CN112730271A - Liquid crystal optical fiber sensor for detecting VOC gas concentration and temperature and preparation method thereof - Google Patents
Liquid crystal optical fiber sensor for detecting VOC gas concentration and temperature and preparation method thereof Download PDFInfo
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- CN112730271A CN112730271A CN202011484581.2A CN202011484581A CN112730271A CN 112730271 A CN112730271 A CN 112730271A CN 202011484581 A CN202011484581 A CN 202011484581A CN 112730271 A CN112730271 A CN 112730271A
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 127
- 239000004973 liquid crystal related substance Substances 0.000 title claims abstract description 93
- 238000002360 preparation method Methods 0.000 title claims abstract description 8
- 239000004986 Cholesteric liquid crystals (ChLC) Substances 0.000 claims abstract description 76
- 239000000523 sample Substances 0.000 claims abstract description 23
- 238000004519 manufacturing process Methods 0.000 claims abstract description 12
- 239000007789 gas Substances 0.000 claims description 84
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 45
- 239000000463 material Substances 0.000 claims description 33
- 238000003466 welding Methods 0.000 claims description 26
- 235000011187 glycerol Nutrition 0.000 claims description 17
- 238000002347 injection Methods 0.000 claims description 15
- 239000007924 injection Substances 0.000 claims description 15
- HVYWMOMLDIMFJA-DPAQBDIFSA-N cholesterol Chemical compound C1C=C2C[C@@H](O)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H]([C@H](C)CCCC(C)C)[C@@]1(C)CC2 HVYWMOMLDIMFJA-DPAQBDIFSA-N 0.000 claims description 14
- 239000011247 coating layer Substances 0.000 claims description 13
- 239000000835 fiber Substances 0.000 claims description 13
- QNEPTKZEXBPDLF-JDTILAPWSA-N [(3s,8s,9s,10r,13r,14s,17r)-10,13-dimethyl-17-[(2r)-6-methylheptan-2-yl]-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1h-cyclopenta[a]phenanthren-3-yl] carbonochloridate Chemical compound C1C=C2C[C@@H](OC(Cl)=O)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H]([C@H](C)CCCC(C)C)[C@@]1(C)CC2 QNEPTKZEXBPDLF-JDTILAPWSA-N 0.000 claims description 10
- OTVRYZXVVMZHHW-DPAQBDIFSA-N cholesteryl chloride Chemical compound C1C=C2C[C@@H](Cl)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H]([C@H](C)CCCC(C)C)[C@@]1(C)CC2 OTVRYZXVVMZHHW-DPAQBDIFSA-N 0.000 claims description 10
- 238000002156 mixing Methods 0.000 claims description 9
- 238000005086 pumping Methods 0.000 claims description 9
- 238000005520 cutting process Methods 0.000 claims description 8
- PMMSDCURSPFTKE-UHFFFAOYSA-N C(O)(O)=O.C(CCCCCCCC=C/CCCCCCCC)(=O)O Chemical compound C(O)(O)=O.C(CCCCCCCC=C/CCCCCCCC)(=O)O PMMSDCURSPFTKE-UHFFFAOYSA-N 0.000 claims description 7
- 235000012000 cholesterol Nutrition 0.000 claims description 7
- 238000010438 heat treatment Methods 0.000 claims description 7
- UWCWUCKPEYNDNV-LBPRGKRZSA-N 2,6-dimethyl-n-[[(2s)-pyrrolidin-2-yl]methyl]aniline Chemical compound CC1=CC=CC(C)=C1NC[C@H]1NCCC1 UWCWUCKPEYNDNV-LBPRGKRZSA-N 0.000 claims description 6
- 239000004988 Nematic liquid crystal Substances 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 5
- 230000007613 environmental effect Effects 0.000 abstract description 6
- 238000005259 measurement Methods 0.000 abstract description 6
- 230000003287 optical effect Effects 0.000 abstract description 6
- 238000012423 maintenance Methods 0.000 abstract description 3
- 239000012855 volatile organic compound Substances 0.000 description 53
- 238000001514 detection method Methods 0.000 description 12
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 5
- 239000011295 pitch Substances 0.000 description 5
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- 238000013461 design Methods 0.000 description 4
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- 239000005140 Cholesterol Oleyl Carbonate Substances 0.000 description 3
- XMPIMLRYNVGZIA-TZOMHRFMSA-N cholesteryl oleyl carbonate Chemical compound C([C@@H]12)C[C@]3(C)[C@@H]([C@H](C)CCCC(C)C)CC[C@H]3[C@@H]1CC=C1[C@]2(C)CC[C@H](OC(=O)OCCCCCCCC\C=C/CCCCCCCC)C1 XMPIMLRYNVGZIA-TZOMHRFMSA-N 0.000 description 3
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- 230000009471 action Effects 0.000 description 1
- 239000000809 air pollutant Substances 0.000 description 1
- 231100001243 air pollutant Toxicity 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 150000001299 aldehydes Chemical class 0.000 description 1
- 150000001335 aliphatic alkanes Chemical class 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- -1 aromatics) Chemical class 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
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- 238000005253 cladding Methods 0.000 description 1
