Carbon dioxide-responsive liquid crystal thin film containing amidine compound and preparation method and application thereof

Abstract

The carbon dioxide responsive liquid crystal film containing amidine compound is formed by a cholesteric liquid crystal polymer capable of reflecting visible light and an amidine compound, and the film is prepared from the amidine compound, cholesteric liquid crystal monomer, crosslinking agent, chiral dopant, photoinitiator and porogen, and the amidine group in the amidine compound reacts with carbon dioxide to increase the hydrophilicity of the polymer network, and when water penetrates into the film, the light reflected by the film is red-shifted and the color is changed accordingly. The carbon dioxide responsive liquid crystal film prepared by the application has stable color change effect, obvious response effect, is easier to distinguish, is still reversible after multiple cycles, and the performance of the film is maintained well after multiple cycles.

Description

Technical Field

[0001] This invention relates to the field of electroresponsive materials technology, and in particular to a carbon dioxide-responsive liquid crystal film containing an amidine compound, its preparation method, and its application. Background Technology

[0002] Carbon dioxide (CO2) is the fourth most abundant gas in Earth's atmosphere, with a normal concentration of approximately 0.03% (300 ppm). It plays a crucial role in various industrial processes as a refrigerant, fire extinguisher, and food additive. However, as a relatively inert gas, CO2 can be dangerous at certain concentrations. Accumulation of CO2 in enclosed spaces, such as mines, freezers, fermentation tanks, and submarines, can lead to unconsciousness and even death. Currently, due to numerous shortcomings in traditional CO2 detection methods, more efficient and convenient CO2 detection technologies remain a research goal for scientists. Traditional CO2 detection methods include non-dispersive infrared (NDIR), gas chromatography-mass spectrometry (GC-MS), and electrochemical detection (EC). These traditional methods are hampered by poor portability, long processing times, and high operating temperatures. In contrast, liquid crystal polymer networks can serve as smart sensors, changing color in response to various stimuli. Furthermore, responsive liquid crystal material CO2 sensors offer advantages such as low cost, ease of operation, rapid indication, reusability, and high visibility, providing a better option for rapid CO2 concentration determination. Summary of the Invention

[0003] One object of the present invention is to provide a carbon dioxide-responsive liquid crystal film containing an amidine compound, aiming to at least solve one of the technical problems existing in the prior art. The raw materials for preparing the carbon dioxide-responsive liquid crystal film containing the amidine compound include: an amidine compound, a cholesteric liquid crystal monomer, a crosslinking agent, a chiral dopant, a photoinitiator, and a pore-forming agent;

[0004] The general structural formula of the amidine-containing compound is as follows:

[0005]

[0006] The R is independently selected from one or more units containing an aromatic ring derivative structure; the structure of the aromatic ring derivative unit is selected from one or more units of ester, alkoxy, aryl, carboxyl, alkyl, carbonyl, alkenyl, aldehyde, and combinations thereof.

[0007] Furthermore, the structural formula of the amidine-containing compound is as follows:

[0008]

[0009] Further, the mass fractions of the raw materials used in the preparation are as follows: 40-60 wt% of amidine compound, 8-15 wt% of cholesteric liquid crystal monomer, 4-10% of crosslinking agent, 16-30 wt% of chiral dopant, 1-2 wt% of photoinitiator, and 5-15 wt% of pore-forming agent. The amount of amidine compound affects the performance and lifespan of the film; therefore, it is necessary to control the amount of amidine compound. Preferably, the mass fraction of the amidine compound is 45-50%.

[0010] Furthermore, the cholesteric liquid crystal monomer is selected from at least one of HCM021 and HCM020.

[0011] Furthermore, the crosslinking agent is selected from at least one of HCM009 and HCM006.

[0012] Furthermore, the pore-forming agent is selected from at least one of 5CB, 6CB, and 8CB.

[0013] Furthermore, the chiral dopant is selected from CB15.

[0014] Furthermore, the amount of the porogen determines the range of color change of the film after responding to carbon dioxide at a certain humidity. Generally speaking, the more porogen there is, the wider the range of color change. However, too much porogen will limit the strain actuation performance of the film. Its amount needs to be controlled within a certain range. The amount of porogen is 5-15 wt%; preferably, the amount of porogen is 10-15%.

[0015] Furthermore, the photoinitiator is selected from one or more of Irgacure 369, Irgacure 651, Irgacure 819, and Irgacure 184.

