zone acting as a reservoir and the inclined ramp.

Claims

1. An installation for forming a compact film of particles on a surface of a carrier fluid, the installation comprising: a zone acting as a carrier fluid reservoir; an inclined ramp situated extending from the zone acting as a reservoir and whereon the particles can circulate gravitationally; a particle storage and transfer zone situated extending from the inclined ramp; moving means for moving the carrier fluid to make the carrier fluid circulate from the zone, acting as a reservoir, to the particle storage and transfer zone, via the inclined ramp; dispensing means for dispensing the particles in solution, the dispensing means dispensing the particles on the surface of the carrier fluid in the zone acting as a reservoir; and raising means for raising a level of the carrier fluid by capillary effect, the raising means arranged at a junction between the zone acting as a reservoir and the inclined ramp.

2. The installation according to claim 1, wherein the means for raising the level of carrier fluid by capillary effect includes a barrier of contacts spaced out from one another.

3. The installation according to claim 2, wherein the contacts are fitted with an interval of approximately 2 to 4 mm.

4. The installation according to claim 2, wherein the contacts have an overall conical, pyramidal, or tubular shape.

5. The installation according to claim 2, wherein the contacts are made of a hydrophobic material.

6. The installation according to claim 2, wherein the contacts have a ratio between height in mm and maximum width in mm thereof between 1:1 and 1:30.

7. The installation according to claim 2, wherein the contacts have a base approximately 2 mm in width and between 2 and 3 mm air height.

8. The installation according to claim 1, wherein the means for raising the level of the carrier fluid by capillary effect extends along a transverse direction of the installation parallel with the surface of the carrier fluid and orthogonal to a main flow direction of the carrier fluid from the zone acting as a reservoir to the particle storage and transfer zone.

9. The installation according to claim 1, further comprising a substrate for depositing the compact film of particles, the substrate facing an outlet of particles from the storage and transfer zone.

10. The installation according to claim 9, configured to carry out deposition of the compact film of particles on a conveyed substrate, the substrate being flexible or rigid.

11. The installation according to claim 1, further comprising a structure for deflecting particles that pass through the surface of the carrier fluid into the zone acting as a reservoir, the structure arranged downstream from the means for dispensing particles along the main flow direction of the carrier fluid from the zone acting as a reservoir to the particle storage and transfer zone, the structure configured to favour, along the transverse direction of the installation parallel with the surface of the carrier fluid and orthogonal to a main flow direction, spreading of the particles at the outlet of the zone acting as a reservoir, the structure for deflecting particles being permeable to the carrier fluid.

12. A method for forming a compact film of particles on the surface of a carrier fluid, comprising: providing an installation according to claim 1; and moving the carrier fluid to make the carrier fluid circulate from the zone acting as a reservoir to the particle storage and transfer zone, via the inclined ramp, and dispensing the particles in solution on the surface of the moving carrier fluid, in the zone acting as a reservoir, the moving the carrier fluid being carried out to generate, by capillary effect at the raising means, a bulge of carrier fluid.

13. The method according to claim 12, used for forming a compact film of particles having a size between 1 nm and 500 μm.

14. The method according to claim 12, wherein the carrier fluid is deionised water, and the particles are found in solution in a solvent having a surface tension less than that of deionised water, the solvent being n-butanol, methanol, chloroform, or a mixture of at least two thereof.

15. The method according to claim 14, wherein the solvent is n-butanol, methanol, chloroform, or a mixture of at least two thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) This description will be made with reference to the appended figures wherein:

(2) FIG. 1 shows an installation according to a preferred embodiment of the present invention, in a schematic section along the line I-I in FIG. 2;

(3) FIG. 2 represents a schematic top view of the installation shown in FIG. 1;

(4) FIG. 3 represents a perspective view of an example of an embodiment of the structure for deflecting the particles, fitted in the installation shown in the preceding figures;

(5) FIG. 4 shows an enlarged front view of a portion of the structure represented in the preceding figure;

(6) FIG. 5 represents a schematic front view of a further example of an embodiment of the structure for deflecting the particles, fitted in the installation shown in the preceding figures;