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- 239000003292 glue Substances 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
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- 230000006872 improvement Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002825 nitriles Chemical class 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
- G02F1/13718—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on a change of the texture state of a cholesteric liquid crystal
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Abstract
The invention belongs to the technical field of VOC gas measurement, and particularly relates to a liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gas and a preparation method thereof. The invention is a sensing device based on a reflection optical fiber probe type, can simultaneously measure the concentration of VOC gas and the ambient temperature, and has the characteristics of high efficiency, small volume and the like. When the sensing probe for detecting gas concentration and temperature is manufactured, the configured cholesteric liquid crystal and the optical fiber are organically combined to manufacture the conventional sensing device, so that the sensing device can be detached and maintained at any time, and the maintenance cost is reduced to a great extent. The invention utilizes the optical property of the liquid crystal to sense gas, does not destroy the gas molecules to be detected, and realizes the function of simultaneously detecting the concentration of the VOC gas and the environmental temperature.
Description
Technical Field
The invention belongs to the technical field of VOC gas measurement, and particularly relates to a liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gas and a preparation method thereof.
Background
In recent years, with the development of economy and the progress of science and technology, new materials are emerging, and the types of chemical materials around people are increasing. Such as exquisite furniture and practical electric appliances, are popular among the users. However, the gas volatilized from the raw materials of these articles after chemical treatment is not only a threat to the health of people, but also a pollution to the environment. Among the various types of indoor pollutants, Volatile Organic Compounds (VOC) account for the largest proportion of indoor air pollutants. VOC gas generally refers to volatile organic compounds, which are defined in an environmental sense as volatile organic gases that can cause harm. The gas is classified into hydrocarbons (alkanes, alkenes, aromatics), aldehydes, alcohols, cyanides and the like according to the chemical structure, most of the gas has strong pungent smell and certain toxicity, and therefore, the detection of the VOC gas is very important. The traditional measurement method is limited in gas concentration detection, greatly influenced by temperature factors, severe in detection environment requirement, lack of accuracy in result and inconvenient in operation.
Nowadays, with the advancement of technology, VOC gas measurement methods are also continuously improving. The principles for determining the concentration of VOC gases are mainly photo-ionization detection (PID) and Metal Oxide Semiconductor (MOS) sensing. And (3) photoionization detection, namely allowing the gas to be detected to flow into an ionization chamber of the sensor, and ionizing part of VOC molecules under the irradiation of an ultraviolet lamp to generate electrons and ions. The electrons and ions are directed to move to the two poles under the action of the electric field, and an electric signal is generated. And measuring the intensity of the electric signal to obtain the concentration of the gas to be measured. The MOS sensor mainly has surface sensitivity, the resistance of the sensing material is gradually changed along with the change of air pressure, and the VOC gas concentration is tested through the change of current.
The VOC gas measurement based on the two principles converts molecules to be measured into electric signals for concentration measurement, and makes up for the defects of the traditional detection method. However, the temperature has a great influence on the measurement of the VOC gas, the gas-sensitive characteristic of the MOS sensor is controlled and influenced by the heating temperature of the device, the requirement on the detection environment is high, the gas with high humidity cannot be directly detected, a micro probe cannot be realized, and the temperature of the environment cannot be simultaneously detected. And PID needs often to change the ultraviolet lamp, and is with higher costs.
Disclosure of Invention
The invention aims to provide a liquid crystal optical fiber sensor for detecting the concentration and the temperature of VOC gas.
