THERMOGLURESCENT OPTICAL FIBER, MANUFACTURING PROCESSES AND APPLICATIONS

Description

[0001] The invention relates to a thermo-fluorescent optical fiber based on thermo-fluorescent particles, a process for manufacturing it, and its applications, particularly in a fiber optic temperature sensor.

[0002] Fiber optic temperature sensors have been developed to collect precise thermal data on structures or within devices, particularly to detect anomalies that could affect their safety and reliability. This description will focus on the use of sensors for measuring temperatures in batteries to better understand the phenomena that lead to overheating or thermal runaway and to determine their operating status in real time. Of course, the applications of the sensors of the invention are not limited to this field; they extend to any industrial, medical, or biological sector requiring, at some point, the determination of a temperature, ranging from -180°C to 400°C.

[0003] Optical fiber sensors based on sensitive particles employ various technologies involving absorption, interferometry, fluorescence, diffraction, and / or resonance. The document, A. Urrutia et al., "Optical fiber sensors based on nanoparticle-embedded coatings," Journal of Sensors, vol. 2015, Article ID805053, 18 pages, 2015, summarizes the main techniques used to manufacture such sensors. One known method for manufacturing an optical fiber functionalized with sensitive particles involves removing a portion of the cladding at specific points along the fiber's length and replacing it with a coating incorporating luminescent particles that interact with their environment to generate a signal.Another process involves modifying the structure and geometry of the optical fiber over part of its length, whereby, at certain sites, the cladding is removed and then the optical fiber is treated by melting and tapering in the presence of luminescent particles to form sites highly sensitive to the environment in which the optical fiber is exposed.

[0004] In a conventional approach to implementing a thermofluorescent particle-based fiber optic sensor, a probe made of these particles is deposited at one end of an optical fiber and / or at specific points along the fiber's length using a sol-gel process. During operation, absorption or excitation light is sent through the optical fiber to reach the probe. The resulting emitted radiation is collected and sent back through the same fiber to a detector (such as a photodiode, photomultiplier tube, spectrophotometer, etc.) which measures the fluorescence signal and thus the temperature through signal processing.

[0005] The performance of a fiber optic sensor, in terms of selectivity and accuracy, depends primarily on the qualities of the probe, that is, the layer of sensitive particles deposited on the optical fiber. This layer generally consists of a matrix in which sensitive particles have been embedded, allowing these particles to access the environmental conditions to which they are sensitive in order to obtain a signal. The nature of the matrix, the integration of the particles, and the deposition of the layer on the optical fiber are all subjects that have been the focus of development. Examples of matrices include those based on porous materials with a high specific surface area, such as zeolites with high silica content; those based on polymers such as polystyrene, silicone rubber, or Nafion®; and those based on gels obtained through the sol-gel process, such as xerogels.

[0006] According to US2002 / 186748A1, a system for controlling the temperature of tissue during laser treatment is described. The system aims to raise the temperature to a level that ensures effective treatment while preventing damage caused by excessive heat. The system comprises an optical fiber with a silica core, a fluoropolymer sheath surrounding the core, and a buffer layer. The optical fiber is enclosed in a sleeve containing barium sulfate particles.

[0007] Despite the efforts made, these techniques have the drawback of not allowing sufficient control over particle distribution within the matrix, in terms of quantity, homogeneity of particle distribution at the sites concerned, and particle positioning relative to the optical fiber core. All these parameters are crucial for achieving optimal results.

[0008] The invention provides a solution to the aforementioned drawbacks of known processes with a method for manufacturing a thermo-fluorescent optical fiber that allows control of the quantity, distribution, and also the positioning of the sensitive particles in the film deposited on the optical fiber.

[0009] Thus, the invention relates to a method for manufacturing a thermo-fluorescent optical fiber, comprising the following steps: an optical fiber is provided comprising a core capable of propagating light and a cladding, said optical fiber having at least one end and / or a site on its length, without a cladding, said end and / or said site being capable of irradiating light radiation from the core of the optical fiber, at least one photo-polymerizable system comprising at least one photo-polymerizable monomer and thermo-fluorescent particles is deposited on said end and / or said site of the optical fiber, radiation is sent into the optical fiber activating the photo-polymerization of said photo-polymerizable system to form a photo-polymerized matrix comprising said particles, and thus obtain said thermo-fluorescent optical fiber.