(7) FIG. 6 is a similar view to that in FIG. 3, with the zone acting as a reservoir embodied in a multi-compartmentalised fashion;

(8) FIG. 7 is a top view of that shown in FIG. 6;

(9) FIG. 8 is an enlarged side view showing the barrier of spaced contacts fitted in the installation shown in FIGS. 1 and 2;

(10) FIG. 9 is a front view of that shown in FIG. 8; and

(11) FIGS. 10a to 11b represent schematically different steps of a method for forming and depositing a compact film of particles according to one preferred embodiment of the invention, implemented using the installation shown in the preceding figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(12) With reference firstly to FIGS. 1 and 2, an installation 1 for forming a compact film of particles and transferring same onto substrate, which is preferably conveyed, is represented.

(13) The installation 1 includes means 2 for dispensing the particles 4 in solution. These particles have a size which may be between a few nanometers and several hundred micrometers. The particles, preferably spherical in shape, may for example be silica particles. Further particles of interest may be made of metal or metal oxide such as Platinum, TiO2, of polymer such as polystyrene or PMMA, of carbon, etc.

(14) More specifically, in the preferred embodiment, the particles are silica spheres between 1 nm and 500 μm in diameter, and more preferentially of the order of 1 μm. These particles 4 are stored in solution in the means 2. The proportion of the medium is approximately 7 g of particles per 200 ml of solution, in this case such as butanol or chloroform. Naturally, for the purpose of clarity, the particles 4 have been represented with a diameter greater than the actual diameter thereof.

(15) The dispensing means 2 having a controllable injection nozzle, approximately 500 μm in diameter.

(16) The installation also includes a fluid conveyor 10, receiving a carrier fluid 16 whereon the particles 4 are intended to float. The conveyor 10 incorporates a zone acting as a reservoir 11, an inclined ramp 12 for particle circulation, and a particle storage and transfer zone 14. The ramp 12 is situated extending from the reservoir 11, i.e. the inlet thereof is substantially merged with the outlet of the reservoir. The storage and transfer zone 14 is for its part situated extending from the inclined ramp, i.e. the inlet thereof is substantially merged with the outlet of the ramp, whereon the particles are intended to circulate gravitationally. In addition, the inclined ramp 12 creates a separation in the level between the reservoir 11 and the storage and transfer zone 14. The latter has a substantially horizontal bottom, or a slight inclination so as to favour draining of the installation, if required.

(17) The upper end of the inclined ramp 12 is provided to receive the particles from the reservoir 11, previously injected by the dispensing means 2. This ramp is straight, inclined by an angle between 5 and 60°, preferably between 10 and 30°, enabling the particles to be conveyed to the zone 14. Furthermore, the carrier fluid 16 circulates on this ramp 12, up to the storage and transfer zone 14. This fluid 16 is further moved by suitable means, for example a pump 18. This recirculation pump 18 thus ensures movement of the fluid 16 so as to make same circulate from the reservoir 11 to the storage and transfer zone 14, via the inclined ramp 12. Nevertheless, it may alternatively be envisaged to circulate a new fluid, via an open circuit.

(18) The carrier fluid 16 is preferably deionised water, whereon the particles 4 can float. It may also consist of an association of a plurality of non-miscible fluids. As a reminder, solvents such as chloroform or n-butanol have surface tensions of the order of 26.67 and 24.93 mN/m at 25° C., respectively, whereas deionised water has a surface tension of the order of 72 mN/m. The interfacial tension gradients resulting from these differences in values induce hydrodynamic instabilities, which are manifested as convection movements also known as Marangoni instabilities. The effects of these convection movements are attenuated by means specific to the invention, which will be described hereinafter.

(19) Back to the conveyor 10, it is noted that the lower end of the ramp 12 is connected to an inlet of the particle storage and transfer zone 14. This inlet 22 is situated at an inflection line 24 representing the junction between the surface of the carrier fluid present on the inclined plane of the ramp 12, and the surface of the carrier fluid present on the horizontal portion of the zone 14.

