A cholesteric liquid crystal polymer film and its preparation method and application

Abstract

The application discloses a kind of cholesteric liquid crystal polymer film and its preparation method and application, step 1, after mixing liquid crystal monomer, photo initiator, chiral agent, crosslinking agent hydrogen bond molecule trigger agent is placed in oven and heated;Step 2, the mixture after heating is evenly applied on the glass substrate after orientation, fixed on heating stage, then cover the same glass substrate and fixed, then carry out ultraviolet curing;Step 3, after the solidification of liquid crystal film is soaked in organic solvent, then take out and volatilize excess organic solvent;Step 4, the liquid crystal film is soaked in alkaline solution, then take out and dry, obtain cholesteric polymer film.The present application can directly observe the humidity of surrounding environment, and can also feedback the humidity of surrounding environment in real time, and has the characteristics of simple production, low cost, good readability, feedback adjustment, fast response speed and small size.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing and relates to a cholesteric liquid crystal polymer film, its preparation method, and its application. Background Technology

[0002] Humidity monitoring and control are frequently required in industrial and agricultural production, as well as daily life. For example, in agricultural production, the use of greenhouses has become increasingly widespread and is now an important part of modern agriculture. Agricultural production methods are also gradually shifting from traditional extensive management models to modern intensive management models. Advances in science and technology have led to a gradual improvement in the structural quality of greenhouses. Different crops require different environmental conditions for planting and growth. Accurate and real-time monitoring and regulation of humidity levels can effectively promote increased crop yields and income. The preservation of mature crops is also closely related to humidity levels. Therefore, the construction of an intelligent agricultural greenhouse humidity control system is urgently needed by greenhouse crop producers. This system can not only improve crop yield and quality and reduce production costs, but also alleviate the labor intensity of workers. Greenhouse humidity control systems can be applied to the cultivation of crops with stringent humidity requirements, such as greenhouse flowers, greenhouse medicinal herbs, and greenhouse mushrooms, greatly improving the precision and intelligence of modern facility agriculture and propelling modern agriculture towards intelligent development. People typically use hygrometers to measure humidity in greenhouses and control it through artificial humidification and ventilation. However, this method suffers from low accuracy and poor real-time performance, and also involves high labor intensity for operators. Therefore, accurately monitoring ambient humidity and providing real-time humidity feedback and adjustment is a key technical issue for further improving the practicality of humidity sensors.

[0003] Currently, common humidity sensors on the market include wet-bulb and dry-bulb hygrometers, infrared hygrometers, dew point hygrometers, and electronic hygrometers. A wet-bulb and dry-bulb hygrometer places the dry bulb in the air, while the wet bulb is wrapped in hydrophilic gauze. Because the evaporation rate of water vapor between the wet and dry bulbs differs, the thermometer readings differ, and the humidity is calculated from this temperature difference. However, it is easily affected by temperature, and its scale value changes with temperature fluctuations. Infrared hygrometers measure humidity by utilizing the change in light intensity absorbed by water vapor at specific wavelengths. The radiation source emits two wavelengths of radiation: one wavelength is strongly absorbed by water vapor, while the other is not absorbed or is minimally absorbed. The air humidity can be calculated from the ratio of the intensities of these two wavelengths, making it suitable for monitoring the humidity of high-temperature or sealed environments. A typical dew point hygrometer generally consists of an optical mirror, an amplifier, and a power supply. When air continuously passes through an optical mirror, the mirror's temperature is lowered using artificial cooling. Water vapor in the air condenses on the mirror. At the moment condensation occurs, the intensity of light reflected from the mirror decreases sharply. Measuring the temperature of the condensation surface at this instant allows for the calculation of the corresponding humidity. However, this method requires sophisticated manufacturing processes for the mirror. Electronic hygrometers work by encapsulating special materials around electronic components. Changes in humidity cause changes in the physical properties of these materials, which in turn alter the current or voltage of the electronic components. This change is then converted into a numerical value representing the humidity change. However, electronic hygrometers suffer from short lifespans and poor long-term stability. Summary of the Invention

[0004] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is to provide a cholesteric liquid crystal polymer film, its preparation method and application, which realizes real-time humidity sensing and can realize feedback regulation of environmental humidity through single-chip microcomputer control. It has the characteristics of simple structure, fast response speed and low cost.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing a cholesteric phase liquid crystal polymer film, comprising the following steps:

[0006] Step 1: Mix the liquid crystal monomer, photoinitiator, chiral agent, crosslinking agent, hydrogen bond molecule triggering agent, and then place them in an oven for heating;

[0007] Step 2: Apply the heated mixture evenly to the oriented glass substrate fixed on the heating table, then cover it with the same glass substrate and fix it, and then perform UV curing.

