Material phase change in-situ monitoring method

Abstract

The invention discloses a material phase change in-situ monitoring method, and belongs to the technical field of optical fiber sensing. The method provided by the invention comprises the following steps: contacting a to-be-monitored material with a noble metal nano-film end of an optical fiber probe type sensor, then connecting one end, far away from a gold nano-film, of the optical fiber probe type sensor with a first port of an optical fiber circulator, and connecting a second port of the optical fiber circulator with a light source; a third port of the optical fiber circulator is connected with the optical fiber spectrometer; recording the reflection spectrum of the optical fiber probe type sensor on the optical fiber spectrometer, and monitoring the phase change of the material through the resonant wavelength at the resonant valley position in the reflection spectrum. The optical fiber probe type sensor comprises an optical fiber and a precious metal nano film. The precious metal nano-film is arranged on the end face of the optical fiber, and the precious metal nano-film comprises structural units arranged in an array structure. A wavelength modulation type optical fiber probe type sensor is adopted for monitoring. During monitoring, the phase change of the material is monitored by comparing the position change of the resonance valley.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and more specifically to an in-situ monitoring method for material phase change. Background Art

[0002] In the industrial field, it is crucial to predict and control the formation of solid phases, especially in strict process control, monitoring the onset of phase change is indispensable. Whether it is to prevent the occurrence of phase change or to accurately control its process, a deep understanding of the phase change mechanism is of great significance in many fields, such as energy storage systems, food technology, biomedicine, aerospace and other applications that highly rely on precision and safety monitoring.

[0003] Phase changes are somewhat random in nature, and detecting the occurrence of phase changes can effectively meet the needs for prediction accuracy in industry and daily life. At present, common phase change detection techniques include differential scanning calorimetry and differential thermal analysis, which identify temperature fluctuations during phase change by measuring heat conversion and temperature changes. Although these methods provide key information, they are difficult to be widely used in industrial environments due to the complexity of experimental equipment, and cannot accurately measure specific areas in samples or reactors. In addition, some phase change detection techniques are achieved by monitoring changes in the conductivity of materials. For example, by applying electricity to the sample and measuring the increase in its impedance to evaluate the solidification or crystallization process. Since phase changes are accompanied by heat release or heat absorption, electronic temperature sensors are often used to measure local temperature changes. However, such sensors themselves may become heat sources and interfere with the measurement results. For transparent materials, phase changes can also be observed visually, but this requires the measurement container to be transparent, which is not common in industrial reactors or experimental equipment.

[0004] In recent years, researchers have developed fiber-based optical sensors for phase change detection. Fiber-optic sensors can directly monitor the solid forming process by monitoring changes in the refractive index or temperature of the material. Due to their small size and low environmental interference, fiber-optic sensors can be inserted into the object being measured even under low temperature conditions and show good stability. For example, researchers successfully distinguished the state of the material by fusing single-mode optical fiber with coreless optical fiber, using the property that the refractive index of tridecanethane is higher than that of optical fiber in the solid phase and lower than that of optical fiber in the liquid phase. Alternatively, researchers used single-mode optical fiber and fine-core optical fiber fusion splicing technology, combined with fiber gratings, to monitor the phase change process of water and its mixture. In addition, some researchers measured the growth rate of calcium carbonate crystals by using the attenuation of transmitted light in optical fiber with exposed core during crystal growth.

[0005] Although these fiber optic sensors have shown their own advantages, they still have some problems. For example, most of the fiber optic sensors used in existing fiber optic phase change monitoring technologies are intensity modulation sensors, which monitor by detecting changes in light intensity and are easily affected by light source power fluctuations, and have high requirements for light source stability. When using existing fiber optic sensors, the optical fiber needs to be pre-processed and different types of optical fibers need to be fused, which can easily lead to large light losses and reduce the signal-to-noise ratio. In addition, the complex sensing structure is often less robust and has a shorter service life, which in turn increases costs. Summary of the invention

[0006] In view of the above problems, the present invention provides a method for in-situ monitoring of material phase change. During monitoring, the present invention uses a wavelength modulated optical fiber probe sensor for monitoring, which has low requirements on the stability of the light source. During monitoring, the material phase change monitoring can be achieved by simply comparing the position changes of the resonance valley.