(20) The particle inlet 22 is spaced from a particle outlet 26 using two lateral edges 28 retaining the carrier fluid 16 in the zone 14. These edges 28, facing and at a distance from one another, extend parallel with a main flow direction of the carrier fluid and the particles in the installation, this direction being represented schematically by the arrow 30 in FIGS. 1 and 2. The edges 28 extend preferably along the entire length of the conveyor 10, from the reservoir 11 to the zone 14. They are spaced along a transverse direction 31 of the installation, parallel with the surface of the fluid 16 and orthogonal to the main flow direction 30.

(21) The three elements 11, 12, 14 of the conveyor 10 thus each have the shape of a corridor or a path open at the inlet and outlet thereof, although further geometries could be adopted, without leaving the scope of the invention.

(22) The bottom of the downstream portion of the zone 14 has a slightly inclined platform in the upstream direction with respect to the horizontal direction, for example by a value of the order of 5 to 10°. The downstream end of said platform, also known as a “blade”, partially defines the outlet of the particles 26.

(23) The installation 1 is also provided with a substrate conveyor 36, intended to convey the substrate 38. This substrate may be rigid or flexible. In the latter case, it may be moved on a roller 40 the axis whereof is parallel with the outlet 26 of the zone 14, in the vicinity whereof it is situated. Indeed, the substrate 38 is intended to be conveyed very close to the outlet 26, so that the particles reaching this outlet can be transferred easily onto this substrate, via a capillary bridge 42, also known as a meniscus, linking same to the carrier fluid 16. The capillary bridge 42 is provided between the carrier fluid 16 which is situated at the outlet 26, and a portion of the substrate 38 moulding the guide/drive roller 40. Alternatively, the substrate may be in contact directly with the transfer zone, without leaving the scope of the invention. The capillary bridge mentioned above is then no longer required.

(24) By way of information, in the case where the substrate is rigid and the objects to be transferred are also rigid and cannot be adapted to an angle break during transfer, it may be advantageous to immerse the substrate in the fluid of the storage and transfer zone 14, and perform pulling in this configuration. This makes it possible to maximise the angle formed between the horizontal plane of the fluid of the zone 14, and the plane of the substrate.

(25) In the example shown in the figures, the width of the substrate corresponds to the width of the zone 14 and the outlet 26 thereof. This width also corresponds to the maximum width of the film of particles that can be deposited onto the substrate. This width may be of the order of 25 to 30 cm. The width of the substrate whereon the particles are to be deposited may however be less than the width of the zone 14.

(26) The installation 1 also includes a structure 50 for deflecting particles 4, this structure being arranged at the reservoir 11, downstream from the dispensing means 2 along the main flow direction 30.

(27) The deflection structure 50 passes through the surface of the carrier fluid 16. It is configured to favour, along the transverse direction 31, spreading of the particles 4 at the outlet of the reservoir 11. For this purpose, the structure 50 extends all along the carrier fluid along the transverse direction 31, between a first and a second end opposite along said direction 31. It has a general shape defining at least one convex portion 50a viewed from an outlet of the reservoir, the dispensing means 2 being arranged immediately downstream from this convex portion. As seen more clearly in FIG. 2, the structure 50 has a parabolic general shape, with the convex portion 50a corresponding to the apex thereof. In addition, from this apex, the parabolic structure 50 extends downstream and towards the edges 28 up to the vicinity of the outlet of the reservoir, which makes it possible to spread the particles 4 along the direction 31 before they reach the inclined ramp 12. At the outlet of the reservoir 11 feeding the ramp 12, without this structure 50, the density of the particles 4 would be greater at the centre than on the edges of this reservoir 11.

(28) One of the specificities of the invention lies in that the deflecting structure 50 is permeable to the carrier fluid. This function is carried out by an alternation, between the first and second ends thereof, of obstacles 52 and spaces 54 separating these obstacles. FIGS. 3 and 4 show an example of an embodiment wherein the obstacles 52 are screw rods screwed onto a support plate 56, resting for example in the bottom of the reservoir. This plate 56 is thus perforated with holes each receiving a screw 52, these holes being created along an imaginary line of parabolic shape, corresponding to that sought for the structure 50.

