Method for forming a film of particles on a carrier liquid, with movement of an inclined ramp for compressing the particles

Abstract

A method for forming a film of particles on a carrier liquid present in a receptacle, for depositing this film onto a substrate, the method including: making a film blank between a barrier and a head including a tilted ramp, the blank being obtained by dispensing particles via the tilted ramp and carried out until the particles floating on the carrier liquid occupy a space between the barrier and an upstream front of particles located on the tilted ramp; and elongating the film by continuing dispensing the particles, and moving the head to move away from the barrier, the film elongation being performed to hold a front of particles on the ramp.

Claims

1. A method for forming a film of particles on a carrier liquid present in a receptacle, for depositing this film onto a substrate, the method comprising: making a film blank between barrier means and a head including a tilted ramp, the blank being obtained by dispensing particles via the tilted ramp, carried out until the particles floating on the carrier liquid occupy a space between the barrier means against which they abut, and an upstream front of particles located on the tilted ramp; and elongating the film while simultaneously continuing dispensing the particles via the tilted ramp, and moving the head relative to the receptacle to move the head away from the barrier means, this film elongation being performed to hold the upstream front of particles on the tilted ramp.

2. The method according to claim 1, wherein during the elongating the film, the upstream front of particles is held in a same position on the tilted ramp.

3. The method according to claim 1, wherein the head includes sucking means for sucking part of the carrier liquid in proximity of a submerged end of the tilted ramp, the sucking means being activated at least during part of the elongating the film.

4. The method according to claim 1, wherein carrier liquid feed means supplies the head with the carrier liquid such that the same drives the particles onto the tilted ramp.

5. The method according to claim 3, wherein carrier liquid feed means supplies the head with the carrier liquid such that the same drives the particles onto the tilted ramp, and wherein the sucking means communicates with the carrier liquid feed means.

6. The method according to claim 4, wherein the carrier liquid and the particles are dispensed in an overflow tank provided in the head, the tank being configured such that when the tank overflows, a solution of carrier liquid and particles flows out on the tilted ramp.

7. The method according to claim 6, wherein the carrier liquid and the particles are dispensed separately in the tank.

8. A method for depositing a film of particles onto a substrate, comprising a method of forming a film of ordered particles according to claim 1, followed by transferring the film onto the substrate.

9. The method according to claim 8, wherein the transferring is performed with the substrate horizontally orientated.

10. The method according to claim 9, wherein the substrate is brought in contact with the film of particles floating on the carrier liquid, by being vertically moved.

11. The method according to claim 10, wherein the horizontal substrate is submerged in the carrier liquid during formation of the film of particles, and then vertically raised such that the film is deposited onto the horizontal substrate.

12. The method according to claim 8, wherein the transfer is performed with the substrate vertically or obliquely orientated.

13. The method according to claim 12, wherein the transfer is performed by pulling the substrate, and moving the film on the carrier liquid by moving the head towards the substrate.

14. The method according to claim 12, wherein the vertical or oblique substrate is rigid or flexible.

15. The method according to claim 12, wherein the barrier means is formed by the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This description will be made with regard to the appended drawings wherein:

(2) FIG. 1 shows a deposition facility according to a preferred embodiment of the present invention, in a schematic cross section view taken along line I-I of FIG. 2;

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

(4) FIGS. 3a to 3f represent different steps of a deposition method implemented using the facility shown in the preceding figures, according to a first preferred embodiment;

(5) FIGS. 4a and 4b schematize a deposition method according to a second preferred embodiment; and

(6) FIG. 5 schematizes a deposition method according to a third preferred embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) First with reference to FIGS. 1 and 2, a facility 1 for depositing a film of particles onto a substrate, herein a horizontal substrate, is represented.

(8) The facility 1 includes a device 2 for dispensing particles, the size of which can be between a few nanometres and a few hundreds micrometres. The particles, preferably of a spherical shape, can for example be silica particles. Other particles of interest can be made of metal or metal oxide as platinum, TiO2, polymer as polystyrene or PMMA, carbon, etc., or even any type of molecules.

