Hydrophobic surface-modified carbon black based nanocomposite gas sensor and electronic nose system comprising the same

Abstract

A nanocomposite gas sensor and an electronic nose system comprising the same are disclosed, comprising: carbon black particles having hydrophobic functional groups introduced on their surface; and a non-polar or low-polarity polymer matrix capable of non-polar interaction with the hydrophobic functional groups; wherein the carbon black particles are dispersed within the polymer matrix to form a conductive network, and the electrical resistance changes according to the swelling of the polymer matrix upon exposure to volatile organic compounds (VOCs).

Description

Technology Field

[0001] The present invention relates to a gas sensor, particularly a sensor for detecting volatile organic compounds (VOCs), and an electronic nose system comprising the same. More specifically, the invention relates to a nanocomposite gas sensor and an electronic nose system comprising the same, wherein the surface of carbon black nanoparticles is chemically modified to impart hydrophobic or nonpolar properties, and the nonpolar interactions between them are optimized by combining the nanoparticles with a complementary nonpolar or low-polarity polymer matrix, thereby significantly improving dispersibility as well as the sensitivity, selectivity (particularly, moisture selectivity), and stability of the sensor for nonpolar VOCs. Background Technology

[0002] Volatile organic compounds (VOCs) are major substances requiring monitoring in various fields, such as environmental pollution, indoor air quality degradation, and industrial safety. Various types of gas sensors have been developed to effectively detect these VOCs; among them, nanocomposite-based sensors, in which conductive fillers such as carbon black (CB) are dispersed in a polymer matrix, are attracting attention for their advantages, including room-temperature operation, low manufacturing costs, and flexibility. These carbon black / polymer nanocomposite sensors generally utilize the principle that when exposed to VOC vapors, the polymer matrix adsorbs specific VOCs and swells, causing a change in the conductive network between carbon black particles formed within the matrix (primarily an increase in resistance due to increased distance between particles).

[0003] Sensor performance is largely dependent on the dispersion state of carbon black, the interaction between carbon black and the polymer, and the characteristics of the interaction between the sensor material and the target VOC. However, conventional carbon black-based sensors have several limitations. First, carbon black particles tend to aggregate due to strong van der Waals forces, making it difficult to achieve uniform dispersion within a polymer matrix. Second, the surface of carbon black is not inherently completely nonpolar and may contain some polar functional groups during the manufacturing process, resulting in low interfacial affinity with the target nonpolar polymer matrix. This causes poor dispersion and weak interfacial bonding, degrading sensor performance—particularly sensitivity to nonpolar VOCs and long-term stability. In particular, securing excellent dispersibility of carbon black within a nonpolar polymer matrix while simultaneously ensuring sufficient interfacial adhesion in the absence of strong interactions, such as hydrogen bonding in polar systems, has been a dual technical challenge. Third, carbon black or general polymer matrices can interact with polar molecules in the surrounding environment, such as water vapor; consequently, problems such as inaccurate signals or low selectivity caused by moisture interference arise during the detection of nonpolar VOCs.

[0004] Attempts have been made to solve these problems by modifying the surface of carbon black, but most have focused on hydrophilic modification or other applications (Patent Documents 1 to 6). Meanwhile, although hydrophobic surface modification technology itself was known (Non-Patent Document 1), research on specific approaches and their effects regarding intentionally combining it with a specific non-polar / low-polar polymer matrix and optimizing non-polar interactions (van der Waals, hydrophobic effects, etc.) between them to realize high-sensitivity, high-selectivity (especially water selectivity), and high-stability sensors for non-polar VOCs has been insufficient. In particular, optimization studies that consider the structure of hydrophobic functional groups to be introduced to maximize sensor performance—such as phenyl groups, alkylphenyl groups, alkyl groups, mixed functional groups, or core-shell structure formation—or the characteristics of the starting material carbon black—such as the degree of structural development, have been difficult to find.

[0005] Therefore, to effectively and reliably detect non-polar VOCs, there is an urgent need to develop a novel nanocomposite gas sensor technology capable of simultaneously achieving excellent dispersibility, high sensitivity to non-polar VOCs, outstanding selectivity for polar interfering substances such as moisture, and excellent long-term stability and reproducibility. This is achieved by effectively modifying the carbon black surface to be hydrophobic and combining it with an appropriate non-polar / low-polar polymer matrix to realize optimal non-polar interactions. Prior art literature

[0006] Registered Patent Publication No. 10-2486014, U.S. Registered Patent Publication No. 7034677, U.S. Registered Patent Publication No. 7171312, Japanese Registered Patent Publication No. 7064187, U.S. Registered Patent Publication No. 11788985, Chinese Patent Application Publication No. 116964442

[0007] Carbon 2004, 42, 2329-2366; IS&T NIP19 2003, 194 The problem to be solved

[0008] One of the various objectives of the present invention is to solve the problem that conventional carbon black / polymer nanocomposite sensors have poor non-polar VOC detection performance due to low dispersibility within a non-polar polymer matrix, weak interfacial bonding, and vulnerability to polar interfering substances such as moisture.

