Method for coating functional material on U-shaped optical fiber humidity sensor through in-situ polymerization

Abstract

The invention discloses a method for coating a functional material on a U-shaped optical fiber humidity sensor through in-situ polymerization, and belongs to the technical field of optical fiber sensors. The invention relates to a method for coating a functional material on a U-shaped optical fiber humidity sensor through in-situ polymerization, which comprises the following steps: S1, mixing a polymer monomer and an initiator to start polymerization reaction, so that the polymer monomer forms a prepolymer; s2, the polymerization reaction is suspended, and the U-shaped optical fiber is dip-coated into the prepolymer, so that the U-shaped optical fiber is coated with the prepolymer; and S3, continuously carrying out polymerization reaction on the prepolymer on the U-shaped optical fiber until the polymerization reaction is complete, and forming a polymer functional material on the surface of the U-shaped optical fiber. According to the invention, the prepolymer is coated on the U-shaped optical fiber and then polymerization reaction is carried out, and a polymer functional material is formed on the surface of the U-shaped optical fiber, so that the adhesion and the distribution uniformity of the functional material are improved, the sensitivity of the U-shaped optical fiber humidity sensor is improved, and the response speed is increased.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensor technology, and more specifically, to a method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor. Background Technology

[0002] Humidity is closely related to many daily human activities. It not only determines air comfort but also has a significant impact on industrial production, agricultural planting, food storage, weather forecasting, and many other activities. In these fields, much humidity measurement must be performed in harsh environments with strong electromagnetic interference, high temperatures, and corrosive conditions. Therefore, high-performance humidity sensors are crucial, and fiber optic humidity sensors have emerged as a solution. The core technology of these sensors utilizes optical signals transmitted through optical fibers, offering numerous inherent advantages, including immunity to electromagnetic interference, high sensitivity, resistance to chemical corrosion, compact size, robustness, and long transmission distances.

[0003] U-shaped optical fibers utilize the evanescent field principle for sensing. To improve the detection performance of U-shaped optical fibers, coating their surface with a functional thin film is crucial. Solution impregnation is a widely used method due to its simplicity and ease of application. However, achieving a uniform and appropriate coating of functional material onto the U-shaped optical fiber requires precise control of the solution concentration. If the solution concentration is too low, coating becomes difficult. Conversely, if the concentration is too high, the coating will be too thick, affecting sensor performance. Furthermore, there is an upper limit to the solubility of the solvent. Moreover, solvent evaporation during the drying process can lead to uneven coating distribution and potentially coating peeling.

[0004] Existing technology discloses a method for forming a polymethyl methacrylate (PMMA) film on a U-shaped fiber optic humidity sensor. The specific steps are as follows: 0.600 g of PMMA is added to 12.0 mL of dichloromethane in a beaker and stirred with a glass rod for 30 minutes until the PMMA is completely dissolved. The sensing film is fabricated as follows: a single-mode fiber etched with hydrofluoric acid is fixed in a groove, and 0.5 mL of PMMA solution is injected into the groove. After 6 seconds, the single-mode fiber is rotated at a certain speed and removed from the groove. Finally, the single-mode fiber is left at room temperature for 24 hours before use. Its sensitivity is only 0.008 nm / %RH. It can be seen that the sensitivity of this U-shaped fiber optic humidity sensor is too low. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings and deficiencies of existing technologies that directly coat polymer functional materials onto the surface of U-shaped optical fibers, resulting in low sensitivity and slow response of fiber optic humidity sensors. This invention provides a method for in-situ polymer coating of functional materials onto U-shaped optical fiber humidity sensors. By coating a prepolymer onto the U-shaped optical fiber and then performing a polymerization reaction, a polymer functional material is formed on the surface of the U-shaped optical fiber. This improves the adhesion and uniformity of the functional material, thereby increasing the sensitivity and response speed of the U-shaped optical fiber humidity sensor.

[0006] Another object of the present invention is to provide a U-shaped fiber optic sensor.