(9) More precisely, in the preferred embodiment, the particles are silica spheres having a diameter of about 1 μm, possibly stored in a solution in the dispensing device 2. The proportion of the medium is about 7 g particles for 200 mL solution, herein butanol. Naturally, for the sake of clarity, the particles represented in the figures assume a diameter higher than their actual diameter.

(10) The dispensing device 2 has a controllable injection nozzle 6, having a diameter of about 500 μm.

(11) Further, the facility 1 has, in the proximity of the device 2, means 3 for feeding a carrier liquid 16, which are also controllable via a valve 7 or similar.

(12) It also includes a tub-shaped receptacle 10, having for example a rectangular parallelepiped shape, wherein the carrier liquid 16 is located.

(13) Besides, it includes a head 5 integrating a tilted ramp 12 for flowing the particles 4 and the carrier liquid 16. The top end 12a of the tilted ramp bounds the aperture of an overflow tank 9 provided in the head, and wherein the particles 4 as well as the carrier liquid 16 are intended to be dispensed. Consequently, in use, when the liquid 16 overflows from the tank 9, it is discharged by the ramp 12, by driving the particles 4 previously dispensed to the surface of the same tank by the device 2.

(14) The ramp 12 is planar, tilted by an angle between 5 and 60°, preferably between 5 and 25°, enabling the particles to be conveyed to the carrier liquid located in the tub 10, since the top end of the ramp 12 is raised relative to the liquid level in this tub. In use, in spite of the continuous liquid introduction in the tub by the means 3, via the ramp 12, the liquid level in the tub is preferentially held constant by liquid sucking means, bearing the general reference numeral 13. These means enable the liquid 16 to be sucked in the proximity of a lower end 12b of the ramp 12, which is submerged in the same liquid. To do this, the means 13 have a sucking hood 15 at the lower part of the head, which is connected through a channel to a pump 17, all being preferably integrated to a closed hydraulic circuit also comprising the liquid dispensing means 3 located above the overflow tank 9, and thus communicating with the sucking means 13.

(15) The liquid 16 is thus recirculated using the aforesaid means, between the lower end of the ramp and its upper end, even if other designs can be adopted, in particular in an open circuit, without departing from the scope of the invention.

(16) The ramp 12, dipping into the liquid 16 of the tub 10, defines with the horizontal level of this liquid an inflexion line 24, which forms an inlet for particles into the tub. This inlet is located distant from a particle barrier 23, placed in the tub 10 bounded by two side rims 28 retaining the carrier liquid 16. These rims 28, facing away from each other, extend in parallel to a main flow direction of the carrier liquid and the particles in the facility, this direction being schematized by the arrow 30 in FIGS. 1 and 2.

(17) Between the inlet 24 and the barrier 23 at the surface of the carrier liquid, a zone 14 for building up particles is thus created, which consequently takes the shape of a substantially rectangular corridor between the side rims 28. Other geometries could however be adopted without departing from the scope of the invention.

(18) The facility 1 is also provided with a support 35 for the substrate 36 submerged in the tub bottom. The support is equipped with a horizontal tray 37 on which rests the substrate 36, a handle 39 located outside the tub, and a zone 41 for connecting the handle and the tray. Besides, the aforesaid barrier 23 can herein be formed by the part of the connecting zone 41 passing through the surface of the liquid 16 and/or by the downstream end wall 10′ of the tub 10, as will be described hereinafter.

(19) In this first embodiment, the substrate can be rigid or flexible, because it is supported by the tray 37.

(20) One of the features of the present invention lies herein in the fact that the head 5 is translationally moveable relative to the tub 10, along the direction 30, that is in parallel to the surface of the carrier liquid. To do this, conventional translation means 45 can be adopted (only schematically represented), for example driven by a rectilinear motion linear engine. The head 5, equipped with its means 2, 3, is thus movable at the surface of the carrier liquid, so as to be able to be moved away from/closer to the barrier 23.

(21) A method for depositing particles according to a first embodiment will now be described with reference to FIGS. 3a to 3f.

(22) First, the head 5 is sufficiently set back to enable the substrate 36 carried by the support tray 35 to be submerged, as schematized in FIG. 3a. Then, the head is moved in the other direction in order to move closer to the barrier 23. As shown in FIG. 3b, the building up zone 14 between this barrier and the inflection line 24 is then very reduced, so as to be able to make the blank of a film of particles.