The purpose of the invention is realized by the following technical scheme: the device comprises a light source, a spectrometer and a multimode fiber splitter; the light source and the spectrometer are respectively connected with two main path optical fibers of the multimode optical fiber splitter; the split optical fiber reflecting end of the multimode optical fiber branching unit is welded with the capillary to form a sensor probe; cholesteric liquid crystals prepared from liquid crystal materials with different concentrations are injected into the capillary and the outside of the port; the interior of the thin tube is filled with glycerin, so that VOC gas cannot enter the interior of the capillary tube to be in contact with cholesteric liquid crystal inside the capillary tube.
The present invention may further comprise:
the capillary tube is welded with the positive core of the reflecting end of the split optical fiber of the multimode optical fiber branching unit; cholesteric liquid crystal prepared from liquid crystal materials with different concentrations is injected into the interior of the welding end of the capillary and the exterior of the other end of the capillary, and the cholesteric liquid crystal outside the capillary forms a film to cover the end part of the capillary.
The capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber splitter in a staggered manner; the inside and the outside of the capillary welding end are injected with cholesteric liquid crystal prepared by liquid crystal materials with different concentrations.
The capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber splitter in a staggered manner; cholesteric liquid crystals prepared from liquid crystal materials with different concentrations are injected into the interior of the capillary welding end, the exterior of the capillary welding end and the exterior of the other end of the capillary, and the cholesteric liquid crystals on the exterior of the other end of the capillary form a film to cover the end part of the capillary.
The cholesteric liquid crystal outside the capillary tube is prepared from cholesterol chloride, cholesterol oleic acid carbonate and cholesteryl chloroformate in a mass ratio of 13:65: 22; the cholesteric liquid crystal in the capillary is formed by mixing and proportioning an S811 chiral agent and temperature-sensitive nematic liquid crystal, and the reflection bands of the cholesteric liquid crystal in the capillary and the cholesteric liquid crystal outside the capillary are different.
The cholesteric liquid crystal outside the welding end of the capillary tube is prepared from cholesterol chloride, cholesterol oleic acid carbonate and chloroformic acid cholesterol ester according to the mass ratio of 13:65:22, and the cholesteric liquid crystal outside the other end of the capillary tube is prepared from cholesterol chloride, cholesterol oleic acid carbonate and chloroformic acid cholesterol ester according to the mass ratio of 20.5:59.5: 20; the cholesteric liquid crystal in the capillary is formed by mixing and proportioning an S811 chiral agent and temperature-sensitive nematic liquid crystal, and the reflection bands of the cholesteric liquid crystal in the capillary and the two cholesteric liquid crystals outside the capillary are different.
The invention also aims to provide a preparation method of the liquid crystal optical fiber sensor for detecting the concentration and the temperature of the VOC gas.
The purpose of the invention is realized by the following technical scheme: the method comprises the following steps:
step 1: selecting a multimode fiber splitter; connecting a light source and a spectrometer with two main path optical fibers of a multimode optical fiber splitter respectively; cutting the split optical fiber reflecting end of the multimode optical fiber branching unit by using a cutter to enable the end surface of the split optical fiber reflecting end to be flat and clean, and removing the coating layer;
step 2: selecting a capillary tube; heating the outer coating layer of the capillary, removing the outer coating layer of the capillary, cutting the capillary by a cutter, and welding the cut capillary with the reflection end of the split optical fiber of the multimode fiber splitter;
and step 3: mixing the liquid crystal materials according to different proportions to form cholesteric liquid crystals with different concentrations;
and 4, step 4: heating the capillary tube, and slowly stretching the capillary tube at two ends after the capillary tube is softened to form a conical capillary microtube; bonding the unstretched end of the capillary microtube with a syringe needle to form a self-made injection pump;
and 5: turning on a light source and a spectrometer, after debugging is finished, using a self-made injection pump to extract cholesteric liquid crystal, and injecting the cholesteric liquid crystal into a capillary under a microscope without generating bubbles;
step 6: a self-made injection pump is used for pumping the glycerol, the capillary filled with the cholesteric liquid crystal is filled with the glycerol under a microscope, and no air bubble is generated;
and 7: and pumping cholesteric liquid crystals prepared from liquid crystal materials with different concentrations by using a self-made injection pump, and injecting the cholesteric liquid crystals into the outside of the capillary tube to finish the preparation of the liquid crystal optical fiber sensor for detecting the concentration and the temperature of the VOC gas.