[0009] Another objective of the present invention is to provide a high-performance nanocomposite gas sensor in which the surface of carbon black is modified by various chemical methods to introduce specific hydrophobic functional groups, such as phenyl groups, alkylphenyl groups, or alkyl groups having 1 to 30 carbon atoms, and combined with a complementary nonpolar or low-polarity polymer matrix to optimize the nonpolar interactions between them, thereby enabling the modified carbon black to exhibit excellent dispersibility within the nonpolar matrix to form a stable conductive network, exhibit high sensitivity when detecting nonpolar VOCs, achieve excellent selectivity by minimizing interference with polar VOCs and especially moisture, and exhibit excellent long-term stability and reproducibility through enhanced interfacial bonding between the hydrophobic surface and the nonpolar polymer.

[0010] Another objective of the present invention is to provide a high-performance electronic nose system capable of effectively identifying various gas or odor patterns, particularly including non-polar VOCs, using the high-performance nanocomposite gas sensor. means of solving the problem

[0011] According to one aspect, a nanocomposite gas sensor is provided comprising: carbon black particles having hydrophobic functional groups introduced on their surface; and a nonpolar or low-polarity polymer matrix capable of nonpolar interaction with said hydrophobic functional groups; wherein said carbon black particles are dispersed within said polymer matrix to form a conductive network, and the electrical resistance changes according to swelling of said polymer matrix upon exposure to volatile organic compounds (VOCs).

[0012] In one embodiment, the hydrophobic functional group may include a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms.

[0013] In one embodiment, the hydrophobic functional group may be introduced onto the surface of the carbon black through a Diels-Alder reaction with a maleic acid derivative comprising a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms, a silanization reaction with a hydrophobic silane coupling agent comprising a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms, a radical reaction with a dialkyl disulfide compound comprising a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms, or a reaction with hexamethyldisilazane (HMDS).

[0014] In one embodiment, two or more hydrophobic alkyl groups with different carbon numbers may be introduced together on the surface of the carbon black.

[0015] In one embodiment, the carbon black particles before the introduction of the hydrophobic functional group may have a DBP absorption amount of less than 110 cm³ / 100g.

[0016] In one embodiment, the nonpolar or low-polarity polymer matrix has a solubility parameter value of 19 MPa 0.5 The following may be selected from ethylene propylene diene monomer (EPDM), polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polystyrene (PS), polymethyl methacrylate (PMMA), polybutyl methacrylate (PbuMA), and copolymers or blends thereof.

[0017] In one embodiment, the content of the carbon black particles may be 2% to 25% by weight relative to the total weight of the nanocomposite material.

[0018] In one embodiment, the nanocomposite material may have an initial electrical resistance of 1 kΩ or more and 5 MΩ or less before VOC exposure.

[0019] According to another aspect, an electronic nose system comprising the above-mentioned nanocomposite material gas sensor is provided. Effects of the invention

[0020] The hydrophobic surface-modified carbon black-based nanocomposite gas sensor according to the present invention exhibits the following excellent effects:

[0021] (1) Strong nonpolar interactions between the hydrophobic functional groups introduced on the surface of carbon black and the complementary nonpolar / low-polarity polymer matrix ensure excellent dispersibility of the carbon black and form a stable conductive network. As a result, the target appropriate initial resistance (e.g., in the range of several hundred kΩ) can be achieved with a smaller amount compared to when using untreated carbon black, which causes an effective change in resistance despite the slight swelling of the polymer upon exposure to nonpolar VOCs, and exhibits significantly improved high sensitivity to nonpolar VOCs such as toluene and hexane compared to conventional technology.

[0022] (2) Since the entire sensor sensing layer has hydrophobic / non-polar characteristics, interaction with highly polar water molecules or polar VOC molecules such as ethanol is effectively suppressed. On the other hand, it interacts strongly with non-polar VOCs and exhibits selective response. This is particularly advantageous for using the sensor in humid environments or for accurately detecting target non-polar VOCs in environments where polar and non-polar VOCs are mixed, thereby increasing the reliability of the sensor.

