Fire early warning system and fire early warning method

Abstract

The present invention relates to the technical field of material preparation and sensing, and specifically to a structural chromogenic material, a fire early warning system and a fire early warning method, wherein the structural chromogenic material comprises monodisperse nanoparticles, additives and high-absorbency nanoparticles, wherein the monodisperse nanoparticles are mainly one or more of zinc sulfide, silicon dioxide, zinc oxide, polystyrene and polymethyl methacrylate; the additives are mainly one or more of polyvinyl pyrrolidone, polyvinyl alcohol and polybutyl methacrylate; the high-absorbency material is mainly one or more of black nanoparticles such as carbon black, carbon black nanoparticles, graphene, MXene, carbon nanotubes and polydopamine. The structural chromogenic material of the present invention can expand to different degrees during the heating process, causing the spacing of the nanoparticles in the structural chromogenic material to change, resulting in obvious color changes, and has the characteristics of high sensitivity and timely response, thereby achieving the purpose of early warning of fire.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation and sensing, and in particular to an early fire warning system and an early fire warning method. Background Art

[0002] Fire is an important hidden danger that threatens human property and life safety. Its early warning is crucial to fire control and reducing casualties and property losses. At present, fire warning is mainly carried out through smoke and combustible decomposition products produced by the combustion of combustibles. The warning mainly occurs after the material burns, which is not conducive to fire warning. Most fires in buildings, electrical appliances, wires, etc. are caused by local overheating of materials, which causes material deformation, further heating to the ignition point of the material, and material combustion causes fire. Therefore, it is of great significance to develop non-open flame early fire warning materials for the early material heating process. At present, there is a patent (CN 109191763) that uses color changes to achieve fire warning, but all material color contrasts, sensor sensitivity and applicable temperature ranges are not clearly reported.

[0003] Based on the thermal deformation process of the structural chromogenic material during the material heating, the present invention prepares a photonic crystal coating and patch with structural color, which is suitable for non-open flame warning during the heating process of different materials. In combination with the existing camera technology, a non-contact, multi-alarm fire warning sensor for early fire warning is prepared. The color changes of the structural chromogenic coating and patch are monitored by a camera, and high temperature warning of the material can be achieved at the monitoring end such as a computer, alarm, etc. through video monitoring, thereby advancing the fire warning time to achieve the purpose of preventing fire.

[0004] The present invention discloses a method for preparing a traffic light type structural chromogenic coating, patch, etc., and a highly sensitive fire warning sensor is prepared based on the same. The preparation process mainly includes the preparation of the structural chromogenic coating, the preparation of the structural chromogenic patch, and the preparation method of the fire warning sensor. Compared with the traditional method, the fire alarm of the present invention is based on the transition from green to red, which is similar to the principle of traffic lights. Whether it is the naked eye or the sensor picking color, its color contrast is greater, the sensitivity of the sensor is higher, and the temperature range of use is higher, which can greatly reduce false alarms. Summary of the invention

[0005] One of the purposes of the present invention is to provide a structural chromogenic material that can undergo an obvious color change during a heating process and can be used in the field of preparing early fire warnings.

[0006] The second object of the present invention is to provide an early warning system for fire, which can predict the temperature change of the base material by simply monitoring the color change of the color-producing unit, has the characteristics of high sensitivity and timely response, thereby achieving the purpose of early warning of fire.

[0007] The third object of the present invention is to provide a fire early warning method which is simple, easy to implement, and has the characteristics of high sensitivity and timely response.

[0008] The scheme adopted by the present invention to achieve one of the purposes is: a structural chromogenic material, including monodisperse nanoparticles, additives and high-absorbency nanoparticles, wherein the monodisperse nanoparticles are mainly one or more of zinc sulfide, silicon dioxide, zinc oxide, polystyrene, and polymethyl methacrylate; the additives are mainly one or more of polyvinyl pyrrolidone, polyvinyl alcohol, and polybutyl methacrylate; the high-absorbency material is mainly one or more of black nanoparticles such as carbon black, carbon black nanoparticles, graphene, MXene, carbon nanotubes, and polydopamine.

[0009] Preferably, the mass percentage of the monodisperse nanoparticles is 10%-99%, the mass percentage of the additive is 0.1%-20%, and the mass percentage of the high absorbance nanoparticles is 0.005%-10%.

[0010] Preferably, the particle size of the monodisperse nanoparticles is 100-800 nm.

[0011] Preferably, monodisperse nanoparticles are synthesized by any one of a hydrothermal method, a sol-gel method, and a polymerization method, and the reaction temperature, the solvent content, and the amount of each substance are regulated. The particle size range of the nanoparticles finally prepared is mainly: 100nm-800nm, and its polydispersity index PDI is ≤1.4.

[0012] The specific controlled reaction temperature is 60-80°C, and the mass percentage content of the solvent is 10%-30%.

[0013] The solution adopted by the present invention to achieve the second object is: a fire early warning system, a color generating unit, a monitoring unit, a collection unit, a processing unit and an alarm unit;

[0014] The color-forming unit is coated or adhered to the surface of the substrate to sense the deformation caused by thermal expansion of the substrate and produce color change;

[0015] The monitoring unit monitors the real-time color changes of the color-producing unit, and the monitoring data is transmitted to the processing unit through the acquisition unit.

[0016] The processing unit controls whether the alarm sounds an alarm by analyzing changes in the collected RGB or CMYK color parameters.

[0017] Wherein, the chromogenic unit is a structural chromogenic coating or a structural chromogenic patch prepared from the structural chromogenic material, and the structural chromogenic coating is coated on the surface of the substrate to be monitored or the structural chromogenic patch is attached to the surface of the substrate to be detected.

[0018] Preferably, the monodisperse nanoparticles, additives, and high-absorbency nanoparticles are dispersed in a solvent, and applied to the substrate surface by any one of dipping, spraying, and spin coating, and then dried; the method for preparing the structural chromogenic patch is: the monodisperse nanoparticles, additives, and high-absorbency nanoparticles are dispersed in a solvent, and applied to one side of the patch by any one of dipping, spraying, and spin coating, and an adhesive layer is provided on the other side. The material of the patch is mainly one or more of polycarbonate, polyvinyl chloride, polymethyl methacrylate, polyethylene, polypropylene, epoxy resin, etc., which is a plastic with a thermal expansion coefficient greater than 50ppm (room temperature-200°C).

[0019] Preferably, the solvent is mainly one or more of water, ethanol, tetrahydrofuran, methanol, propanol, and dimethyl sulfoxide, and the mass percentage content of the solvent in the structural chromogenic material dispersion is 30%-99%.

[0020] Preferably, when the substrate is plastic or engineering plastic, the chromogenic unit adopts a structural chromogenic coating, and when the thermal expansion coefficient of the substrate material is small, a structural chromogenic patch is used at the chromogenic unit.

[0021] Specifically, when the substrate is polypropylene, polyvinyl chloride, polycarbonate, polyethylene, epoxy resin, nylon, polyphenylene ether ester, cellulose, polyurethane, etc., the chromogenic unit adopts a structural chromogenic coating; when the substrate is iron, polytetrafluoroethylene, polyimide, polystyrene, ceramic, glass, graphite material, stainless steel, etc., a structural chromogenic patch is used at the chromogenic unit.