The present invention may further comprise:
in the step 2, the capillary tube is welded with the split optical fiber reflecting end positive core of the multimode optical fiber branching unit; and 7, injecting cholesteric liquid crystal prepared from liquid crystal materials with different concentrations into the outside of the other end of the capillary tube to coat the end of the capillary tube to form the liquid crystal film.
In the step 2, the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber branching unit in a staggered mode; and in the step 7, cholesteric liquid crystal prepared from liquid crystal materials with different concentrations is injected outside the capillary welding end.
In the step 2, the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber branching unit in a staggered mode; in the step 7, cholesteric liquid crystal prepared by liquid crystal materials with different concentrations is injected outside the capillary welding end; and injecting cholesteric liquid crystal prepared from liquid crystal materials with different concentrations into the outside of the other end of the capillary tube to coat the end of the capillary tube to form the liquid crystal film.
The invention has the beneficial effects that:
the invention is a sensing device based on a reflection optical fiber probe type, can simultaneously measure the concentration of VOC gas and the ambient temperature, and has the characteristics of high efficiency, small volume and the like. When the sensing probe for detecting gas concentration and temperature is manufactured, the configured cholesteric liquid crystal and the optical fiber are organically combined to manufacture the conventional sensing device, so that the sensing device can be detached and maintained at any time, and the maintenance cost is reduced to a great extent. The invention utilizes the optical property of the liquid crystal to sense gas, does not destroy the gas molecules to be detected, and realizes the function of simultaneously detecting the concentration of the VOC gas and the environmental temperature.
Drawings
Fig. 1 is a schematic diagram of a liquid crystal optical fiber sensor for detecting VOC gas concentration and temperature, in which a capillary tube is welded to a positive core of an optical fiber.
FIG. 2 is a schematic diagram of a liquid crystal fiber sensor for detecting VOC gas concentration and temperature by welding a capillary tube and an optical fiber core dislocation.
FIG. 3 is a schematic diagram of a liquid crystal fiber sensor for detecting the concentration and temperature of VOC gases, which can identify the concentration ratio of two VOC gases.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The invention relates to a sensing device capable of simultaneously detecting the concentration of organic Volatile (VOC) gas and the ambient temperature, and provides a sensing device which can realize simultaneous detection of the concentration of the VOC gas and the ambient temperature by attaching liquid crystal to the end face of an optical fiber and a manufacturing method thereof.
The invention provides a design and a manufacturing method of a multifunctional sensor which uses cholesteric liquid crystals with different concentrations to be injected into a capillary welded with an optical fiber so as to realize the simultaneous detection of the concentration of organic Volatile (VOC) gas and the ambient temperature. The liquid crystal optical fiber sensor is characterized in that a sensing probe is designed into a reflection type structure, the characteristic that the pitch of cholesteric liquid crystal molecules can be changed by VOC gas and temperature is utilized, the wavelength of reflected light in the optical fiber is changed, and therefore simultaneous sensing of the gas and the temperature is achieved. On the basis, the welding position of the optical fiber port and the capillary can be changed to manufacture sensing probes with different shapes, and further the simultaneous sensing of the identification sensing and the temperature of the mixed gas can be realized. The invention solves the problem that the traditional VOC gas sensor only measures single physical quantity, simultaneously considers temperature compensation, eliminates the influence of environmental temperature change on gas sensing, and further provides a design capable of realizing the concentration ratio of two mixed VOC gases. The design has the advantages of simple manufacturing process and hundred-micron-sized sensing probe.
Example 1:
the liquid crystal optical fiber sensor for detecting the concentration and the temperature of the VOC gas as shown in the figure 1 comprises a light source, a spectrometer and a multimode optical fiber branching unit; the light source and the spectrometer are respectively connected with two main path optical fibers of the multimode optical fiber splitter; the split optical fiber reflecting end of the multimode optical fiber branching unit is welded with the capillary to form a sensor probe; the capillary tube is welded with the positive core of the reflecting end of the split optical fiber of the multimode optical fiber branching unit; cholesteric liquid crystals prepared from liquid crystal materials with different concentrations are injected into the interior of the welding end of the capillary and the exterior of the other end of the capillary, and the cholesteric liquid crystals outside the capillary form a film to cover the end part of the capillary; the interior of the thin tube is filled with glycerin, so that VOC gas cannot enter the interior of the capillary tube to be in contact with cholesteric liquid crystal inside the capillary tube.