[0007] The object of the present invention is to provide a method for in-situ monitoring of material phase change, comprising the following steps: The material to be monitored is brought into contact with the noble metal nanofilm end of the optical fiber probe sensor, and then the end of the optical fiber probe sensor away from the gold nanofilm is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the light source, and the third port of the optical fiber circulator is connected to the optical fiber spectrometer.

[0008] The reflection spectrum of the optical fiber probe sensor on the optical fiber spectrometer is recorded, and the phase change monitoring of the material to be monitored is realized by comparing the change of the resonance wavelength at the resonance valley position in the reflection spectrum.

[0009] The optical fiber probe sensor comprises: an optical fiber and a noble metal nano film.

[0010] The noble metal nanofilm is arranged on the end face of the optical fiber, and the noble metal film includes structural units arranged in an array structure.

[0011] During monitoring, since the refractive index of the material will continue to change during the phase change process, the resonance valley of the optical fiber probe sensor spectrum will continue to move. When the liquid-solid phase changes, the material's refractive index increases and the resonance valley will redshift. When the solid-liquid phase changes or the liquid-gas phase changes, the material's refractive index decreases and the resonance valley will blueshift. When the spectrum no longer changes, it means that the material phase change process is over.

[0012] The present invention selects the noble metal nanofilm because the resistivity of the noble metal is low, and by reducing the resistance of the film, the quality of the plasmon mode on the film surface can be effectively improved. Many active metals of the first main group have high quality factors, but will show obvious negative dispersion phenomenon in the long-wave band, while the noble metal will not have negative dispersion phenomenon.

[0013] In a preferred embodiment of the present invention, the noble metal nanofilm is a gold nanofilm because gold has good stability and is more commonly used.

[0014] In a preferred embodiment of the present invention, the period of the structural unit is 400nm~700nm.

[0015] It should be noted that the requirement for the structural unit is that the period of the structural unit is of the order of wavelength, and there is no particularly high requirement for the specific shape of the structural unit. Generally, a circular, rectangular or square shape that is easy to realize in micro-nano processing is preferred. If a resonance peak or resonance valley with a smaller bandwidth is required, the shape of the structural unit needs to be limited.

[0016] In a preferred embodiment of the present invention, the optical fiber is a multimode optical fiber. Compared with a single-mode optical fiber, a multimode optical fiber has a thicker core and a signal strength that can meet the use requirements.

[0017] In a preferred embodiment of the present invention, the core diameter of the multimode optical fiber is 50 μm-1000 μm, and the cladding diameter is 125 μm-1100 μm.

[0018] In a preferred embodiment of the present invention, the preparation of the optical fiber probe sensor includes the following steps: The noble metal nanofilm is deposited on the surface of the substrate by a resistance thermal evaporation method to obtain a substrate containing the noble metal nanofilm.

[0019] Fix the bottom surface of the substrate containing the precious metal nanofilm on the first operating table, fix the optical fiber on the second operating table, apply curing glue on the end face of the optical fiber, move the second operating table, and fit the end face of the optical fiber coated with the curing glue with the precious metal nanofilm on the substrate containing the precious metal nanofilm, and then perform a curing treatment. After the curing is completed, move the second operating table to peel off the precious metal nanofilm from the substrate to obtain a fiber optic probe sensor.

[0020] In a preferred embodiment of the present invention, the substrate is a silicon wafer.

[0021] In a preferred embodiment of the present invention, during the resistance thermal evaporation method, the pressure in the vacuum chamber is 8×10 -4 Pa~10×10 -4 Pa, the deposition rate of gold nanofilm is 0.1Å / s~0.5Å / s.

