JP5885015B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor.

  Traditionally, odor has been one of the most unseen sensations in human sense and has not been quantified. However, there are few levels of odor molecules (odor substances) in food production management and factory odor. Detection is required.

  What is important as a gas sensor for detecting odorous substances is a sufficiently high sensitivity. Although human olfaction varies depending on the substance, odorous substances of several tens of ppm to 0.01 ppb can be detected. Therefore, the performance required for the gas sensor is that it is possible to detect an odorous substance at a ppm to ppb level.

  If a large-scale analyzer such as gas chromatography is used, high-accuracy measurement at the ppb level is possible. However, the introduction of the device and the running cost are high, and an engineer with specialized knowledge is required. There is a strong demand for low-cost gas sensors.

  Therefore, in order to detect an odor substance, a technique (QCM device) for forming a polymer film that adheres a specific odor substance on a crystal resonator has been studied (Patent Documents 1 to 6).

JP 2009-222619 A JP 2008-268170 A JP 2006-53059 A JP 2005-189146 A JP 2000-304673 A JP-A-9-189663

  However, in patent document 1, the sensitivity with respect to toluene (petroleum component) of the gas sensor using each film | membrane of polybutadiene, polyacrylonitrile-butadiene, polyisoprene, and polystyrene is about several dozen ppm. Moreover, in patent document 2, it can be estimated that the detection limit with respect to toluene of the gas sensor using each film | membrane of a polybutadiene, a polystyrene, a polyacrylonitrile, and a polycaprolactan copolymer is about 100 ppm. In patent document 3, the detection sensitivity with respect to alcohol of the gas sensor using the film | membrane which hold | maintained the ionic liquid to the phenylalanine plasma polymerization film | membrane is several dozen ppm. Moreover, in patent document 4, the detection sensitivity with respect to a volatile sulfide of the gas sensor using each film | membrane of D-phenylalanine, polyethylene, and polychlorotrifluoroethylene is sub ppm. Moreover, in patent document 5, the sensitivity with respect to the optical isomer of the gas sensor using an amino acid thin film is about 10 ppm. In Patent Document 6, a gas sensor using copper phthalocyanine has a sensitivity of about several tens of ppm.

  As described above, the sensitivity of the gas sensor is about several ppm, which cannot be said to be high. For example, detection of a ppb level odorous substance is desirable for a sensitive film that reaches the human sensitivity threshold.

  Accordingly, an object of the present invention is to provide a gas sensor that has higher detection sensitivity with respect to several ppm level of odorous substances than before and can detect odorous substances of several tens of ppb levels.

  The present inventors have intensively studied to solve the above problems. As a result, the present inventors have found that the above problems can be solved by a gas sensor including a specific polymer in at least a part of a crystal resonator, and completed the present invention.

That is, the present invention is as follows.
[1]
A gas sensor comprising a polymer having a fluorene structure in at least a part of a crystal resonator.
[2]
The gas sensor according to [1], wherein the polymer includes a fluorene structural unit represented by the following chemical formula (1) and has a weight average molecular weight of 100,000 to 1,000,000.
(In the above formula, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms, R ³ , R ^{3 ′} , and R ^{3 ″} , and R ⁴ , R ^{4 ′} , and R ^{4. ''} Independently of one another, a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an allyl group, an allyloxy group, an allylthio group, an allylalkyl group, an allylalkoxy group, an allylalkylthio group, Allyl alkenyl group, allyl alkynyl group, monovalent heterocyclic group, heterocyclic thio group, optionally substituted amino group, optionally substituted silyl group, acyl group, imine residue, amide group, acid imide group, substituted Which may be a carboxyl group, a cyano group, or a nitro group.)
[3]
The gas sensor according to [1] or [2], wherein the polymer includes a copolymer of a monomer having a fluorene structure and one or more other monomers.
[4]
The gas sensor according to [3], wherein the copolymer is constituted by 50% or more of monomer units of the monomer having the fluorene structure.
[5]
The gas sensor according to [3] or [4], wherein the other monomer is a monomer that forms π conjugation with the monomer having the fluorene structure.