The cholesteric liquid crystal prepared from cholesterol oleyl carbonate, cholesterol chloroformate and cholesterol chloride (not limited to the three liquid crystal materials) with different mixture concentrations (not limited to the mixture concentrations) is injected into a capillary welded on the end face of the optical fiber, the thickness of the cholesteric liquid crystal is about 20-50 microns, then the capillary is sealed by glycerol, and a liquid crystal film with other concentrations is adhered to a sealed port.
Example 2:
as shown in fig. 2, the liquid crystal optical fiber sensor for detecting the concentration and temperature of the VOC gas includes a light source, a spectrometer, and a multimode optical fiber splitter; the light source and the spectrometer are respectively connected with two main path optical fibers of the multimode optical fiber splitter; the split optical fiber reflecting end of the multimode optical fiber branching unit is welded with the capillary to form a sensor probe; the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber splitter in a staggered manner; cholesteric liquid crystal prepared from liquid crystal materials with different concentrations is injected into the interior and the exterior of the capillary welding end; the interior of the thin tube is filled with glycerin, so that VOC gas cannot enter the interior of the capillary tube to be in contact with cholesteric liquid crystal inside the capillary tube.
The end face staggered core of the optical fiber is welded with a capillary, cholesteric phase liquid crystal prepared from cholesterol oleyl carbonate, cholesterol chloroformate and cholesterol chloride (not limited to the three liquid crystal materials) in different proportioning concentrations (not limited to the proportioning concentrations) is injected into the capillary, the thickness of the liquid crystal is about 20-50 microns, and then the capillary is sealed by glycerol. And simultaneously coating liquid crystal films with other concentrations on the end faces of the optical fibers with staggered cores.
Example 3:
as shown in fig. 3, the liquid crystal optical fiber sensor for detecting the concentration and temperature of the VOC gas includes a light source, a spectrometer, and a multimode optical fiber splitter; the light source and the spectrometer are respectively connected with two main path optical fibers of the multimode optical fiber splitter; the split optical fiber reflecting end of the multimode optical fiber branching unit is welded with the capillary to form a sensor probe; the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber splitter in a staggered manner; cholesteric liquid crystals prepared from liquid crystal materials with different concentrations are injected into the interior of the capillary welding end, the exterior of the capillary welding end and the exterior of the other end of the capillary, and the cholesteric liquid crystals on the exterior of the other end of the capillary form a film to cover the end part of the capillary; the interior of the thin tube is filled with glycerin, so that VOC gas cannot enter the interior of the capillary tube to be in contact with cholesteric liquid crystal inside the capillary tube. The liquid crystal optical fiber sensor for detecting the concentration of VOC gas versus temperature as shown in fig. 3 can recognize the ratio of the two VOC gas concentrations.
Example 4:
according to the invention, liquid crystal is attached to different positions away from the end face of the optical fiber, the liquid crystal probe is placed in the VOC gas, the reflection band of the cholesteric liquid crystal to light depends on the length of the molecular screw pitch to a great extent, and the screw pitch can be changed by the VOC gas molecules and the ambient temperature, so that the reflection spectrum transmitted by the optical fiber is changed. The gas concentration value and the temperature are respectively calculated by utilizing the moving size of the reflection spectrum, and finally the function of simultaneously detecting the gas concentration and the ambient temperature is achieved.
The VOC gas concentration and temperature detection optical fiber sensor based on the liquid crystal is prepared by adopting the method as follows:
firstly, selecting a multi-mode box type optical splitter, and cutting an optical fiber reflecting end of the splitter by using an optical fiber cutter to enable the end surface of the optical fiber reflecting end to be flat and clean;
secondly, heating the outer coating layer of the capillary tube by using alcohol lamp flame for a short time, wiping the capillary tube by using a piece of lens wiping paper stained with alcohol, removing the outer coating layer of the capillary tube, cutting the capillary tube by using a cutter, and welding the cut capillary tube with the optical fiber;
selecting liquid crystal materials such as cholesterol oleyl carbonate, cholesterol chloroformate, cholesterol chloride and the like, and mixing the liquid crystal materials according to different proportions to form cholesteric liquid crystals with different concentrations; meanwhile, the cholesteric liquid crystal which is obviously different from the reflection bands of the first two materials is prepared by mixing the S811 chiral agent and the temperature-sensitive nematic liquid crystal.