[0010] The invention also relates to a thermo-fluorescent optical fiber comprising a light-propagating core and a cladding, said fiber having at least one end or a cladding-free point along its length carrying a probe made of a matrix comprising thermo-fluorescent particles, the matrix being photopolymerized, and extends to any application of such a thermo-fluorescent optical fiber, and in particular to a temperature sensor comprising such a thermo-fluorescent optical fiber. Thus, the invention relates to the use of such a temperature sensor to determine the temperature of an electrochemical generator, such as a battery, and in particular a Li-ion battery.

[0011] Before describing the invention in more detail, certain terms / expressions used in this text are defined.

[0012] By particles, we mean inorganic or organic particles of any size, being totally or partially coated, encapsulating and / or incorporating at least one thermo-fluorescent molecule. They are of micrometer, sub-micrometer, or nanometer size. For the purpose of measuring temperatures in batteries according to a particular application of the invention, they advantageously have a size between 1 nm and 10 µm.

[0013] Thermofluorescence refers to the ability of a material to emit light almost instantaneously, at a given temperature and under the influence of light radiation (known as absorption or excitation radiation), either of the same wavelength or of a different wavelength (known as emission radiation). The light emitted by the thermofluorescent material is characterized by an emission spectrum containing one or more peaks whose intensity and / or luminescence lifetime varies with temperature.

[0014] In accordance with the above description of the invention, the process of the invention allows, by photo-activated polymerization conducted in situ,to obtain a probe comprising a polymer matrix in which the thermo-fluorescent particles are trapped. By using light radiation passing through the optical fiber as a polymerization agent, the invention is particularly advantageous in promoting the formation of a particle-rich film near the core of the optical fiber, which contributes to the performance of a probe.

[0015] Not only does the method of the invention overcome the limitations of known methods, but it also offers other advantages, such as simple implementation. Thus, since the polymerization of the precursor is photo-activated, the first step of the method, which consists of depositing at least one photopolymerizable precursor and thermo-fluorescent particles onto the end and / or site of the optical fiber, can be carried out by simply dipping the fiber into the precursor and the thermo-fluorescent particles. As only the end and / or site are accessible to the light irradiated into the optical fiber, the polymerization of the precursor will occur only at these locations.

[0016] The various objects of the invention and particular implementations thereof are described in detail below, the various characteristics stated being optional and to be considered alone or in combination.

[0017] As indicated above, the matrix of a probe of an optical fiber according to the invention is obtained by photopolymerization of at least one monomer.

[0018] The photo-polymerization of a polymer or polymers is a reaction well known to those skilled in the art, and the choice of ingredients for an appropriate photo-polymerization system, namely the monomer(s), the photo-initiator(s), and any additional ingredient which would increase the qualities of the matrix for greater probe efficiency or facilitate its preparation, belong to the general knowledge of those skilled in the art.It is of course necessary to choose ingredients compatible with the requirements of the desired matrix; in particular the polymer must be substantially inert with respect to the thermo-fluorescent particles which will be contained in the matrix; it must also resist the physical / chemical conditions of the environment in which the optical fiber is used; as previously stated, a sensor of the invention is in particular intended for measuring temperatures in batteries which are very acidic environments and whose temperature can reach 150°C in the event of malfunction.

[0019] A photo-polymerizable monomer can be chosen from among the acrylates and methacrylates and in particular the methyl-acrylates and methyl-methacrylates; thus, the photo-polymerized matrix is ​​chosen from the group of polymers including polyacrylates and polymethacrylates and their mixtures.Methacrylates, being less reactive, are preferred because they offer greater flexibility in use; these acrylates and methacrylates are advantageously functionalized by at least one function chosen from among halogens such as bromine or fluorine, sulfur, and aromatic rings; they have the advantage of acting on the refractive index, thus allowing control of this parameter in the matrix; thus, fluorinated acrylate or methacrylate monomers allow refractive index values ​​of around 1.4 to be achieved, while brominated, sulfurized, or aromatic acrylate or methacrylate monomers allow refractive index values ​​of around 1.8 to be achieved. Of course, several monomers can be used.