[0007] Another object of the present invention is to provide an application of a U-shaped fiber optic sensor.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution: A method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor includes the following steps: S1. Mix the polymer monomers and initiator to start the polymerization reaction, so that the polymer monomers form a prepolymer; S2. Pause the polymerization reaction and dip the U-shaped optical fiber into the prepolymer, so that the prepolymer is coated on the U-shaped optical fiber; S3. Continue the polymerization reaction of the prepolymer on the U-shaped optical fiber until the reaction is complete, forming a polymer functionalized material on the surface of the U-shaped optical fiber.

[0009] In specific embodiments, the polymer monomer can be functionalized materials capable of in-situ polymerization, such as methyl methacrylate and polyethylene glycol diacrylate.

[0010] In step S1 of this invention, the polymer monomers are initiated to form a prepolymer concentration suitable for coating.

[0011] The purpose of pausing the polymerization reaction in step S2 of this invention is to keep the prepolymer concentration constant and prevent the prepolymer concentration from continuously increasing with the increase of conversion rate. After obtaining a suitable concentration for coating functional materials, the U-shaped optical fiber is then immersed in the prepolymer, so that the prepolymer is coated on the U-shaped optical fiber.

[0012] In step S3 of this invention, the prepolymer on the U-shaped optical fiber continues to polymerize until the polymerization reaction is complete. During the final curing stage, monomer molecules are connected by covalent bonds to form long chains, which further cross-link to form a three-dimensional polymer network. This covalent cross-linking forms a three-dimensional network, which undergoes volume shrinkage, generating internal stress, ultimately achieving tight encapsulation of the U-shaped optical fiber and realizing in-situ polymerization and coating of functional materials on the U-shaped optical fiber humidity sensor.

[0013] This invention discloses a method for in-situ polymerization and coating of functional materials onto U-shaped optical fibers. The internal stress of the in-situ polymerization reaction enables the functional material film to be tightly adhered to the U-shaped optical fiber, improving the adhesion of the functional material. Furthermore, by coating the prepolymer onto the U-shaped optical fiber, the functional material film formed during the in-situ polymerization process can be uniformly distributed.

[0014] In a specific implementation, in step S2, a dip-coating machine can be used to dip-coat the U-shaped optical fiber into the prepolymer. The more dip-coating cycles, the thicker the film formed after the functionalized material cures, allowing for flexible control of the film thickness. The thickness of the film formed after curing the functionalized material can be 100~300nm. A thinner film thickness is beneficial for improving the sensitivity and response speed of the U-shaped optical fiber humidity sensor.

[0015] Preferably, the optical fiber can be multimode optical fiber or single-mode optical fiber, and the material of the optical fiber can be silicon dioxide or plastic. More preferably, the optical fiber is single-mode silicon dioxide optical fiber.

[0016] Preferably, in step S1, the polymer monomer is methyl methacrylate; in step S3, the polymerization is thermal polymerization.

[0017] In a specific embodiment, when the polymer monomer is methyl methacrylate, the initiator can be an initiator such as benzoyl peroxide (BPO) that can initiate the polymerization reaction of methyl methacrylate.

[0018] Preferably, when the polymer monomer is methyl methacrylate, in step S1, the polymer monomer and initiator are mixed and polymerized at 70~80°C for 0.5~1h; in step S3, the polymerization temperature is 90~110°C and the polymerization time is 1.5~2.5h.

[0019] Preferably, when the polymer monomer is methyl methacrylate, in step S2, pausing the polymerization reaction means placing the prepolymer from step S1 in an environment below 20°C; the number of dip coatings is 1 to 2.

[0020] When the polymerization reaction is a thermal polymerization reaction, the polymerization reaction can be paused by lowering the temperature in order to keep the concentration of the prepolymer constant.

[0021] Preferably, in step S1, the polymer monomer is polyethylene glycol diacrylate, and the relative molecular mass of polyethylene glycol diacrylate is 200~400; in step S3, the polymerization is photopolymerization.

