CN111234275A - Multilayer humidity-sensitive film based on activated carbon combined with inorganic material doped polyimide and composite humidity-sensitive element - Google Patents
Multilayer humidity-sensitive film based on activated carbon combined with inorganic material doped polyimide and composite humidity-sensitive element Download PDFInfo
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Abstract
The invention belongs to the cross field of sensitive materials and optical fiber sensing, and provides a multilayer humidity sensitive film based on inorganic material doped polyimide and a composite humidity sensitive element. The composite humidity sensitive element consists of a waveguide grating and a multilayer humidity sensitive film; wherein, the humidity sensitive film is compounded by active carbon, humidity sensitive inorganic salt and polyimide. The invention also discloses a preparation method of the humidity-sensitive film, which comprises the steps of taking polyimide as a main body, adding humidity-sensitive inorganic salt to compound to obtain a primary composite film, and coating activated carbon powder on the surface of the film to obtain the final humidity-sensitive film. The composite humidity sensitive element prepared by the invention has the advantages of good response linearity, high sensitivity, small humidity stagnation, short response time, good repeatability and the like, and compared with a humidity sensitive element based on pure polyimide, the composite humidity sensitive element has the advantages of low sensitivity, large humidity stagnation, poor long-term stability and the like, and can be widely applied to the accurate measurement of humidity.
Description
Technical Field
The invention belongs to the field of crossing of material science and optical fiber sensing, and particularly relates to a multilayer humidity sensitive film based on activated carbon combined with inorganic material doped polyimide and a composite humidity sensitive element.
Background
The humidity of the environment has a crucial influence on production and life. The influence caused by humidity and temperature is considered in the aspects of material storage, medical health, livestock breeding, manufacturing and production and the like. With the precision of production equipment, the requirement on environment is higher and higher, and the equipment is misaligned and damaged due to overhigh humidity, so that the optical fiber-based humidity element has the advantages of small volume, high intrinsic safety and the like, and is developed rapidly.
The humidity element based on the polymer sensitive film has the advantages of easy integration, small-sized batch production, strong environmental pollution resistance, linear response, good chemical stability and the like, is widely used, but the sensitivity and the wet hysteresis phenomenon of the humidity element are increased along with the thickness, and the good sensitivity, stability and repeatability cannot be simultaneously maintained.
The traditional humidity element based on inorganic salt has the advantages of high sensitivity, quick response, convenience in operation and the like, but the traditional humidity element is gradually eliminated due to the problems of short service life, easiness in forming corrosive solution, damage to other positions and the like.
The organic-inorganic composite material can maintain the advantages of the material and offset the respective defects to a certain extent. Simply combining an inorganic salt with a polymer can improve the sensitivity and response speed of the sensitive film to humidity, but can reduce the stability of the sensitive film.
Disclosure of Invention
The invention aims to solve the technical problem of providing a multilayer humidity sensitive film based on activated carbon combined with inorganic material doped polyimide, compounding the activated carbon, humidity sensitive inorganic salt and polyimide into a novel organic-inorganic humidity sensitive film, and ensuring the high sensitivity and the fast response speed of a humidity sensitive element and the stability and the repeatability of the humidity sensitive film on the premise of ensuring the normal response time.
The technical scheme adopted by the invention for solving the problems is as follows:
the multilayer humidity-sensitive film based on the combination of activated carbon and inorganic material doped polyimide is formed by compounding the activated carbon, humidity-sensitive inorganic salt and the polyimide. Wherein the mass ratio of the polyimide to the humidity-sensitive inorganic salt is 100: (0.3-1); the mass ratio of activated carbon to polyimide was about 1: 10.
according to the scheme, the humidity-sensitive inorganic salt is any one or a mixture of any more of lithium chloride, sodium bromide, ammonium chloride and the like.
According to the scheme, the activated carbon is powder, and the mesh number of the particle size is larger than 200 meshes.
According to the scheme, the viscosity of the polyamic acid is within the range of 7000cp to 10000 cp.
The preparation method of the multilayer humidity-sensitive film comprises the steps of taking polyimide as a main body, adding humidity-sensitive inorganic salt for compounding to obtain a primary composite film, and depositing activated carbon powder on the surface of the film to obtain the multilayer humidity-sensitive film.
The invention also provides a composite humidity sensitive element which consists of a waveguide grating and the multilayer humidity sensitive film, wherein the multilayer humidity sensitive film is attached to the surface of the waveguide grating. Wherein the thickness of the multilayer humidity sensitive film is 5-50 mu m.