[0023] (3) Strong nonpolar interactions and interfacial adhesion between the hydrophobically modified carbon black surface and the nonpolar polymer matrix maintain the structural stability of the nanocomposite film even during repeated swelling-shrinking cycles. As a result, the underlying resistance drift is suppressed and consistent response characteristics are shown during repeated measurements, ensuring excellent long-term stability and reproducibility.

[0024] (4) In particular, certain embodiments of the present invention, such as the introduction of phenyl groups, alkylphenyl groups or alkyl groups, the introduction of mixed alkyl groups, and the use of low-structure carbon black, provide unexpected synergistic effects that go beyond simple hydrophobic modification and further improve selectivity for certain non-polar VOCs, moisture resistance, response dynamics, or long-term stability.

[0025] (5) By configuring a hydrophobic modified sensor with the above characteristics and a hydrophilic modified sensor together in an array, polar VOCs and non-polar VOCs can be comprehensively detected and effectively distinguished, thereby significantly expanding the application range and identification capabilities of the electronic nose system.

[0026] The effects of one aspect of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configurations described in the detailed description of this specification or the claims. Specific details for implementing the invention

[0027] The present invention will be described in more detail below. However, the present invention may be embodied in various different forms and should not be interpreted as being limited to the embodiments described herein. The embodiments presented in this specification are provided to clearly convey the disclosure of the present invention to those skilled in the art.

[0028] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0029] As used herein, the term “may” indicates that the applicable thing is a possibility or option, and does not mean that it must be so. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0030] Where a numerical range is described in this specification, unless otherwise specified, the range is interpreted to include a starting value and an ending value of the range, and to include all values ​​in between. For example, "1 to 5" includes not only 1 and 5 but also all values ​​between 1 and 5.

[0031] Additionally, when a numerical range is described in this specification, unless a specific range is otherwise described, the value has the precision of the significant figures provided according to the standard rules in chemistry for significant figures. For example, 10 includes a range of 5.0 to 14.9, and the number 10.0 includes a range of 9.50 to 10.49.

[0032] Nanocomposite material gas sensor

[0033] A nanocomposite gas sensor according to one aspect of the present invention may have a structure in which a sensing layer comprising carbon black particles having hydrophobic functional groups introduced on their surface and a nonpolar or low-polarity polymer matrix capable of nonpolar interaction with the hydrophobic functional groups is formed as a sensing material between electrodes on a substrate.

[0034] The above carbon black particles are conductive carbon nanoparticles and may be, for example, furnace black, acetylene black, or channel black.

[0035] The particle size, specific surface area, and degree of structural development (e.g., DBP absorption amount) of the above carbon black particles may affect sensor performance, and for example, particles with an average particle size of 10 nm to 100 nm and a specific surface area of ​​50 m² / g to 1500 m² / g may be used.

[0036] In one embodiment of the present invention, using carbon black with a particularly low degree of structural development, for example, one with a DBP (Dibutyl Phthalate) absorption of less than 110 cm³ / 100g, as a starting material may be advantageous for improving the final performance of the sensor, particularly dispersion stability and response characteristics. The structure of carbon black (represented by the DBP value) exhibits a three-dimensional aggregate form of particles, and carbon black with a low structure generally tends to have smaller aggregates or less dense aggregate structures. These structural characteristics can contribute to maintaining appropriate inter-particle distances within the non-polar polymer after hydrophobic modification and facilitating the penetration and swelling of polymer chains, thereby consequently improving the uniformity of response to non-polar VOCs, response / recovery speed, and reproducibility.

[0037] Essentially, the carbon black particles of the present invention have their surfaces chemically modified to include hydrophobic functional groups. This lowers the polarity of the carbon black surface and increases its affinity for non-polar environments, thereby strengthening non-polar interactions (van der Waals interactions, hydrophobic interactions, etc.) with the non-polar / low-polar polymer matrix described later. This serves to enhance the selectivity and environmental stability of the sensor by improving dispersibility within the non-polar matrix, increasing interfacial adhesion, and suppressing the adsorption of polar molecules (especially water).

[0038] The introduced hydrophobic functional group is a phenyl group, an alkylphenyl group such as a benzyl group or a p-tolyl group, or a straight-chain or branched-chain alkyl group having 1 to 30 carbon atoms (-C n H 2n+1It is desirable to include (n=1~30) for effective hydrophobicity. In particular, phenyl groups or alkylphenyl groups can enhance interactions with specific non-polar aromatic VOCs due to their aromatic properties, and long alkyl chains with 8 or more carbon atoms provide excellent hydrophobicity, prevent particle aggregation through steric hindrance, and maximize van der Waals forces with non-polar polymer chains. Additionally, alkylsilyl groups with fewer carbon atoms, such as trimethylsilyl groups (-Si(CH₃)₃) introduced through a reaction with hexamethyldisilazane (HMDS), can also provide effective hydrophobicity.

