A gas detection probe, its preparation method and application

Abstract

This application belongs to the technical field of gas detection, and particularly relates to a gas detection probe, a preparation method thereof, and an application. The gas detection probe provided by this application includes an optical fiber and a polymer cholesteric liquid crystal film layer coated on one end face of the optical fiber after compression. Among them, the polymer cholesteric liquid crystal film layer is formed by in-situ polymerization of a polymer monomer and a cholesteric liquid crystal, and then compressed through a liquid crystal extraction process, so that the reflection stop band of the polymer cholesteric liquid crystal film layer undergoes a blue shift, making it more susceptible to external stimuli and thus being excited and responsive. As a result, the gas detection probe provided by this application has a wider detection range, higher sensitivity, and a more stable spectral shift direction.

Description

Technical Field

[0001] This application belongs to the technical field of gas detection, and particularly relates to a gas detection probe, a preparation method thereof, and an application thereof. Background Art

[0002] Liquid crystal is a special physical state between solid crystal and traditional liquid. Nowadays, liquid crystals have been widely used in displays and various optical and photonic devices. The physical parameters of liquid crystals are very sensitive to external stimuli, such as temperature, organic solvents, or volatile gases. Therefore, they are used as tunable optical materials in many fields.

[0003] Liquid crystal molecules will change from an anisotropic state to an isotropic state, or the refractive index and the arrangement direction will change under certain external stimuli. Utilizing these characteristics of liquid crystals, when liquid crystal molecules are stimulated by the outside world, the parameters of liquid crystal molecules change, which causes the demodulation parameters of the sensor to change, and finally the detection of the substance to be detected. Many optical sensors such as those mentioned above can be prepared using the above characteristics. For example, liquid crystals are prepared into photonic crystals and combined with existing sensors or interferometers. At present, many liquid crystal-based sensors have been reported, but there are few reports on using polymer cholesteric liquid crystal film layers for the detection of organic volatile gases. Generally, there are several problems, such as low sensitivity, narrow detection range, spectral red shift and blue shift both exist in actual use, with strong interference and inaccurate detection results. Summary of the Invention

[0004] The purpose of this application is to provide a gas detection probe, a preparation method thereof, and an application thereof, aiming to solve the problem of detecting organic volatile gases by existing liquid crystal sensor probes to a certain extent.

[0005] To achieve the above application purpose, the technical solution adopted in this application is as follows:

[0006] In the first aspect, this application provides a preparation method of a gas detection probe, including the following steps:

[0007] Pretreat one end face of the optical fiber;

[0008] Prepare cholesteric liquid crystal, and mix the cholesteric liquid crystal, polymer monomer, and initiator to obtain a cholesteric liquid crystal prepolymer;

[0009] Transfer the cholesteric liquid crystal prepolymer to the pretreated end face and perform in-situ polymerization treatment to form a polymer cholesteric liquid crystal film layer on the end face;

[0010] Perform liquid crystal suction treatment on the polymer cholesteric liquid crystal film layer to make the reflection stop band of the polymer cholesteric liquid crystal film layer blue-shift, and obtain a gas detection probe.

[0011] In a second aspect, the present application provides a gas detection probe, which is made by the above preparation method.

[0012] In a third aspect, the present application provides an application of a gas detection probe prepared by the above preparation method in detecting the concentration of organic volatile gases.

[0013] The preparation method of the gas detection probe provided in the first aspect of the present application can prepare a gas detection probe with a wider detection range, higher sensitivity, and more stable spectral shift direction. Moreover, the preparation process is simple and easy to control, and the raw materials are cheap and easily available.

[0014] For the gas detection probe provided in the second aspect of the present application, the polymer cholesteric liquid crystal film layer has been subjected to liquid crystal extraction treatment, making it more susceptible to external stimuli and thus being excited and responsive. This enables the gas detection probe provided by the present application to have a wider detection range, higher sensitivity, and more stable spectral shift direction.

