Highly sensitive micro liquid crystal sensor for detecting propanol gas and preparation method thereof

Abstract

The application provides a high-sensitivity micrometer liquid crystal sensor for detecting propanol gas and a preparation method thereof, and belongs to the field of gas detection.A brand-new liquid crystal composite sensing system is constructed, P-type semiconductor nickel oxide nanomaterial is used as the response material of propanol gas, the sensing signal is displayed in the form of light by virtue of the orientation characteristics of liquid crystal, the liquid crystal sensor for efficiently detecting propanol gas in a portable mode is prepared, the preparation method is simple, and economic benefits are high.Based on the excellent gas adsorption of the P-type nickel oxide nanomaterial, the sensor can have a rapid and sensitive response to trace propanol gas, the result is convenient to observe, and the sensor is suitable for most scenes of propanol gas detection.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a high-sensitivity micrometer liquid crystal sensor for detecting propanol gas and belongs to the field of propanol detection. BACKGROUND

[0002] Propanol is a colorless and transparent liquid volatile organic compound (VOC) with a smell similar to that of ethanol and capable of being mixed with water, alcohol, ether and various organic solvents, and is an important solvent in the industries of industrial synthesis, coating, adhesive, pharmaceutical, paint, cosmetics, food additive and the like. In industrial sites such as chemical production workshops and storage warehouses, a large amount of propanol vapor is easily generated. Propanol gas is flammable and can form an explosive mixture with air, and can cause safety accidents when encountering fire or high heat. In terms of physiological health, propanol has certain toxicity, and inhaling a certain amount of propanol gas can stimulate the respiratory tract and cause discomfort symptoms such as headache, dizziness and drowsiness, and can even lead to coma in severe cases. In the field of disease monitoring, propanol gas can be used as an important marker for diseases such as lung cancer, diabetes and intestinal dysfunction. In view of the above hazards and medical application potential of propanol gas, detecting propanol gas in the environment can reduce the safety hazards in some industrial scenes and can also be used as one of the means for medical diagnosis.

[0003] Developing a new method for detecting propanol gas can improve the efficiency of protecting against safety hazards of propanol gas in industry and also provide a new idea for diagnosing diseases in the medical field. The commonly used methods for detecting propanol gas at present include gas chromatography, semiconductor detection and electrochemical detection. For example, Zhang Lei et al. used the internal standard method of gas chromatography to determine the propanol gas component in mixed VOCs gas through multiple steps, which has high accuracy, good precision and strong stability. Ren Xiang et al. prepared an alcohol gas sensitive sensor by using ferroferric oxide hybrid carbon material to detect propanol gas. Although the above methods have certain responsiveness and accuracy in detecting propanol gas, they are usually expensive, difficult to make, complex in signal conversion and have a long analysis time, which limits their possibility of being used as portable, real-time and rapid detection sensors. In addition, there may be cross interference between gases, poor reusability and other problems in application.

[0004] Liquid crystal material is a kind of functional material emerging in recent years. Liquid crystal is a kind of high molecular ordered material between liquid and crystal, which has incomplete orientation long-range order and orientation position order, and has both fluidity like liquid and anisotropy like crystal. The liquid crystal sensor responds to specific input signals by using the special molecular orientation characteristics of liquid crystal, and presents special optical images. Part of the optical changes can be observed by the naked eye, and the liquid crystal sensor has the advantages of portability, low cost and simple operation, and has great application prospect in the field of propanol gas detection. SUMMARY

[0005] TECHNICAL PROBLEM

[0006] Traditional sensors for detecting propanol gas are susceptible to cross-interference from gases in complex environments, resulting in poor stability, low sensitivity, and long detection cycles. At the same time, the detection equipment is complex, requires a large detection space, is difficult to assemble and manufacture, and has a high cost, making it unsuitable for practical applications in certain scenarios.

[0007] Technical solution

[0008] Based on the above research status, this invention provides a highly sensitive micron-sized liquid crystal sensor for detecting the harmful VOC gas propanol. This sensor uses a modified glass template instruction layer as a substrate and a micron-sized mesh structure to support a doped nematic liquid crystal composite system. It can provide a rapid and sensitive optical response to trace amounts of propanol gas in the environment, and its performance is stable, meeting practical requirements.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] One object of the present invention is to provide a highly sensitive micron-sized liquid crystal sensor for detecting propanol gas, the sensor comprising a substrate, a support grid, and a composite liquid crystal system; the support grid is placed on the substrate; and the composite liquid crystal system is filled in the support grid.

[0011] In one embodiment of the present invention, the substrate is a colorless and transparent material that has been rinsed or soaked in a vertical modifier solution.

[0012] In one embodiment of the present invention, the vertical modifier is an organosilicon modifier, including one or more of DMOAP (dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride), DMDTAC (dimethyldodecyl[3-(trimethoxysilyl)propyl]ammonium chloride), DMHPTAC (dimethylhexadecyl[3-(trimethoxysilyl)propyl]ammonium chloride), and KH550 (γ-aminopropyltriethoxysilane);

[0013] Alternatively, it can be an inorganic salt modifier, including one or more of copper perchlorate, iron perchlorate, aluminum perchlorate, and nickel perchlorate.