The invention also provides a preparation method of the composite humidity sensitive element, which mainly comprises the following steps:
a. selecting inorganic salt and polyamic acid according to the mass ratio (0.03-0.1): 10, fully stirring, standing for 1-2 hours at 60-80 ℃, and exhausting gas to obtain polyamic acid doped with inorganic salt;
b. c, placing the waveguide grating in the polyamic acid doped with the inorganic salt obtained in the step a, forming a primary composite film on the surface of the waveguide grating, and then continuing to add activated carbon powder into the polyamic acid doped with the inorganic salt to deposit on the surface of the primary composite film through physical adsorption (the adding mass of the activated carbon is about one tenth of that of the polyamic acid in the step a); after dipping for a certain time, pulling out the waveguide grating by a pulling coating machine, forming a liquid film on the surface of the waveguide grating at the moment, and forming an activated carbon and inorganic salt doped polyimide film on the surface of the waveguide grating through heating and pre-curing;
c. and (c) repeating the step (b) for a plurality of times to obtain a humidity-sensitive combination body formed by combining the activated carbon, the inorganic salt doped polyimide film and the waveguide grating, and then performing post-curing and aging to obtain the humidity-sensitive element of the multilayer humidity-sensitive film based on the activated carbon and the inorganic material doped polyimide.
According to the scheme, the humidity-sensitive inorganic salt and the active carbon are dried and ground into powder in advance before use; the waveguide grating is previously cleaned and dried. Wherein the drying temperature of the humidity-sensitive inorganic salt and the activated carbon can be about 100 ℃.
According to the scheme, the inorganic salt is dissolved in the polyamic acid at the temperature of 80 ℃, so that the solution is uniform, and a uniform film is formed.
According to the scheme, the thickness of the moisture-sensitive functional layer is mainly controlled by adjusting the repetition times of the step b.
According to the scheme, in the step b, the dipping time is generally about 60 to 180 s.
According to the scheme, in the step b, the waveguide grating is vertically pulled upwards at a constant speed, and the pulling speed is 260-.
According to the scheme, in the step b, the pre-curing temperature is 200-220 ℃, and the pre-curing time is 5-10 minutes.
According to the scheme, in the step c, the post-curing temperature is 220 ℃, the post-curing time is 240-; the aging procedure is as follows: the humidity sensor was placed in a temperature shock chamber and shocked back and forth between 80 ℃ and 0 ℃ with each temperature being maintained for 2 hours and aged for 72 hours.
Compared with the prior art, the invention has the beneficial effects that:
firstly, the novel organic-inorganic humidity sensitive film is compounded by the active carbon, the humidity sensitive inorganic salt and the polyimide, so that the high sensitivity and the high response speed of the humidity sensitive element are ensured, and the stability and the repeatability of the humidity sensitive film are ensured on the premise of ensuring the normal response time. In addition, the surface of the composite humidity-sensitive film is provided with the activated carbon, so that the humidity stagnation property of the film can be reduced by utilizing low water absorption, and the contact area between polyimide and moisture can be provided by utilizing the large specific surface area of the film; the inorganic salt is embedded in the polyimide, and a water absorption center is formed during precuring, so that the water molecule adsorption capacity of the film is improved.
The organic-inorganic composite film humidity-sensitive element has good humidity-sensitive response performance, the humidity measurement range is 0-100%, the measurement range is wide, the response linearity is good, the sensitivity is high, the humidity hysteresis is small, the response time of adsorption and desorption is shorter than that of a traditional capacitance-type humidity sensor, the long-term stability is good, and the response is almost unchanged after one month. Is especially suitable for measuring the humidity of medium and low humidity environment.
In a word, the method for preparing the organic-inorganic composite transparent film humidity sensitive element has the characteristics of low cost, simple manufacture, high yield and suitability for batch production. The composite humidity sensitive element prepared by the invention has the advantages of good response linearity, high sensitivity, small humidity stagnation, short response time, good repeatability and the like, and compared with a humidity sensitive element based on pure polyimide, the composite humidity sensitive element has the advantages of low sensitivity, large humidity stagnation, poor long-term stability and the like, and can be widely applied to the accurate measurement of humidity.