[0015] For the application of the gas detection probe provided in the third aspect of the present application in detecting the concentration of organic volatile gases, gas sensing is carried out through the optical properties of the liquid crystal in the gas detection probe, and the gas molecules to be detected are not damaged, thereby realizing the function of detecting the concentration of VOC gases. At the same time, the gas detection probe has the characteristics of small volume, low manufacturing cost, fast response speed, high sensitivity, wide detection range, and weak interference. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic diagram of the cholesteric liquid crystal spring theory in the embodiment of the present invention;

[0018] Figure 2 It is a physical diagram of the liquid crystal extraction process in the embodiment of the present invention;

[0019] Figure 3 It is a test spectrogram of the gas detection probe prepared by the preparation method provided in Comparative Example 1 of the present invention for detecting the concentration of acetone gas;

[0020] Figure 4 It is a graph showing the change of the bandgap center position of the gas detection probe prepared by the preparation method provided in Comparative Example 1 of the present invention with the concentration of acetone gas;

[0021] Figure 5The test spectrogram of the acetone gas concentration detected by the gas detection probe prepared by the preparation method provided in Embodiment 1 of the present invention;

[0022] Figure 6 The variation diagram of the position of the bandgap center of the gas detection probe prepared by the preparation method provided in Embodiment 1 of the present invention with the acetone gas concentration

[0023] Figure 7 The variation process diagram of the reflection bandgap during the preparation process of the gas detection probe provided in the embodiment of the present invention. Detailed implementation manners

[0024] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] In the present application, the term "and / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B may be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0026] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or similar expressions thereof refer to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b or c", or, "at least one (item) of a, b and c" can both represent: a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively.

[0027] It should be understood that in various embodiments of the present application, the order numbers of the above processes do not mean the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0028] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0029] In the description of the embodiments of the present application, the weight of the relevant components mentioned not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the description of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the description of the embodiments of the present application. Specifically, the mass described in the description of the embodiments of the present application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0030] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be referred to as the second XX. Similarly, the second XX can also be referred to as the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0031] The term "VOC" is an abbreviation for "Volatile Organic Compounds", which represents volatile organic compounds and is defined as harmful volatile organic gases in the environmental protection sense.

[0032] Currently, many sensors based on liquid crystals have been reported. There are few reports on using polymer liquid crystals for detecting organic volatile gases. There are generally several problems with polymer liquid crystals in the prior art, such as low sensitivity, narrow detection range, and both spectral red shift and blue shift in actual use. In view of the above technical problems, the first aspect of the embodiments of the present application provides a method for preparing a gas detection probe, including the following steps:

[0033] S1: Pretreat one end face of the optical fiber;

[0034] S2: Prepare a cholesteric liquid crystal, and mix the cholesteric liquid crystal, a polymer monomer, and an initiator to obtain a cholesteric liquid crystal prepolymer;

[0035] S3: Transfer the cholesteric liquid crystal prepolymer to the pretreated end face and perform in-situ polymerization treatment to form a polymer cholesteric liquid crystal film layer on the end face;

[0036] S4: Perform liquid crystal suction treatment on the polymer cholesteric liquid crystal film layer to make the reflection stop band of the cholesteric liquid crystal in the polymer cholesteric liquid crystal film layer blue shift to obtain a gas detection probe.

[0037] The method for preparing a gas detection probe provided by the first aspect of the present application can prepare a gas detection probe with a wider detection range, higher sensitivity, and more stable spectral shift direction, and the preparation process is simple and easy to control, and the raw materials are cheap and easy to obtain.

[0038] In step S1, in the embodiments of the present application, the pretreatment includes the following steps: performing end surface flattening treatment and end surface cleaning treatment on the end surface of the optical fiber. In a further embodiment of the present application, the inclination angle of the end surface after the end surface flattening treatment is not greater than 0.5°. In a specific embodiment of the present application, the end surface flattening treatment is a cutting treatment, cutting the end surface of the optical fiber to form a flat and smooth end surface. In a further embodiment of the present application, the end surface cleaning treatment includes one of ultraviolet ozone cleaning treatment and vacuum type plasma cleaning treatment. In a specific embodiment of the present application, the end surface of the optical fiber after the end surface flattening treatment is placed in an ultraviolet ozone cleaning machine or a vacuum type plasma cleaning machine and cleaned for about 10 minutes, so that the end surface of the optical fiber is clean and the contact angle of the end surface is reduced, facilitating the attachment of the cholesteric liquid crystal prepolymer to the end surface of the optical fiber.