[0014] In one embodiment of the present invention, the solvent in the vertical modifier solution is water or alcohol.

[0015] In one embodiment of the present invention, the concentration of the vertical modifier in the vertical modifier solution is 0.1 to 10 wt%.

[0016] Preferably, the concentration of the vertical modifier in the vertical modifier solution is 0.15–5 wt%.

[0017] Preferably, the concentration of the vertical modifier in the vertical modifier solution is 0.25-1 wt%.

[0018] In a specific embodiment, the vertical modifier is DMOAP.

[0019] In a specific embodiment, the mass fraction of DMOAP in the vertical modifier solution is 0.25-0.5%.

[0020] In an embodiment of the present application, the colorless transparent material comprises a cellulose transparent film, a polyurethane transparent film, a glass slide or a hydrogel transparent film.

[0021] In an embodiment of the present application, the colorless transparent material has a size of 5-100 x 5-100 mm and a height of 1-10 mm.

[0022] In an embodiment of the present application, the material of the glass slide comprises glass or quartz.

[0023] In an embodiment of the present application, the support grid is a sheet mesh structure; the mesh structure has a single grid aperture of 25-300 μm and a hole depth of 0.05-20 μm.

[0024] Preferably, the mesh structure has a single grid aperture of 100-150 μm and a hole depth of 1-10 μm.

[0025] In an embodiment of the present application, the shape of the single grid in the mesh structure is not limited and can be circular, square, trapezoidal or irregular.

[0026] In an embodiment of the present application, the material of the support grid is inert material; the inert material comprises one or more of copper, aluminum, zinc, tin and stainless steel.

[0027] In an embodiment of the present application, the composite liquid crystal system is composed of liquid crystal and dopant.

[0028] In an embodiment of the present application, the liquid crystal comprises nematic liquid crystal, cholesteric liquid crystal or chiral nematic liquid crystal.

[0029] In an embodiment of the present application, the nematic liquid crystal comprises one or more of 5CB (4-cyano-4'-pentylbiphenyl), 7CB (4-cyano-4'-heptylbiphenyl), 8CB (4-cyano-4'-(n-octyloxy)biphenyl) and E7 (a commercial liquid crystal material mixed with multiple nematic liquid crystals).

[0030] In an embodiment of the present application, the cholesteric liquid crystal comprises one or more of cholesteryl nonanoate, cholesteryl chloride, cholesteryl oleate carbonate, cholesteryl acetate, cholesteryl propionate, cholesteryl n-butyrate, cholesteryl oleate, cholesteryl linoleate, cholesteryl benzoate, cholesteryl cinnamate, cholesteryl ethyl carbonate, cholesteryl isostearate carbonate, cholesteryl butenyl carbonate, cholesteryl carbonate.

[0031] In an embodiment of the present application, the cholesteric liquid crystal comprises one or more of cholesteryl nonanoate, cholesteryl chloride, cholesteryl oleate carbonate, cholesteryl acetate, cholesteryl propionate, cholesteryl n-butyrate, cholesteryl oleate, cholesteryl linoleate, cholesteryl benzoate, cholesteryl cinnamate, cholesteryl ethyl carbonate, cholesteryl isostearate carbonate, cholesteryl butenyl carbonate, cholesteryl carbonate.

[0032] Preferably, the liquid crystal is a nematic liquid crystal, comprising 5CB, 7CB, 8CB or E7.

[0033] In an embodiment of the present application, the dopant comprises one or more of P-type nickel oxide nanomaterial, indium oxide-nickel oxide heterojunction, zinc oxide-nickel oxide heterojunction, zinc stannate-nickel oxide nanoflower.

[0034] Preferably, the dopant is a P-type nickel oxide nanomaterial.

[0035] In an embodiment of the present application, the P-type nickel oxide nanomaterial comprises P-type nickel oxide nanoparticles, P-type nickel oxide nanowires or P-type nickel oxide nanosheets.

[0036] Further, the P-type nickel oxide nanoparticles have a particle size of 5-15 nm.

[0037] Further, the P-type nickel oxide nanowires have a length of 5-500 μm and a diameter of 50-200 nm.

[0038] Further, the P-type nickel oxide nanosheets have a thickness of 5-50 nm and an area of 50-200 x 50-200 nm. 2 .

[0039] In an embodiment of the present application, the preparation method of the dopant comprises one or more of hydrothermal method, solvothermal method, sol-gel method, chemical precipitation method.

[0040] In an embodiment of the present application, the mass fraction of the dopant in the composite liquid crystal system is 0.01-1%.

[0041] Preferably, the mass fraction of the dopant in the composite liquid crystal system is 0.025-0.05%.

[0042] The second objective of this invention is to provide a method for preparing a highly sensitive micron-sized liquid crystal sensor for detecting propanol gas, the method comprising the following steps:

[0043] (1) A composite liquid crystal system is prepared by stirring and mixing liquid crystal and dopant evenly.

[0044] (2) Rinse or soak the colorless and transparent material with a vertical modifier solution, and then dry the rinsed colorless and transparent material to obtain the substrate;

[0045] (3) Place the support grid on the substrate, and then fill the support grid with the composite liquid crystal system to obtain a high-sensitivity micron liquid crystal sensor.