Drawings
FIG. 1 is a schematic diagram of a component; wherein, the waveguide grating (1), the multilayer humidity sensitive film (2), the active carbon (2.2), the humidity sensitive inorganic salt (2.3) and the polyimide (2.1);
FIG. 2 is a diagram of a test and demodulation system;
FIG. 3 is a graph showing the actual relative humidity response of the first multilayer moisture-sensitive film prepared in example 1;
FIG. 4 is a graph showing the actual relative humidity response of the second multilayer moisture-sensitive film prepared in example 1;
FIG. 5 is a graph showing the actual relative humidity response of the multilayer moisture-sensitive film III prepared in example 2;
FIG. 6 is a relative humidity response diagram of a conventional polyimide waveguide grating;
FIG. 7 is a graph showing the results of a two-week element stability test of the first multilayer moisture-sensitive film;
FIG. 8 is a graph showing the results of a two-week element stability test of a conventional polyimide film.
The above drawings and description of the drawings in which each film represents a humidity sensitive element prepared therefrom.
Detailed Description
In order to better understand the present invention, the following examples are further provided to illustrate the content of the present invention, but the present invention is not limited to the following examples.
In the following examples, the viscosity of the polyamic acid was in the range of 7000cp to 10000 cp.
The following examples mentioned a conventional polyimide optical fiber humidity sensitive element different from example 1 in that: the inorganic salt and the active carbon in the embodiment are directly omitted, and the common polyimide film and the common polyimide optical fiber humidity sensitive element are prepared.
Example 1
The preparation method of the multilayer humidity-sensitive film based on the activated carbon combined with the lithium chloride doped polyimide and the composite humidity-sensitive element comprises the following specific steps:
a. baking lithium chloride at 100 ℃ for 1 hour, and grinding into powder; mixing 0.05g of lithium chloride and 10g of polyamic acid, stirring fully, standing for 2 hours at 80 ℃, fully welding, and exhausting gas to obtain lithium chloride-doped polyamic acid;
b. c, cleaning and drying the waveguide grating in advance, then placing the waveguide grating in the lithium chloride-doped polyamic acid obtained in the step a, forming a primary composite film on the surface of the waveguide grating, then adding 1g of activated carbon powder into the lithium chloride-doped polyamic acid, depositing the activated carbon powder on the surface of the primary composite film, dipping the surface of the primary composite film for 120s, then lifting the waveguide grating out through a lifting coating machine at a speed of 270 mu m/s, forming a liquid film on the surface of the waveguide grating at the moment, heating the liquid film, and precuring at 220 ℃ for 5-10 minutes, and forming a multilayer polyimide film doped with activated carbon and lithium chloride on the surface of the waveguide grating;
c. repeating the step b for 4 times, wherein the thickness of the film layer is 15 mu m, so as to obtain a humidity-sensitive combination body formed by combining the activated carbon, the lithium chloride doped polyimide film and the waveguide grating, and numbering a plurality of layers of humidity-sensitive films I;
d. repeating the step b for 8 times, heating and curing to obtain a humidity-sensitive combination body formed by combining the activated carbon, the lithium chloride doped polyimide film and the waveguide grating, and numbering a second multilayer humidity-sensitive film;
e. and respectively baking the multilayer humidity-sensitive film I and the multilayer humidity-sensitive film II at 220 ℃ for 4 hours, then curing, then putting into a temperature impact box, impacting back and forth at 80 ℃ and 0 ℃, keeping each temperature for 2 hours, and aging for 72 hours to respectively obtain the humidity-sensitive element I based on the activated carbon and the lithium chloride doped polyimide and the humidity-sensitive element II based on the activated carbon and the lithium chloride doped polyimide.
Example 2
The preparation method of the multilayer humidity-sensitive film based on the combination of the activated carbon and the lithium bromide doped polyimide and the composite humidity-sensitive element comprises the following specific steps:
a. baking lithium bromide at 100 ℃ for 1 hour, and grinding into powder; mixing 0.05g of lithium bromide and 10g of polyamic acid, fully stirring, standing at 80 ℃ for 2 hours, fully welding, and exhausting gas to obtain lithium bromide-doped polyamic acid;
b. c, cleaning and drying the waveguide grating in advance, then placing the waveguide grating in the polyamic acid doped with lithium bromide obtained in the step a, forming a primary composite film on the surface of the waveguide grating, then adding 1g of activated carbon powder into the polyamic acid doped with lithium bromide, depositing the activated carbon powder on the surface of the primary composite film, dipping the surface of the primary composite film for 120s, then lifting the waveguide grating out through a lifting coating machine at a speed of 270 mu m/s, forming a liquid film on the surface of the waveguide grating at the moment, heating the liquid film, and precuring at 220 ℃ for 5-10 minutes, and forming a multilayer polyimide film doped with activated carbon and lithium bromide on the surface of the waveguide grating;
c. repeating the step b for 4 times to obtain a humidity-sensitive combination body formed by combining the activated carbon, the lithium bromide doped polyimide film and the waveguide grating, and numbering a plurality of layers of humidity-sensitive films III;
d. and (3) baking the multilayer humidity-sensitive film III at 220 ℃ for 4 hours for post-curing, then putting the multilayer humidity-sensitive film III into a temperature impact box, impacting back and forth at 80 ℃ and 0 ℃, keeping each temperature for 2 hours, and aging for 72 hours to obtain a humidity-sensitive element III based on activated carbon and lithium chloride doped polyimide.