And fourthly, pumping the cholesteric liquid crystal by using a self-made injection pump, and injecting the cholesteric liquid crystal into a capillary tube welded with the end face of the optical fiber.
And fifthly, pumping the glycerol by using a self-made injection pump, filling the glycerol into the port of the capillary tube, coating a liquid crystal film at the port, and avoiding bubbles during injection to form the liquid crystal optical fiber sensing probe for measuring the concentration and the temperature of the VOC gas.
The main difference between the VOC gas concentration and temperature detection sensing probe and the existing gas concentration detector is as follows: the invention is a sensing device based on a reflection optical fiber probe type, can simultaneously measure the concentration of VOC gas and the ambient temperature, and has the characteristics of high efficiency, small volume and the like. When the sensing probe for detecting gas concentration and temperature is manufactured, the configured cholesteric liquid crystal and the optical fiber are organically combined to manufacture the conventional sensing device, so that the sensing device can be detached and maintained at any time, and the maintenance cost is reduced to a great extent. The optical property of the liquid crystal is utilized to carry out gas sensing, the molecules of the gas to be detected are not damaged, and the function of simultaneously detecting the concentration of the VOC gas and the environmental temperature is realized.
Example 5:
the invention provides a sensing device which uses liquid crystal to coat an optical fiber and can simultaneously measure the concentration of VOC gas and the ambient temperature. The probe part of the gas sensing device is mainly formed by welding an optical fiber and a capillary tube. Cholesteric liquid crystals with different concentrations are injected into the capillary and the outside of the port, and are separated by glycerin, so that VOC gas cannot enter the capillary and contact with the liquid crystals. When light reaches the welding position of the optical fiber and the capillary, the fiber core is simultaneously contacted with the capillary wall and the liquid crystal, and the transmitted light is divided into two paths: one reflecting after reaching the end face along the capillary wall and the other propagating the reflection in the liquid crystal inside it. When the VOC gas is absorbed by the liquid crystal or the external temperature changes, the molecular pitch of the liquid crystal changes, and the wavelength of the reflected light changes correspondingly. In the spectrum, because two liquid crystals with different pitches can generate two independent reflection peaks, the VOC gas can enable the reflection peaks generated at the end face of the capillary tube to drift, but the reflection peaks generated by the liquid crystals in the capillary tube cannot be influenced, and after spectral analysis, two parameters of gas concentration and ambient temperature can be obtained.
The invention is designed based on the optical property of cholesteric liquid crystal, avoids the problem of environmental temperature influence in the traditional detection, simultaneously considers the characteristics of simple manufacture, a miniature sensing probe, multi-parameter simultaneous measurement (high efficiency) and the like, can provide a more accurate and rapid novel VOC gas concentration and temperature detection sensing device, and simultaneously further designs a structure for distinguishing the concentration ratio of two mixed VOC gases.
The invention provides a sensor for efficiently and sensitively detecting the concentration of VOC gas and the ambient temperature, provides a manufacturing method for attaching cholesteric liquid crystal to the end face of an optical fiber, and has the characteristics of high sensitivity and accurate detection.
Firstly, selecting liquid crystal materials such as cholesterol chloride, cholesterol oleic acid carbonate and cholesterol chloroformate from Aladdin reagent company Limited, mixing the liquid crystal materials according to different proportions (the mass ratio is respectively 13:65:22 (liquid crystal I)) and 20.5:59.5:20 (liquid crystal II)), putting the mixture into an electric heating air blowing drying oven for drying, adjusting the temperature to 120 ℃, keeping the temperature for 10 minutes, turning off the power supply of the electric heating air blowing drying oven, taking out, and slowly recovering the temperature to the room temperature. When the liquid crystal returns to the room temperature, the liquid crystal is subjected to ultrasonic treatment by an ultrasonic instrument to be uniformly mixed. Meanwhile, the S811 chiral agent is mixed with the temperature-sensitive nematic liquid crystal (such as CB15, the selection of the specific liquid crystal depends on the temperature sensing temperature range) to prepare the cholesteric liquid crystal (liquid crystal III) which is obviously different from the reflection bands of the first two materials. In FIG. 1, (i), (j) and (g) are liquid crystals I, II and III with different ratios, respectively, (h) is glycerol, (d) is an enlarged schematic diagram of a single optical fiber sensing probe, and (f) is a capillary tube welded with an optical fiber.