[0022] The solution adopted by the present invention to achieve the third purpose is: a method for early warning of fire, comprising the following steps:

[0023] (1) attaching a structural chromogenic coating or structural chromogenic patch prepared from the structural chromogenic material to the surface of a substrate to be detected as a chromogenic unit;

[0024] (2) Determine the monitoring area, install the monitoring unit, and monitor the color of the chromogenic unit in real time;

[0025] (3) Collecting the color of the chromogenic unit monitored in real time and transmitting it to the processing unit;

[0026] (4) The processing unit captures and calculates the changes in RGB values ​​or CMYK values ​​throughout the process, compares them with the set thresholds, and issues a fire warning through the alarm unit.

[0027] Preferably, after the material changes color, when RGB value is used for calculation, the specific threshold B value changes by greater than or equal to 20, the G value changes by greater than or equal to 30, and the R value changes in the range of 32 to 50; when CMYK value is used for calculation, the specific threshold C value changes in the range of 20 to 30, the M value changes in the range of 0 to 90, the Y value changes in the range of 90 to 95, and the K value changes in the range of less than 5.

[0028] Monodisperse nanoparticles form long-range ordered and short-range ordered structures on the surface of the base material, which gives the base material a bright color. When the base material is heated, its chain movement increases the distance between the above-mentioned coating materials, and the base material enters the gap between the coatings when it is heated, which eventually causes the color of the material to change, thereby achieving early warning of fire.

[0029] The base material is mainly one or more of thermoplastic materials such as polyethylene, polypropylene, polyvinyl chloride, polybutylene terephthalate, epoxy resin board, polycarbonate, etc. If the equipment to be tested itself has good thermal deformation ability, it can be directly used as the base material to construct a structural color coating on its surface.

[0030] For materials with little obvious thermal deformation or low thermal expansion coefficient (such as metals, ceramics, polytetrafluoroethylene, etc.), a structural chromogenic patch is prepared. The base material of the patch is a material that has good thermal deformation ability, such as one or more thermoplastic materials such as polyethylene, polypropylene, polyvinyl chloride, polybutylene terephthalate, epoxy resin board, polycarbonate, etc. The patch can be pasted to the surface of the material to be tested. The above-mentioned structural chromogenic coating or patch can change color rapidly during the heating process.

[0031] For materials with large thermal expansion coefficients such as plastics and rubber, they can be directly coated or sprayed, which is easy to operate. This material is suitable for monitoring areas prone to thermal fires such as transformer boxes, refrigerators, electrical boxes, and wires. Even the monitoring parts such as metal shells and ceramic shells can be pasted by patching for early warning of material fires. The alarm can be used in conjunction with home monitoring equipment in the later stage to realize alarm while monitoring.

[0032] The color change of the color-producing unit of the present invention can cause the change of color parameters such as RGB and CMYK of the material monitored by the monitoring equipment. The change of the color B value is more than 20, the change of the G value is more than 30, which is easy to observe, and the change of the R value can be up to 50. The changes of the G value and the R value are easy to observe. Preferably, the fire alarm of the present invention is based on the transition from green to red. This transition is similar to the principle of traffic lights. Whether it is the naked eye or the sensor to pick up the color, its color contrast is greater, the sensitivity of the sensor is higher, and the temperature range of use is higher, which can greatly reduce false alarms.

[0033] The present invention has the following advantages and beneficial effects:

[0034] The structural chromogenic material of the present invention can expand to different degrees during the heating process, causing the spacing between nanoparticles in the structural chromogenic material to change and causing obvious color changes, and can be used in the field of preparing early fire warnings.

[0035] The fire early warning system of the present invention can predict the temperature change of the base material by simply monitoring the color change of the chromogenic unit, and has the characteristics of high sensitivity and timely response, thereby achieving the purpose of early warning of fire.

[0036] In the fire early warning system of the present invention, the color development temperature of the color-forming unit occurs near the thermal deformation temperature of the material. When the material has not yet produced obvious smoke or combustion, a temperature rise warning can be prompted by monitoring the color change of the color-forming unit, thereby significantly advancing the fire warning time. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 These are digital photos of the green photonic crystal polycarbonate with a thickness of 0.5 mm*5 cm*5 cm in Example 1 after being heated at different temperatures for 5 minutes;

[0038] Figure 2 The temperature variation spectrum of the green photonic crystal polycarbonate at different temperatures in Example 1;

[0039] Figure 3 It is a comparison diagram of the actual pictures of the green ER, PC, PVC, PP and PE prepared in Examples 1-6 after being heated at 290°C, 250°C, 250°C, 240°C and 220°C for 5 minutes respectively;

[0040] Figure 4 The time required for the warning signal to change from "0" to "1" at temperatures of 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, and 250°C for the green polycarbonate photonic crystal with a thickness of 0.09 mm in Example 1;

[0041] Figure 5 The change of RGB value detected by the sensor system during the color change process of the green polycarbonate photonic crystal with a thickness of about 0.09 mm from room temperature to 220° C. in Example 1;

[0042] Figure 6 In Example 1, the sensor system detects the change of the RGB value of the center point of the G-PC with a thickness of 0.09 mm during the constant temperature color change process at 260°C;

[0043] Figure 7 The temperature variation spectra of the green photonic crystal patches in Examples 2-6 at their respective maximum temperatures;

[0044] Figure 8 The time required for ER, PC, PVC, PP, and PE with a thickness of about 0.01 mm in Examples 2-6 to change color from the beginning to the complete color change at their respective specific temperatures as observed by the naked eye;

[0045] Fig. 9 This is a schematic diagram of the visualized sensing process of the photonic crystal patch of the present invention. DETAILED DESCRIPTION

[0046] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0047] In the present invention, the monitoring unit of the fire early warning system is a camera, the camera of the fire warning sensor (resolution is not less than 240P), and the data acquisition system can select the detection position, the number of monitoring points, and set the alarm threshold in the area of ​​the structural color-forming material to be detected, so as to realize real-time monitoring of the material color. The computer and the alarm can synchronously display the monitoring data status of the material.

[0048] Specifically, the fire early warning system of the present invention includes a camera, a data acquisition system, a computer and an alarm, and can be used for early warning of fire.

[0049] The main technical routes of the present invention are as follows:

[0050] Step 1: Synthesis of monodisperse nanoparticles. Monodisperse nanoparticles are synthesized by hydrothermal method, sol-gel method, polymerization method and other methods, and the reaction temperature, solvent content and the amount of each substance are regulated. The particle size range of the final prepared nanoparticles is mainly: 100 nm-800 nm, and its polydispersity index PDI ≤ 1.4.

[0051] Step 2: Preparation of coating material dispersion. Monodisperse nanoparticles, additives, high absorbance nanoparticles, etc. are dispersed in a solvent, and the content of the solvent is mainly 30%-99%. In order to make it dispersed evenly, ultrasound, stirring, etc. can be added.

[0052] Step 3: Preparation of structural chromogenic coating. The structural chromogenic coating is mainly applied to the surface of the substrate material by dipping, spraying, spin coating, etc., mainly to control the arrangement of monodisperse nanoparticles on the surface of the substrate material, so that it forms a long-range ordered or short-range ordered structure, and finally displays bright colors.