[0022] In a preferred embodiment of the present invention, the curing adhesive is a UV curing adhesive.

[0023] Compared with the prior art, the present invention has the following beneficial effects: Compared with the intensity modulated sensors used in traditional monitoring technologies, the present invention provides a method for monitoring material phase change using a wavelength modulated optical fiber probe sensor. When monitoring the material to be monitored, it is only necessary to compare the resonant wavelength change at the resonance valley position to monitor the phase change process of the material to be monitored, thereby realizing the phase change monitoring of the material to be monitored. Compared with traditional intensity modulated optical sensors, the optical fiber probe sensor used in the present invention has stronger stability and lower requirements for the light source during monitoring.

[0024] The optical fiber probe sensor used in the present invention only needs to transfer the precious metal nanofilm to the end face of the optical fiber, and does not need to be machined or fused on the optical fiber, thus avoiding the problem of optical path loss. In addition, the optical fiber probe sensor used in the present invention has a simple basic structure, does not need additional mechanical processing on the optical fiber, has strong robustness, long service life and low processing difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the curing treatment of the optical fiber probe sensor prepared in the present invention.

[0026] Figure 2 Schematic diagram of the optical fiber probe sensor prepared in the present invention.

[0027] Figure 3 Schematic diagram of the structural unit in Example 2.

[0028] Figure 4 This is a reflection spectrum diagram of the optical fiber probe sensor of Example 2 of the present invention for sodium chloride solutions with different refractive indices.

[0029] Figure 5 This is a graph showing the change in resonance valley wavelength during the solidification process of polyvinyl pyrrolidone solution monitored by an optical fiber probe sensor according to Example 3 of the present invention.

[0030] Figure 6 This is a graph showing the change in resonance valley wavelength during the dissolution process of polyvinyl pyrrolidone monitored by using an optical fiber probe sensor in Example 3 of the present invention.

[0031] Figure 7 This is a graph showing the change in resonance valley wavelength during pure water evaporation monitored by an optical fiber probe sensor according to Example 4 of the present invention.

[0032] Figure numerals: 1-substrate, 2-precious metal nanofilm, 3-optical fiber, 4-optical fiber fixture, 5-cured adhesive, P is the period of the structural unit, D is the center distance, W is the width of the rectangle, and L is the length of the rectangle. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention utilizes the localized surface plasmon effect of precious metals. The position of the resonance valley changes with the change of the refractive index of the environment in which the optical fiber probe sensor is located. Under normal circumstances, the position of the resonance valley will redshift with the increase of the refractive index of the environment in which the sensor is located. The resonance wavelength λr can be calculated by the following formula:

[0035] Where P is the period of the structural unit, i and j are the diffraction orders of the incident light in the orthogonal direction of the two-dimensional periodic structure, representing the order of the surface plasmon effect. i and j are non-zero integers, such as the lowest order is (0, 1) or (1, 0), ε m is the dielectric constant of the metal, ε d is the dielectric constant of the environment. Since the period P of the structural unit and the refractive index of the UV-curing adhesive are fixed, only the refractive index of the environment will change, causing the resonance valley position to change. When the material to be monitored is dropped onto the end face of the optical fiber or the end face of the optical fiber is directly immersed in the material to be measured, when the phase of the material changes, its refractive index will change significantly, which will cause a significant mutation in the resonant wavelength λr of the resonance valley position in the reflection spectrum, thereby monitoring the phase change of the phase change material.

[0036] Example 1 This embodiment provides a fiber optic probe sensor, which includes an optical fiber 3 and a noble metal nanofilm 2 .

[0037] The noble metal nanofilm 2 is disposed on the end face of the optical fiber 3 , and the noble metal nanofilm 2 includes structural units arranged in an array structure.