[0039] In the embodiments of the present application, the optical fiber is a multimode optical fiber. The multimode optical fiber has a thicker core diameter and a larger numerical aperture than the single-mode optical fiber, and can couple more optical power from the light source.

[0040] In a specific embodiment of the present application, step S1 can be carried out in the following manner:

[0041] S11: Take a multimode optical fiber with a core diameter of 62.5 μm and a cladding diameter of 125 μm, cut the end surface of the optical fiber flat, and the cutting angle is less than 0.5°;

[0042] S12: Put the cut optical fiber into an ultraviolet ozone cleaning machine and clean it for 10 minutes.

[0043] In step S2, in the embodiments of the present application, preparing the cholesteric liquid crystal includes the following steps: mixing the nematic liquid crystal with a chiral agent to obtain the cholesteric liquid crystal. By adding the chiral agent, it is possible to affect the helical shape of the liquid crystal molecules in the nematic liquid crystal, so that it selectively reflects the incident light corresponding to the wavelength of the helical pitch and is derived into the cholesteric liquid crystal. The cholesteric liquid crystal can be used in fields such as sensors and lasers. In a specific embodiment of the present application, the chiral agent includes, but is not limited to, one of the 5011, 811, and 1011 series.

[0044] It should be noted that, in the embodiments of the present application, the cholesteric liquid crystal can be prepared first, and then the cholesteric liquid crystal is mixed with the polymer monomer and the initiator, or the nematic liquid crystal and the chiral agent required for preparing the cholesteric liquid crystal can be directly mixed with the polymer monomer and the initiator for treatment.

[0045] In the embodiments of the present application, the polymer monomer includes, but is not limited to, RM257, RM021, RM006, HRM1001, RM82, which are used for in-situ curing and crosslinking after being mixed with the cholesteric liquid crystal to form a solid polymer cholesteric liquid crystal film layer, and are directly connected to the optical fiber as a probe.

[0046] In the embodiments of the present application, before the in-situ polymerization treatment, the cholesteric liquid crystal is also subjected to an alignment treatment to obtain a cholesteric liquid crystal with a better alignment effect. In a further embodiment of the present application, the alignment treatment is to perform ultraviolet polarized light irradiation on the photo-aligning agent with ultraviolet polarized light and add the photo-aligning agent to the cholesteric liquid crystal. The photo-aligning agent includes but is not limited to SD1 material and Yellow B material, and the solvent can be a common organic solvent such as dimethylformamide (DMF), toluene, etc.

[0047] In a specific embodiment of the present application, the alignment treatment includes the following steps: Dip the end face of the optical fiber after pretreatment in a photo-aligning agent with a concentration of 0.5-2 wt%, bake the end face until the solvent volatilizes, and perform ultraviolet polarized light irradiation on the photo-aligning agent on the end face of the optical fiber with ultraviolet polarized light. The wavelength of the ultraviolet polarized light is 350 nm-500 nm, and the power density of the ultraviolet polarized light irradiation treatment is 40-60 mW / cm 2 , and the treatment duration is 150-250 seconds.

[0048] In another specific embodiment of the present application, the alignment treatment includes the following steps: Add the photo-aligning agent to the mixture of cholesteric liquid crystal, polymer monomer, and initiator, and then perform ultraviolet polarized light irradiation on the above mixture containing the photo-aligning agent with ultraviolet polarized light of 350 nm-500 nm. The power density of the ultraviolet polarized light irradiation treatment is 40-60 mW / cm 2 , and the treatment duration is 150-250 seconds.