The multilayer humidity sensitive film and humidity sensitive element prepared in the above examples were subjected to the response, response linearity and repeatability tests as follows:
as shown in fig. 2, the experimental apparatus is composed of a set of fiber-optic waveguide demodulation system, a temperature and humidity test chamber, a computer and a probe. The waveguide grating demodulation system comprises a C-band laser light source, a 1X2 coupler and a waveguide grating demodulator, the demodulation wavelength range is 1520-1570 nm, the precision is +/-0.1 pm, and the demodulator is connected with a computer through a serial port and used for displaying and recording the wavelength value of each channel in real time. The temperature and humidity test box has the precision of +/-0.3 ℃ (+1 to +60 ℃), +/-3% RH (20-90% RH), the resolution of 0.1 ℃ and 0.1% RH.
Firstly, in order to test the sensitivity of an element, the humidity of a temperature and humidity test box is set to be 25% -95%; the gradients were set at 10%, each gradient was held for 1 hour; the temperature was set at 25 ℃. As regards the stability and reproducibility of the test elements, the temperature was set at 25 ℃ and the humidity at 80% -55% -35% -55% -80%, each phase being maintained for 1 hour. Cycling was performed once daily for 2 weeks and element stability and repeatability data were obtained. To test the temperature sensitivity of the element, humidity was set to 60%; the temperature was set at 20-25-30-35-40 ℃ and each gradient was maintained for 1 hour. The actual relative humidity is monitored by the elements within the temperature and humidity test chamber. The wavelength value of the reflected light passing through the sample is demodulated by a demodulation system, and the wavelength value is returned to the computer and stored by the computer.
As shown in fig. 3-6, the relative humidity is from 25% RH to 95% RH, based on the wavelength drift diagram of the humidity sensitive element of the activated carbon and the polyimide multilayer sensitive film doped with lithium chloride, it can be seen from the diagram that the humidity changes by 70% RH, the central wavelength of the first multilayer humidity sensitive film changes by 165pm, and the sensitivity reaches 2.36 pm/% RH; the second multilayer humidity-sensitive film has increased operation times, thickened film thickness, changed central wavelength of 340pm and sensitivity of 5.66 pm/% RH; and the multi-layer humidity-sensitive film III changes doped inorganic salt, the central wavelength change of the multi-layer humidity-sensitive film III reaches 270pm, and the sensitivity reaches 4.5/% RH. As can be seen from FIGS. 3-6, the polyimide multilayer sensitive film based on activated carbon and doped inorganic salt has good stability under various humidity platforms, and the drift amount is less than +/-0.1 pm/h. FIG. 4 shows that the test was performed under the same environment without any doped ordinary polyimide film, the wavelength variation was only 42pm, and the sensitivity was 0.6 pm/% RH.
FIG. 7 shows the results of the two-week cycle humidity test of the humidity sensor according to the example. The maximum deviation and standard deviation of the wavelength shift from the standard values are considered as criteria for judging the repeatability of the components. Taking the multilayer humidity sensitive film as an example, the maximum deviation of the drift amounts of the humidity sensitive element at the same humidity wavelength within a two-week period is + -2.5 pm, and the standard deviation is 0.91. FIG. 8 shows the measurement results of a conventional polyimide optical fiber humidity element, with the corresponding parameters of + -3.9 pm and 1.25 respectively. According to the above sensitivity analysis, the maximum deviation of the humidity sensor according to the examples from the conventional polyimide optical fiber humidity sensor in the humidity measurement was 1.6% and 6.5%, respectively.