And secondly, selecting a 2X 1 multimode box type optical splitter (c), removing the optical fiber coating layer at the splitting end, and cutting the optical fiber coating layer by using an optical fiber cutter. As shown in the sensing probe fiber (e) in FIG. 1, the fiber structure of the sensing probe fiber is 125 microns in diameter of the cladding and 50-100 microns in diameter of the fiber core.
And thirdly, selecting a quartz capillary tube produced by Zhengzhou Yingnuo Gaokou company limited, wherein the diameter of an air core of the quartz capillary tube is about 60 micrometers, and the outer diameter of the air core is about 150 micrometers. After the outer coating layer of the capillary tube is heated by the flame of the alcohol lamp for a short time, the capillary tube is wiped by using a piece of lens wiping paper stained with alcohol, and the outer coating layer of the capillary tube is removed. And cutting the capillary tube with the outer coating layer removed by using an optical fiber cutter, and welding the optical fiber and the capillary tube, wherein the length of the welded capillary tube is about 60 micrometers.
Fourthly, heating the capillary tube by using the flame of an alcohol burner, slowly stretching the capillary tube at two ends after the capillary tube is softened to form a conical capillary microtube, wherein the outer diameter of the capillary microtube is about 15 microns; and (3) bonding the unstretched end of the capillary microtube and the needle head of the medical syringe by using AB glue to form the self-made injection pump.
And fifthly, turning on the light source (a) and the spectrometer (b), after debugging is finished, pumping the temperature-sensitive liquid crystal III (g) by using a self-made injection pump, and injecting the liquid crystal into a capillary tube welded with the optical fiber under a microscope without generating bubbles.
Pumping glycerol (h) by a self-made injection pump, injecting the glycerol into the capillary filled with the liquid crystal under a microscope, filling the capillary, and paying attention to no bubble generation.
Pumping the liquid crystal I (i) sensitive to the VOC gas by using a self-made injection pump, injecting the liquid crystal into the outer end of a capillary tube welded with the optical fiber under a microscope, and coating the optical fiber port to form a liquid crystal film.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A detect liquid crystal optical fiber sensor of VOC gas concentration and temperature which characterized in that: the device comprises a light source, a spectrometer and a multimode fiber splitter; the light source and the spectrometer are respectively connected with two main path optical fibers of the multimode optical fiber splitter; the split optical fiber reflecting end of the multimode optical fiber branching unit is welded with the capillary to form a sensor probe; cholesteric liquid crystals prepared from liquid crystal materials with different concentrations are injected into the capillary and the outside of the port; the interior of the thin tube is filled with glycerin, so that VOC gas cannot enter the interior of the capillary tube to be in contact with cholesteric liquid crystal inside the capillary tube.
2. The liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gases as claimed in claim 1, wherein: the capillary tube is welded with the positive core of the reflecting end of the split optical fiber of the multimode optical fiber branching unit; cholesteric liquid crystal prepared from liquid crystal materials with different concentrations is injected into the interior of the welding end of the capillary and the exterior of the other end of the capillary, and the cholesteric liquid crystal outside the capillary forms a film to cover the end part of the capillary.
3. The liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gases as claimed in claim 1, wherein: the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber splitter in a staggered manner; the inside and the outside of the capillary welding end are injected with cholesteric liquid crystal prepared by liquid crystal materials with different concentrations.
4. The liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gases as claimed in claim 1, wherein: the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber splitter in a staggered manner; cholesteric liquid crystals prepared from liquid crystal materials with different concentrations are injected into the interior of the capillary welding end, the exterior of the capillary welding end and the exterior of the other end of the capillary, and the cholesteric liquid crystals on the exterior of the other end of the capillary form a film to cover the end part of the capillary.