[0053] Step 4: Paste the structural chromogenic patch. If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above structural chromogenic coating is pasted to the surface of the material with glue. The glue can be 502 glue, epoxy resin glue, etc.

[0054] Step 5: Design and preparation of disaster warning sensors. Adjust the position of the camera and install it, determine the monitoring area, the number of monitoring points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0055] Embodiment 1:

[0056] S1. Preparation of monodisperse zinc sulfide nanoparticles by hydrothermal method. Dissolve 3.00 g of polyvinyl pyrrolidone (PVP) in 100 mL of deionized water. Ultrasonicate until all the polymer is completely dissolved, and transfer the solution to a round-bottom three-necked flask (250 mL). Heat to 70°C with stirring, and quickly pour 2.8 g of TAA into the flask. After vigorously stirring for 10 min, add 100 μL of nitric acid. After reacting for 10 min, 5 mL of Zn(NO3)2 solution (1.0 g / mL) is quickly poured into the flask under vigorous stirring. After reacting for 5 min, reduce the stirring speed to 20 rpm. After stirring for 3 h, add 1.5 mL of Zn(NO3)2 solution (0.2 g / mL). After slowly stirring for another 1 h, remove the heat source, cool to room temperature, stop the reaction, centrifuge the system, and wash the obtained solid with anhydrous ethanol for more than three times. Finally, dry under vacuum conditions at 70°C for more than 24 h to obtain ZnS nanoparticles.

[0057] S2. Preparation of coating material dispersion. ZnS was dispersed in anhydrous ethanol by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. Carbon black with a mass fraction of 2%-4% as high absorbance nanoparticles and polyvinyl pyrrolidone with a mass fraction of 1%-5% were weighed separately as additives, and both were added to the dispersion. The dispersion was fully dispersed in the zinc sulfide dispersion by ultrasound and stirring for more than 10 min. The solvent content in the final dispersion was about 60%.

[0058] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black polycarbonate surface by spraying. A spray gun with an inner diameter of 0.2 mm and filled with a well-dispersed ZnS dispersion with a mass fraction of 20% was placed 10 cm away from the black polycarbonate plate and driven by compressed air with a pressure of 0.103 MPa. By controlling the evaporation rate and drying temperature of the solvent, the solvent evaporated as quickly as possible during the spraying process, and the particles assembled into an orderly structure on the black polycarbonate surface. A patch of highly saturated green photonic crystal polycarbonate was obtained.

[0059] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0060] S4. Design and preparation of fire warning sensor. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the positions of the detection points, set the alarm threshold, connect the alarm light and install it, and monitor the color of the material. Specifically, the external camera is used to capture the color changes of the external photonic crystal in time, and the system will capture and calculate the changes in the RGB value throughout the process. The program will judge the degree of danger according to the calculation results of the RGB change value. According to the different degrees of danger, the alarm light will display different colors, and at the same time, different degrees of alarm warnings will be displayed on the program. The alarm light and the external computer program output display alarm prompts and dual response alarms. When there is no high temperature danger and no alarm prompt, the alarm light will display a green light, and the computer program will not output. When there is a high temperature danger, the response light and the alarm program will both alarm. The alarm prompt is divided into two levels. Level 1 is the alarm prompt detected initially, the program will display Warning 1, and the alarm light will display a blue light. Level 2 is when the program detects most of the alarm prompts, the program will display Warning 2, and the alarm light will display a red light.

[0061] Because the photonic crystal patch is placed flat on the hot plate for heating, and the temperature is highest at the center of the hot plate surface, and the thermochromic photonic crystal patch is square, even if it is placed in the middle of the hot plate every time, it is inevitable that the photonic crystal patch has the highest temperature in the middle, so it will start to expand first and then spread to the surroundings. Therefore, in our alarm system setting, nine detection points are evenly taken for the thermochromic photonic crystal patch. In the alarm system, we set an absolute deviation value X (alarm threshold). The real-time absolute deviation value of each point is calculated based on the real-time RGB value of the corresponding point, and it is stipulated that if the alarm threshold of any point exceeds 30, Warning 1 will appear, and when the absolute deviation of more than three points exceeds 30, the program will appear Warning 2 alarm.

[0062] After the system is set up, under the external camera, 0.05 mm*3 cm*3 cm green photonic crystal polycarbonate is placed in the middle of the hot stage for heat treatment. It is heated at 150℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ and 250℃ for 5 minutes respectively, and the RGB values ​​of the color change of the photonic crystal and the spectrum before and after the test are captured.

[0063] Figure 1 The digital photos of the green photonic crystal polycarbonate with a thickness of 0.5 mm*5 cm*5 cm in Example 1 after being heated at different temperatures for 5 minutes can be seen from the figure: as the heating temperature increases, the 0.5 mm thick G-PC expands locally and bulges appear, and the bulges change color. The greater the deformation, the larger the area of ​​color change. This shows that the expansion of polycarbonate plastic when heated will cause the spacing of the nanoparticles attached to it to change, thereby changing the color. From a macroscopic perspective, it describes the degree of thermochromic phenomenon of polycarbonate photonic crystals after being heated at different temperatures.

[0064] Figure 2The temperature variation spectrum of the green photonic crystal polycarbonate at different temperatures in Example 1, from which two points can be seen: first, as the temperature increases, the corresponding spectrum maximum peak position has undergone a significant red shift from 537-662 nm. This is because when the heat increases macroscopically, the volume of the matrix expands, resulting in an increase in the spacing between the nanoparticles, and the reflection spectrum peak position is red shifted. Second, the change in its peak intensity first increases with the increase in temperature, and then decreases with the increase in temperature. This is because during the heating process, the photonic crystal undergoes a certain rearrangement, and under the drive of thermal energy, the arrangement is more regular, making its color more vivid. However, when the temperature exceeds a certain value, the nanoparticles on the surface of the plastic sink into the interior of the plastic in large quantities, causing the photonic crystal to be surrounded by a large number of polymers, and the contact distance with the incident light becomes larger. Thereby reducing the appearance of color. Therefore, it is proved from a microscopic optical point of view that the polycarbonate photonic crystal undergoes a thermochromic phenomenon after being subjected to different heating. The spectrum peak position red shift degree.

[0065] Figure 4 In Example 1, the green polycarbonate photonic crystal with a thickness of 0.09 mm is at 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, and 250°C. The time required for the warning signal to change from "0" to "1" can be seen from the figure: polycarbonate with a relatively obvious thermochromic phenomenon is selected as the matrix of the photonic crystal, and the green polycarbonate photonic crystal with a thickness of 0.09 mm is placed on the hot stage surface at 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, and 250°C under the monitoring system. From the start of the sample, the system program starts to count the time, and the camera starts to capture the numerical changes of RGB and calculates at the same time. By counting the corresponding time required for the sample at each temperature, it can be seen that with the increase of the heating temperature, the time required for the color change detected by the system gradually decreases. Therefore, appropriately increasing the heating temperature of the polycarbonate photonic crystal can effectively reduce the time required for the color change.