[0020] According to a preferred embodiment of a process of the invention, the photo-polymerization system contains from 70 to 95% by weight relative to the weight of the system, of an acrylate or a methacrylate above, or any mixture thereof.

[0021] As a replacement for, or preferably as a complement to, one of the above monomers, the photopolymerization system may include one or more other monomers capable of giving the matrix a more or less rigid three-dimensional network. For a rigid and mechanically resistant three-dimensional network, a monomer such as dipropylene glycol diacrylate (DPGDA), pentaerythritol tetracrylate (PETA), tris[2-(acryloyl)ethyl]TAEI isocyanurate, isobornyl acrylate (IBOA), or tricyclodecandimethanol diacrylate (DCPDA) is suitable. Conversely, for a mechanically flexible network, substituted silicone-thiol and -vinyl monomers or oligomers are preferred. The addition of these ingredients also allows for modulation of the mixture's viscosity before polymerization.

[0022] According to a preferred embodiment of a process of the invention, the photo-polymerization system contains up to 29% by weight relative to the weight of the system, of a monomer or oligomer above influencing the three-dimensional network, or of any mixture thereof.

[0023] The photopolymerization system may include one or more photoinitiators. The choice of photoinitiator depends on the wavelength of the radiation used to activate radical generation and thus photopolymerization. This, in turn, depends on the light source and the fiber's ability to transport photons within the chosen energy range.

[0024] In general, type 1 photoinitiators are preferred, and ideally those that do not cause yellowing of the matrix. Type 2 photoinitiators can be used, however, they require an amine to stabilize the radicals, which has the drawback of causing yellowing of the matrix over time. Methylbenzoyl formate, although a type 2 photoinitiator, is one example, as it does not cause yellowing.

[0025] Some preferred photo-initiators are: 1-Hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184) 2,2-Dimethoxy-1,2-diphenylethan-1-one (Irgacure 651) 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (Irgacure 2959) 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (Irgacure 369) 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (Irgacure 1173) Ivocerin-dibenzoyl germanium (IVO), provided that the medium in which the fiber of the invention will be used is not sensitive to the presence of germanium. trimethylbenzoyldiphenylphosphine oxide (TPO) Bisacylphosphine oxide BAPO

[0026] Typically, the photoinitiator(s) have a weight content relative to the weight of the photopolymerization system of approximately 0.01% to 1%. According to a preferred embodiment of a process of the invention, rather high photoinitiator(s) concentrations are used to achieve rapid setting of the matrix. High concentrations allow for the introduction of other ingredients, such as additives, into the photopolymerization system without risk of disrupting the near-instantaneous setting of the matrix.

[0027] As an example, it may be beneficial to introduce a fluorescent dye which will complement the signal from the thermo-fluorescent particles (or thermo-fluorophore).

[0028] A good description of photocurable resins can be found in this review, Samuel Clark Ligon, Robert Liska, Jürgen Stampfl, Matthias Gurr, and Rolf Mülhaupt, Chem. Rev. 2017, 117, 10212-10290.

[0029] The photopolymerization system may also contain one or more stabilizers, which can be chosen from among those commonly used, such as butylhydroxytoluene (BHT) and monomethyl hydroquinone ether (MEHQ). In a preferred operating procedure, these ingredients are added to the photostabilization system to stabilize the acrylate and / or methacrylate monomers and are then removed from the system before the addition of the photoinitiator(s), for example, by passing the mixture through an Al(OH)3 column.

[0030] The photopolymerization system can be enhanced with any ingredient that optimizes the probe. For example, adding a fluorescent molecule such as fluorescein or any other organic fluorochrome could be considered.

[0031] A solvent can also be added to promote the wettability of the thermo-fluoroluminescent particles.