(23) To do this, the injection nozzle 6 is activated for the purpose of starting dispensing the particles 4 into the tank, as well as, beforehand, the means for sucking the liquid 13 and feeding the liquid 3 are also activated. The flow rates of the means 13 and 3 are preferably held constant for the entire duration of dispensing the particles, in order to achieve constant film formation conditions, regardless on the other hand the position of the head during the formation of this film.

(24) For the step of making the film blank in the reduced building up zone 14, the object is simply to fill this zone 14 with particles 4 floating on the carrier liquid.

(25) During this phase, the particles 4 overflowing from the tank flow on the ramp 12, and then penetrate the zone 14 wherein they are dispersed. As these particles 4 penetrate the zone 14, they abut against the barrier 23, and then the upstream front of these particles tends to shift upstream, towards the inflection line 24. The injection of particles continues even after this upstream front goes over the line 24, so that it rises on the tilted ramp 12, as shown in FIG. 3c.

(26) Actually, the upstream front of particles 54 is such that it can rise onto the ramp 12 such that it is located at a given horizontal distance “d” from the inflection line 24, wherein this distance “d” can be in the order of 15 mm.

(27) At this time, the particles 4 forming the blank are ordered/compacted in the reduced zone 14 and on the ramp 12, wherein they are automatically ordered/compacted, without assistance, thanks in particular to their kinetic energy and to the capillary forces exploited at the time of the impact onto the front 54. In the case of spherical particles as presented in this embodiment, the ordering is such that the compact film blank obtained has a so-called “hexagonal compact” structure, wherein each particle 4 is surrounded and contacted by six other particles 4 in contact with each other. This is then indiscriminately referred to as a compact film of particles, or film of ordered particles, the later terminology being preferentially adopted in the case of spherical particles.

(28) Once the ordered particles 4 forming the film blank 4′ cover the entire carrier liquid located in the reduced building up zone 14, a new step is started, aiming at elongating the film length.

(29) This elongating step is implemented by continuing the liquid sucking and feeding, as well as the particle dispense. On the other hand, the head 5 is set back so as to move away from the barrier 23, in order to elongate the building up zone 14 wherein the film 4″ of particles 4 is formed. This movement is performed at a rate which enables the front of particles 54 to be kept on the ramp 12, preferably in a constant position, as schematized in FIG. 3d. Consequently, the film 4″ is gradually elongated as the head 5 sets back relative to the tank 10, while holding the ordering of the particles 4 already deposited onto the ramp 12 and into the zone 14. This principle of elongating the film to upstream, in the reverse direction of the particles dispense, enables substantially constant film formation conditions to be kept, making the quality thereof independent of its length. The film 4″ can be formed on a great length, being close to the total length of the tank, and thus allows high quality depositions on large areas. Besides, as schematically shown in FIG. 3e, a heterogeneous film 4″ can be controllably obtained, since when new particles 4 pass through the ramp 12, they directly reach the upstream front 54 on which they adopt an ordering which is kept throughout the film formation. Then, it is simply sufficient to dispense particles 4 of different natures in turn, for example of different sizes as schematized in FIG. 3e, which then are found in the film 4″ in an order corresponding to that wherein they have been dispensed.

(30) For that purpose, it is possible to position several particle injectors in order to actuate the one desired at the desired time. It is also possible to divide the ramp into sections, each section being separated from the other by one or two walls parallel to the edges, and to associate one or more injectors to each section. It is also possible to make a gradient in the movement direction of the head but also in the direction perpendicular to this movement.

(31) Once the film 4″ is elongated to the desired length, still held by the tilted ramp 12 of the head at shutdown, this film is transferred onto the substrate 36 according to a technique analogous to that of Langmuir-Schaefer. A schematic representation of this step is shown in FIG. 3f. It consists in vertically moving the substrate 36 using the handle 39 of the support 35, in a manual or automated manner. Being horizontally held during this movement, when the substrate 36 comes into contact with the particles of the film 4″, the latter is deposited onto the upper surface of the substrate. The excess of particles 4 remaining on the carrier liquid can then be moved so as to form all or part of the blank of a next film to be deposited. Alternatively, the excess can be sucked in.