[0066] Figure 5In Example 1, the green polycarbonate photonic crystal with a thickness of about 0.09 mm changes in the RGB value detected by the sensor system during the temperature change process from room temperature to 220°C. In the visual sensor designed in the present invention, the photonic crystal plastic plate is placed flat on the hot stage for heating treatment, and the temperature at the center of the hot stage surface is the highest. Our thermochromic photonic crystal plastic plate is a square sheet. Even if it is placed in the middle of the hot stage every time, it is still inevitable that the highest temperature of the photonic crystal plastic plate is in the middle, so it will start to expand first and then spread to the surroundings. Therefore, in the simulation alarm system of the present invention, nine detection points are uniformly taken for the thermochromic photonic crystal plastic plate. In the alarm system, we set an absolute deviation value X. The real-time absolute deviation value of each point is calculated based on the real-time RGB value of the corresponding point, and it is stipulated that if the absolute deviation value of any point exceeds 30, Warning 1 will appear. If the absolute deviation of more than three points exceeds 30, Warning 2 will appear (as shown in Figure S20). Figure 5 The data is a graph of the change of G value and X value at the most central detection point during the color change process of a green polycarbonate photonic crystal with a thickness of about 0.09mm from room temperature to 220℃. The change trend of the G value detected by the sensor system shows that the G value decreases significantly at 4 minutes, which means that the color changes from green to red at this time. The change in G value proves the occurrence of thermochromic phenomenon of polycarbonate photonic crystal.

[0067] Figure 6 In Example 1, the sensor system detects the change of the RGB value of the center point of the G-PC with a thickness of 0.09 mm at a constant temperature of 260°C. It can be seen from the figure that at the beginning, the temperature of the hot stage did not cause expansion, and the G value of the polycarbonate photonic crystal can be regarded as unchanged. However, as the heating time increases, the G value of the polycarbonate photonic crystal begins to decrease and finally stabilizes. Due to the high temperature, the change time of the entire G value is relatively long. Figure 5 The color change response time is less than one second, which can achieve a fast response, indicating that the temperature response sensor of the present invention can effectively improve the response time by simply increasing the heating temperature or reducing the thickness of the substrate, thereby reaching the standard of the temperature response sensor.

[0068] Table 1. The time required for the color change from room temperature to the corresponding maximum temperature and the corresponding error

[0069]

[0070] Table 2. The time required for a 0.09 mm thick green polycarbonate patch to change color at the maximum temperature and the corresponding error

[0071]

[0072] Table 3. Changes in R value, G value, and B value of a green polycarbonate patch with a thickness of 0.09 mm at a constant temperature of 260°C

[0073]

[0074] According to the data in Table 1-3, we can see that:

[0075] Table 1 shows the time and error required for a 0.5mm thick polycarbonate photonic crystal to change color from room temperature to the corresponding maximum temperature. It can be seen from the table that as the heating temperature increases, the time required for the polycarbonate photonic crystal to change color gradually decreases. Therefore, by increasing the heating temperature of the polycarbonate photonic crystal, the time for the polycarbonate photonic crystal to respond to the color change can be effectively reduced.

[0076] Table 2 shows the time and corresponding error required for the polycarbonate photonic crystal with a thickness of 0.09 mm to change color at 220°C, 230°C, 240°C, 250°C, and 260°C. It can be seen from the table that as the heating temperature increases, the time required for the polycarbonate photonic crystal to change color decreases exponentially. Therefore, by increasing the heating temperature of the polycarbonate photonic crystal, the time for the polycarbonate photonic crystal to respond to the color change can be effectively reduced.

[0077] Table 3. Changes in R, G, and B values ​​of a 0.09 mm thick green polycarbonate patch during the color change process at a constant temperature of 260°C. From the table, it can be seen that with the increase in heating time, the B and G values ​​of the polycarbonate photonic crystal are decreasing, while the R value is increasing, confirming the change from green to red. In addition, the initial color change only takes 853 ms, and the changes in the values ​​of R, G, and B are not obvious as time goes by.

[0078] Embodiment 2:

[0079] S1. Preparation of monodisperse ZnS nanoparticles by hydrothermal method. Dissolve 3.00 g of polyvinyl pyrrolidone (PVP) in 100 mL of deionized water. Ultrasonicate until all the polymer is completely dissolved and transfer the solution to a round-bottom three-necked flask (250 mL). Heat to 70 °C with stirring and quickly pour 2.8 g of TAA into the flask. After vigorous stirring for 10 min, add 100 μL of nitric acid. After reacting for 10 min, pour 5 mL of Zn(NO3)2 solution (1.0 g / mL) into the flask quickly with vigorous stirring. After reacting for 5 min, reduce the stirring speed to 20 rpm. After stirring for 3 h, add 1.5 mL of Zn(NO3)2 solution (0.2 g / mL). After stirring slowly for another 1 h, remove the heat source, cool to room temperature, stop the reaction, separate the solid product by centrifugation, and wash with deionized water for more than three times. Finally, dry under vacuum conditions at 70 °C for more than 24 h to obtain ZnS nanoparticles.

[0080] S2. Preparation of coating material dispersion. ZnS was dispersed in deionized water by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. Carbon black nanoparticles with a mass fraction of 2%-4% as high absorbance nanoparticles and polyvinyl pyrrolidone with a mass fraction of 1%-5% as an additive were weighed separately, and both were added to the dispersion, and fully dispersed in the zinc sulfide dispersion by ultrasound and stirring for more than 10 minutes. The solvent content in the final dispersion was about 60%.

[0081] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black polyvinyl chloride surface by dip coating. The above dispersion was evenly dispersed in a glass culture dish with a diameter of 20 cm and a height of 3 cm. Clamp a corner of the polyvinyl chloride plate with hemostatic forceps, dip the dispersion in the glass culture dish, make the liquid cover the surface of the polyvinyl chloride plate as evenly as possible, and place it in a 90°C forced air drying oven for 10 min. After drying, repeat the above operation 3 times. By controlling the evaporation rate and drying temperature of the solvent, the solvent is allowed to evaporate as quickly as possible during the spraying process, and the particles are assembled into an orderly structure on the surface of the patch. A highly saturated green photonic crystal polyvinyl chloride patch can be obtained.

[0082] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0083] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0084] After setting up, under the external camera, place 0.5 mm*3 cm*3 cm green photonic crystal polyvinyl chloride in the middle of the hot stage for heating treatment, and heat at 100℃, 150℃, 200℃, 210℃, 220℃, 230℃, 240℃, and 250℃ for 5 minutes respectively. Capture the RGB value of the color change of the photonic crystal and the spectrum before and after the test.

[0085] Embodiment 3:

[0086] S1. Preparation of monodisperse zinc sulfide nanoparticles by hydrothermal method. Dissolve 3.00 g of polyvinyl pyrrolidone (PVP) in 100 mL of deionized water. Ultrasonicate until all the polymer is completely dissolved, and transfer the solution to a round-bottom three-necked flask (250 mL). Heat to 70 °C with stirring, and quickly pour 2.8 g of TAA into the flask. After vigorously stirring for 10 min, add 100 μL of nitric acid. After reacting for 10 min, 5 mL of Zn(NO3)2 solution (1.0 g / mL) is quickly poured into the flask under vigorous stirring. After reacting for 5 min, reduce the stirring speed to 20 rpm. After stirring for 3 h, add 1.5 mL of Zn(NO3)2 solution (0.2 g / mL). After stirring slowly for another 1 h, remove the heat source, cool to room temperature, stop the reaction, separate the solid product by centrifugation, and wash it more than three times with a mixed solvent (deionized water: anhydrous ethanol = 1:1). Finally, the ZnS nanoparticles were obtained by drying at 70 °C under vacuum conditions for more than 24 h.