[0022] In a specific embodiment, the polymer monomer is polyethylene glycol diacrylate, and the initiator can be an initiator such as 2-hydroxy-2-methyl-phenylacetone that can initiate the polymerization reaction of polyethylene glycol diacrylate.

[0023] Preferably, when the polymer monomer is polyethylene glycol diacrylate, in step S1, the polymer monomer and photoinitiator are mixed, and the polymerization reaction is started by ultraviolet light irradiation, and the polymerization reaction time is 4~10 min.

[0024] Preferably, when the polymer monomer is polyethylene glycol diacrylate, in step S2, pausing the polymerization reaction means stopping the irradiation with ultraviolet light.

[0025] When the polymerization reaction is a photopolymerization reaction, the polymerization reaction can be paused by stopping the light irradiation, so as to maintain the concentration of the prepolymer at a constant level.

[0026] This invention also protects the U-shaped fiber optic humidity sensor prepared by the method described in any of the preceding claims, which involves in-situ polymerization coating of functionalized materials onto a U-shaped fiber optic humidity sensor.

[0027] This invention also protects the application of the aforementioned U-shaped fiber optic humidity sensor in humidity sensing.

[0028] Preferably, in the application, the humidity detection range is 32%-85%.

[0029] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a method for in-situ polymer coating of functional materials on a U-shaped fiber optic humidity sensor. By coating a prepolymer onto a U-shaped fiber and then performing a polymerization reaction, a polymer functional material is formed on the surface of the U-shaped fiber. This improves the adhesion and distribution uniformity of the functional material, thereby enhancing the sensitivity and response speed of the U-shaped fiber optic humidity sensor. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of step S1 in Example 1.

[0031] Figure 2 This is a schematic diagram of step S2 in Example 1.

[0032] Figure 3 and Figure 4 This is a schematic diagram of step S3 in Example 1.

[0033] Figure 5 This is a schematic diagram of the experimental detection.

[0034] Figure 6 The sensitivity of the U-shaped fiber optic humidity sensor in Example 1 is shown.

[0035] Figure 7 The response time of the U-shaped fiber optic humidity sensor in Example 1 is denoted as .

[0036] Figure 8The sensitivity of the U-shaped fiber optic humidity sensor in Example 2 is shown. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0038] U-shaped optical fibers are fabricated using an optical fiber tapering machine. This device mainly consists of an oxyhydrogen flame heating unit and a displacement platform stretching assembly. Standard single-mode silica optical fibers are heated and stretched to a length of 1.2 cm at a uniform rate, ultimately obtaining microfibers with a diameter of approximately 7 micrometers. Subsequently, these microfibers are fixed within a capillary glass tube using ultraviolet photoresist, forming a U-shaped optical fiber structure with a radius of curvature of approximately 2 millimeters.

[0039] Example 1 A method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor includes the following steps: Take 10 mL of methyl methacrylate (MMA) and wash repeatedly with 2 mL of 5% sodium hydroxide solution until the solution is colorless. Then wash with distilled water until neutral. After the aqueous layer is completely separated, add 5% anhydrous sodium sulfate by volume of the monomer. Shake well and let stand for more than 24 hours to dry.

[0040] S1. As Figure 1 As shown, 10 ml of polymer monomer methyl methacrylate and 0.01 g of initiator benzoyl peroxide were mixed and added to the bottle, then the bottle was sealed tightly, and the polymerization reaction was carried out in a water bath at 75°C for 0.5 h; so that the polymer monomers formed a prepolymer. S2. For example Figure 2 As shown, the prepolymer from step S1 is placed in an environment of 10°C to stop the polymerization reaction. The U-shaped optical fiber is dipped into the prepolymer using a dip coating machine and coated once to coat the prepolymer onto the U-shaped optical fiber. S3. For example Figure 3 and Figure 4 As shown, the U-shaped optical fiber coated with prepolymer is placed in a vacuum drying oven and heated to 100°C. The prepolymer on the U-shaped optical fiber continues to polymerize for 2 hours until the liquid methyl methacrylate is completely polymerized and solidified to form polymethyl methacrylate, forming a tightly adhered polymer functionalized material on the surface of the U-shaped optical fiber.