[0049] In the embodiments of the present application, the ratio of nematic liquid crystal, polymer monomer, chiral agent, and photoinitiator in parts by mass is 70-79 parts of nematic liquid crystal, 20-25 parts of polymer monomer, 0.5-3 parts of chiral agent, and 0.5-2 parts of photoinitiator. In a specific embodiment of the present application, the ratio of nematic liquid crystal, polymer monomer, chiral agent, and photoinitiator by mass is 77.5:20:1.5:1. The prepared gas detection probe can maintain high sensitivity while achieving a large detection range, and the photonic band gap moves unidirectionally, and it can be fully used for the detection of organic volatile gases in life and factory production.

[0050] In a specific embodiment of the present application, step S2 can be carried out in the following manner:

[0051] S21: Fix the end face of the cleaned optical fiber under a microscope with a fixture, dip it in an SD1 solution with a concentration of 1 wt%, the solvent is DMF, transfer the optical fiber to a hot stage at 100 °C, and heat for 100 seconds to completely volatilize the solvent;

[0052] S22: Orient the photo - aligning agent on the end face of the optical fiber using 365 - nm ultraviolet polarized light, with an optical power density of 50 mW / cm 2 , and the exposure time is 200 seconds;

[0053] S23: Mix liquid crystal E7, polymer monomer RM257, chiral agent R5011, and photo - initiator Irgacure651 in a mass ratio of 72.5:25:1.5:1 to form a cholesteric liquid crystal prepolymer.

[0054] In step S3, transfer the cholesteric liquid crystal prepolymer to the pretreated end face and perform in - situ polymerization treatment to form a polymer cholesteric liquid crystal film layer on the end face.

[0055] In the embodiments of the present application, the coating thickness of the cholesteric liquid crystal prepolymer on the end face is not limited and can be determined according to the actual needs of probe preparation, generally ranging from dozens to hundreds of micrometers. When combined with an optical fiber to form a micro - probe, compared with conventional large - size probes, it has more application scenarios. In a specific embodiment of the present application, a 20 - micron - diameter capillary is used to dip the cholesteric liquid crystal mixture, and a 45 - μm - thick cholesteric liquid crystal is transferred to the end face of the optical fiber under a microscope.

[0056] In the embodiments of the present application, the in - situ polymerization treatment is ultraviolet light irradiation treatment, and the initiator is a photo - initiator. In a further embodiment of the present application, the wavelength of the ultraviolet light for the ultraviolet light irradiation treatment is 290 nm - 330 nm, the power density of the ultraviolet light irradiation treatment is 3 - 7 mW / cm 2 , and the treatment duration is 5 - 15 minutes, which can promote the in - situ polymerization of the polymer monomer and the cholesteric liquid crystal with high efficiency.

[0057] In a further embodiment of the present application, the initiator is convenient for initiating the in - situ polymerization of the polymer monomer and the cholesteric liquid crystal. In a further embodiment of the present application, the initiator is a photo - initiator, and the photo - initiator includes but is not limited to at least one of the 1173, 651, and 2925 series. The photo - initiated cross - linking method can absorb energy of a certain wavelength under ultraviolet light to generate free radicals, cations, etc., thereby initiating the polymerization and cross - linking curing of monomers. It belongs to a non - contact cross - linking method, simplifies the preparation process, shortens the time of the polymer monomer cross - linking network, and better fixes the orientation of the liquid crystal structural units in the polymer cholesteric liquid crystal film layer.

[0058] In a further embodiment of the present application, the in - situ polymerization treatment is carried out in an oxygen - free environment to avoid oxygen hindering the in - situ polymerization reaction of the polymer monomer and the cholesteric liquid crystal, thereby reducing the polymerization rate.

[0059] In a specific embodiment of the present application, step S3 can be carried out in the following manner:

[0060] S31: Dip a capillary with a diameter of 20 microns into the cholesteric liquid crystal prepolymer, and transfer the 45-micron-thick cholesteric liquid crystal to the end face of the optical fiber under a microscope.