[0087] S2. Preparation of coating material dispersion. ZnS was dispersed in a mixed solvent by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. 2%-4% of graphene as high absorbance nanoparticles and 1%-5% of polyvinyl pyrrolidone as an additive were weighed separately, and both were added to the dispersion, and fully dispersed in the zinc sulfide dispersion by ultrasound and stirring for more than 10 min. The content of the solvent in the final dispersion was about 60%.

[0088] S3. Preparation of structural chromogenic coating. Spin coating was used to construct photonic crystals on the black polyethylene surface. The black polyethylene plate was fixed on a clamp, and a dispersion with a mass fraction of 10%-30% of ZnS was poured into the coating nozzle. The substrate was rotated at a high speed in the range of 500-600 rpm. When a thin layer of photonic crystals was covered on the substrate, it was placed in an oven at 90°C for drying. After drying, the above steps were repeated twice. A highly saturated green photonic crystal polyethylene patch was obtained.

[0089] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0090] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0091] After setting up, under the external camera, place 0.5 mm*3 cm*3 cm green photonic crystal polyethylene in the middle of the hot stage for heating treatment, and heat at 100℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃ for 5 minutes respectively. Capture the RGB value of the color change of the photonic crystal and the spectrum before and after the test.

[0092] Embodiment 4:

[0093] S1. Preparation of monodisperse ZnS nanoparticles by hydrothermal method. Dissolve 3.00 g of polyvinyl pyrrolidone (PVP) in 100 mL of deionized water. Ultrasonicate until all the polymer is completely dissolved and transfer the solution to a round-bottom three-necked flask (250 mL). Heat to 70 °C with stirring and quickly pour 2.8 g of TAA into the flask. After vigorous stirring for 10 min, add 100 μL of nitric acid. After reacting for 10 min, pour 5 mL of Zn(NO3)2 solution (1.0 g / mL) into the flask quickly with vigorous stirring. After reacting for 5 min, reduce the stirring speed to 20 rpm. After stirring for 3 h, add 1.5 mL of Zn(NO3)2 solution (0.2 g / mL). After stirring slowly for another 1 h, remove the heat source, cool to room temperature, stop the reaction, separate the solid product by centrifugation, and wash with ethylene glycol solvent for more than three times. Finally, dry under vacuum conditions at 70 °C for more than 24 h to obtain ZnS nanoparticles.

[0094] S2. Preparation of coating material dispersion. ZnS was dispersed in ethylene glycol solvent by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. 2%-4% of Mxene as high absorbance nanoparticles and 1%-5% of polyvinyl pyrrolidone as an additive were weighed separately, and both were added to the dispersion, and fully dispersed in the zinc sulfide dispersion by ultrasound and stirring for more than 10 min. The content of the solvent in the final dispersion was about 60%.

[0095] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black epoxy resin surface by spraying. A spray gun with an inner diameter of 0.2 mm and filled with a well-dispersed ZnS dispersion with a mass fraction of 20% was placed 10 cm away from the black epoxy resin plate and driven by compressed air with a pressure of 0.103 MPa. By controlling the evaporation rate and drying temperature of the solvent, the solvent evaporated as quickly as possible during the spraying process, and the particles assembled into an orderly structure on the patch surface. A highly saturated green photonic crystal polycarbonate patch was obtained.

[0096] Pasting of structural chromogenic patch. If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above structural chromogenic coating is pasted to the surface of the material with glue. The glue can be 502 glue, epoxy resin glue, etc.

[0097] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0098] After setting up, under the external camera, place 0.5 mm*3 cm*3 cm green photonic crystal epoxy resin in the middle of the hot stage for heating treatment, and heat at 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, and 290℃ for 5 minutes respectively. Capture the RGB value of the color change of the photonic crystal and the spectrum before and after the test. Example

[0099] S1. Preparation of monodisperse ZnS nanoparticles by hydrothermal method. Dissolve 3.00 g of polyvinyl pyrrolidone (PVP) in 100 mL of deionized water. Ultrasonicate until all the polymer is completely dissolved and transfer the solution to a round-bottom three-necked flask (250 mL). Heat to 70 °C with stirring and quickly pour 2.8 g of TAA into the flask. After vigorous stirring for 10 min, add 100 μL of nitric acid. After reacting for 10 min, pour 5 mL of Zn(NO3)2 solution (1.0 g / mL) into the flask quickly with vigorous stirring. After reacting for 5 min, reduce the stirring speed to 20 rpm. After stirring for 3 h, add 1.5 mL of Zn(NO3)2 solution (0.2 g / mL). After stirring slowly for another 1 h, remove the heat source, cool to room temperature, stop the reaction, separate the solid product by centrifugation, and wash with methanol for more than three times. Finally, dry under vacuum conditions at 70 °C for more than 24 h to obtain ZnS nanoparticles.

[0100] S2. Preparation of coating material dispersion. ZnS was dispersed in methanol by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. 2%-4% of polydopamine as high absorbance nanoparticles and 1%-5% of polyvinylpyrrolidone as an additive were weighed separately, and both were added to the dispersion, and fully dispersed in the zinc sulfide dispersion by ultrasound and stirring for more than 10 min. The solvent content of the final dispersion was about 60%.

[0101] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black polybutylene terephthalate surface by dip coating. The above dispersion was evenly dispersed in a glass culture dish with a diameter of 20 cm and a height of 3 cm. Clamp a corner of the polybutylene terephthalate plate with hemostatic forceps, dip the dispersion in the glass culture dish, make the liquid cover the surface of the polybutylene terephthalate plate as evenly as possible, and place it in a 90°C blast drying oven for 10 min. After drying, repeat the above operation 3 times. By controlling the evaporation rate and drying temperature of the solvent, the solvent evaporates as quickly as possible during the spraying process, and the particles are assembled into an orderly structure on the surface of the patch. Highly saturated green photonic crystal polybutylene terephthalate can be obtained.

[0102] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0103] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0104] After setting up, under the external camera, place 0.5 mm*3 cm*3 cm green photonic crystal polybutylene terephthalate in the middle of the hot stage for heating treatment, and heat at 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, and 265℃ for 5 minutes respectively. Capture the RGB value of the color change of the photonic crystal and the spectrum before and after the test. Example

[0105] S1. Preparation of monodisperse zinc sulfide nanoparticles by hydrothermal method. Dissolve 3.00 g of polyvinyl pyrrolidone (PVP) in 100 mL of deionized water. Ultrasonicate until all the polymer is completely dissolved and transfer the solution to a round-bottom three-necked flask (250 mL). Heat to 70 °C with stirring and quickly pour 2.8 g of TAA into the flask. After vigorous stirring for 10 min, add 100 μL of nitric acid. After 10 min of reaction, 5 mL of Zn(NO3)2 solution (1.0 g / mL) is quickly poured into the flask under vigorous stirring. After 5 min of reaction, reduce the stirring speed to 20 rpm. After stirring for 3 h, add 1.5 mL of Zn(NO3)2 solution (0.2 g / mL). After stirring slowly for another 1 h, remove the heat source, cool to room temperature, stop the reaction, separate the solid product by centrifugation, and wash it more than three times with a mixed solvent (methanol:ethylene glycol = 1:1). Finally, the ZnS nanoparticles were obtained by drying at 70 °C under vacuum conditions for more than 24 h.