[0046] Furthermore, in step (1), the stirring speed is 500-1000 rpm and the stirring time is 30-60 min.

[0047] Furthermore, in step (1), uniform mixing means that there are no large particles of nanomaterials agglomerated in the composite liquid crystal system, and the color of the liquid crystal itself is not covered by dopants.

[0048] Furthermore, in step (2), drying involves placing the product at 50–100°C for 10 min–24 h.

[0049] The application of the high-sensitivity micron liquid crystal sensor provided by this invention in the field of propanol detection.

[0050] The application of the high-sensitivity micron liquid crystal sensor provided by this invention in the preparation of propanol detection equipment or apparatus.

[0051] The present invention also provides a method for detecting propanol using the above-mentioned high-sensitivity micron liquid crystal sensor. The method involves placing the high-sensitivity micron liquid crystal sensor in an environment and then observing it under a polarizing microscope.

[0052] In one embodiment of the present invention, if the area of ​​the light spot is observed to be 0, then there is no propanol in the environment; if a light spot appears, then propanol is present in the environment.

[0053] In one embodiment of the present invention, the settling time shall not exceed 15 days and shall not be less than 1 minute.

[0054] Specifically, the dopant used in this invention is P-type nickel oxide nanomaterial, which is doped into a nematic liquid crystal to form a composite liquid crystal system. At the same time, a glass substrate is modified with a vertical modifier to prepare a substrate, and a liquid crystal support grid is placed on it. The liquid crystal composite system is uniformly filled into the grid in a certain way to form a three-layer stable sensing system of micron-sized liquid crystal-support grid-modified substrate, thus preparing a liquid crystal sensor for detecting propanol gas.

[0055] P-type nickel oxide as a semiconductor metal oxide has certain gas sensing performance. The specific surface area of the material is large, the size is uniform, and the microstructure is loose and porous. Based on the ion adsorption model and the oxygen vacancy model, a large number of adsorbed oxygen ions and electron hole accumulation layers are formed on the surface. The reducing gas can exchange electrons with the oxidizing oxygen ions in the hole accumulation layer, fill the holes, change the conductivity of the material, and show the response, so it can quickly and sensitively respond to trace reducing gas propanol in the environment. The material is doped in the liquid crystal system. Since the size of the nanomaterial is extremely small, it can be filled between the liquid crystal molecules to form a liquid crystal composite system. The present application uses a micromesh support structure to provide space for the liquid crystal composite material, so that most of the liquid crystal molecules can form an anchoring effect with the modifier molecules of the substrate, and then uniformly orient. At the same time, the micromesh restricts the overall flow trend of the liquid crystal. Under the dual action of the support grid, the liquid crystal molecules have stable and uniform molecular orientation and arrangement. In a propanol atmosphere, the P-type nickel oxide nanomaterial transmits the response of the propanol gas to the liquid crystal molecules, changes the initial orientation of the liquid crystal molecules, and realizes the optical response change from dark state to bright state under specific optical conditions. In summary, the sensor realizes rapid and sensitive detection of trace propanol gas with a micromesh structure, requires a small space for detection, is simple to prepare and operate, and has low economic cost.

[0056] The present application has the following advantages:

[0057] The present application constructs a brand-new liquid crystal composite sensing system, uses P-type semiconductor nickel oxide nanomaterial as the response material of propanol gas, and uses the orientation characteristics of liquid crystal to display the sensing signal in the form of light, thereby preparing a liquid crystal sensor that can detect propanol gas in a portable and efficient manner. The preparation method is simple, and the economic benefit is high. Based on the excellent gas adsorption property of the P-type nickel oxide nanomaterial, the sensor can quickly and sensitively respond to trace propanol gas (10 ppm), and the result is easy to observe, and is suitable for most propanol gas detection scene applications.

[0058] The propanol gas liquid crystal sensor prepared by the present application has certain stability, reversibility and anti-interference property. Based on the control of the substrate on the orientation of the liquid crystal, the liquid crystal system is stable, can be placed for 15 days and still responds to propanol, and is not easily disturbed by the external environment. It does not respond to other alcohols and common organic reagents. After response, it can be restored and repeatedly detected, and has a long effective use period. The liquid crystal sensor provided by the present application has great application prospect in the fields of chemical industry, medical treatment and environmental monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 It is a schematic diagram of the response of the liquid crystal sensor to propanol gas.

[0060] Figure 2Optical images of P-type nickel oxide nanoparticle doped liquid crystal sensor before and after response to different concentrations of VOC vapor in Example 1. DETAILED DESCRIPTION

[0061] The application will be further described by specific examples, but the embodiments of the application are not limited to this.

[0062] Raw material sources

[0063] 5CB and other liquid crystals were purchased from Beijing Eight Billion Time and Space Liquid Crystal Technology Co., Ltd.; Decon 90, nickel nitrate hexahydrate, indium chloride tetrahydrate, and anhydrous ethanol were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.; DMOAP was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.; microscope slides were conventional commercially available products, with a size of 25x75mm, 1mm-1.2mm; copper sheets were purchased from Micro to Nano (UK).