[0061] S32: Place the end face of the optical fiber into a sealed box in an oxygen-free environment, continuously fill it with nitrogen, and use 295-nm ultraviolet light with a power density of 5 mW / cm 2 to induce polymerization of the polymer monomer for 10 minutes.

[0062] In step S4, a liquid crystal suction treatment is performed on the polymer cholesteric liquid crystal film layer to blue-shift the reflection stop band of the polymer cholesteric liquid crystal film layer, thereby obtaining a gas detection probe.

[0063] In an embodiment of the present application, the liquid crystal suction treatment includes the following steps: bringing a liquid crystal suction material close to the polymer cholesteric liquid crystal film layer to blue-shift the reflection stop band of the polymer cholesteric liquid crystal film layer, thereby obtaining a compressed polymer cholesteric liquid crystal film layer.

[0064] It should be noted that for the liquid crystal suction treatment, any material that can suck out the liquid crystal is acceptable. In a further embodiment of the present application, the liquid crystal suction material includes oil-absorbing paper, cotton, non-woven fabric, and devices with slits, such as capillaries and syringes. While sucking out part of the liquid crystal, the internal and external structures of the polymer liquid crystal device itself are not damaged, so that the remaining liquid crystal is compressed and thus has more sufficient elasticity, improving the sensitivity of the gas detection probe and expanding the detection range.

[0065] In an embodiment of the present application, the amount of liquid crystal suction in the liquid crystal suction treatment is not limited. Theoretically, as long as some liquid crystal is sucked out, as Figure 1 shown, according to the spring theory, the calculation formula of the spring force, Hooke's law F = K×Δx, where F is the magnitude of the restoring force, Δx is the deformation of the spring, and K is the spring constant, whose magnitude is determined by the material, thickness, spring diameter, winding method, and length of the spring. When only the pitch of the winding method of a spring is changed and other conditions remain unchanged, the spring constant decreases as the pitch increases. The larger the pitch, the greater the deformation of the spring when it is subjected to the same external force. According to a theory similar to that of a spring, as Figure 1As shown, with the spring length remaining unchanged, the number of turns is changed to vary the pitch. After the pitch increases, the spring is more easily deformed by force. Then, a pressure is applied to the spring. Finally, when encountering the same magnitude of tensile force, the spring can have a greater deformation amount (2Δx) compared to the original deformation amount (Δx). The cholesteric liquid crystal structure is very similar to the spring. For a polymer cholesteric liquid crystal film layer of the same thickness, reducing the polymer doping concentration and increasing the pitch can also enable the polymer cholesteric liquid crystal film layer to have a greater deformation amount. Sucking out a part of the liquid crystal in the polymer cholesteric liquid crystal film layer is equivalent to compressing the spring. When stimulated by organic volatile gases, the pitch of the cholesteric liquid crystal is stretched longer, and the sensitivity to gases and the detection limit will also be improved. In a specific embodiment of the present application, the other end of the optical fiber connected to the polymer cholesteric liquid crystal film layer is connected to a Y-shaped optical fiber. The reflection stop band of the polymer cholesteric liquid crystal film layer is observed in real time using a spectrometer, and a part of the liquid crystal is sucked out with an oil-absorbing paper to make the reflection stop band blue-shift. When the reflection stop band no longer moves, the sucking stops, so that the liquid crystal in the polymer cholesteric liquid crystal film layer is compressed to the greatest extent, and the sensitivity and detection range are maximally improved. At the same time, when actually detecting the concentration of organic volatile gases, there will be no simultaneous red-shift and blue-shift phenomena, with less interference information and more accurate concentration measurement.

[0066] In a specific embodiment of the present application, step S4 can be carried out in the following manner:

[0067] S41: Connect the polymerized optical fiber to the Y-shaped optical fiber, observe the reflection stop band of the polymer cholesteric liquid crystal film layer in real time using a spectrometer, and suck out a part of the liquid crystal with an oil-absorbing paper to make the reflection stop band blue-shift. When the reflection stop band no longer moves, stop sucking.