It is the schematic showing the cross section of the odor detection element which concerns on one Embodiment of this invention typically. It is the schematic showing an example of the composition of the gas sensor concerning one embodiment of the present invention. It is the schematic showing other examples of composition of a gas sensor concerning one embodiment of the present invention. It is the schematic showing the manufacturing process of the gas sensor implemented in the Example.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, A various deformation | transformation can be implemented within the range of the summary.

[Odor detection element]
One embodiment of the present invention relates to an odor detection element. FIG. 1 is a schematic view schematically showing a cross section of an odor detecting element. The odor detecting element according to the present embodiment is a part of a gas sensor to be described later, and includes a crystal resonator 11, an electrode 13 formed on the front and back surfaces of the crystal resonator 11, and a crystal so as to cover the electrode 13. The polymer film 12 formed on the front surface and the back surface of the vibrator 11 and the lead wire 14 for connecting the electrode 13 and an external circuit, that is, an oscillation circuit (DSC) are provided.

The crystal resonator 11 operates in a so-called thickness-shear vibration mode in which a voltage is applied to the electrode 13 and the front surface and the back surface slide and vibrate alternately. The resonance frequency f ₀ (MHz) during operation is inversely proportional to the quartz plate thickness t (μm) at the site where the electrode 13 is formed, and is generally expressed by the following formula (1).

  The relationship between the adsorbed substance amount ΔM and the frequency change amount Δf in the crystal unit 11 is expressed by the following Sauerbrey equation (2).

In the above formula (2), f ₀ is the resonance frequency of the vibrator, ρ is the density of the crystal, μ is the shear elastic constant of the crystal, and A is an effective vibration area substantially equal to the electrode area. From equation (2), it is understood that the sensitivity, that is, the frequency change amount Δf per adsorbed substance amount ΔM can be increased by increasing the resonance frequency f _{0 of the} vibrator.

  As the material of the electrode 13, a conventionally known material can be used, for example, gold. As the material of the lead wire 14, a conventionally known material can be used.

The polymer film 12 is an adsorption film having a characteristic of selectively adsorbing a specific substance. The polymer film 12 is exposed in the surrounding gas to be detected for odorous substances. The polymer film 12 is formed on at least a part (one surface) of the crystal unit 11. Among these, the polymer film 12 is preferably formed on both surfaces, that is, the front surface and the back surface of the quartz crystal resonator 11, because a substance to be adsorbed can be more effectively adsorbed.
The thickness of the polymer film 12 is not particularly limited, but is preferably several nm to several μm, and preferably about several μm. The polymer film 12 is preferably a solid at normal temperature and pressure because it is excellent in moldability and shape stability. Hereinafter, the constituent materials of the polymer film 12 will be described in detail.

  The constituent material of the polymer film 12 includes at least a polymer having one or more fluorene structures (hereinafter also simply referred to as “fluorene structure-containing polymer”). The fluorene structure-containing polymer includes at least one of a homopolymer and a copolymer as described later.

  Examples of the fluorene structure include, but are not limited to, those represented by the following chemical formula (1).

  The fluorene structure-containing polymer may be composed of the fluorene structural unit represented by the chemical formula (1), and is composed of the fluorene structural unit and other structural units (hereinafter also referred to as “other monomers”). Also good. Further, the fluorene structural unit in one molecule of the polymer may be composed of one kind or two or more kinds.

In the above chemical formula (1), R ¹ and R ² each independently have a substituent. Examples of the substituent include, but are not limited to, hydrogen atom, halogen atom, alkyl group, alkenyl group, alkynyl group, alkoxy group, alkylthio group, allyl group, allyloxy group, allylthio group, allylalkyl group, allylalkoxy group, Allylalkylthio group, allylalkenyl group, allylacynyl group, monovalent heterocyclic group, heterocyclic thio group, amino group which may be substituted, silyl group which may be substituted, acyl group, imine residue, amide group, acid Examples thereof include an imide group, an optionally substituted carboxyl group, a cyano group, and a nitro group. Among these, in order to further improve the solubility in a solvent, an alkyl group is preferable, and an alkyl group having 1 to 10 carbon atoms is more preferable.