[0041] Example 2 A method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor includes the following steps: S1. Mix polyethylene glycol diacrylate (PEG-DA), a polymer monomer with a relative molecular mass of 200, and 2-hydroxy-2-methylpropiophenone (2-Hydroxy-2-methylpropiophenone), at a weight ratio of 50:1. Add the mixture to a bottle, then seal the bottle tightly. Sonicate the mixture for 10 minutes in the dark to ensure thorough mixing. Irradiate the mixture with a UV lamp for 5 minutes to allow the polymer monomers to form a prepolymer. S2. Stop the UV lamp to pause the polymerization reaction, and use a dip-coating machine to dip the U-shaped optical fiber into the prepolymer. Coat once to coat the U-shaped optical fiber with the prepolymer. S3. Irradiate the U-shaped optical fiber coated with prepolymer with a UV lamp for 10 minutes until the polyethylene glycol diacrylate is completely photocured to form a polyethylene glycol diacrylate with a three-dimensional network structure, forming a tightly adhered polymer functionalized material on the surface of the U-shaped optical fiber.

[0042] Example 3 A method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor includes the following steps: Take 10 mL of methyl methacrylate (MMA) and wash repeatedly with 2 mL of 5% sodium hydroxide solution until the solution is colorless. Then wash with distilled water until neutral. After the aqueous layer is completely separated, add 5% anhydrous sodium sulfate by volume of the monomer. Shake well and let stand for more than 24 hours to dry.

[0043] S1. Add 10 ml of polymer monomer methyl methacrylate and 0.01 g of initiator benzoyl peroxide to the bottle, then seal the bottle tightly and polymerize in a water bath at 75°C for 0.5 h; so that the polymer monomer forms a prepolymer; S2. Place the prepolymer from step S1 in an environment of 10°C to stop the polymerization reaction. Use a dip-coating machine to dip the U-shaped optical fiber into the prepolymer, and coat it twice to coat the U-shaped optical fiber with the prepolymer. S3. Place the U-shaped optical fiber coated with prepolymer in a vacuum drying oven and heat it to 100°C. Continue to polymerize the prepolymer on the U-shaped optical fiber for 2 hours until the liquid methyl methacrylate is completely polymerized and cured to form polymethyl methacrylate, forming a tightly adhered polymer functionalized material on the surface of the U-shaped optical fiber.

[0044] The difference from Example 1 is that in step S2, the coating is applied twice.

[0045] Example 4 A method for in-situ polymer coating of functionalized materials on U-shaped optical fibers includes the following steps: Take 10 mL of methyl methacrylate (MMA) and wash repeatedly with 2 mL of 5% sodium hydroxide solution until the solution is colorless. Then wash with distilled water until neutral. After the aqueous layer is completely separated, add 5% anhydrous sodium sulfate by volume of the monomer. Shake well and let stand for more than 24 hours to dry.

[0046] S1. Add 10 ml of polymer monomer methyl methacrylate and 0.01 g of initiator benzoyl peroxide to the bottle, then seal the bottle tightly and polymerize in a water bath at 75°C for 1 h; so that the polymer monomer forms a prepolymer; S2. Place the prepolymer from step S1 in an environment of 10°C to stop the polymerization reaction, and use a dip-coating machine to dip the U-shaped optical fiber into the prepolymer, coating once, so that the prepolymer is coated on the U-shaped optical fiber. S3. Place the U-shaped optical fiber coated with prepolymer in a vacuum drying oven and heat it to 100°C. Continue to polymerize the prepolymer on the U-shaped optical fiber for 2 hours until the liquid methyl methacrylate is completely polymerized and cured to form polymethyl methacrylate, forming a tightly adhered polymer functionalized material on the surface of the U-shaped optical fiber.