[0106] S2. Preparation of coating material dispersion. ZnS was dispersed in a mixed solvent by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. 2%-4% of carbon nanotubes as high absorbance nanoparticles and 1%-5% of polyvinyl pyrrolidone as an additive were weighed separately, and both were added to the dispersion, and the mixture was fully dispersed in the zinc sulfide dispersion by ultrasound and stirring for more than 10 min. The solvent content of the final dispersion was about 60%.

[0107] S3. Preparation of structural chromogenic coating. Spin coating was used to construct photonic crystals on the black polypropylene surface. The black polypropylene plate was fixed on the clamping plate, and the dispersion with a mass fraction of ZnS of 10%-30% was poured into the coating nozzle. The substrate was rotated at a high speed in the range of 500-600 rpm. When a thin layer of photonic crystals was covered on the substrate, it was placed in an oven at 90°C for drying. After drying, the above steps were repeated twice. A highly saturated green photonic crystal polypropylene patch was obtained.

[0108] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0109] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0110] After setting up, under the external camera, place 0.5 mm*3 cm*3 cm green photonic crystal polypropylene in the middle of the hot stage for heating treatment, and heat at 100℃, 150℃, 190℃, 200℃, 210℃, 220℃, 230℃, and 240℃ for 5 minutes respectively. Capture the RGB value of the color change of the photonic crystal and the spectrum before and after the test.

[0111] Figure 3 It is a comparison of the actual pictures of the green ER, PC, PVC, PP and PE prepared in Examples 1-6 after being heated at 290°C, 250°C, 250°C, 240°C and 220°C for 5 minutes. It can be seen from the figure that the color obviously changes from green to red after heating. Although there are bulges, the bulges are the most obvious place for the color change. Because the materials of these plastics are different and the thermal expansion coefficients are different, the time required for obvious color change is also different, but they can all undergo thermochromic change under a certain degree of heating. Therefore, the substrate with a certain thermal expansion coefficient of the photonic crystal coating can undergo thermochromic change when subjected to a certain temperature.

[0112] Figure 7It is the temperature change spectrum of the green photonic crystal patch at each maximum temperature in Example 2-6. It can be seen from the figure: It can be seen from the figure that although the types of substrates are different and the thermal expansion coefficients are different, the changes in the spectral peak position in the phenomenon of thermochromism are the same, and the reflection peak position is red-shifted. It can also be seen from the data that the degree of red-shift of different materials is different. What is presented is that the degree of red-shift of the reflection peak position is: PE>PVC>PP>ER. This is exactly the same as the size of their thermal expansion coefficients, so the thermal thermochromic phenomenon of the photonic crystal patch is closely related to the size of the thermal expansion coefficient of its matrix material. The larger the thermal expansion coefficient, the more obvious the thermochromic phenomenon, on the contrary, the smaller the thermal expansion coefficient, the less obvious the thermochromic phenomenon, or even no thermochromic phenomenon.

[0113] Figure 8 The time required for ER, PC, PVC, PP, and PE with a thickness of about 0.01 mm in Examples 2-6 to change color from the beginning to the complete color change at their respective specific temperatures as observed by the naked eye. It can be seen from the figure that: Figure 8 It is the time required for ER, PC, PVC, PP, and PE to change color from the beginning to the complete color change at 275℃, 220℃, 220℃, 220℃, and 170℃ respectively. It can be seen from the figure that although PE has the lowest heating temperature, its color change time is the shortest, and ER has the highest heating temperature, but the color change time is the longest. This is because PE has the largest thermal expansion coefficient, while ER has the smallest thermal expansion coefficient, so it further proves the great influence of the matrix thermal expansion coefficient on the photonic crystal, and also confirms the relationship between the thermochromic phenomenon and thermal deformation of the photonic crystal patch.

[0114] Fig. 9 This is a schematic diagram of the visualized sensing process of the photonic crystal patch of the present invention. It can be seen from the figure that the process of the thermochromic temperature response set by the present invention is described. It can be seen that when the green photonic crystal patch changes from green to red at the first point when it starts to be heated, the display will show the alarm Warning 1. When more than half of the area of ​​the green photonic crystal patch turns red, the display will show the alarm Warning 2. It shows the characteristics of the thermochromic photonic crystal patch in temperature response applications.

[0115] It should be noted that in Examples 1-6:

[0116] The reason why polar solvents are selected as dispersants for zinc sulfide in S2 is that the zinc sulfide particles are mainly affected by electrostatic forces and solvation forces during assembly, and electrostatic repulsion is the main driving force. Dispersing zinc sulfide particles in polar solvents can give silica particles strong electrostatic repulsion, thereby driving the zinc sulfide particles to assemble into an ordered structure. In addition, adjusting the evaporation temperature of the zinc sulfide solution can further promote the orderly assembly of zinc sulfide on the patch surface at low concentrations, creating conditions for a wide adjustable wavelength range.

[0117] In addition, the mass fraction of zinc sulfide in S2 will affect the distribution density of zinc sulfide particles on the surface of the patch. If the mass fraction is too small, the distribution concentration is low, the reflectivity of the obtained photonic crystal is low, and the structural color change is not obvious. If the mass fraction is too large, the zinc sulfide is densely arranged and the particle spacing is small. It is easy to rearrange when heated, and the adjustable wavelength range becomes narrower. If the mass fraction is too large, zinc sulfide is prone to a large amount of disordered accumulation after ethanol evaporates, which affects the color brightness of the photonic crystal and makes it impossible to prepare highly saturated photonic crystals.

[0118] The drying temperature in S3 will affect the self-assembly of zinc sulfide on the surface of the patch. If the temperature is too low, there will be too much residual organic solvent, and the wavelength will change due to the volatilization of the solvent after long-term storage; when the temperature is too high, due to the low melting point of the patch, the patch will be thermally deformed before it is combined with the photonic crystal, affecting the orderly self-assembly of zinc sulfide particles on its surface, further affecting the preparation of the photonic crystal. The drying temperature is preferably 80-100°C, more preferably 90°C. Example

[0119] S1. Synthesis of monodisperse SiO2 nanoparticles. Taking the synthesis process of nanoparticles with a particle size of 167 nm as an example, the reaction condition is 30°C. First, 159 mL of anhydrous ethanol, 30 mL of ammonia solution, and 16 mL of deionized water were added to a 500 mL round-bottom flask under stirring. Then, 10 mL of tetraethyl orthosilicate was added to the solution under vigorous stirring for 1-2 min. The reaction was stirred gently for another 5 h, washed with pure water, and then dried under vacuum conditions at 60°C for 24 h. By adjusting the amount of ammonia solution and deionized water, SiO2 nanoparticles of different particle sizes (100 nm-400 nm) can be prepared. The solid product was separated by centrifugation and washed with anhydrous ethanol for more than three times. Finally, it was dried under vacuum conditions at 70°C for more than 24 h to obtain SiO2 nanoparticles.