[0032] Thermofluorescent particles can be selected from families of inorganic, organic, or hybrid thermoluminophores (see XD Wang, OS Wolfbeis, and RJ Meier, "Luminescent probes and sensors for temperature," Chem. Soc. Rev., vol. 42, no. 19, pp. 7834-7869, 2013, doi: 10.1039 / C3CS60102A). Inorganic agents are generally composed of an inorganic matrix co-doped with metals whose luminescence varies with temperature (see CDS Brites et al., "Lanthanide-Based Thermometers: At the Cutting-Edge of Luminescence Thermometry," Advanced Optical Materials, vol. 7, no. 5, Art. no. 5, 2019, doi: 10.1002 / adom.201801239). Thus, we can consider cadmium selenide-based nanocrystals, such as those involved in Quantum Dot technology; chromic ion-based materials (Cr 3+< ) as well as lanthanide-based particles such as lanthanum ions (Ln 3+< ), and europium or terbium-based chelates.Representative thermoluminophores include rhodamine and its derivatives, fluorescein and its derivatives, 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NDB), laurodan, boro-triaryl-based compounds, perylene, N-allyl-N-methylaniline, 1,3-bis-(1-pyrenyl)propane, 1-(Np-anisyl-N-methyl)-amino-3-anthryl-(9)-propane, acridine, and C60 and C70 fullerenes. Among the hybrid agents, metal-ligand complexes such as ruthenium-based complexes (Ru(bpy)3, Ru(phen)3) can be chosen, as well as iridium-based complexes (Ir(ppy)2 (carbac)) or platinum-based complexes (Ptll(Br-thq)(acac), PtOEP). Selecting an appropriate agent, particularly with regard to the temperature range in which the probe will operate, falls within the general knowledge of a person skilled in the art.

[0033] After the ingredients of the photo-polymerization system and the preparation of a photo-polymerization system, a process for manufacturing a thermo-fluorescent optical fiber according to the invention is described in detail. Preparation of the optical fiber for the deposition of the photopolymerization system.

[0034] The method of the invention is compatible with all types of optical fiber. Preferably, optical fibers with a silica core and a silica-doped cladding or a fluorocarbon polymer cladding (Tefzel®) are preferred. These are preferably multimode optical fibers with a diameter preferably ranging from 5 to 200 µm.

[0035] If the probe is placed at one end of the optical fiber, it must be prepared to receive the probe and, above all, to collect the light radiation correctly. For this purpose, the end of the fiber can, for example, be flat, although other configurations could be considered.

[0036] Alternatively, or in addition, the probe can be placed along the fiber for measurement using evanescent waves. For this purpose, the fiber cladding must be removed over a sufficient distance, which depends on the probe wavelength used for the thermoluminophore. The size of the site is on the order of a few tens of micrometers or even a few millimeters. Deposition of the photosensitive precursor onto the optical fiber

[0037] The optical fiber is immersed in the photopolymerization system, which, upon fiber withdrawal, forms a droplet at its tip. The volume of the droplet will depend on the fiber diameter, its wettability relative to the photopolymerization system, and the viscosity of the latter. Deposition of thermo-fluorescent particles at the end of the optical fiber

[0038] The optical fiber, with its dangling droplet, is then brought into contact with thermoluminescent particles. This contact can be achieved by immersing the fiber in the powder, or simply by placing the end of the fiber in contact with the powder mat, which is placed on a rigid support or container. The fiber can also be placed under a cascade of particles: in this case, only the particles in contact with the part of the fiber wetted by the polymer will be retained by capillary action. The particles are advantageously in powder form and can be of the same type or in mixtures. Thus, a mixture can consist of thermofluorescent particles, absorbent particles, and particles with optical properties in order to modify the final optical properties of the probe at the fiber end. It is also possible to add inorganic, organic, or hybrid luminescent nanoparticles.Metallic nanoparticles can also be added to increase absorption through the plasmon effect.