[0047] The difference from Example 1 is that in step S1, the polymerization reaction is carried out in a water bath at 75°C for 1 hour.

[0048] Example 5 A method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor includes the following steps: S1. Mix the polymer monomer polyethylene glycol diacrylate (PEG-DA) and the photoinitiator 2-hydroxy-2-methylpropiophenone at a weight ratio of 50:1, add the mixture to a bottle, then seal the bottle tightly and sonicate for 10 minutes under light-protected conditions to ensure uniform mixing. Irradiate with a UV lamp for 8 minutes to allow the polymer monomers to form a prepolymer. S2. Stop the UV lamp to pause the polymerization reaction, and use a dip-coating machine to dip the U-shaped optical fiber into the prepolymer. Coat once to coat the U-shaped optical fiber with the prepolymer. S3. Irradiate the U-shaped optical fiber coated with prepolymer with a UV lamp for 10 minutes until the polyethylene glycol diacrylate is completely photocured to form a polyethylene glycol diacrylate with a three-dimensional network structure, forming a tightly adhered polymer functionalized material on the surface of the U-shaped optical fiber.

[0049] The difference from Example 2 is that in step S1, the sample is irradiated with an ultraviolet lamp for 8 minutes.

[0050] Comparative Example 1 A method for coating a functionalized material onto a U-shaped fiber optic humidity sensor includes the following steps: First, a certain mass of PMMA powder was prepared and dissolved in DMF. Then, magnetic particles were added to the prepared solution, and the solution was stirred on a stirrer for 8 hours until the PMMA powder was completely dissolved. Finally, after standing for 2 hours, the air bubbles in the solution were removed, resulting in a PMMA solution with a mass fraction of 20%.

[0051] The U-shaped optical fiber was dipped into a PMMA solution using a dip-coating machine, and the coating was performed once. Finally, it was dried in a vacuum drying oven at 100°C for 2 hours to complete the coating of functional materials onto the U-shaped optical fiber humidity sensor.

[0052] Comparative Example 2 A method for coating a functionalized material onto a U-shaped fiber optic humidity sensor includes the following steps: Weigh 1g of solid polyethylene glycol diacrylate, dissolve it in 20ml of water, then coat the U-shaped optical fiber once using a dip-coating machine, and finally dry it in a vacuum drying oven at 100℃ for 2 hours to complete the coating of functional materials on the U-shaped optical fiber humidity sensor.

[0053] Result detection Figure 5 This is a schematic diagram of the experimental detection. The detection method is as follows: The detection method uses a supercontinuum light source (wavelength range: 480–2200 nm) as the input light, which is coupled into the U-shaped humidity sensor. The output light in the range of 1100–1700 nm is collected using a spectrometer (resolution: 0.02 nm), and the transmission spectrum of the U-shaped fiber optic humidity sensor is finally obtained through spectral analysis. In each test, the U-shaped fiber optic humidity sensor is placed in a sealed glass container for approximately 5 minutes to allow the humidity inside the container to stabilize. It is important to note that all laboratory tests were conducted under constant experimental conditions (temperature: 26°C, humidity: 50% relative humidity). The specific test results of Example 1 are as follows: Figure 6 and Figure 7 As shown, Figure 6 The sensitivity of the U-shaped fiber optic humidity sensor in Example 1 is shown. Figure 7 The response time of the U-shaped fiber optic humidity sensor in Example 1. From Figure 6 and Figure 7 As can be seen, the humidity detection sensitivity of the U-shaped fiber optic humidity sensor in Embodiment 1 of the present invention can reach up to 0.3019 nm / % RH, the fastest response time is 2s, and the humidity detection range is 32%-85%.

[0054] The specific test results of Example 2 are as follows: Figure 8 As shown, Figure 8 The sensitivity of the U-shaped fiber optic humidity sensor in Example 2 is shown. The humidity detection sensitivity of the U-shaped fiber optic humidity sensor in Example 2 of this invention can reach up to 0.1094 nm / % RH, the fastest response time is 2.65 s, and the humidity detection range is 32%-85%.