[0008] Step 3: Immerse the cured liquid crystal film in an organic solvent, and then remove it to evaporate the excess organic solvent;

[0009] Step 4: Immerse the liquid crystal film in an alkaline solution, then remove and dry it to obtain a cholesteric polymer film.

[0010] Furthermore, the liquid crystal monomer is RM105, the photoinitiator is Ig819, the chiral agent is LC756, the crosslinking agent is C6M, and the hydrogen bond triggering agents are 4OBA and 6OBA.

[0011] Furthermore, the mass ratio of RM105, Ig819, LC756, C6M, 4OBA, and 6OBA is 38:0.6:A:13:21.9:21.9. By adjusting the mass A of LC756, the film prepared turns red when the ambient humidity reaches the set upper boundary and turns blue when the ambient humidity reaches the set lower boundary.

[0012] Furthermore, in step 1, the oven is heated to 140°C and then kept at that temperature for 10 minutes.

[0013] Furthermore, after step 1, the mixture is ultrasonically treated at 80°C to ensure uniform mixing.

[0014] Furthermore, the organic solvent mentioned in step 3 is tetrahydrofuran.

[0015] Furthermore, the alkaline solution mentioned in step 4 is a KOH solution with a concentration of 1 mole per liter.

[0016] The present invention also includes a cholesteric liquid crystal polymer film, which is prepared by any of the above preparation methods.

[0017] The present invention also includes the application of the above-mentioned cholesteric liquid crystal polymer film, wherein any of the above-mentioned cholesteric liquid crystal polymer films is used for environmental humidity detection.

[0018] This invention also includes the application of the above-mentioned cholesteric liquid crystal polymer film, and the specific application method is as follows:

[0019] Blue light source and red light source respectively irradiate cholesteric liquid crystal polymer film, the cholesteric liquid crystal polymer film turns red when the ambient humidity reaches the set upper boundary, and turns blue when the ambient humidity reaches the set lower boundary;

[0020] When the ambient humidity reaches the set upper limit, the red light band photodetector detects the red light reflected by the cholesteric liquid crystal polymer film and transmits it to the microcontroller. The microcontroller then controls the humidification controller and alarm controller to issue an alarm.

[0021] When the ambient humidity reaches the set lower limit, the blue light band photodetector detects the blue light reflected by the cholesteric liquid crystal polymer film and transmits it to the microcontroller. The microcontroller then controls the humidification controller and alarm controller to perform humidification.

[0022] The beneficial effects of this invention are:

[0023] This invention proposes a cholesteric liquid crystal polymer film capable of measuring humidity and its preparation method, and proposes an application for a system for real-time monitoring and control of ambient humidity. The cholesteric liquid crystal polymer film forms a polymer mesh through the H-bonding interaction of hydrogen-bonding molecular triggers 4-(6-(acryloyloxy)hexyloxy)benzoic acid (6OBA) and 4-(4-(acryloyloxy)butoxy)benzoic acid (4OBA). After alkaline treatment, the hydrogen bonds form a hygroscopic polymer. Based on the characteristic of cholesteric liquid crystals reflecting circularly polarized light with a single rotation, changes in humidity cause the polymer mesh to expand or compress, thereby altering the pitch of the cholesteric liquid crystal and adjusting its reflective band, i.e., changing the color of the polymer film. Different colors of the polymer film represent different humidity levels in the surrounding environment, thus collecting ambient humidity data. The feedback control system is implemented by defining the upper and lower boundaries of the relative humidity based on the color change range of the polymer film. By adjusting the concentration of the chiral agent, the film displays red when the ambient humidity reaches the upper boundary and blue when the ambient humidity reaches the lower boundary. When the relative humidity reaches the upper limit, the cholesteric liquid crystal reflects red light onto the detector, stopping humidification. When the relative humidity reaches the lower limit, the cholesteric liquid crystal reflects blue light onto the detector, initiating humidification. This invention is designed based on the optical properties of cholesteric liquid crystals, allowing for direct observation of ambient humidity while simultaneously providing real-time feedback and adjustment. It avoids the problems inherent in traditional detection methods and offers advantages such as simple manufacturing, low cost, good readability, feedback adjustment, fast response, and small size. It provides a novel, more accurate, and faster humidity control sensing device. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the humidity acquisition module device;

[0025] Figure 2 This is the flowchart of the main program module of the feedback control system. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] The objective of this invention is achieved as follows:

[0028] Hydrogen-bonding molecular triggers 6OBA and 4OBA are mixed and treated with an alkaline solution to create a hygroscopic polymer network. Polymerizable cholesteric liquid crystals fill this network. Since the light reflection band of the cholesteric liquid crystal largely depends on the molecular pitch, changes in ambient humidity cause the polymer network to expand or compress, thus altering the pitch of the cholesteric liquid crystal, which macroscopically manifests as a color change in the film. Based on this color change, a reasonable ambient humidity level is designed. By adjusting the concentration of the chiral agent, the wavelength range of the reflection band at the upper and lower humidity boundaries of the film is made approximately consistent with the wavelength range of the light source used. When the ambient humidity reaches the critical range, due to the effect of the cholesteric liquid crystal reflection band, light from a specific light source is reflected to a specific detector. A microcontroller controls the comparison; if the collected data is below the set humidity range, a humidification program is initiated until the ambient humidity reaches the set range; if the collected data is above the set humidity range, an alarm is triggered.

[0029] The specific method for preparing the cholesteric phase liquid crystal polymer film of the present invention is as follows:

[0030] 1. Select liquid crystal monomers, photoinitiators, chiral agents, crosslinking agents, and hydrogen bond triggering agents, and mix these materials in different proportions;

[0031] 2. After heating the mixed material in an oven, it is evenly coated onto the oriented glass substrate to form a liquid crystal cell, and then UV cured.

[0032] 3. Immerse the cured liquid crystal film in an organic solvent, then remove it and allow the organic solvent to evaporate completely. Then, place it in an alkaline solution for alkaline treatment, and then remove and dry it. The preparation of the humidity-responsive cholesteric polymer film is then complete.

[0033] The feedback regulation system uses an Arduino microcontroller as its main controller, and a photodetector handles humidity acquisition. When a light source shines on a humidity-responsive polymer film, different colors of the film result in varying amounts of energy reflected onto the photodetector. The humidity level is set appropriately through Arduino programming. When the blue light band photodetector detects high intensity, it indicates that the ambient humidity is too low, triggering the microcontroller to humidify until the humidity reaches the standard range. Conversely, when the red light band photodetector detects high intensity, it indicates that the ambient humidity is too high, triggering an alarm.

[0034] The following is an example with specific parameters:

[0035] Figure 1This is a schematic diagram of a humidity acquisition module device. In the diagram, (a) and (b) are blue light source and red light source, respectively; (c) is a humidity-responsive polymer film; (d) is a photodetector (blue light band); (e) is a photodetector (red light band); (f) is a microcontroller; and (g) is a humidification controller and an alarm controller.

[0036] The method for preparing the cholesteric phase liquid crystal polymer film of the present invention includes:

[0037] 1. Blow away surface dust and impurities from the glass substrate with nitrogen gas, soak it in deionized water for 3 minutes, then place it in an ultrasonic cleaner for 3 minutes. After drying, apply PVA solution evenly to the substrate, place it in a spin coater and rotate it at 500 rpm for 3 minutes. After drying, perform rubbing alignment.

[0038] 2. Selected liquid crystal monomers, photoinitiator Ig819, chiral agents, crosslinking agents C6M, and hydrogen bond triggering agents 4OBA and 6OBA are mixed in a mass ratio of 38:0.6:B:13:21.9:21.9, where the ratio of liquid crystal monomers to chiral agents A:B is determined by the application environment. The mixture is then placed in an electric heating drying oven and heated to 140°C. After maintaining the temperature for 10 minutes, the power to the electric heating drying oven is turned off and the mixture is removed. Finally, it is ultrasonically treated at 80°C to ensure uniform mixing.

[0039] 3. Fix the treated glass substrate on an 80°C heating table and add 10-micron spacers on both sides. Apply the uniformly mixed liquid crystal evenly onto the lower glass substrate, cover it with the substrate and fix it. Then, cure it by irradiating it with an ultraviolet lamp for 5 minutes.

[0040] 4. After immersing the cured liquid crystal film in tetrahydrofuran solvent for 3 minutes, remove it and place it in an electric heating drying oven to evaporate excess organic solvent.

[0041] 5. Immerse the liquid crystal film in a 1 mol / L KOH solution for 2 minutes, then remove and dry. The preparation of the humidity-responsive cholesteric phase liquid crystal polymer film is complete.

[0042] The main control of the feedback regulation system uses an Arduino microcontroller. The main program module of the microcontroller is that after the microcontroller is powered on, the microcontroller port is initialized, the humidity of the surrounding environment is read, the read data is sent to the microcontroller, and the microcontroller determines whether it is within a reasonable humidity range. If it is not within the range, the microcontroller is activated to humidify the surrounding environment or sound an alarm.