In the above chemical formula (1), having R ^3, R ^{3 ',} and R ^3' ', and R ^4, R ^4', and R ^{4 ''} independently of one another are a substituent. Examples of the substituent include, but are not limited to, hydrogen atom, halogen atom, alkyl group, alkenyl group, alkynyl group, alkoxy group, alkylthio group, allyl group, allyloxy group, allylthio group, allylalkyl group, allylalkoxy group, Allylalkylthio group, allylalkenyl group, allylacynyl group, monovalent heterocyclic group, heterocyclic thio group, amino group which may be substituted, silyl group which may be substituted, acyl group, imine residue, amide group, acid Examples thereof include an imide group, an optionally substituted carboxyl group, a cyano group, and a nitro group. Among these, since it is excellent in the solubility with respect to an organic solvent, an alkyl group is preferable and an alkyl group having 6 or more carbon atoms is more preferable.

  Examples of the above-mentioned “optionally substituted” group include, but are not limited to, a hydroxyl group and a halo group.

Further, in the above chemical formula (1), since the film forming property is excellent, the weight average molecular weight is more preferably 100,000 to 1,000,000.
The weight average molecular weight in the present specification is intended to mean a value measured by gel permeation black Conclusions chromatography (GPC).

  The fluorene structure-containing polymer is at least one of a homopolymer and a copolymer. Examples of the homopolymer include a monomer having a fluorene structure (hereinafter also referred to as “fluorene monomer”), and specifically, a monomer composed of a single fluorene structural unit represented by the above chemical formula (1). .

  Examples of the copolymer include those composed of two or more fluorene monomers and those composed of one or more fluorene monomers and other monomers not having a fluorene structure. Specific examples of the former include those composed of two or more fluorene structural units represented by the above chemical formula (1). Specific examples of the latter include those composed of one or more fluorene structural units represented by the above chemical formula (1) and one or more other monomers.

  Although it does not specifically limit as said other monomer, It is preferable that it is a monomer which forms (pi) conjugation with a fluorene monomer. Monomers that form π conjugation with fluorene monomers include, but are not limited to, for example, benzothiazole, carbazole, thiophene, bithiophene, cyclic thiophene, vinylenephenylene, pyrrole, acetylene, triphenylamine, and benzothiophene. It is done.

  In the copolymer, the monomer unit of the fluorene monomer is preferably 50% or more in terms of the number of units. As demonstrated in the examples below, the present inventors have found that when the monomer unit of the fluorene monomer is 100% and 50%, an excellent effect is obtained, whereas when the monomer unit is 0%, the effect is inferior. Revealed.

In addition to the fluorene structure-containing polymer, the constituent material of the polymer film 12 may include one or more polymers that do not have a fluorene structure, low-molecular compounds, inorganic compounds, and the like. Examples of the polymer having no fluorene structure include, but are not limited to, polyethylene, polypropylene, polyethylene oxide, polyvinyl alcohol, polyvinyl acetate, polyvinyl carbazole, polyvinyl chloride, polyvinyl phenol, polyvinyl pyridine, polyvinyl polyvinylidene fluoride, polymethacryl Acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polylauryl methacrylate, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyisobutyl acrylate, polydodecyl acrylate, polyethylene terephthalate, 6-nylon, 6,6- Nylon, polybutylene terephthalate, polyacetylene, polyethylene dioxythiophene, polyvinyl Sulfonic acid, poly-3-hexylthiophene, poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine], poly [2-methoxy-5- (2-ethylhexyloxy) -1,4 -Phenylene vinylene], poly (benzobisimidazobenzophenanthroline, polydimethylsiloxane, polydimethylsilane, cellulose, and methylcellulose. Examples of the low molecular weight compound include, but are not limited to, tris (2-phenylpyridinate ) Iridium (III), tris (acetylacetonato) iridium (III), bathocuproine, 4,4′-bis [9-dicarbazoyl] 2-2′-biphenyl, 2,6-tert-butyl-4-methylphenol, 2,4-dihydroxybenzotriazole, (2,2′-hydride Xyl-5'-methylphenyl) benzotriazole, bis (2,2,6,6-tetramethyl-4-piperazine) sebacate, tetrabromocyclooctane, and 2,4,6-tetrabromophenol. Examples of inorganic compounds include, but are not limited to, SiO ₂ , TiO ₂ , SnO, CuO, Cu ₂ O, Al ₂ O ₃ , Fe ₂ O ₃ , FeO, MgO, CaO, CeO ₂ , MnO ₃ , NiO, and InO. Metal oxides such as ₂ O ₃ , V ₂ O ₅ , P ₂ O ₅ , ZnO, and Li ₂ O, and NaCl, KCl, LiCl, MgCl ₂ , CaCl ₂ , LiF, MgF ₂ , LiI, LiBr, MgI ₂ , MgBr ₂ , CaI ₂ , and CaBr ₂ .