(32) It is besides noted that the barrier 23 can possibly be formed not only by the support 35, but also in combination with the downstream end wall 10′ of the tank, when the junction zone 41 has a width lower than the total width of the tank between both side rims. In such a case, after the film 4″ is deposited onto the substrate, particles 4 remain on either side of the film carried away on the same substrate 36, as shown in FIG. 3f. Another solution consists in making this barrier such that it is integrally formed by this downstream end wall 10′ of the tank facing the ramp 12. In such a case, the connecting zone 41 is then preferably located close to either one of the side rims 28.

(33) To facilitate deposition and adhesion of the particles 4 onto the substrate 36, preferably made of a polymer, a thermal annealing is provided subsequently to the transfer. This thermal annealing is for example made at 80° C., using a polyester based low temperature matte laminating film, for example marketed as PERFEX-MATT™, having a 125 μm thickness.

(34) The advantage of such a film as a substrate is that one of its faces becomes sticky at the temperature in the order of 80° C., which enables adhesion of the particles 4 to be facilitated. Alternatively, the substrate 36 can be of the silicon, glass or even piezoelectric film type.

(35) As discussed above, during the film elongation, the injection of particles/liquid and the movement rate of the head are adjusted such that the front of particles 54 remains in a substantially identical position. For this, the flow rate of particles can be in the order of 0.01 mL/min to 10 mL/min, whereas the linear rate of the head 5 can be in the order of a few mm/min to 30 cm/min. The flow rate of carrier liquid is in turn set between 100 and 1000 mL/min.

(36) FIGS. 4a and 4b schematize a second preferred embodiment, wherein the film transfer is performed on a vertically orientated substrate 36. The formation of the film 4″ of ordered particles 4 onto the carrier liquid 16 is performed in an identical or analogous manner to that presented within the scope of the first embodiment, with the barrier 23 herein consisting of a part of the substrate 36 is located at the periphery of the tub, as shown in FIG. 4a. The particles are thus in direct contact with this substrate. Then, for the transfer, the substrate is vertically moved at the same time as the film 4″ is pushed by the head 5 moving in the opposite direction to the one that enabled the film elongation. A conventional pulling is then achieved, as schematized in FIG. 4b. This embodiment could be implemented with the substrate 36 previously partly submerged in the carrier liquid, without departing from the scope of the invention. Besides, this is the solution preferentially adopted for the third embodiment shown in FIG. 5, wherein the substrate 36 previously partly submerged, is obliquely arranged, that is tilted with respect to the vertical and horizontal directions. For pulling, the substrate 36 is preferentially moved in the plane wherein it lies during the previous step of forming the film, during which its part passing through the carrier liquid acts as the barrier 23.

(37) For the second and third embodiments, the substrate 36 is preferentially rigid, but could be replaced by a flexible substrate in the form of a moving strip, passing through rolls or the like.

(38) Possible applications for the methods just described have been mentioned above. Concrete examples are also described below.

(39) These are for example heat exchangers. The structuration of the walls of exchangers is a means to adjust the heat exchanges. These structurations can be made by lithography with a mask of particles. With the methods described above, the implementation of heterogeneous depositions associating particles of different dimensions makes possible to obtain geometries usually made by lithography, and in particular geometries with gradients of particle sizes. It is thus possible, with this technique, to form surfaces with energy gradients, for example to promote formation and flow of surface condensed drops.

(40) Another example relates to the field of tribology. For mechanical applications, compact films can be used as a lithography mask to create micro/nanovessels enabling the lubricant to be retained at the surface of rubbing objects. The adjustment of the dimensions of these retention micro/nanovessels is a parameter for adjusting the friction coefficient. A simple means to change the dimensions of these micro/nanovessels is to use as an etching mask a heterogeneous compact film comprised of different particle sizes, easy to be obtained with the method specific to the present invention.

(41) Of course, various modifications can be provided by those skilled in the art to the invention just described, only by way of non-limiting examples.