(29) The obstacles 52 are fitted with an interval “p” of approximately 5 mm. Furthermore, the deflecting structure 50 is embodied so as to present, at the surface of the fluid 16, an open area ratio of approximately 0.5. This open area ratio corresponds to the ratio between the sum of the lengths “d1” of the spaces 54, and the sum of the lengths “d1” and the lengths “d2” of the screw rods 52 corresponding to the diameter thereof, for example of the order of 3 mm.

(30) The screw rods 52 and the support plate 56 are preferentially made of hydrophobic material, for example, polymer material.

(31) In addition, when the fluid 16 is moved in the reservoir 11 towards the ramp 12, it passes through the spaces 54 and abuts against the screw rods 52, so as to spread and impede the Marangoni instabilities. The risks of dewetting of the ramp 12 are thus considerably reduced, even when the surface tensions differ considerably between the carrier fluid and the solution incorporating the particles.

(32) According to one alternative embodiment shown in FIG. 5, the obstacles 52 could be connected to an upper supporting member 56, similar to a comb. The supporting member 56 would then no longer be immersed in the carrier fluid traversed by the rods 52, but situated above this fluid by being for example connected to the edges 28 of the conveyor.

(33) Regardless of the solution selected, it may be supplemented by the embodiment, in the reservoir 11 downstream from the deflecting structure 50, of at least one compartment 60 defined by a wall 62 permeable to the carrier fluid 16. Such an arrangement is represented in FIGS. 6 and 7, wherein the reservoir 11 is multi-compartmentalised downstream from the deflecting structure 50.

(34) The walls 62, which also pass through the surface of the fluid 16, make it possible to impede the propagation of the hydrodynamic instabilities even further. These permeable walls 62 are embodied in a manner substantially identical or similar to the structure 50, i.e. by obstacles and spaces allowing the passage of the carrier fluid. In addition, all the features described for the structure 50 are applicable to the walls 62 defining the compartments 60, the surface area whereof on the surface of the fluid 16 may be between 2 and 500 cm.sup.2. In particular, the wall 62 may be embodied by screw rods passing through the surface of the carrier fluid, and screwed into corresponding screws created via the support plate 56 also bearing the deflecting structure 50.

(35) The shape of the compartments 60 may vary. In the example represented, some walls 62, defining a plurality of compartments, have a parabolic shape substantially homothetic in respect of that of the deflecting structure 50.

(36) The walls 62 being arranged downstream from the means 2 for dispensing the particles 4, these may hence be brought to pass through these walls 62 before reaching the inlet of the ramp 12.

(37) It is noted that the instabilities and particles may pass through the structure 50 from downstream to upstream. This is a temporary phenomenon since the flow of carrier fluid pushes the whole back to the inclined plane, downstream. The advantage of such a situation is that of also benefiting from the upstream structure 50 to deconfine the instabilities further. Furthermore, the profile of the structure 50, for example parabolic, circular, V-shaped, sinusoidal, etc., distorts the flow lines on the surface to favour spreading of the particles and instabilities over the width 31.

(38) A further specificity of the invention lies in that it envisages, arranged at a junction 73 between the reservoir 11 and the inclined ramp 12, means 70 for raising the level of the fluid 16 by a capillary effect. It is noted that this junction 73 between the reservoir 11 and the ramp 12 is situated at an inflection point of the fluid between these two elements of the conveyor 10.

(39) These means 70, preferably embodied by a transverse barrier of contacts 72 spaced from one another, locally raise the level of carrier fluid 16, immediately before the entry thereof onto the inclined ramp 12. This barrier is represented in more detail in FIGS. 8 and 9. Indeed, the constituent blocks 72 thereof enable the creation of a transverse bulge of fluid 74 at the junction between the reservoir 11 and the ramp 12, by means of a capillary effect compensating for the weight of this carrier fluid. This technique, intended to create the bulge 74 protruding upwards, makes it possible to reduce the fluid thickness variation phenomenon further, resulting from the interfacial tension gradients between this fluid 16 and the solution including the particles 4. The risks of dewetting the ramp 12 are thus reduced further by the use of this arrangement.

(40) The contacts 72 are arranged along the entire width of the reservoir 11, along the direction 31. They are fitted with an interval “p′” of approximately 2 to 4 mm. The contacts have a conical overall shape, with the base situated at the bottom, having a width/diameter “d3” of approximately 2 mm, and a height “h” between 2 and 3 mm. These contacts are made of hydrophobic material, for example silicone.