[Gas sensor]
(Configuration of gas sensor)
One embodiment of the invention relates to a gas sensor. FIG. 2 is a schematic diagram illustrating an example of the configuration of the gas sensor. The gas sensor according to the present embodiment includes a computer 31, an odor detection element array 32 (arrangement of the above odor detection elements in an array), a gas inlet 33, a filter 34, a chamber 35, and a pump 36. And a gas exhaust port 37.

  The computer 31 reads the output frequency of the oscillation circuit (DSC) and the frequency measurement circuit (CNT) and analyzes the amount of change in frequency. The computer 31 stores information necessary for specifying odors, and is configured to transmit the information in response to a request from a data processing algorithm (not shown). Here, the specific required information of odor includes, for example, the frequency variation of the oscillation signal in each crystal resonator 11 and the adsorption amount of the substance to be adsorbed by each odor detection element in the odor detection element array 32. , And the like table showing the relationship.

  The gas inlet 33 is an inlet through which odorous substances (gas) are taken. The filter 34 is provided in the gas flow path in order to remove dust and the like from the gas. The chamber 35 connects the gas suction port 34 and the gas exhaust port 37 to both ends of a cylindrical body that houses the odor detection element, and is a part where gas is adsorbed. The gas exhaust port 37 is for exhausting the gas processed in the chamber 35 to the outside, and the pump 36 is for promoting introduction and exhaust of gas into the chamber 35 from the gas exhaust port 37. .

(Gas sensor operation)
First, the CPU oscillates the odor detecting element array 32, that is, a required number (one or more) of odor detecting elements under reference air (preferably odorless air treated with activated carbon or the like), and the odor detecting element array 32 is The frequency of the signal output from the frequency measuring circuit (CNT) connected to each odor detecting element to be configured is read.

  Next, the odor detecting element array 32 including the required number of odor detecting elements is exposed to the gas to be measured. Here, if the gas has an odor, the gas contains an odor molecule that constitutes the odor, and the odor molecule is adsorbed to the polymer film 12 formed on the surface of the crystal unit 11. Since this odor molecule has a mass, the crystal oscillator 11 having the polymer film 12 that adsorbs the odor molecule has an increased load corresponding to the mass of the adsorbed odor molecule, and this increase in load is observed as a decrease in frequency. Is done. That is, the decrease in frequency is specified by a data processing algorithm (not shown) in the computer 31, and the amount of adsorption of odorous molecules can be obtained. In this way, if the amount of change in the frequency of each sensor is analyzed in the computer 31 and the gas to be observed has an odor of about 100 ppb, the type and strength of the odor can be specified.

[Modification of gas sensor]
FIG. 3 is a schematic diagram illustrating a modification of the configuration of the gas sensor. This modification differs from the gas sensor described in FIG. 2 (there are nine odor detection elements) in that there is one odor detection element in the odor detection element array 32. Thus, the number of odor detecting elements in the gas sensor may be one or more.

  Thus, according to the present embodiment, a gas sensor is provided that has higher detection sensitivity for odorous substances at several ppm level (10 ppm) than conventional ones and can detect odorous substances at several tens of ppb levels (100 ppb). can do.

  Specifically, first, at least one of a homopolymer and a copolymer having a fluorene structure is used as a polymer film to improve the sensitivity of petroleum-related substances such as paraffin, olefin, and aromatic compound to odor. In addition, it is possible to detect an odorous substance of several tens of ppb level.