[0039] Only the end of the optical fiber is brought into contact with the powder Deposition of thermo-fluorescent particles at sites along the length of the optical fiber

[0040] The principle is the same as that of deposition at one end of the optical fiber. However, the cladding is first removed from a section of the optical fiber to create evanescent waves. Cladding removal can be achieved through chemical etching or mechanical removal. Both methods are familiar to those skilled in the art. The precursor solution can also be deposited by dipping; in this case, the entire fiber is coated, but only the area where the evanescent wave is created when the photopolymerization activation light passes through the fiber will be polymerized. Alternatively, the photopolymerization system can be deposited onto these exposed areas in a single droplet using a process such as inkjet printing. Polymerization of the monomer(s) of the photopolymerization system

[0041] Once the optical fiber is in contact with the powder, and without changing its position, light is directed into the fiber from the other end to activate photopolymerization. This light travels through the fiber core to irradiate the end in contact with the particles. Once activated, polymerization occurs at the fiber tip, starting from the surface of the fiber core. This traps the particles directly in contact with the fiber, forming a film or probe deposit on the fiber tip.

[0042] In cases where the entire surface of the tip is not completely covered by the film, or even to add a supplementary film to the deposited film, the operation can be repeated, as long as the light activating the polymerization can penetrate the film(s) already deposited. This is an additional advantage of the invention, which allows the probe to be layered with one or more films, using, for each film, the same photopolymerization system and the same thermofluorescent particles, or a photopolymerizable system and / or identical or different thermofluorescent particles from one application to the next, namely using the same photopolymerization system and different thermofluorescent particles, a different photopolymerization system and the same thermofluorescent particles, or a different photopolymerization system and different thermofluorescent particles.

[0043] This process is simple to implement and relatively versatile because it allows for the incorporation of different types of particles. It is quick to implement and allows for precise control of the deposition location, thanks to light.

[0044] This is illustrated in the following examples in support of the [FIG. 1] to [FIG. 3] according to which: [ FIG. 1] and [FIG. 2 ] are optical microscope photographs of an optical fiber (diameter 150 µm, Thorlabs ®< reference M137L02 of 200µm diameter) on one end of which a first film of a matrix containing PTIR545F particles from Phosphor Technology ®< has been deposited [ FIG. 1 ] and a second film from the same matrix [ FIG. 2 ] ; And [ FIG. 3.1] to [FIG. 3.7] illustrate variations in the implementation of the process of the invention. Example 1: Preparation of a photopolymerization system

[0045] 50g of Al(OH)₃ is placed in an oven at 150°C (industrial origin: SASOL) overnight. It is then cooled under argon in a Schlenk tube. Next, a 20 ml plastic syringe is loaded with 2g of the powder. A 0.1µm filter tip is attached to the syringe. The syringe is filled with methyl methacrylate, the plunger is reinserted, and the unprotected monomer is pushed into an opaque bottle containing argon. Argon is bubbled through the bottle to remove any traces of O₂.

[0046] Next, a second opaque flask is prepared under argon, into which Irgacure 2959 photoinitiator powder (5% by mass relative to the mass of monomer) is introduced, followed by 0.5 ml of THF and 1 ml of acetone. The quantity is intentionally oversized to ensure optimal reactivity of the photopolymerization system. The THF is not strictly necessary but improves wettability. Example 2: Fabrication of an optical fiber according to the invention carrying a probe at one of its ends

[0047] An example of implementation is illustrated in [ FIG. 1] and [FIG. 2 ]. To the [ FIG. 1 ], we observe the deposition of a first film of a matrix containing thermo-fluorescent particles. The particles are located exactly at the end of the fiber and nowhere else. The polymer deposit is sufficiently thin and conforms to the optical fiber so as not to be visible in the photograph. At the [ FIG. 2 ], we observe the deposition of a second film on the first film of the [ FIG. 1 We observe that the quantity of particles on the surface has increased. But the deposit remains localized at the end of the fiber. Example 3: Fabrication of an optical fiber according to the invention carrying probes, at several sites along its length

[0048] This example, in support of the [ FIG. 3], illustrates one of the multiple implementation variants that a process according to the invention allows.