[0068] As Figure 7 shown, it is the change process of the reflection stop band during the preparation of the gas detection probe based on the polymer cholesteric liquid crystal film layer. Before polymerization, the central wavelength of the photonic stop band position of the cholesteric liquid crystal prepolymer is 1010 nm. After polymerization, the central wavelength of the photonic stop band position blue-shifts to 769 nm. Due to the influence of the polymerization shrinkage effect, the central wavelength of the photonic stop band moves 241 nm. This phenomenon proves that the polymer cholesteric liquid crystal film layer has completed polymerization. When a part of the liquid crystal is sucked out with an oil-absorbing paper, the central wavelength of the photonic stop band continues to blue-shift 115 nm to 654 nm.

[0069] In the second aspect of the embodiments of the present application, a gas detection probe is provided, which is made by the above preparation method and includes an optical fiber and a polymer cholesteric liquid crystal film layer that is subjected to liquid crystal extraction treatment and coated on one end face of the optical fiber. The polymer cholesteric liquid crystal film layer is formed by in-situ polymerization of a polymer monomer and a cholesteric liquid crystal, and then is compressed by liquid crystal extraction treatment, so that the reflection stop band of the polymer cholesteric liquid crystal film layer is blue-shifted. The polymer cholesteric liquid crystal film layer that has undergone liquid crystal extraction treatment is more susceptible to external stimuli and thus can be excited and respond, making the gas detection probe provided by the present application have a wider detection range, higher sensitivity, and a more stable spectral shift direction.

[0070] In the third aspect of the embodiments of the present application, the application of the above gas detection probe in detecting the concentration of organic volatile gases is provided. Gas sensing is carried out through the optical properties of the liquid crystal in the gas detection probe, and the gas molecules to be measured are not damaged, realizing the function of detecting the concentration of VOC gases. At the same time, the gas detection probe has the characteristics of small volume, low manufacturing cost, fast response speed, high sensitivity, wide detection range, and weak interference.

[0071] To enable those skilled in the art to clearly understand the above implementation details and operations of the present application, and to significantly demonstrate the improved performance of the gas detection probe and its preparation method and application in the embodiments of the present application, the following technical solutions will be illustrated by multiple examples.

[0072] Example 1

[0073] (1) Take a multimode optical fiber with a core diameter of 62.5 μm and a cladding diameter of 125 μm. Cut the end face of the optical fiber flat, and the cutting angle is less than 0.5°.

[0074] (2) Place the cut optical fiber in an ultraviolet ozone cleaning machine and clean it for 10 minutes.

[0075] (3) Fix the end face of the cleaned optical fiber under a microscope using a fixture, and dip it in an SD1 solution with a concentration of 1 wt%, and the solvent is DMF. Transfer the optical fiber to a hot stage at 100 °C and heat it for 100 seconds to completely volatilize the solvent.

[0076] (4) Use 365 nm ultraviolet polarized light to perform orientation treatment on the photo-orienting agent on the end face of the optical fiber, with an optical power density of 50 mW / cm 2 , and the exposure time is 200 seconds.

[0077] (5) Mix liquid crystal E7, polymer monomer RM257, chiral agent R5011, and photoinitiator Irgacure651 in a mass ratio of 77.5:20:1.5:1 to form a cholesteric liquid crystal prepolymer.

[0078] (6) Using a capillary with a diameter of 20 microns to dip up the cholesteric liquid crystal mixture, and transferring a 45-micron-thick cholesteric liquid crystal prepolymer to the end face of the optical fiber under a microscope;

[0079] (7) Placing the end face of the optical fiber into a sealed box in an oxygen-free environment, continuously filling it with nitrogen, and using 295 nm ultraviolet light with a power density of 5 mW / cm 2 to induce polymerization of the polymer monomer for 10 minutes to obtain a 45-micron-thick polymer cholesteric liquid crystal film layer;

[0080] (8) Connecting the polymerized optical fiber to a Y-shaped optical fiber, using a spectrometer to observe the reflection stop band of the polymer cholesteric liquid crystal film layer in real time, and using blotting paper to suck out part of the liquid crystal to blue-shift the reflection stop band. When the reflection stop band no longer moves, stop sucking to obtain a gas detection probe. Among them, as Figure 2 shown, the thickness of the polymer cholesteric liquid crystal film layer formed after the liquid crystal sucking treatment is 33 μm.