[0038] The structural unit is composed of two basic units, the center distance D between the two basic units is 200nm, and the period P of the structural unit is 500nm. The present invention does not limit the shape of the basic unit, as long as it can stimulate the localized surface plasmon effect, for example, the basic unit is rectangular, circular or square.

[0039] The preparation method of the optical fiber probe sensor comprises the following steps: The noble metal nanofilm 2 is deposited on the surface of the substrate 1 by resistance thermal evaporation to obtain the substrate 1 containing the noble metal nanofilm 2.

[0040] The bottom surface of the substrate containing the precious metal nanofilm is fixed on the first operating table, and the optical fiber 3 is inserted into the optical fiber clamp 4. Specifically, the optical fiber clamp 4 used in the present invention is a core, and then fixed on the second operating table, and the curing glue 5 is coated on the end face of the optical fiber 3. The second operating table is moved, and the end face of the optical fiber 3 coated with the curing glue 5 is bonded to the precious metal nanofilm 2 on the substrate containing the precious metal nanofilm, and then a curing treatment is performed, such as Figure 1 As shown, after the curing is completed, the second operating table is moved to peel off the noble metal nanofilm 2 from the substrate 1 to obtain an optical fiber probe sensor, as shown in FIG. Figure 2 shown.

[0041] Example 2 This embodiment provides a fiber optic probe sensor, which includes: a multimode optical fiber and a gold nanofilm.

[0042] Multimode optical fiber is a multimode silica optical fiber with a core diameter of 200μm and a cladding diameter of 220μm.

[0043] The gold nanofilm is located on the end face of the optical fiber, and the gold nanofilm includes structural units arranged in an array structure.

[0044] The schematic diagram of the structural unit is as follows: Figure 3 As shown, the structural unit consists of two rectangles, the length L of the rectangle is 206nm, the width W of the rectangle is 75.8nm, the center distance D between the two rectangles is 200nm, the period P of the structural unit is 500nm, and the area of ​​the structural unit is 2mm×2mm.

[0045] The method for preparing the optical fiber probe sensor comprises the following steps: Step 1: Using the resistive thermal evaporation method, a gold nanofilm layer is deposited on a silicon wafer with a rectangular array structure. The pressure in the vacuum chamber is 9×10 -4 Pa, the gold film deposition rate is 0.4Å / s, and the film thickness is 100nm; a silicon wafer containing a gold nanofilm is obtained, and the thickness of the gold nanofilm is 100nm.

[0046] Step 2, fix the silicon wafer containing the gold nanofilm on the metal plate located on the first operating table so that the gold nanofilm of the silicon wafer containing the gold nanofilm faces downward, fix the multimode optical fiber on the second operating table through the optical fiber clamp 4, apply UV curing glue NOA61 on the end face of the multimode optical fiber, then move the position of the second operating table so that the multimode optical fiber is located below the silicon wafer and the reflection signal of the gold nanofilm can be observed on the optical fiber spectrometer, adjust the position of the optical fiber according to the change of the reflection spectrum on the spectrometer, until the reflection spectrum is most obvious, indicating that the core of the multimode optical fiber is completely aligned with the gold nanofilm area, at this time, operate the first operating table so that the multimode optical fiber is upward Move until the UV curing glue contacts the gold nanofilm. After ensuring that the UV curing glue is in full contact with the gold nanofilm, use a 365nm wavelength UV lamp to irradiate the connection area of ​​the gold nanofilm and the multimode optical fiber for curing. The irradiation time is 5s~10s. After irradiation, place the optical fiber for 1 to 2 days to allow it to be completely cured. After it is completely cured, operate the first operating table to move the multimode optical fiber downward. At this time, since the adhesion between the gold nanofilm and the UV curing glue is stronger than the adhesion between the gold nanofilm and the silicon wafer, the gold nanofilm will peel off the silicon wafer and be tightly combined with the end face of the optical fiber through the UV curing glue to obtain a fiber optic probe sensor.