In summary, a humidity sensor based on activated carbon and inorganic salt doped polyimide multilayer sensitive film is prepared by combining activated carbon and inorganic salt doped polyimide multilayer sensitive film. The kind of the inorganic salt can be selected according to actual requirements to regulate the sensitivity. Taking lithium chloride as an example, the humidity response range of the element is 20-90% RH, the temperature response range is 5-60 ℃, the humidity sensitivity reaches 2.56 pm/% RH, the maximum error in two weeks is 1.6%, and the temperature sensitivity is 10.15pm/° C. The invention not only improves the stability and the precision of the humidity sensitive element, but also overcomes the defects of an electronic humidity element, resists electromagnetic interference, realizes remote distributed sensing, and has simple structure, low cost and high linearity.
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (10)
1. The multilayer humidity-sensitive film based on activated carbon combined with inorganic material doped polyimide is characterized by being mainly formed by compounding activated carbon, humidity-sensitive inorganic salt and polyimide; wherein the mass ratio of the polyimide to the humidity-sensitive inorganic salt is 100: (0.3-1), adsorbing and depositing the activated carbon on the surface of a film formed by the humidity-sensitive inorganic salt and the polyimide.
2. The activated carbon-bonded inorganic material doped polyimide-based multilayer moisture-sensitive film according to claim 1, wherein the moisture-sensitive inorganic salt is any one or a mixture of any several of lithium chloride, sodium bromide or ammonium chloride.
3. The activated carbon-bonded inorganic material doped polyimide-based multilayer moisture sensitive film according to claim 1, characterized in that the activated carbon is a powder with a mesh size of more than 200 mesh; the viscosity of the polyamic acid is within the range of 7000cp to 10000 cp.
4. The method for preparing a multilayer moisture-sensitive film according to claim 1, wherein the multilayer moisture-sensitive film is obtained by using polyimide as a main body, adding a moisture-sensitive inorganic salt to compound the polyimide and the moisture-sensitive inorganic salt to obtain a primary composite film, and adsorbing activated carbon powder on the surface of the primary composite film.
5. A composite humidity-sensitive element comprising a waveguide grating and the multilayer humidity-sensitive film of claim 1, wherein the multilayer humidity-sensitive film of claim 1 is attached to the surface of the waveguide grating; wherein the thickness of the multilayer humidity sensitive film is 5-50 μm.
6. A preparation method of a composite humidity sensitive element is characterized by mainly comprising the following steps:
a. selecting inorganic salt and polyamic acid according to the mass ratio (0.03-0.1): 10, mixing, fully stirring and then exhausting gas to obtain polyamic acid doped with inorganic salt;
b. c, placing the waveguide grating in the polyamide acid doped with the inorganic salt obtained in the step a, forming a primary composite film on the surface of the waveguide grating, and then continuously adding activated carbon powder into the polyamide acid doped with the inorganic salt, wherein the activated carbon is deposited on the surface of the primary composite film; after dipping for a certain time, extracting the waveguide grating, and forming an active carbon and inorganic salt doped polyimide film on the surface of the waveguide grating through heating and precuring;
c. and (c) repeating the step (b) for a plurality of times to obtain a humidity-sensitive combination body formed by combining the activated carbon, the inorganic salt doped polyimide film and the waveguide grating, and then performing post-curing and aging to obtain the humidity-sensitive element of the multilayer humidity-sensitive film based on the activated carbon and the inorganic material doped polyimide.
7. The method for preparing a composite humidity sensor according to claim 6, wherein in the step a, the mixture is left to stand at 60 to 80 ℃ for 1 to 2 hours after stirring to discharge the gas.
8. The method for preparing a composite humidity sensitive element according to claim 6 wherein in step b, the dipping time is 60 to 180 s.
9. The method for preparing a composite humidity sensitive element according to claim 6, wherein in step b, the waveguide grating is pulled vertically upward at a constant speed, the pulling speed is 260-320 μm/s.
10. The method for preparing a composite humidity sensor according to claim 6, wherein in step b, the pre-curing temperature is 200 ℃ to 220 ℃, and the pre-curing time is 5 to 10 minutes; in the step c, the repetition frequency of the step b is 4-15 times, the post-curing temperature is 210-; the aging procedure is as follows: putting the humidity sensitive element into a temperature impact box, impacting back and forth between 70 ℃ and 90 ℃ and between 0 ℃ and 5 ℃, keeping each temperature for 1.5 to 2.5 hours, and aging for 60 to 80 hours.
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