[0016] Another object of the present invention is to provide a method for preparing the carbon dioxide-responsive liquid crystal film containing the amidine compound, the method comprising the following steps:

[0017] S1. Preparation of cholesteric liquid crystal polymer. An amidine-containing compound, cholesteric liquid crystal monomer, chiral dopant, crosslinking agent, photoinitiator, and porogen are added to a solvent and heated and stirred to form a cholesteric liquid crystal polymer.

[0018] S2. A parallel alignment layer is obtained by rubbing the glass coated with the alignment layer with a cloth. A cholesteric liquid crystal polymer is coated between two glass sheets with parallel alignment layers to form a liquid crystal cell. The pore-forming agent is removed by irradiation with ultraviolet light to obtain a cholesteric liquid crystal film.

[0019] Furthermore, in step S1, the heating and stirring temperature is 50℃-80℃, and the time is 2h-4h.

[0020] Further, in step S1, the solvent is selected from halogenated hydrocarbon solvents; preferably, the solvent is dichloromethane.

[0021] In step S1, a cholesteric liquid crystal polymer was prepared by mixing an amidine-containing compound, a cholesteric liquid crystal monomer, and other raw materials, which resulted in a higher degree of dispersion of the amidine-containing compound in the film.

[0022] Another object of the present invention is to disclose the application of the carbon dioxide-responsive liquid crystal film containing the amidine compound in the field of sensors, wherein the sensor is used to monitor high carbon dioxide concentrations or high carbon dioxide concentrations in humid environments.

[0023] The present invention has the following beneficial effects:

[0024] (1) The carbon dioxide-responsive liquid crystal film containing an amidine compound of the present invention is composed of a cholesteric liquid crystal polymer that reflects visible light and an amidine compound forming a polymer network. The amidine groups in the amidine compound react with carbon dioxide, increasing the hydrophilicity of the polymer network. When water permeates into the film, the light reflected by the film undergoes a redshift and a corresponding color change (from greenish-yellow to deep red). After removing carbon dioxide and water, the film returns to its initial color, and the recovery process is extremely short, approximately 30-45 seconds. Compared with existing similar technologies, this film has a wider color change range, approximately 160 nm. Simultaneously, the color change effect of the film is more stable, and the response effect is more obvious and easier to distinguish. It remains reversible after multiple cycles, and the color change process remains very stable. During multiple cycles, a transmission band of similar wavelength is obtained after each response to carbon dioxide, and the same wavelength transmission band is restored after each removal of carbon dioxide. The performance of the film remains excellent after multiple cycles. Furthermore, this carbon dioxide-responsive liquid crystal film containing an amidine compound can also monitor the concentration of acidic gases and acidic solutions other than carbon dioxide.

[0025] (2) The present invention obtains an interpenetrating network structure film by using the above preparation method with cholesteric liquid crystal and an amidoside compound. An appropriate amount of the amidoside compound and the cholesteric liquid crystal polymer support each other. The amidoside compound has good dispersibility in the polymer, which makes the structure of the entire liquid crystal film more stable and able to withstand external stress and deformation, thereby increasing the service life and repeatability of the film. Attached Figure Description

[0026] Figure 1 A schematic diagram of the reaction between an amidine-containing compound and carbon dioxide and water is shown.

[0027] Figure 2 A schematic diagram showing the structural changes of a carbon dioxide-responsive liquid crystal film after treatment with carbon dioxide and water is presented.

[0028] Figure 3 A schematic diagram showing the transmission spectrum of a carbon dioxide responsive thin film after treatment with carbon dioxide and water is shown, returning it to its original state before treatment.

[0029] Figure 4 (a)-(b) show the peak bar graphs of the transmission spectrum of the carbon dioxide responsive thin film prepared in Example 1 after multiple carbon dioxide response tests (a) and the peak bar graphs of the transmission spectrum of the thin film after restoring the initial state (b). Detailed Implementation

[0030] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. The embodiments described below are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0031] The amidine-containing compound has the following structural formula:

[0032]

[0033] HCM009: Crosslinking agent, purchased from Henan Daken Chemical Products Co., Ltd., chemical structural formula is:

[0034]

[0035] HCM021: Cholesteric liquid crystal, purchased from Jiangsu Synthetic Display Technology Co., Ltd., chemical structural formula is:

[0036]

[0037] 8CB: Pore-forming agent, purchased from Jiangsu Chuangtuo New Materials Co., Ltd., chemical structural formula is:

[0038]

[0039] CB15: Chiral dopant, purchased from Jiangsu Synthetic Display Technology Co., Ltd., with the following chemical structure:

[0040]

[0041] Irgacure 819: a photoinitiator, purchased from Tianjin Xiens Biochemical Technology Co., Ltd.