[0120] S2. Preparation of coating material dispersion. SiO2 nanoparticles were dispersed in anhydrous ethanol by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. Carbon black with a mass fraction of 2%-4% as high absorbance nanoparticles and polyvinyl alcohol with a mass fraction of 1%-5% as an additive were weighed separately, and both were added to the dispersion, and the dispersion was fully dispersed in the SiO2 dispersion by ultrasound and stirring for more than 10 min. The solvent content in the final dispersion was about 60%.

[0121] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black polycarbonate surface by spraying. A spray gun with an inner diameter of 0.2 mm and a well-dispersed ZnS dispersion of 20% by mass was placed 10 cm away from the black polycarbonate plate and driven by compressed air with a pressure of 0.103 MPa. By controlling the evaporation rate and drying temperature of the solvent, the solvent evaporated as quickly as possible during the spraying process, and the particles assembled into an orderly structure on the surface of the patch. A highly saturated green photonic crystal polycarbonate patch was obtained.

[0122] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0123] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material. Example

[0124] S1. Synthesis of monodisperse SiO2 nanoparticles. Taking the synthesis process of nanoparticles with a particle size of 167 nm as an example, the reaction condition is 30°C. First, 159 mL of anhydrous ethanol, 30 mL of ammonia solution and 16 mL of deionized water were added to a 500 mL round-bottom flask under stirring. Then, 10 mL of tetraethyl orthosilicate was added to the solution under vigorous stirring for 1-2 min. The reaction was gently stirred for another 3 h, washed with pure water, and then dried under vacuum conditions at 60°C for 24 h. By adjusting the amount of ammonia solution and deionized water, SiO2 nanoparticles of different particle sizes can be prepared, and the solid product was separated by centrifugation and washed with tetrahydrofuran for more than three times. Finally, it was dried under vacuum conditions at 70°C for more than 24 h to obtain SiO2 nanoparticles.

[0125] S2. Preparation of coating material dispersion. SiO2 nanoparticles were dispersed in tetrahydrofuran by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. MXene with a mass fraction of 2%-4% as high absorbance nanoparticles and polyvinyl alcohol with a mass fraction of 1%-5% as an additive were weighed separately, and both were added to the dispersion, and the dispersion was fully dispersed in the SiO2 dispersion by ultrasound and stirring for more than 10 min. The solvent content of the final dispersion was about 60%.

[0126] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black polycarbonate surface by dip coating. The above dispersion was evenly dispersed in a glass culture dish with a diameter of 20 cm and a height of 3 cm. Clamp a corner of the polycarbonate plate with hemostatic forceps, dip the dispersion in the glass culture dish, make the liquid cover the polycarbonate surface as evenly as possible, and place it in a 90°C blast drying oven for 10 min. After drying, repeat the above operation 3 times. By controlling the evaporation rate and drying temperature of the solvent, the solvent evaporates as quickly as possible during the spraying process, and the particles assemble into an orderly structure on the surface of the patch. A highly saturated green photonic crystal polycarbonate patch can be obtained.

[0127] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0128] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material. Example

[0129] S1. Synthesis of monodisperse SiO2 nanoparticles. Taking the synthesis process of nanoparticles with a particle size of 167 nm as an example, the reaction condition is 30°C. First, 159 mL of methanol, 30 mL of ammonia solution and 16 mL of deionized water were added to a 500 mL round-bottom flask under stirring. Then, 10 mL of tetraethyl orthosilicate was added to the solution under vigorous stirring for 1-2 min. The reaction was gently stirred for another 3 h, washed with pure water, and then dried under vacuum conditions at 60°C for 24 h. By adjusting the amount of ammonia solution and deionized water, SiO2 nanoparticles of different particle sizes can be prepared, and the solid product was separated by centrifugation and washed with methanol for more than three times. Finally, it was dried under vacuum conditions at 70°C for more than 24 h to obtain SiO2 nanoparticles.

[0130] S2. Preparation of coating material dispersion. The SiO2 nanoparticles were dispersed in methanol by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. 2%-4% of polydopamine as high absorbance nanoparticles and 1%-5% of polyvinyl alcohol as an additive were weighed separately, and both were added to the dispersion. The dispersion was fully dispersed in the SiO2 dispersion by ultrasound and stirring for more than 10 min. The solvent content of the dispersion obtained was about 60%.

[0131] S3. Preparation of structural chromogenic coating. Spin coating is used to construct photonic crystals on the black polycarbonate surface. Fix the black polycarbonate plate on the clamping plate, pour the dispersion with a SiO2 mass fraction of 10%-30% into the coating nozzle, and rotate the substrate at a high speed in the range of 500-600 rpm. When a thin layer of photonic crystal is covered on the substrate, put it in an oven at 90℃ for drying, and repeat the above steps twice after drying. A highly saturated green photonic crystal polycarbonate patch can be obtained.

[0132] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0133] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0134] Embodiment 10:

[0135] S1. Use Zn (CH3COO)2⋅2H2O (0.5 M) stock solution, and then add 25 mL of NaOH (0.2M ~ 0.5 M) solution prepared in methanol under stirring to make the pH value of the reactant between 8 and 11. Then, these solutions were transferred to a polytetrafluoroethylene-lined autoclave and kept at different temperatures of 200°C for 6 to 12 hours. After stopping heating, the autoclave was naturally cooled to room temperature, soaked with methanol, filtered, and dried in a vacuum oven at 60°C to obtain ZnO nanoparticles.

[0136] S2. Disperse ZnO in methanol by ultrasound for 30 min to prepare a dispersion with a mass fraction of 10%-30%. Weigh 2%-4% of carbon black as high absorbance nanoparticles and 1%-5% of polyvinyl alcohol as an additive, add them to the dispersion, and fully disperse them in the ZnO dispersion by ultrasound and stirring for more than 10 min. The final dispersion has a solvent content of about 60%.

[0137] S3. Preparation of structural chromogenic coating. Photonic crystals were constructed on the black polycarbonate surface by spraying. A spray gun with an inner diameter of 0.2 mm and filled with a well-dispersed ZnO dispersion with a mass fraction of 20% was placed 10 cm away from the black polycarbonate plate and driven by compressed air with a pressure of 0.103 MPa. By controlling the evaporation rate and drying temperature of the solvent, the solvent evaporated as quickly as possible during the spraying process, and the particles assembled into an orderly structure on the surface of the patch. A highly saturated green photonic crystal polycarbonate patch was obtained.

[0138] If the surface to be tested is plastic or engineering plastic, it can be directly used as the base material without pasting. If the material to be tested is a material with a small thermal expansion coefficient, such as metal, wood, polytetrafluoroethylene, etc., the above-mentioned structural color-forming coating is pasted to the surface of the material by glue. The glue can be 502 glue, epoxy resin glue, etc.