[0039] In some embodiments, two or more hydrophobic alkyl groups with different carbon numbers (e.g., C4-C6 alkyl groups and C 12 -C 18 Combinations of alkyl groups can be introduced together on the carbon black surface. For example, short-chain alkyl groups can be packed more densely on the carbon black surface, while long-chain alkyl groups can provide greater steric hindrance and flexibility; thus, their combination provides a means to finely control surface energy, roughness, and the mode of interaction with polymers. This can contribute to improving the pattern recognition capabilities of sensor arrays by enhancing compatibility with specific nonpolar polymer blends or by inducing subtle differences in interaction between similar nonpolar VOCs with different molecular sizes or structures (e.g., toluene vs. xylene, or n-hexane vs. n-octane).

[0040] These hydrophobic functional groups can be introduced to the surface of carbon black particles through various chemical methods.

[0041] (1) Diels-Alder alkylation

[0042] Hydrophobic functional groups can be introduced as stable CC bonds through a Diels-Alder reaction between the diene structure on the surface of carbon black and a maleic acid derivative containing a phenyl group, a benzyl group, a p-tolyl group, or an alkyl group having 1 to 30 carbon atoms, such as N-alkylmaleimide or N-phenylmaleimide. This method can be carried out under relatively mild conditions and has the advantage of forming stable covalent bonds.

[0043] (2) Silanization alkylation

[0044] Hydrophobic alkylsilyl groups can be introduced through Si-OC or Si-O-Si bonds by reacting a hydrophobic silane coupling agent containing a hydroxyl group (-OH) present on the surface of carbon black or a hydroxyl group artificially introduced through oxidation, etc., with an alkylphenyl group such as a phenyl group, a benzyl group, or a p-tolyl group, or an alkyl group having 1 to 30 carbon atoms. Specific examples of such hydrophobic silane coupling agents include phenyltrimethoxysilane, benzyltriethoxysilane, octyltriethoxysilane (OTS), and hexamethyldisilazane (HMDS). Although this method allows the use of silanes with various alkyl chain lengths and is relatively easy to control, the modification efficiency may vary depending on the density of -OH groups on the surface of carbon black, and hydrolytic stability may need to be considered.

[0045] (3) Disulfide alkylation

[0046] An alkylthio radical (RS·) can be generated by reacting a dialkyl disulfide compound containing an alkylphenyl group such as a phenyl group, a benzyl group, or a p-tolyl group, or an alkyl group having 1 to 30 carbon atoms, such as Di-n-dodecyl disulfide, in the presence of heat or a photoinitiator, and then adding this to the surface of carbon black to introduce a hydrophobic alkylthio group (-SR). This method can form strong SC bonds and can be carried out as a relatively simple process.

[0047] Since the type, chain length, and density of hydrophobic functional groups introduced on the surface affect the degree of hydrophobicity of carbon black and the way it interacts with nonpolar polymers, they need to be appropriately selected and controlled to achieve target sensor performance (e.g., high sensitivity / high selectivity for specific nonpolar VOCs).

[0048] The polymer matrix described above serves as a medium for dispersing hydrophobically modified carbon black particles, and also acts as a sensing material that induces a change in the resistance of a sensor by effectively absorbing / adsorbing non-polar VOC molecules and causing them to swell. Crucially, the polymer matrix used in the present invention is a non-polar or low-polar polymer capable of strong non-polar interactions (van der Waals interactions, hydrophobic interactions, etc.) with hydrophobic functional groups introduced on the surface of the carbon black. This is essential for promoting the uniform dispersion of hydrophobic CB, securing strong interfacial adhesion, achieving high sensitivity to non-polar VOCs, and low sensitivity (high selectivity) to polar interfering substances (moisture, etc.).

[0049] The degree of polarity or non-polarity of a polymer can be evaluated by the solubility parameter (δ) value, and the lower the value, the stronger the non-polarity. In the present invention, as a non-polar or low-polarity polymer matrix, for example, a solubility parameter value of 19 MPa 0.5 It is preferable to use a polymer with a δ value of 24 or less. This is clearly distinguishable from typical polar polymers (e.g., PVA, PAA, etc., δ > 24) and is a range capable of effective nonpolar interaction with the hydrophobically modified carbon black surface and nonpolar VOC analytes.