[0047] In order to further verify that the optical fiber probe sensor prepared by the present invention can be used for in-situ monitoring of material phase change, the optical fiber probe sensor of Example 2 of the present invention was placed in salt solutions with different refractive indices for monitoring.

[0048] Specifically, the end of the optical fiber probe sensor of Example 2 away from the gold nanofilm is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the light source, and the third port of the optical fiber circulator is connected to the optical fiber spectrometer. The gold nanofilm end of the optical fiber probe sensor is immersed in pure water, 5%, 10%, 15%, and 20% sodium chloride solutions of five different mass fractions, and the corresponding reflection spectra are obtained by the optical fiber spectrometer, as shown in FIG. Figure 4 As shown in the figure, as the mass fraction of the sodium chloride solution increases, its refractive index increases, and the position of the sensor resonance valley also redshifts. Figure 4 It indicates that the sensitivity of the resonance valley D1 and the resonance valley D2 of the optical fiber probe sensor to the change of the ambient refractive index are 193.13 nm / RIU and 92.89 nm / RIU respectively.

[0049] Example 3 This embodiment provides a method for in-situ monitoring of material phase change using an optical fiber probe sensor. The material to be monitored used in this embodiment is a 10% by mass aqueous solution of polyvinyl pyrrolidone, recorded as 10% PVP-K30. It should be noted that the polyvinyl pyrrolidone in this embodiment is PVP-K30. Polyvinyl pyrrolidone is a water-soluble polymer compound. As the water in the solution evaporates, PVP-K30 will gradually solidify. When the solidified PVP-K30 is immersed in pure water, PVP-K30 will dissolve again.

[0050] The monitoring method specifically includes the following steps: 10% PVP-K30 was dripped onto the gold nanofilm end of the optical fiber probe sensor prepared in Example 2, and then the end of the optical fiber probe sensor away from the gold nanofilm was connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator was connected to the light source, and the third port of the optical fiber circulator was connected to the optical fiber spectrometer.

[0051] Turn on the light source and record the reflection spectrum on the fiber optic spectrometer until the spectrum stops changing. Obtain the reflection spectrum evolution result of the fiber optic probe sensor during the phase change of the material. Analyze the phase change process of the material by the evolution law of the reflection spectrum. When the material undergoes a liquid-solid phase change, its refractive index increases, and the resonance valley of the reflection spectrum redshifts, that is, the wavelength becomes longer. When the material undergoes a solid-liquid phase change, its refractive index decreases, and the resonance valley of the reflection spectrum blueshifts, that is, the wavelength becomes shorter. When the resonance valley wavelength of the reflection spectrum no longer changes, it indicates that the refractive index of the material tends to be stable, and the phase change process of the material is over.

[0052] Figure 5 This is a graph showing the change in resonance valley wavelength during the solidification process of polyvinyl pyrrolidone solution monitored by an optical fiber probe sensor in Example 3 of the present invention. Figure 5 As shown in the figure, after 10% PVP-K30 is dropped onto the gold nanofilm end of the optical fiber probe sensor, as PVP-K30 gradually solidifies, its refractive index gradually increases, and the resonance valley position gradually red-shifts. After 36 minutes, the resonance valley position remains stable, indicating that the refractive index of PVP-K30 no longer changes and the solidification process ends, indicating that 10% PVP-K30 has undergone a liquid-solid phase transition.

[0053] Figure 6 The graph of the change of the resonance valley wavelength during the dissolution process of PVP-K30 monitored by the optical fiber probe sensor in Example 3 of the present invention is shown. The completely solidified PVP-K30 on the gold nanofilm end of the optical fiber probe sensor is re-immersed in pure water. As the PVP-K30 gradually dissolves, its refractive index gradually decreases, and the resonance valley position gradually blue-shifts. After 200 seconds, the spectrum tends to be stable, indicating that PVP-K30 has completed the solid-liquid phase transition.