  Moreover, since a odorous substance can be detected by combining a specific polymer and a crystal resonator, it is not necessary to introduce a large-scale device and the running cost can be reduced. In addition, since a sensor can be manufactured by combining inexpensive materials such as a polymer and a crystal resonator, a highly sensitive sensor can be provided at a low cost. Furthermore, since a device composed of a combination of a polymer and a crystal resonator does not require special knowledge or technology, it can detect odorous substances with a simple operation.

Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the embodiments are not limited to these examples.
[Production of gas sensor]

  A gas sensor was produced as shown in FIG. First, an AT cut 30 MHz was used as a crystal resonator.

  Further, as a polymer, poly-9,9-dioctylfluorene (hereinafter referred to as “F8”), a copolymer of poly-9,9-dioctylfluorene and benzothiazole (dioctylfluorene has a monomer unit of 50%, hereinafter “F8BT”). ), A copolymer of poly-9,9-dioctylfluorene and bithiophene (the monomer unit of dioctylfluorene is 50%, hereinafter referred to as “F8T2”) is dissolved in an organic solvent (p-xylene), respectively. A coating solution 41 was obtained. Each obtained coating solution 41 was applied onto a crystal resonator by spin coating, and the solvent was dried to form a polymer film 12 on the crystal resonator. Thus, the gas sensor 42 was formed by forming the F8 film, the F8BT film, and the F8T2 film as the polymer film 12, respectively.

[Detection of odorous substances]
N-hexane, cyclohexane, n-octane, xylene, and toluene, the concentration of which was controlled by dry air, were exposed to the sensor 42, and the amount of change in frequency was measured. As a comparative control, the same operation was performed using polystyrene (PS) and polymethyl methacrylate (PMMA) instead of the fluorene structure-containing polymer. The evaluation results are shown in Tables 1 and 2 below.

  Further, when the thiophene polymer was exposed to 100 ppb gas instead of the fluorene structure-containing polymer, the frequency change amount was 0 for any of n-hexane, cyclohexane, n-octane, toluene, and p-xylene. It was.

  From the above results, a gas sensor having a polymer having a fluorene structure in at least a part of a quartz resonator has a significantly higher detection sensitivity for a few ppm level (10 ppm) odorous substances than a gas sensor that does not. It was also found that odorous substances of several tens of ppb level (100 ppb) can be detected. And it turned out that it is excellent in the detection performance of an odor substance that the monomer unit of the fluorene monomer in a copolymer is 50%-100%.

  The fact that the performance of the copolymers F8BT and F8T2 is superior to that of the homopolymer F8 is presumed to be a synergistic effect due to the copolymerization of the fluorene monomer and other monomers.

  DESCRIPTION OF SYMBOLS 11 ... Crystal oscillator, 12 ... Polymer film, 13 ... Electrode, 14 ... Lead wire, 31 ... Computer, 32 ... Smell detection element array, 33 ... Gas inlet, 34 ... Filter, 35 ... Chamber, 36 ... Pump, 37 ... gas exhaust port, 41 ... coating solution, 42 ... gas sensor.

Claims (3)

E Bei a polymer having a fluorene structure in at least a part of the crystal oscillator,
The gas sensor includes at least one of a copolymer of poly-9,9-dioctylfluorene and benzothiazole and a copolymer of poly-9,9-dioctylfluorene and bithiophene . The gas sensor according to claim 1, wherein the polymer includes a fluorene structural unit represented by the following chemical formula (1) and has a weight average molecular weight of 100,000 to 1,000,000.
(In the above formula, R 1 and R 2 are each independently an alkyl group having 1 to 10 carbon atoms; R 3, R 3 ′ and R 3 ″ and R 4, R 4 ′ and R 4 ″ are independently Hydrogen, halogen, alkyl, alkenyl, alkynyl, alkoxy, alkylthio, allyl, allyloxy, allylthio, allylalkyl, allylalkoxy, allylalkylthio, allylalkenyl, allylalkynyl, 1 Valent heterocyclic group, heterocyclic thio group, optionally substituted amino group, optionally substituted silyl group, acyl group, imine residue, amide group, acid imide group, optionally substituted carboxyl group, cyano Group or nitro group.) The gas sensor according to claim 1 or 2 , wherein the copolymer is composed of 50% or more of monomer units of the monomer having the fluorene structure.