[0064] Preparation method of P-type nickel oxide nanoparticles: dissolve nickel nitrate hexahydrate and ammonium bicarbonate in a molar ratio of 1:2 in 150 mL of deionized water, add 100 mL of anhydrous ethanol, and stir at 60°C to obtain a green solution. Centrifuge the obtained solution to obtain a precipitate. Dry the precipitate in an 80°C oven for 12 h to obtain a precursor. Calcine the obtained precursor at 250°C for 1 h to finally obtain P-type nickel oxide nanoparticles with a particle size of 6.5-10 nm.

[0065] Preparation method of P-type nickel oxide nanowires: dissolve 0.475 g of nickel nitrate hexahydrate in a 50 mL beaker containing 15 mL of deionized water, stir uniformly, then add 0.134 g of sodium oxalate, 0.1 g of polyethylene glycol, and 25 mL of ethylene glycol, stir again, and finally transfer the transparent solution to a high-pressure reaction kettle, calcine at 180°C for 15 h, obtain the blue-green product, remove impurity ions by multiple centrifugation and washing with ethanol and deionized water, and finally dry the precursor at 60°C under vacuum. Calcine the obtained precursor at 400°C for 2 h to finally obtain P-type nickel oxide nanowires with a length of 10-12 μm and a diameter of 80-100 nm.

[0066] Preparation method of P-type nickel oxide nanosheet: 0.475 g of nickel nitrate hexahydrate was dissolved into a beaker containing 25 mL of deionized water and 15 mL of ethylene glycol, and stirred uniformly to form a green transparent solution. Ammonia water with a concentration of 25% was added dropwise until the pH value of the whole solution reached 9.5, and then transferred into a reaction kettle after stirring for 5 minutes, and calcined at 140°C for 12 h. A green product was obtained, which was centrifuged for several times, and cleaned with ethanol and deionized water to remove impurity ions, and finally vacuum dried at 60°C to obtain a precursor. The precursor was calcined at 450°C for 2 h, and finally obtained a square P-type nickel oxide nanosheet with a thickness of 30 nm and a side length of 150 nm.

[0067] Example 1

[0068] 1. Preparation of liquid crystal doped P-type semiconductor nickel oxide nanomaterial composite system

[0069] A certain amount of 5CB (4-cyano-4'-pentyl biphenyl) liquid crystal was mixed with P-type nickel oxide nanoparticles, P-type nickel oxide nanowires, and P-type nickel oxide nanosheets prepared by a hydrothermal method in a beaker, respectively, and the mass fraction of the dopant (nanoparticles, nanowires, nanosheets) was controlled to be 0.05%. After adding a magnetic rotor, the mixture was mixed and stirred at 500 rpm for 1 h or at 1000 rpm for 30 min (the stirring speed and time can be adjusted in a timely manner) on a magnetic stirrer at room temperature until the P-type nickel oxide nanomaterial was uniformly dispersed in the liquid crystal system, and a liquid crystal composite material was obtained. The obtained material was sealed for standby use.

[0070] 2. Preparation of glass substrate for liquid crystal by vertical modifier DMOAP

[0071] (1) Cleaning of glass slides

[0072] The microscope glass slides were immersed in Decon-90 detergent for 1 hour or immersed in a beaker containing Decon-90 in an ultrasonic cleaner for 20 min, and then sequentially washed with anhydrous ethanol and deionized water to completely wash away the residual washing liquid. The surface liquid of the glass slides was blown dry with nitrogen, and the glass slides were placed in a 60°C oven for drying for about 15 min. After taking out, the glass slides were dustproofed and standby used.

[0073] (2) Preparation of vertical modifier solution

[0074] A certain amount of DMOAP liquid was taken with a plastic dropper and dropped into a beaker containing deionized water, and the mass fraction of DMOAP was controlled to be 0.25%. After adding a magnetic rotor, the mixture was mixed and stirred at 500 rpm for 10 min on a magnetic stirrer at room temperature to form a transparent DMOAP aqueous solution, which was sealed for standby use.

[0075] (3) Preparation of modified glass substrate

[0076] The DMOAP aqueous solution was used to rinse the cleaned glass slides with a plastic dropper for 1 min, and then the glass slides were washed with deionized water, dried with nitrogen, and dried in an oven at 100°C for 15 min to obtain a modified glass substrate, which was ready for use.

[0077] 3. Preparation of a high-sensitivity micro liquid crystal sensor for detecting propanol gas and test of response performance

[0078] (1) Preparation of a liquid crystal sensor

[0079] The liquid crystal composite material prepared above was taken with a capillary tube and dropped on the modified glass substrate in an amount of 0.5 μL. A copper sheet with a size of 3.05 mm x 3.05 mm and a hole (with a diameter of 150 μm and a depth of 5 μm) was covered on the liquid crystal droplet with a special bent tweezers for copper sheets, and the excess liquid crystal was absorbed from the outer edge of the grid with an absorbent paper. The liquid crystal material filled into the grid by using the flowability of the liquid crystal, and the liquid crystal sensor was obtained. Then, the filling state of the liquid crystal in the copper grid was checked with a polarized light microscope. When the optical image of the liquid crystal in the grid showed a uniform dark field without bright edges of protrusions or depressions, it was ensured that the liquid crystal material filled the grid without gaps or overflow.