5. The liquid crystal optical fiber sensor for detecting VOC gas concentration and temperature according to claim 1, 2 or 3, wherein: the cholesteric liquid crystal outside the capillary tube is prepared from cholesterol chloride, cholesterol oleic acid carbonate and cholesteryl chloroformate in a mass ratio of 13:65: 22; the cholesteric liquid crystal in the capillary is formed by mixing and proportioning an S811 chiral agent and temperature-sensitive nematic liquid crystal, and the reflection bands of the cholesteric liquid crystal in the capillary and the cholesteric liquid crystal outside the capillary are different.
6. The liquid crystal optical fiber sensor for detecting VOC gas concentration and temperature according to claim 4, wherein: the cholesteric liquid crystal outside the welding end of the capillary tube is prepared from cholesterol chloride, cholesterol oleic acid carbonate and chloroformic acid cholesterol ester according to the mass ratio of 13:65:22, and the cholesteric liquid crystal outside the other end of the capillary tube is prepared from cholesterol chloride, cholesterol oleic acid carbonate and chloroformic acid cholesterol ester according to the mass ratio of 20.5:59.5: 20; the cholesteric liquid crystal in the capillary is formed by mixing and proportioning an S811 chiral agent and temperature-sensitive nematic liquid crystal, and the reflection bands of the cholesteric liquid crystal in the capillary and the two cholesteric liquid crystals outside the capillary are different.
7. A preparation method of a liquid crystal optical fiber sensor for detecting VOC gas concentration and temperature is characterized by comprising the following steps:
step 1: selecting a multimode fiber splitter; connecting a light source and a spectrometer with two main path optical fibers of a multimode optical fiber splitter respectively; cutting the split optical fiber reflecting end of the multimode optical fiber branching unit by using a cutter to enable the end surface of the split optical fiber reflecting end to be flat and clean, and removing the coating layer;
step 2: selecting a capillary tube; heating the outer coating layer of the capillary, removing the outer coating layer of the capillary, cutting the capillary by a cutter, and welding the cut capillary with the reflection end of the split optical fiber of the multimode fiber splitter;
and step 3: mixing the liquid crystal materials according to different proportions to form cholesteric liquid crystals with different concentrations;
and 4, step 4: heating the capillary tube, and slowly stretching the capillary tube at two ends after the capillary tube is softened to form a conical capillary microtube; bonding the unstretched end of the capillary microtube with a syringe needle to form a self-made injection pump;
and 5: turning on a light source and a spectrometer, after debugging is finished, using a self-made injection pump to extract cholesteric liquid crystal, and injecting the cholesteric liquid crystal into a capillary under a microscope without generating bubbles;
step 6: a self-made injection pump is used for pumping the glycerol, the capillary filled with the cholesteric liquid crystal is filled with the glycerol under a microscope, and no air bubble is generated;
and 7: and pumping cholesteric liquid crystals prepared from liquid crystal materials with different concentrations by using a self-made injection pump, and injecting the cholesteric liquid crystals into the outside of the capillary tube to finish the preparation of the liquid crystal optical fiber sensor for detecting the concentration and the temperature of the VOC gas.
8. The method for manufacturing a liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gas as claimed in claim 7, wherein: in the step 2, the capillary tube is welded with the split optical fiber reflecting end positive core of the multimode optical fiber branching unit; and 7, injecting cholesteric liquid crystal prepared from liquid crystal materials with different concentrations into the outside of the other end of the capillary tube to coat the end of the capillary tube to form the liquid crystal film.
9. The method for manufacturing a liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gas as claimed in claim 7, wherein: in the step 2, the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber branching unit in a staggered mode; and in the step 7, cholesteric liquid crystal prepared from liquid crystal materials with different concentrations is injected outside the capillary welding end.
10. The method for manufacturing a liquid crystal optical fiber sensor for detecting the concentration and temperature of VOC gas as claimed in claim 7, wherein: in the step 2, the capillary tube is welded with the split optical fiber reflecting end of the multimode optical fiber branching unit in a staggered mode; in the step 7, cholesteric liquid crystal prepared by liquid crystal materials with different concentrations is injected outside the capillary welding end; and injecting cholesteric liquid crystal prepared from liquid crystal materials with different concentrations into the outside of the other end of the capillary tube to coat the end of the capillary tube to form the liquid crystal film.
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