[0049] According to the illustrated embodiment, the process of the invention is carried out on an optical fiber having sites along its length that are devoid of cladding. A mask is applied to some of the exposed sites, so that at the end of the process, the photopolymerizable system has been activated only on the remaining unmasked sites. Then, at least some of the masks are removed and the process is repeated with a different photopolymerizable system, and so on to obtain an optical fiber equipped with different probes.

[0050] [ FIG. 3 illustrates this sequence:

[0051] According to [FIG. 3.1] , we have an optical fiber comprising a core capable of propagating light and a cladding.

[0052] According to [FIG. 3.2] , some sites are exposed along the length of the optical fiber by removing the sheath.

[0053] According to [FIG. 3.3] Some of the exposed areas are masked.

[0054] According to [FIG. 3.] , the optical fiber is exposed to a first photo-polymerizable system and photo-polymerization is activated on the unmasked sites.

[0055] According to [FIG. 3.5] , we remove the masking in some of the exposed sites.

[0056] According to [FIG. 3.6] , the optical fiber is exposed to a second photo-polymerizable system and photo-polymerization is activated on the unmasked sites.

[0057] According to [FIG. 3.7] The process is repeated as above to obtain an optical fiber equipped along its length with different probes.

[0058] As an example, a polymer that is easy to remove can be used to mask exposed fiber sites. Typically, this is a polymer that is insoluble in the solvent used to deposit the UV-curable polymer used for particle deposition. For example, water-soluble polymers with a high molecular point such as PVA (polyvinyl alcohol) or PVP (polyvinylpyrrolidone).

Claims

1. A thermo-fluorescent optical fiber comprising a core able to propagate light and a sheath, said fiber carrying at least at one of its ends or at one site along its length, devoid of sheath, a probe consisting of a matrix comprising thermo-fluorescent particles, characterized in that the matrix is a polymer and photo-polymerized in the presence of at least one photo-polymerizable system comprising at least one photo-polymerizable monomer and said thermo-fluorescent particles.

2. The fiber according to claim 1, characterized in that the photo-polymerized matrix is selected from the group of polymers comprising polyacrylates and polymethacrylates and mixtures thereof.

3. The fiber according to claim 1 or 2, characterized in that the matrix is in the form of at least two layers, made of identical or different polymers and identical or different thermo-fluorescent particles.

4. A method for manufacturing a thermo-fluorescent optical fiber, comprising the following steps: An optical fiber is provided, comprising a core able to propagate light and a sheath, said optical fiber having at least one end or one site along its length, devoid of sheath, said end or said site being able to irradiate a light radiation, coming from the core of the optical fiber, At least one photo-polymerizable system comprising at least one photo-polymerizable monomer and thermo-fluorescent particles is deposited on said end and / or said site of the optical fiber, and Radiation is sent into the optical fiber activating the photo-polymerization of said photo-polymerizable system to form a photo-polymerized matrix comprising said particles, and thus obtain said thermo-fluorescent optical fiber.

5. The method according to claim 4, characterized in that the photo-polymerizable system comprises at least one photo-polymerizable monomer selected from acrylates and methacrylates and mixtures thereof.

6. The method according to claim 5, characterized in that the content of acrylate(s) and / or methacrylate(s) is from 70 to 95% by weight relative to the weight of the photo-polymerizable system.

7. The method according to any one of claims 4 to 6, characterized in that the photo-polymerizable system comprises at least one photo-initiator selected from type 1 photo-initiators and methyl benzoyl formate.

8. The method according to any one of claims 4 to 7, characterized in that, after the formation of the photo-polymerized matrix, the steps of depositing on said end and / or said site of the optical fiber, at least one photo-polymerizable system and thermo-fluorescent particles, and activating the photo-polymerization of said photo-polymerizable system by sending radiation into the optical fiber activating said photo-polymerization, are repeated one or several times.

9. The method according to claim 8, characterized in that the photo-polymerizable system and / or the thermo-fluorescent particles are different from one time to another.

10. A temperature sensor comprising a thermo-fluorescent optical fiber according to any one of claims 1 to 3.

11. Use of a temperature sensor according to claim 10, to determine the temperature of an electrochemical generator, such as a battery and in particular a Li-ion battery.