[0080] (2) Test of response performance

[0081] A certain amount of propanol liquid was added to deionized water to prepare a propanol aqueous solution with a concentration of 0.33-33.34 mg / mL. 1.0 μL of the solution was taken with a pipette with a range of 2.5 μL and dropped on a filter paper in a 10 mL sterile syringe. The needle cap was a special resin-sealed needle cap, and the syringe plunger was kept at the 10 mL scale by mechanical action. The filter paper was heated with an electric hair dryer until the liquid on the filter paper was completely evaporated. The electric hair dryer was turned off, and the temperature of the syringe was reduced to room temperature (20-25°C). Then, 10-1000 ppm propanol vapor was formed in the syringe at room temperature. The propanol gas was slowly injected into the liquid crystal sensor prepared above through the syringe, and the contact time between the gas and the liquid crystal sensor was 1-5 min. The response of the sensor to the propanol gas was observed under a polarized light microscope, and the optical image of the liquid crystal material was observed. The results are shown in Table 1 and Figure 2

[0082] ​The results show that the sensor presents a uniform dark field without responding to the propyl alcohol gas. When the sensor contacts each concentration of propyl alcohol gas, the image of the liquid crystal sensor changes obviously, from dark state to bright field, and a large number of light spots are generated, indicating that the liquid crystal sensor has a good response effect to propyl alcohol vapor, and can achieve the sensitivity of detecting 10 ppm of trace propyl alcohol gas. The sensing performances of the sensors prepared by the three types of dopants are almost the same, and the optical brightness of the nickel oxide nanowires and nanosheets is slightly worse at trace propyl alcohol gas, but the light spot area is larger. In summary, the response effect of the liquid crystal sensor doped with nickel oxide nanoparticles is the best.

[0083] Table 1 Response performance of liquid crystal sensors prepared by different dopants to propyl alcohol gas with different concentrations

[0084]

[0085] (Note: The brightness level is based on the response of the liquid crystal sensor in this embodiment to 1000 ppm propyl alcohol gas, which is divided into bright, relatively bright, relatively dark, and dark. The light spot area is expressed by the percentage of the light part in the total area of 4x4 grids, which is divided into 100%, 75%, 50%, 25%, and 0%. The grading of the data in the tables of the subsequent examples and comparative examples is the same as this.)

[0086] Example 2

[0087] The liquid crystal sensor prepared in Example 1 was placed in a closed gas generation and diffusion system for response performance test. The specific steps were as follows: the liquid crystal sensor was placed in a 500 mL transparent metal airtight box at the top, aligned with the gas outlet of the airtight box and kept at a distance of 3-5 cm. 0.0167-1.67 mg of propyl alcohol liquid was taken and configured into 50 mL of propyl alcohol aqueous solution, which was stored in a 250 mL conical flask with a conical tip. The conical flask was placed on a non-magnetic stirring heating table to generate propyl alcohol vapor by heating at 98°C. The propyl alcohol vapor was introduced into the airtight box through a rubber tube connected between the airtight box and the conical flask. When the vapor was stable, 10-1000 ppm propyl alcohol vapor was formed in the airtight box. The liquid crystal sensor responded in the propyl alcohol atmosphere. Then the airtight box with the sensor was placed under a polarizing microscope for response, and the optical image of the liquid crystal material was observed. The results are shown in Table 2.

[0088] The results show that when the sensor is in the propyl alcohol atmosphere in a closed space, the optical change of the image of the liquid crystal sensor is basically the same as that in Example 1, and the light spot area is larger. This indicates that the propyl alcohol gas is more uniformly dispersed in the closed environment, and the contact with the liquid crystal sensor is more sufficient, making the sensing effect more uniform.

[0089] Table 2 Response performance of liquid crystal sensor to propyl alcohol gas with different concentrations in a closed environment

[0090]

[0091] Example 3

[0092] The P-type nickel oxide nanoparticle doped liquid crystal sensor prepared in Example 1 was placed in an open environment at normal temperature and pressure (25℃, 101.325kPa) and normal humidity (50%) for 0.5-15 days. The response of the sensor was tested using 10-1000ppm propanol vapor during the placement process, and the response of the same sensor was tested at intervals. The test procedure was consistent with that of Example 1, and the results are shown in Table 3.

[0093] The results show that the liquid crystal sensor has the ability to recover orientation and certain response performance after being placed for different periods of time, indicating that the liquid crystal sensor has not been completely disturbed by the propanol gas and the external environment during the previous test and has good stability and reusability after being placed in a normal environment.

[0094] Table 3 Response performance of liquid crystal sensor to propanol gas after being placed for different days

[0095]

[0096]

[0097] (Note: The orientation recovery degree at a certain placement time in the table is the orientation recovery degree of the same liquid crystal sensor after the previous response performance test.)

[0098] Example 4

[0099] The mass fraction of the vertical modifier solution in Example 1 was adjusted to 0-0.5%, and the speed of the magnetic stirrer was adjusted to 0-1000rpm. The stirring time and speed were adjusted according to the dissolution state of DMOAP in the aqueous solution until complete dissolution. The other procedures were consistent with the steps for preparing the glass substrate in Example 1, and the results are shown in Table 4.