(41) A method for forming and depositing a compact film of particles according to one preferred embodiment of the invention will now be described with reference to FIGS. 10a to 11b.

(42) Firstly, the injection nozzle 6 is activated to start dispensing the particles 4 into the reservoir 11. This involves implementing an initial step for filling the storage and transfer zone 14, by the particles 4, with the carrier fluid 16 already at the required level in the zone 14. This step is represented schematically in FIGS. 10a and 10b.

(43) During this activation phase, the dispensed particles 4 are guided by the structure 50 and pass through the compartments when said compartments are provided in the reservoir 11, before reaching the ramp 12. The particles 4 then enter the zone 14 wherein they are dispersed.

(44) As the particles 4 are injected and enter the storage and transfer zone 14, they abut against the substrate 38, then the upstream leading edge of these particles tends to be shifted upstream, towards the inflection line 24. The injection of particles is continued even after this upstream leading edge has exceeded the line 24, so that they move up on the inclined ramp 12.

(45) Indeed, it is ensured that the upstream leading edge of particles 55 moves up on the ramp 12 such that it is situated at a given horizontal distance “d4” from the inflection line 24, as shown in FIG. 11a. The distance “d4” may be of the order of 30 mm.

(46) At this time represented in FIGS. 11a and 11b, the particles 4 are organised in the zone 14 and on the ramp 12, whereon they are organised automatically, without assistance, notably due to the kinetic energy thereof and the capillary forces used at the time of impact on the leading edge 55. The organisation is such that the first compact film obtained has a so-called “compact hexagonal” structure in the case of spheres, wherein each particle 4 is surrounded and contacted by six other particles 4 in contact with one another. The terms compact film of particles or film of organised particles are then used equally.

(47) Once the organised particles 4 forming the film cover all the carrier fluid situated in the zone 14, a step for structuring this film may be carried out, which will not be detailed herein, but which is known to those skilled in the art. It consists for example of positioning objects on the compact film.

(48) Then, the movement of the substrate 38 is carried out, initiated once the leading edge 55 has reached the required level represented in FIG. 11a, and after any structuring process mentioned above. Alternatively, the structuring could be carried out after the deposition of the film on the substrate, without leaving the scope of the invention.

(49) When the substrate 38 starts to be conveyed, the film of particles 4 is deposited thereon while passing via the outlet 26 and taking the capillary bridge 42, similar to the that described in the document CA 2 695 449. A solution using contact rather than using a capillary bridge can also be envisaged, without leaving the scope of the invention.

(50) To facilitate the deposition and adherence of the particles 4 on the substrate 38, preferably made of polymer, thermal annealing after the transfer is envisaged. This thermal annealing is for example carried out at 80° C., using a polyester-based low-temperature matt laminating film, for example marketed under the reference PERFEX-MATT™, 125 μm in thickness.

(51) The advantage of such a film as a substrate is that one of the faces thereof becomes adhesive at the temperature of the order of 80° C., which makes it possible to facilitate the adherence of the particles 4 thereon. More specifically, at this temperature, the particles 4 sink into the softened film 38, and thus enable direct contact with the film, resulting in the bonding thereof.

(52) Alternatively, the substrate 38 may of the silicon, glass, or piezoelectric film type.

(53) During the formation of the film and the transfer, the injection of particles and the conveyance speed of the substrate are set such that the leading edge of particles remains in a substantially identical position. For this purpose, the flow rate of particles may be of the order of 0.1 ml/min to several ml/min, whereas the linear speed of the substrate 38, also known as the pull rate, may be of the order of 0.1 cm/min to 100 cm/min. This high pull rate, which may be greater by more than 30% with respect to the possible maximum speeds with the installations according to the prior art, is obtained in particularly by means of the circulation of the carrier fluid via the permeable deflecting structure 50, and by means of the creation, by the capillary effect, of the bulge of fluid before the introduction thereof onto the inclined ramp 12.

(54) Obviously, various modifications may be made by those skilled in the art to the invention described above, merely by way of non-limiting examples.