[0043] After the microcontroller starts, it first performs program initialization. During initialization, all input and output ports are at a high level. The main initialization program includes assigning values ​​to variables, enabling interrupts, and clearing counters. After initialization, the microcontroller first calls the humidity acquisition module function. The humidity acquisition module is mainly implemented by a photodetector. Through reasonable design of the ambient humidity levels, different colors of the polymer film correspond to different humidity levels. The photodetector will only detect data when the ambient humidity reaches or is near the upper or lower boundary. The microcontroller compares the acquired data with the data in the register. When the upper boundary is reached, it indicates that the ambient humidity is too high, and an alarm will be triggered. When the lower boundary is reached, it indicates that the ambient humidity is too low, and the microcontroller will start humidifying the environment.

[0044] Blue light source a and red light source b irradiate cholesteric liquid crystal polymer film c respectively. Cholesteric liquid crystal polymer film c satisfies the condition that it turns red when the ambient humidity reaches the set upper boundary and turns blue when the ambient humidity reaches the set lower boundary.

[0045] When the ambient humidity reaches the set upper limit, the red light band photodetector e detects the red light reflected by the cholesteric liquid crystal polymer film c and transmits it to the microcontroller f. The microcontroller controls the humidification controller and alarm controller g to trigger an alarm.

[0046] When the ambient humidity reaches the set lower boundary, the blue light band photodetector d detects the blue light reflected by the cholesteric liquid crystal polymer film c and transmits it to the microcontroller f. The microcontroller then controls the humidification controller and alarm controller g to perform humidification.

Claims

1. A method for preparing a cholesteric liquid crystal polymer film, characterized by, The method comprises the following steps: Step 1, mixing liquid crystal monomer, photo initiator, chiral agent, crosslinking agent, hydrogen bond molecule trigger, and then heating in an oven; the liquid crystal monomer is RM105, the photo initiator is Ig819, the chiral agent is LC756, the crosslinking agent is C6M, and the hydrogen bond molecule trigger is 4OBA and 6OBA; the mass ratio of RM105, Ig819, LC756, C6M, 4OBA and 6OBA is 38:0.6:A:13:21.9:21.9, wherein the mass A of LC756 is adjusted so that the prepared film becomes red when the environmental humidity reaches the set upper limit, and the prepared film becomes blue when the environmental humidity reaches the set lower limit; Step 2, uniformly applying the heated mixture on the glass substrate after orientation and fixed on the heating table, then covering the same glass substrate and fixing, and then performing ultraviolet curing; Step 3, immersing the cured liquid crystal film in an organic solvent, and then taking out and volatilizing the excess organic solvent; Step 4, immersing the liquid crystal film in an alkaline solution, then taking out and drying to obtain a cholesteric polymer film.

2. The method for preparing a cholesteric phase liquid crystal polymer thin film according to claim 1, characterized in that: The oven in step 1 is heated to 140℃, and then kept at 140℃ for 10 minutes.

3. The method for preparing a cholesteric phase liquid crystal polymer thin film according to claim 1, characterized in that: After the operation in step 1, ultrasonic treatment is performed at 80℃ using ultrasonic instrument to uniformly mix the mixture.

4. The method for preparing a cholesteric phase liquid crystal polymer thin film according to claim 1, characterized in that: The organic solvent in step 3 is tetrahydrofuran.

5. The method for preparing a cholesteric phase liquid crystal polymer thin film according to claim 1, characterized in that: The alkaline solution in step 4 is 1 mol / L KOH solution.

6. A cholesteric liquid crystal polymer film characterized by: The cholesteric liquid crystal polymer film is prepared by any one of the preparation methods in claims 1 to 5.

7. Use of a cholesteric liquid crystal polymer film, characterized in that: The cholesteric liquid crystal polymer film prepared by any one of the preparation methods in claims 1 to 5 or the cholesteric liquid crystal polymer film in claim 6 is used for environmental humidity detection.

8. Use of a cholesteric liquid crystal polymer film according to claim 7, characterized in that The specific application method is as follows: Blue light source (a) and red light source (b) irradiate cholesteric liquid crystal polymer film (c) respectively, and the cholesteric liquid crystal polymer film (c) satisfies that it becomes red when the environmental humidity reaches the set upper limit, and it becomes blue when the environmental humidity reaches the set lower limit; When the environmental humidity reaches the set upper limit, the red light band photodetector (e) detects the reflected red light of the cholesteric liquid crystal polymer film (c) and transmits to the single-chip microcomputer (f), and the single-chip microcomputer controls the humidification controller and alarm controller (g) to alarm; When the environmental humidity reaches the set lower limit, the blue light band photodetector (d) detects the reflected blue light of the cholesteric liquid crystal polymer film (c) and transmits to the single-chip microcomputer (f), and the single-chip microcomputer controls the humidification controller and alarm controller (g) to humidify.

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