[0139] S4. Design and preparation of fire warning sensors. Adjust the position of the camera and install it, determine the monitoring area, set the number of monitoring points and evenly arrange the locations of the detection points, set the alarm threshold, connect and install the alarm light, and monitor the color of the material.

[0140] Table 4. The time required for the structural chromogenic patches prepared in Examples 7-8 to change color at 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C and 260°C, respectively.

[0141]

[0142] Table 4 shows the time required for the color change of ZnO-G-PC and SiO2-G-PC at 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C and 260°C in Implementation Examples 7-10. It can be seen that no matter which photonic crystal composite material is ZnO-G-PC or SiO2-G-PC, the time required for color change is decreasing as the temperature increases. Among them, the color change time of SiO2-G-PC is the shortest, and the lowest can reach 0.1s. A more sensitive temperature response can be achieved.

[0143] Table 5. Main raw materials and methods in Examples 1-10

[0144]

[0145] The present invention obtains a photonic crystal patch by spraying, spin coating, and dipping at a certain evaporation temperature. After drying, there is no solvent in the photonic crystal, and the wavelength will not change due to the volatilization of the solvent. Therefore, the obtained photonic crystal has good cycle stability and is durable. After heat treatment, zinc sulfide, silicon dioxide, zinc oxide, and polymethyl methacrylate methyl ester particles enter the interior of the patch, and it is not easy to reduce the color saturation due to external acid and alkali, friction, impact and other harsh environments. Therefore, the obtained photonic crystal patch has good stability and optical performance before and after heat treatment.

[0146] In all embodiments, the polar solvent in S2 is any one of anhydrous ethanol, methanol, propanol, isopropanol, acetonitrile, and water, and is more preferably anhydrous ethanol. Anhydrous ethanol has high polarity, low boiling point, and is easily volatile, and is more suitable as a dispersant in the evaporation concentration assembly.

[0147] The preparation of nanoparticles in the above manner can better control the uniformity of zinc sulfide particles, and the PDI of the obtained nanoparticles is ≤1.4.

[0148] The present invention particularly protects the use of a thermo-induced photonic crystal patch in a visualization sensor.

[0149] The visual sensor is a temperature sensor, which can judge the real-time temperature through the change of color, and then realize temperature warning through the change of color.

[0150] The thermochromic photonic crystal patch prepared by the invention has high sensitivity and thermochromic performance with a wide adjustable wavelength and good stability, and is suitable for use in visualization sensors.

[0151] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A fire early warning system, characterized in that: It includes a color-generating unit, a monitoring unit, a collection unit, a processing unit and an alarm unit; The color-forming unit is coated or adhered to the surface of the substrate to sense the deformation caused by thermal expansion of the substrate and produce color change; The monitoring unit monitors the real-time color change of the color-producing unit, and the monitoring data is transmitted to the processing unit through the acquisition unit; The processing unit controls whether the alarm sounds an alarm by analyzing the changes in the collected RGB or CMYK color parameters; Wherein, the chromogenic unit is a structural chromogenic coating or a structural chromogenic patch prepared from a structural chromogenic material, and the structural chromogenic coating is coated on the surface of the substrate to be monitored or the structural chromogenic patch is attached to the surface of the substrate to be detected; The structural chromogenic material comprises monodisperse nanoparticles, additives and high-absorbency nanoparticles, wherein the monodisperse nanoparticles are mainly one or more of zinc sulfide, silicon dioxide, zinc oxide, polystyrene and polymethyl methacrylate; the additives are mainly one or more of polyvinyl pyrrolidone, polyvinyl alcohol and polybutyl methacrylate; the high-absorbency material is mainly one or more of carbon black, carbon black nanoparticles, graphene, MXene, carbon nanotubes and polydopamine nanoparticles; The fire early warning system is based on the green to red transition.

2. The fire early warning system according to claim 1, characterized in that: The mass percentage of the monodisperse nanoparticles is 10%-99%, the mass percentage of the additive is 0.1%-20%, and the mass percentage of the high absorbance nanoparticles is 0.005%-10%.

3. The fire early warning system according to claim 1, characterized in that: The particle size of the monodisperse nanoparticles is 100-800 nm.

4. The fire early warning system according to claim 1, characterized in that: Monodisperse nanoparticles are synthesized by any one of a hydrothermal method, a sol-gel method, and a polymerization method. The particle size range of the nanoparticles finally prepared is mainly: 100 nm-800 nm, and the polydispersity index PDI thereof is ≤1.

4.

5. The fire early warning system according to claim 1, characterized in that: The preparation method of the structural chromogenic coating is as follows: monodisperse nanoparticles, additives, and high-absorbency nanoparticles are dispersed in a solvent, and the mixture is applied to the surface of a substrate by any one of dipping, spraying, and spin coating, and then dried; the preparation method of the structural chromogenic patch is as follows: monodisperse nanoparticles, additives, and high-absorbency nanoparticles are dispersed in a solvent, and the mixture is applied to one side of the patch by any one of dipping, spraying, and spin coating, and an adhesive layer is provided on the other side; the material of the patch is mainly one or more of polycarbonate, polyvinyl chloride, polymethyl methacrylate, polyethylene, polypropylene, and epoxy resin.

6. The fire early warning system according to claim 5, characterized in that: The solvent is mainly one or more of water, ethanol, tetrahydrofuran, methanol, propanol and dimethyl sulfoxide, and the mass percentage of the solvent in the structural chromogenic material dispersion is 30%-99%.

7. The fire early warning system according to claim 1, characterized in that: When the substrate is plastic or engineering plastic, the chromogenic unit adopts a structural chromogenic coating. When the substrate is metal, ceramic, wood or glass, a structural chromogenic patch is used at the chromogenic unit.

8. A method for early warning of fire, characterized in that: The following steps are involved: (1) A structural chromogenic coating or a structural chromogenic patch prepared from a structural chromogenic material is attached to the surface of a substrate to be detected as a chromogenic unit; (2) Determine the monitoring area, install the monitoring unit, and monitor the color of the chromogenic unit in real time; (3) Collecting the color of the chromogenic unit monitored in real time and transmitting it to the processing unit; (4) The processing unit captures and calculates the changes in RGB values ​​or CMYK values ​​throughout the process, compares them with the set thresholds, and issues a fire warning through the alarm unit; The structural chromogenic material includes monodisperse nanoparticles, additives and high-absorbency nanoparticles, wherein the monodisperse nanoparticles are mainly one or more of zinc sulfide, silicon dioxide, zinc oxide, polystyrene and polymethyl methacrylate; the additives are mainly one or more of polyvinyl pyrrolidone, polyvinyl alcohol and polybutyl methacrylate; the high-absorbency materials are mainly one or more of carbon black, carbon black nanoparticles, graphene, MXene, carbon nanotubes and polydopamine nanoparticles.

9. The method for early fire warning according to claim 8, characterized in that: After the material changes color, when RGB value is used for calculation, the specific threshold B value changes greater than or equal to 20, the G value changes greater than or equal to 30, and the R value changes in the range of 32~50; when CMYK value is used for calculation, the specific threshold C value changes in the range of 20~30, the M value changes in the range of 0~90, the Y value changes in the range of 90~95, and the K value changes in the range of less than 5.

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