[0042] Example 1

[0043] A carbon dioxide responsive thin film, the preparation method of which includes the following steps:

[0044] S1. Preparation of a cholesteric liquid crystal polymer network. 50 wt% of an amidine-containing compound, 11 wt% of cholesteric liquid crystal HCM021, 10 wt% of crosslinking agent HCM009, 18 wt% of chiral dopant CB15, 1 wt% of photoinitiator Irg819 and 10 wt% of porogen 8CB were mixed, and dichloromethane was added as a solvent. The mixture was stirred thoroughly at 60 °C for 3 h to form a polymer network.

[0045] S2. A parallel alignment layer is obtained by rubbing an alignment layer onto glass with a velvet cloth. The mixture is uniformly coated between two glass sheets with parallel alignment layers to form a 20 μm liquid crystal cell. The cell is then irradiated with ultraviolet light for 30 min to obtain a cholesteric liquid crystal film. The obtained liquid crystal cell is then opened and heated at 120°C for 5 h to remove the pore-forming agent, yielding a film responsive to carbon dioxide gas.

[0046] Example 2

[0047] A carbon dioxide-responsive liquid crystal film, the preparation method of which includes the following steps:

[0048] S1. Preparation of a cholesteric liquid crystal polymer network. 40 wt% of an amidine-containing compound, 14 wt% of cholesteric liquid crystal HCM021, 7 wt% of crosslinking agent HCM009, 25 wt% of chiral dopant CB15, 1 wt% of photoinitiator Irg 819, and 13 wt% of porogen 8CB were mixed, and dichloromethane was added as a solvent. The mixture was stirred thoroughly at 60 °C for 3 h to form a polymer network.

[0049] S2. A parallel alignment layer is obtained by rubbing an alignment layer onto glass with a velvet cloth. The mixture is uniformly coated between two glass sheets with parallel alignment layers to form a 20 μm liquid crystal cell. The cell is then irradiated with ultraviolet light for 30 min to obtain a cholesteric liquid crystal film. The obtained liquid crystal cell is then opened and heated at 120°C for 5 h to remove the pore-forming agent, yielding a film responsive to carbon dioxide gas.

[0050] Test case

[0051] The carbon dioxide responsive liquid crystal film prepared in Example 1 was tested for carbon dioxide response.

[0052] Test method: The carbon dioxide responsive liquid crystal film was placed in a sealed container in a high-humidity carbon dioxide environment (high-humidity carbon dioxide environment: relative humidity 80%, carbon dioxide concentration 40% VOL). The change in the reflectance band of the film in Example 1 after interacting with carbon dioxide gas was measured using a spectrometer.

[0053] Figure 1 A schematic diagram of the reaction between an amidine-containing compound and carbon dioxide and water is shown.

[0054] Figure 2 A schematic diagram showing the structural changes of a carbon dioxide-responsive liquid crystal film after treatment with carbon dioxide and water is presented.

[0055] Figure 3 A schematic diagram showing the transmission spectrum of a carbon dioxide responsive thin film after treatment with carbon dioxide and water is shown, returning it to its original state before treatment.

[0056] In the experiment, it was observed that the transmission wavelength of the film prepared in Example 1 changed by about 160 nm after responding to high humidity carbon dioxide, shifting from 600 nm to about 760 nm, and the color changed from greenish-yellow to deep red. This change was obvious and easily distinguishable within the visible range. The continuous red shift of the reflection band of the film over time is due to the fact that when the film is exposed to a humid carbon dioxide environment, the amidine groups in the polymer network react with the aqueous solution of carbon dioxide to form hydrophilic salts. This causes carbon dioxide and water to enter the voids left by the pore-forming agent, resulting in expansion and an increase in the pitch of the cholesteric liquid crystal polymer network. According to the formula: Δλ=Δn×p (Δλ is the reflection wavelength, Δn is the average refractive index, and p is the pitch), the color of the cholesteric film is selectively produced due to radial light diffraction. The increase in pitch causes the reflection wavelength to shift towards longer wavelengths, thus causing the film color to redshift.

[0057] After the film responded to carbon dioxide and the color stabilized, the film was transferred out of the high-humidity carbon dioxide environment and placed indoors (relative humidity 40%, carbon dioxide concentration 0.03% VOL) ​​to evaporate carbon dioxide and water. The film transmission spectra at different time points after evaporation (2s, 5s, 10s, 15s, 20s, 30s) were recorded.