[0081] Example 2

[0082] When performing the liquid crystal sucking treatment, stop sucking when the reflection stop band of the polymer cholesteric liquid crystal film layer moves to half of the reflection stop band movement in Example 1. The remaining steps and parameters are the same as those in Example 1. Among them, the thickness of the polymer cholesteric liquid crystal film layer formed after the liquid crystal sucking treatment is 36 μm.

[0083] Example 3

[0084] When performing the liquid crystal sucking treatment, stop sucking when the reflection stop band of the polymer cholesteric liquid crystal film layer moves to 1 / 3 of the reflection stop band movement in Example 1. The remaining steps and parameters are the same as those in Example 1. Among them, the thickness of the polymer cholesteric liquid crystal film layer formed after the liquid crystal sucking treatment is 40 μm.

[0085] Comparative Example 1

[0086] Without performing the liquid crystal sucking treatment, the remaining steps and parameters are the same as those in Example 1. The thickness of the polymer cholesteric liquid crystal film layer formed without the liquid crystal sucking treatment is 45 μm.

[0087] Further, in order to verify the progressiveness of a gas detection probe and its preparation method and application in an embodiment of the present application, the following performance tests were carried out.

[0088] Table 1. Performance parameter table of gas detection probes prepared in different examples and comparative examples

[0089]

[0090] Figure 3The test spectrogram of the gas detection probe prepared by the preparation method provided in Comparative Example 1 for detecting the concentration of acetone gas. Figure 3 The measurement results were statistically analyzed. The average sensitivity of the gas detection probe to acetone gas was 0.45 pm / ppm when the concentration of acetone gas was in the range of 0 ppm to 4×10 4 ppm, and -0.24 pm / ppm when the concentration of acetone gas was in the range of 4×10 4 ppm to 16×10 4 ppm. As Figure 3 shown, both red shift and blue shift phenomena occurred simultaneously. This was mainly because the reflection wavelength was not only related to the pitch of the cholesteric liquid crystal but also related to the refractive index inside the cholesteric liquid crystal. When the concentration of acetone gas was low, the change in pitch of the cholesteric liquid crystal played a dominant role, forcing the position of the reflection stop band to continuously red shift. However, when the concentration of acetone gas continued to increase, the increase in the pitch of the cholesteric liquid crystal became smaller and smaller, and as more and more acetone was absorbed, the refractive index of the entire probe decreased. When the decrease in refractive index played a dominant role, it forced the position of the reflection stop band to stop red shifting and instead blue shift.

[0091] Figure 4 The graph of the change in the center position of the stop band of the gas detection probe prepared by the preparation method provided in Comparative Example 1 with the concentration of acetone gas. As Figure 4 shown, when the concentration of acetone gas increased from 0 ppm to 4×10 4 ppm, the center wavelength position of the stop band of the gas detection probe increased with the increase in the concentration of acetone gas. When the concentration of acetone gas continued to rise, the center wavelength position of the photonic stop band began to blue shift in the opposite direction. When the concentration of acetone gas was 16×10 4 ppm, the center wavelength position of the photonic stop band blue shifted to 577.9 nm.

[0092] Figure 5 The test spectrogram of the gas detection probe prepared by the preparation method provided in Example 1 for detecting the concentration of acetone gas. As Figure 5 shown, for this gas detection probe prepared by the optimized treatment of sucking out part of the liquid crystal to compress the structure, within the range of 0 ppm to 50×10 4 ppm of the change in acetone gas, the sensitivity was 0.23 pm / ppm, and the chaotic situation of red shift and blue shift of the photonic stop band no longer occurred.