[0100] The results show that the liquid crystal composite on the glass substrate without DMOAP modification is oriented randomly, while the glass substrate with modification can make the liquid crystal material present a uniform black image in the grid, and the greater the concentration of the DMOAP aqueous solution, the more complete the vertical orientation. When the mass fraction is above 0.25%, the liquid crystal orientation degree is almost unchanged, because at this concentration, the substrate can ensure the vertical orientation of all liquid crystal molecules, and the sensor grid presents complete darkness, which does not change with the increase of the mass fraction. Considering economic benefits, a 0.25% DMOAP aqueous solution can be used as the optimal mass fraction of the glass substrate modifier.

[0101] Table 4 Effect of different mass fractions of vertical modifier on liquid crystal orientation degree

[0102]

[0103] (Note: The degree of orientation of liquid crystal molecules on the glass substrate is taken as the benchmark at a modifier mass fraction of 0.25%, and is classified as disordered, partially vertical, and completely vertical. The classification of the data in the table is the same thereafter.)

[0104] Example 5

[0105] The mass fraction of P-type nickel oxide nanoparticles in Example 1 was adjusted to 0.01-1%, and the stirring speed and stirring time were appropriately adjusted until the nanoparticles were uniformly dispersed in the 5CB liquid crystal at each mass fraction. Response tests were performed using 10-1000 ppm of propanol vapor, and the other procedures were the same as in Example 1. The results are shown in Table 5.

[0106] The results show that the liquid crystal sensors prepared using P-type nickel oxide nanoparticles with a mass fraction of 0.025%, 0.05%, 0.1%, and 0.5% can respond to 10-1000 ppm of propanol vapor, indicating that the orientation of the liquid crystal molecules is affected by the absorption of gas by the dopant nanoparticles. The response effect is better when the mass fraction of P-type nickel oxide nanoparticles is between 0.025% and 0.05%. At a high mass fraction, such as 1%, the nanoparticles may agglomerate to form large particles, affecting the response effect of the liquid crystal sensor and making it difficult to observe and respond to the sensor.

[0107] Table 5 Response performance of liquid crystal sensors prepared using different mass fractions of dopants to propanol gas

[0108]

[0109] Comparative Example 1

[0110] Only the liquid crystal material in Example 1 was changed to nematic liquid crystals 7CB (4-cyano-4'-heptyl biphenyl), 8CB (4-n-octyl-4'-cyanobiphenyl), and E7, and the dopant was still P-type nickel oxide nanoparticles. Response tests were performed using 10-1000 ppm of propanol vapor, and the other procedures were the same as in Example 1. The results are shown in Table 6.

[0111] The results show that the optical changes in the response of the liquid crystal sensors to propanol gas are basically the same when different nematic liquid crystals are used, and the area and brightness of the bright spots decrease slightly. This may be because the molecular weight of the liquid crystal molecules increases, making it more difficult for the nickel oxide dopant to affect the orientation of the liquid crystal molecules after absorbing gas, so the response effect is slightly worse than that of the liquid crystal sensor prepared in Example 1.

[0112] Table 6 Response performance of different nematic liquid crystal sensors to 10-1000 ppm propanol gas

[0113]

[0114] Comparative Example 2

[0115] Only the liquid crystal material in Example 1 was adjusted to be a mixed cholesteric liquid crystal and a chiral liquid crystal E7 to which chiral agent S811 was added. The mixed cholesteric liquid crystal was COC (cholesterol oleic acid ester), CN (cholesterol nonanoate), and CC (cholesterol chloride) mixed in a mass ratio of 5:5:3 in a beaker, a magnetic rotor was added, and the mixture was stirred on a magnetic stirrer to obtain a cholesteric liquid crystal CLC. The CLC was heated to above the clearing point, P-type nickel oxide nanoparticles were added to control the doping mass fraction to be 0.05%, and the mixture was stirred at 500 rpm for 1 h to disperse the nickel oxide particles uniformly above the clearing point; E7 and chiral additive S811 were mixed in a ratio of 7:3 to form a chiral nematic liquid crystal, P-type nickel oxide nanoparticles were added to the chiral nematic liquid crystal to control the doping mass fraction to be 0.05%, and the mixture was stirred at 500 rpm for 1 h to disperse the nickel oxide particles uniformly. Comparative Example 2 was tested for response using 1000 ppm propanol vapor, and the other procedures were the same as those in Example 1. The results are shown in Table 7.

[0116] The results show that the sensor made of a cholesteric liquid crystal and a chiral nematic liquid crystal composite material has a random initial orientation, and there are light spots (bright state) before and after the response performance test, making it difficult to observe the optical changes in response to propanol gas. Since the molecules of these two liquid crystal materials are arranged in a helical structure, and the viscosity of the liquid crystal material is large, it is difficult to form a uniform molecular arrangement in the support grid, so the overall optical image is relatively chaotic, making it difficult to use and observe.