[0058] Table 1. Changes in transmission wavelength of the carbon dioxide-responsive thin film after treatment with carbon dioxide and water, returning to its pre-treatment state.

[0059]

[0060] From Table 1 and Figure 3 As can be seen, 30 seconds after the water and carbon dioxide evaporate from the membrane, the transmission wavelength of the membrane recovered to around 600 nm (e.g., Figure 3 As shown in the figure (the arrows in the figure indicate the direction of change of the transmission spectrum peaks), it can be observed macroscopically that the morphology and color of the cholesteric liquid crystal polymer network film have been restored to their original colors, and the restoration time is extremely short.

[0061] Then, the above cyclical experiment was repeated many times, and the results were as follows: Figure 4 As shown in (a)-(b), Figure 4 (a) is the peak of the transmission spectrum after the film color stabilizes following each response to high humidity carbon dioxide in the repeated experiment. Figure 4(b) The peaks of the transmission spectrum after the film color stabilizes following each removal of the high-humidity carbon dioxide environment and evaporation of water and carbon dioxide in repeated experiments. As shown in the figure above, after multiple responses and responses to high-humidity carbon dioxide, the film consistently reaches a transmission band of approximately 760 nm. After multiple responses and evaporation of water and carbon dioxide, the film consistently recovers to approximately 600 nm. Furthermore, the color change process of the film remains very stable. During multiple cycles of use, a transmission band of similar wavelength is obtained after each response to carbon dioxide, and the same wavelength is recovered after each removal of carbon dioxide, verifying that the film can be stably reused multiple times.

[0062] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments and test examples described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments and test examples should be considered in all respects as exemplary and not restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0063] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A carbon dioxide-responsive liquid crystal film containing an amidine compound, characterized in that, The raw materials for preparing the carbon dioxide responsive liquid crystal film containing amidine compounds include: amidine compounds, cholesteric liquid crystal monomers, crosslinking agents, chiral dopants, photoinitiators, and pore-forming agents; The structural formula of the amidine-containing compound is as follows: ； The mass fractions of the raw materials used in the preparation are as follows: 40-60 wt% of amidine compound, 8-15 wt% of cholesteric liquid crystal monomer, 4-10% of crosslinking agent, 16-30 wt% of chiral dopant, 1-2 wt% of photoinitiator and 5-15 wt% of pore maker.

2. The carbon dioxide-responsive liquid crystal film containing an amidine compound according to claim 1, characterized in that, The cholesteric liquid crystal monomer is selected from at least one of HCM021 and HCM020.

3. The carbon dioxide-responsive liquid crystal film containing an amidine compound according to claim 1, characterized in that, The crosslinking agent is selected from at least one of HCM009 and HCM006.

4. The carbon dioxide-responsive liquid crystal film containing an amidine compound according to claim 1, characterized in that, The pore-forming agent is selected from at least one of 5CB, 6CB, and 8CB.

5. A method for preparing a carbon dioxide-responsive liquid crystal thin film containing an amidine compound as described in any one of claims 1-4, characterized in that, The method for preparing carbon dioxide-responsive liquid crystal thin films containing amidine compounds includes the following steps: S1. Preparation of cholesteric liquid crystal polymer: Mix an amidine-containing compound, a cholesteric liquid crystal monomer, a chiral dopant, a crosslinking agent, a photoinitiator, and a pore-forming agent, add a solvent, and heat and stir to form a cholesteric liquid crystal polymer; S2. A parallel alignment layer is obtained by rubbing the glass coated with the alignment layer with a cloth. A cholesteric liquid crystal polymer is coated between two glass sheets with parallel alignment layers to form a liquid crystal cell. The pore-forming agent is removed by irradiation with ultraviolet light to obtain a cholesteric liquid crystal film.

6. The method for preparing a carbon dioxide-responsive liquid crystal thin film containing an amidine compound according to claim 5, characterized in that, In step S1, the heating and stirring temperature is 50℃-80℃, and the time is 2 h-4 h.

7. The method for preparing a carbon dioxide-responsive liquid crystal thin film containing an amidine compound according to claim 5, characterized in that, In step S1, the solvent is selected from halogenated hydrocarbon solvents.

8. The application of the carbon dioxide-responsive liquid crystal film containing an amidine compound as described in any one of claims 1-4 in the field of sensors.

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