[0055] The U-shaped fiber optic humidity sensor of Embodiment 3 of the present invention has a sensitivity of up to 0.1604 nm% / RH, a response time of 2.6 s, and a humidity detection range of 32%-85%.

[0056] The U-shaped fiber optic humidity sensor of Embodiment 4 of the present invention has a sensitivity of up to 0.16 nm% / RH, a response time of 2.9 s, and a humidity detection range of 32%-85%.

[0057] The U-shaped fiber optic humidity sensor of Embodiment 5 of the present invention has a sensitivity of up to 0.0899 nm% / RH, a response time of 3.2 s, and a humidity detection range of 32%-85%.

[0058] The U-shaped fiber optic humidity sensor in Comparative Example 1 had a sensitivity of 0 nm / %RH and no response, which may be because the polymethyl methacrylate film peeled off during solvent evaporation or the coating thickness of the polymethyl methacrylate film was too thick.

[0059] The U-shaped fiber optic humidity sensor in Comparative Example 2 had a sensitivity of 0 nm / %RH and no response, which may be because the polyethylene glycol diacrylate film detached during solvent evaporation or because the coating thickness of the polyethylene glycol diacrylate film was too thick.

[0060] As can be seen, in this embodiment of the invention, the polymer is formed by in-situ polymerization and coating of polymer monomers. The polymerization reaction generates internal stress that tightly adheres the U-shaped optical fiber, preventing detachment. Moreover, the in-situ polymerization method of this invention can improve the sensitivity of the U-shaped optical fiber humidity sensor and increase its response speed.

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for in-situ polymer coating of functionalized materials onto a U-shaped fiber optic humidity sensor, characterized in that, Includes the following steps: S1. Mix the polymer monomers and initiator to start the polymerization reaction, so that the polymer monomers form a prepolymer; S2. Pause the polymerization reaction and dip the U-shaped optical fiber into the prepolymer, so that the prepolymer is coated on the U-shaped optical fiber; S3. Continue the polymerization reaction of the prepolymer on the U-shaped optical fiber until the polymerization reaction is complete, and form a polymer functionalized material on the surface of the U-shaped optical fiber.

2. The method for in-situ polymer coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in claim 1, characterized in that, In step S1, the polymer monomer is methyl methacrylate; in step S3, the polymerization is thermal polymerization.

3. The method for in-situ polymer coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in claim 2, characterized in that, In step S1, the polymer monomer and initiator are mixed and polymerized at 70-80°C for 0.5-1 h; in step S3, the polymerization temperature is 90-110°C and the polymerization time is 1.5-2.5 h.

4. The method for in-situ polymer coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in claim 2, characterized in that, In step S2, pausing the polymerization reaction means placing the prepolymer from step S1 in an environment below 20°C; the number of dip coatings is 1 to 2.

5. The method for in-situ polymer coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in claim 1, characterized in that, In step S1, the polymer monomer is polyethylene glycol diacrylate, and the relative molecular mass of polyethylene glycol diacrylate is 200~400; in step S3, the polymerization is photopolymerization.

6. The method for in-situ polymer coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in claim 5, characterized in that, In step S1, the polymer monomer and photoinitiator are mixed, and the polymerization reaction is started by irradiation with ultraviolet light. The polymerization reaction time is 4~10 min.

7. The method for in-situ polymer coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in claim 5, characterized in that, In step S2, pausing the polymerization reaction means stopping the irradiation with ultraviolet light.

8. The U-shaped fiber optic humidity sensor prepared by the method of in-situ polymerization coating of functionalized materials on a U-shaped fiber optic humidity sensor as described in any one of claims 1 to 7.

9. The application of the U-shaped fiber optic humidity sensor as described in claim 8 in humidity sensing.

10. The application as described in claim 9, characterized in that, In this application, the humidity detection range is 32%-85%.

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