[0117] Table 7 Response performance of chiral nematic liquid crystal and cholesteric liquid crystal sensors to 1000 ppm propanol gas

[0118]

[0119] Comparative Example 3

[0120] Only the doping agent of the liquid crystal system was adjusted to be nickel oxide nanoparticles prepared by sol-gel method and indium oxide-nickel oxide heterojunction, silver-modified nickel oxide nanoparticles, and zinc stannate-nickel oxide nanoflower.

[0121] The operation of preparing the nickel oxide nanoparticles by the sol-gel method is as follows: nickel acetate tetrahydrate and zinc acetate are dissolved in ethylene glycol monomethyl ether solution according to a molar ratio of 25:1, and stirred magnetically at 60°C for 1h. A small amount of ethanolamine solution is added dropwise, one drop per second, until a uniformly distributed dark green solution is formed. The mixed solution is heated in a muffle furnace at 60°C for 2h, and then left to stand at room temperature for 24h to obtain the nickel oxide nanoparticles.

[0122] The preparation method of the indium oxide-nickel oxide heterojunction is as follows: 4.73g of nickel sulfate hexahydrate and 1.06g of indium chloride tetrahydrate are dissolved in 180mL of deionized water, 1g of potassium persulfate and 3mL of ammonia solution are added under stirring, and stirring is continued for 20min. The above solution is centrifuged to obtain an intermediate product, which is washed with deionized water and dried at 60°C in air, and then annealed at 600°C for 4h to obtain the indium oxide-nickel oxide heterojunction material.

[0123] The preparation method of the silver-modified nickel oxide nanoparticles is as follows: nickel nitrate hexahydrate and ammonium bicarbonate (molar ratio 1:2) and a small amount of silver nitrate are dissolved in 150mL of deionized water, 100mL of anhydrous ethanol is added, and a green solution is obtained by stirring at 60°C. The obtained solution is centrifuged to obtain a precipitate. The precipitate is dried in an 80°C oven for 12h to obtain a precursor. The obtained precursor is calcined at 250°C for 1h to finally obtain P-type nickel oxide nanoparticles with a particle size of 6.5-10nm.

[0124] The preparation method of the zinc stannate-nickel oxide nanoflower is as follows: 50mg of zinc stannate nanoflower is ultrasonically dispersed in 10mL of anhydrous ethanol for 20min, an appropriate amount of nickel nitrate hexahydrate is added under magnetic stirring at room temperature, until the ethanol is basically volatilized, the product is dried at 70°C overnight, and is calcined at 500°C for 2h to obtain the zinc stannate-nickel oxide nanoflower.

[0125] The mass percentage of the above-mentioned dopant is controlled to be 0.05%, 10-1000ppm of propanol vapor is used for response testing, and other procedures remain the same as in Example 1. The obtained results are shown in Table 8.

[0126] The results show that the response performance of the nickel oxide nanoparticles prepared by the sol-gel method to 1000ppm of propanol gas is closest to the results in Example 1, but the response effect decreases under low concentration conditions, and cannot meet the sensitivity requirements. The other modified and modified nickel oxide doped liquid crystal sensors cannot produce obvious optical response to propanol gas from high concentration to low concentration, and cannot meet the basic requirements of the present application.

[0127] Table 8 Response performance of liquid crystal sensors of other types of dopants to 10-1000ppm of propanol gas

[0128]

[0129] Comparative Example 4

[0130] The preparation method of the glass substrate in this comparative example is adjusted as follows:

[0131] A certain amount of copper perchlorate was dissolved in anhydrous ethanol to prepare a copper perchlorate anhydrous ethanol solution with a concentration of 50-300 mmol / L. 50 μL of the copper perchlorate solution was spin-coated onto a clean glass slide by a spin coater at 4000 rpm for 2-5 min or immersed for 1 h, and then dried in a 100°C oven for 1 d before being used. The copper perchlorate molecules can form a monolayer on the surface of the microscope glass slide, and through the coordination of metal ions and cyano groups, the liquid crystal molecules are anchored to form vertical alignment. The response test was performed using 10-1000 ppm of propanol vapor, and other procedures were consistent with Example 1. The results are shown in Table 9.

[0132] The results show that the glass substrate modified by 100-300 mmol / L copper perchlorate has the best anchoring effect on the liquid crystal composite material. However, when responding to propanol gas, the liquid crystal sensor with 100 mmol / L copper perchlorate has the best optical response effect. When the concentration of the modifier is too high, the force of the substrate on the liquid crystal composite material is too large, and it is more difficult for gas molecules to change the orientation of the liquid crystal molecules; if the concentration of the modifier is too low, it cannot ensure the uniformity of the sensor response. Compared with Example 1, the response of the liquid crystal sensor to propanol gas in this example is slightly worse, the optical change of the sensor is not obvious enough, the light spot area is small, and the brightness is not enough.