[0054] Example 4 This embodiment provides a method for in-situ monitoring of material phase change using an optical fiber probe sensor. The material to be monitored used in this embodiment is pure water.

[0055] The monitoring method specifically includes the following steps: A small amount of pure water is dropped on the gold nanofilm of the optical fiber probe sensor prepared in Example 2, and then the end of the optical fiber probe sensor away from the gold nanofilm is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the light source, and the third port of the optical fiber circulator is connected to the optical fiber spectrometer; turn on the light source, and record the reflection spectrum on the optical fiber spectrometer until the spectrum no longer changes.

[0056] Figure 7 This is a graph showing the change in resonance valley wavelength of pure water evaporation process monitored by an optical fiber probe sensor in Example 4 of the present invention. Figure 7 As shown in the figure, after a trace amount of pure water is dropped onto the gold nanofilm of the optical fiber probe sensor, the water gradually evaporates, and the position of the resonance valley changes suddenly at 860s, blue-shifting from 886nm to 883.5nm. At this time, the environmental medium of the gold nanofilm changes from water with a refractive index of 1.333 to air with a refractive index of 1.0, indicating that the pure water undergoes a liquid-gas phase transition, and the liquid water on the gold nanofilm at the end face of the optical fiber is completely evaporated.

[0057] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0058] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for in-situ monitoring of material phase change, characterized in that: The following steps are involved: The material to be monitored is brought into contact with the noble metal nanofilm end of the optical fiber probe sensor, and then the end of the optical fiber probe sensor away from the gold nanofilm is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the light source, and the third port of the optical fiber circulator is connected to the optical fiber spectrometer; Record the reflection spectrum of the optical fiber probe sensor on the optical fiber spectrometer, and realize the phase change monitoring of the material to be monitored by comparing the resonant wavelength change at the resonance valley position in the reflection spectrum; The optical fiber probe sensor comprises: an optical fiber and a precious metal nano film; The noble metal nanofilm is arranged on the end face of the optical fiber, and the noble metal film includes structural units arranged in an array structure.

2. The in-situ monitoring method for material phase change according to claim 1, characterized in that: The noble metal nanofilm is a gold nanofilm.

3. The in-situ monitoring method for material phase change according to claim 1, characterized in that: The period of the structural unit is 400nm~700nm.

4. The in-situ monitoring method for material phase change according to claim 1, characterized in that: The optical fiber is a multimode optical fiber.

5. According to the in-situ monitoring method of material phase change according to claim 4, the core diameter of the multimode optical fiber is 50 μm~1000 μm, and the cladding diameter is 125 μm~1100 μm.

6. The in-situ monitoring method for material phase change according to claim 1, characterized in that: The preparation method of the optical fiber probe sensor comprises the following steps: Depositing a noble metal nanofilm (2) on the surface of a substrate (1) by a resistance thermal evaporation method to obtain a substrate containing the noble metal nanofilm; The bottom surface of the substrate containing the precious metal nanofilm is fixed on a first operating table, the optical fiber (3) is fixed on a second operating table, a curing glue (5) is coated on the end surface of the optical fiber (3), the second operating table is moved, the end surface of the optical fiber (3) coated with the curing glue (5) is bonded to the precious metal nanofilm (2) on the substrate containing the precious metal nanofilm, and then a curing treatment is performed. After the curing is completed, the second operating table is moved so that the precious metal nanofilm (2) is peeled off from the substrate (1), thereby obtaining an optical fiber probe sensor.

7. The in-situ monitoring method for material phase change according to claim 6, characterized in that: The substrate is a silicon wafer.

8. The in-situ monitoring method for material phase change according to claim 6, characterized in that: During the resistance thermal evaporation method, the pressure in the vacuum chamber is 8×10 -4 Pa~10×10 -4 Pa, the deposition rate of gold nanofilm is 0.1Å / s~0.5Å / s.

9. The in-situ monitoring method for material phase change according to claim 6, characterized in that: The curing glue (5) is a UV curing glue.

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