[0093] Figure 6 The graph of the change in the center position of the stop band of the gas detection probe prepared by the preparation method provided in Example 1 with the concentration of acetone gas. As Figure 6 shown, when the concentration of acetone gas gradually increased from 0 ppm to 50×10 4When the concentration is ppm, the central wavelength of the photonic bandgap position of the gas detection probe using the liquid crystal extraction treatment technology redshifts from 646 nm to 761 nm. The optimized polymer cholesteric liquid crystal film layer fiber optic probe can maintain high sensitivity while achieving a large detection range, and the photonic bandgap moves unidirectionally, which can be fully used for the detection of organic volatile gases in life and factory production.

[0094] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0095] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a gas detection probe, characterized in that, It includes the following steps: Pre-treat one end face of the optical fiber; Prepare cholesteric liquid crystal, and mix the cholesteric liquid crystal, polymer monomer and initiator to obtain a cholesteric liquid crystal prepolymer; Coat the cholesteric liquid crystal prepolymer onto the pre-treated end face and perform in-situ polymerization treatment to form a polymer cholesteric liquid crystal film layer on the end face; Perform liquid crystal suction treatment on the polymer cholesteric liquid crystal film layer to make the reflection stop band of the polymer cholesteric liquid crystal film layer blue-shift, thereby obtaining a gas detection probe.

2. The preparation method of the gas detection probe according to claim 1, characterized in that, The pre-treatment includes the following steps: performing end face flattening treatment and end face cleaning treatment on the end face of the optical fiber; and / or The method for preparing the cholesteric liquid crystal includes the following steps: mixing a nematic liquid crystal and a chiral agent to obtain a cholesteric liquid crystal; and / or The in-situ polymerization treatment is ultraviolet light irradiation treatment, and the initiator is a photoinitiator; and / or Before performing the in-situ polymerization treatment, the cholesteric liquid crystal is also subjected to alignment treatment; and / or The liquid crystal suction treatment includes the following steps: using a liquid crystal suction material to be close to the polymer cholesteric liquid crystal film layer to make the reflection stop band of the polymer cholesteric liquid crystal film layer blue-shift.

3. The preparation method of the gas detection probe according to claim 2, characterized in that, The liquid crystal suction material includes at least one of blotting paper, cotton, non-woven fabric, capillary tube, and syringe.

4. The preparation method of the gas detection probe according to claim 2, characterized in that, The inclination angle of the end face after the end face flattening treatment is not greater than 0.5°; and / or The end face cleaning treatment includes one of ultraviolet ozone cleaning treatment and vacuum-type plasma cleaning treatment.

5. The preparation method of the gas detection probe according to claim 2, wherein, The wavelength of the ultraviolet light in the ultraviolet light irradiation treatment is 290 nm to 330 nm; and / or The power density of the ultraviolet light irradiation treatment is 3 to 7 mW / cm 2 , the treatment duration is 5 to 15 minutes; and / or The in-situ polymerization treatment is carried out in an oxygen-free environment.

6. The preparation method of the gas detection probe according to claim 2, characterized in that The alignment treatment is to perform ultraviolet polarized light irradiation treatment on a photo-aligning agent with ultraviolet polarized light and add the photo-aligning agent to the cholesteric liquid crystal.

7. The preparation method of the gas detection probe according to claim 6, wherein The wavelength of the ultraviolet polarized light is 350 nm to 500 nm, and / or The power density of the ultraviolet polarized light irradiation treatment is 40-60 mW / cm 2 , and the treatment duration is 150-250 seconds.

8. The preparation method of the gas detection probe according to claim 2, characterized in that, The optical fiber is a multimode optical fiber; and / or The ratio of the nematic liquid crystal, polymer monomer, chiral agent and photoinitiator by mass is: 70-79 parts of the nematic liquid crystal, 20-25 parts of the polymer monomer, 0.5-3 parts of the chiral agent, and 0.5-2 parts of the photoinitiator.

9. A gas detection probe, characterized in that, It is made by the method for preparing a gas detection probe according to any one of claims 1 to 8.

10. Application of the gas detection probe prepared by the method for preparing a gas detection probe according to any one of claims 1 to 8 in detecting the concentration of organic volatile gases.

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