[0133] Table 9 Response performance of liquid crystal sensors prepared by copper perchlorate vertical modifier to 10-1000 ppm propanol gas

[0134]

[0135]

[0136] Comparative Example 5

[0137] This comparative example compares the specificity of the liquid crystal sensor. The sensor prepared in Example 1 was still used, and the VOC gas was adjusted to acetic acid (118°C), butanol (100°C), acetone (60°C), benzene (80°C), toluene (110°C), and styrene (145°C) gas (the minimum temperature for generating the corresponding VOC vapor is in parentheses). Other procedures were consistent with Example 1, and the specific steps are as follows:

[0138] Formulate 10.72 mg / mL acetic acid in water, 13.24 mg / mL butanol-water mixture, 10.37 mg / mL acetone in water, 13.95 mg / mL benzene-water mixture, 16.45 mg / mL toluene-water mixture, 18.60 mg / mL styrene-water mixture, pipette 2.5 μL of the above substances with a 2.5 μL pipette gun, drop on the filter paper in the same 10 mL sterile syringe needle injector as in Example 1, ensure that the needle injector pusher is kept at the 10 mL scale under heating by mechanical action, form 1000 ppm of each VOC vapor. Slowly push the gas out of the syringe onto the sensor made above, keep the gas in contact with the sensor for 1-5 min, and the final results are shown in Table 10.

[0139] The results show that, compared with Example 1, the liquid crystal sensor doped with nickel oxide nanoparticles has no obvious response to other VOCs gases, proving its anti-gas cross interference and specificity in detecting propanol gas.

[0140] Table 10 Response performance of the liquid crystal sensor to other 1000 ppm VOCs gases

[0141]

[0142] In summary, in the preparation method provided by the present application, the sensing effect is best when the liquid crystal material is nematic liquid crystal 5CB, the liquid crystal can present uniform vertical alignment effect when the mass fraction of the glass substrate modifier DMOAP aqueous solution is greater than 0.25%, the P-type semiconductor oxide nano material should be nickel oxide nanoparticles, nanowires or nanosheets, and the mass fraction of the doped liquid crystal 5CB is 0.025-0.05%, which can make the liquid crystal sensor respond quickly and sensitively to propanol gas. The liquid crystal sensor in the present application has obvious effect in detecting each concentration of propanol gas, and the lower limit threshold of detection is 10 ppm.

[0143] Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application, and anyone skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be defined by the claims.

Claims

1. A highly sensitive micron-sized liquid crystal sensor for detecting propanol gas, characterized in that, The sensor consists of a substrate, a support grid, and a composite liquid crystal system. The support grid is placed on the substrate, and the composite liquid crystal system is filled in the support grid. The substrate is a colorless and transparent material that has been rinsed or soaked in a vertical modifier solution; the vertical modifier is an organosilicon modifier including one or more of dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, dimethyldodecyl[3-(trimethoxysilyl)propyl]ammonium chloride, dimethylhexadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and γ-aminopropyltriethoxysilane, or an inorganic salt modifier including one or more of copper perchlorate, ferric perchlorate, aluminum perchlorate, and nickel perchlorate; the concentration of the vertical modifier in the vertical modifier solution is 0.1~10wt%; The supporting grid is a thin mesh structure; The mesh structure has individual mesh pores with diameters ranging from 25 to 300 μm and depths ranging from 0.05 to 20 μm. The composite liquid crystal system consists of liquid crystal and dopant. The liquid crystal is a nematic liquid crystal, and the dopant is a p-type nickel oxide nanomaterial. The mass fraction of the dopant in the composite liquid crystal system is 0.025~0.05%.

2. The high-sensitivity micron liquid crystal sensor according to claim 1, characterized in that, The concentration of the vertical modifier in the vertical modifier solution is 0.15~5wt%; the vertical modifier is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride.

3. The high-sensitivity micron liquid crystal sensor according to claim 1, characterized in that, The colorless and transparent material includes cellulose transparent film, polyurethane transparent film, glass slide or hydrogel transparent film.

4. The high-sensitivity micron liquid crystal sensor according to claim 1, characterized in that, The material of the supporting mesh is an inert material; the inert material includes one or more of copper, aluminum, zinc, tin, and stainless steel.

5. The high-sensitivity micron liquid crystal sensor according to claim 1, characterized in that, The liquid crystal includes 5CB, 7CB, 8CB, or E7.

6. A method for preparing the high-sensitivity micron liquid crystal sensor according to any one of claims 1 to 5, characterized in that, The preparation method includes the following steps: (1) A composite liquid crystal system is prepared by stirring and mixing the liquid crystal and the dopant evenly; even mixing means that there are no large particles of nanomaterials in the composite liquid crystal system and the color of the liquid crystal itself is not covered by the dopant. (2) Rinse or soak the colorless and transparent material with a vertical modifier solution, and then dry the rinsed colorless and transparent material to obtain the substrate; (3) Place the support grid on the substrate, and then fill the support grid with the composite liquid crystal system to obtain a high-sensitivity micron liquid crystal sensor.

7. The application of the high-sensitivity micron liquid crystal sensor according to any one of claims 1 to 5 in the field of propanol detection or in the preparation of propanol detection equipment.

8. A method for detecting propanol using the high-sensitivity micron liquid crystal sensor according to any one of claims 1 to 5, characterized in that, The method involves placing a high-sensitivity micron liquid crystal sensor in an environment and then observing it under a polarizing microscope. If the observed spot area is 0, then there is no propanol in the environment; if a spot appears, then propanol is present in the environment.

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