[0050] A specific example is ethylene propylene diene monomer (EPDM) (δ, a representative nonpolar polymer with low solubility parameter values). 16-17.2), polyethylene (PE) (δ 16), polypropylene (PP) (δ 16-18), polyisobutylene (PIB) (δ 15-16), polybutadiene (PB) (δ 16-17 MPa 0.5 ), polyisoprene (PI) (δ 16-17 MPa 0.5 ), polymethylpentene (PMP) (δ 17-18 MPa 0.5 Polyolefin series such as ) etc.; polystyrene (PS) (δ) which has an aromatic ring structure but is relatively low polar. 18-19); contains chlorine groups but maintains hydrophobicity, with a solubility parameter value of approximately 18.2-19 MPa 0.5 Polyvinyl chloride (PVC); and polymethyl methacrylate (PMMA), an acrylate series having ester groups but with decreasing polarity as the alkyl chain length increases (δ 19-20, low-polarity boundary), polyethyl methacrylate (PEMA) (δ 18 MPa 0.5 ), polybutyl methacrylate (PBuMA) (δ 17-18 MPa 0.5 , lower than PMMA), poly(2-ethylhexyl methacrylate) (P(2-EHMA)) (δ 16-17 MPa 0.5 ), polymethyl acrylate (PMA) (δ 19 MPa 0.5 , low-polarity boundary), polyethyl acrylate (PEA) (δ 18 MPa 0.5 ), polybutyl acrylate (PBA) (δ 17-18 MPa 0.5 ) etc. can be used alone, in a blend of two or more types, or in copolymer form. In particular, among these, the solubility parameter value is approximately 12 to 17 MPa 0.5Strongly nonpolar polymers such as EPDM, PIB, PE, PP, PB, PI, and P(2-EHMA) within the range may be more advantageous for interaction with hydrophobically modified carbon black and for detecting nonpolar VOCs, and PBuMA can also be used as an effective low-polarity matrix. In addition, silicone-based polymers with low solubility parameter values, such as polydimethylsiloxane (PDMS), can also be used. The type of polymer used, molecular weight, copolymerization ratio, etc., can be optimized by considering the affinity with the target VOC, compatibility with carbon black, film-forming ability, and mechanical properties.

[0051] The above nanocomposite material can be obtained by dispersing / dissolving the surface-modified carbon black particles and a selected non-polar or low-polarity polymer matrix in a suitable non-polar or low-polarity organic solvent, such as toluene, xylene, hexane, tetrahydrofuran (THF), chloroform, chlorohexane, etc., then uniformly mixing them through sonication, mechanical stirring, or the use of a homogenizer to prepare a nanocomposite material solution or suspension, and then drying under appropriate conditions to remove the solvent. Alternatively, it may be obtained by a melt mixing method without a solvent.

[0052] The carbon black content in the above nanocomposite material needs to be optimized within a range that maintains a uniform dispersion state while exceeding the percolation threshold for forming an electrically conductive network, and does not impede the swelling characteristics of the polymer matrix. If the carbon black content is too low (below the percolation threshold), it is difficult to secure sufficient initial conductivity; if the content is too high, re-aggregation between carbon black particles occurs, leading to reduced dispersibility, or the relative volume fraction of the polymer matrix decreases, weakening the swelling effect due to VOC adsorption and potentially reducing sensor sensitivity. In the present invention, excellent dispersibility and the formation of a conductive network may be possible over a relatively wide content range due to enhanced carbon black-polymer interactions; however, it is generally preferable to include carbon black in a range of 2% to 25% by weight relative to the total weight of the nanocomposite material, for example, in a range of 10% to 20% by weight. In practice, since the hydrophobic modification according to the present invention significantly improves the dispersibility of carbon black, the carbon black content required to obtain the same target initial resistance value can be significantly reduced compared to untreated carbon black.

[0053] The nanocomposite material according to the present invention exhibits significantly improved initial electrical conductivity (i.e., low initial resistance value) compared to the case where untreated carbon black particles are used, due to excellent dispersibility resulting from strong interactions between surface-modified carbon black particles and non-polar or low-polar polymers. For example, when manufactured in the form of a sensor element to be described later and measured by the 4-probe method or the 2-probe method, the initial electrical resistance (R0) in a dry state prior to VOC exposure can have a value of 1 kΩ or more and 5 MΩ or less (preferably 1.5 MΩ or less, more preferably 800 kΩ or less, and even more preferably 500 kΩ or less). Such low initial resistance can be advantageous for facilitating the design of the sensor driving circuit and improving the signal-to-noise ratio.

[0054] The above nanocomposite material can be preferably used in the manufacture of gas sensor devices. Generally, a gas sensor device may include an insulating substrate, one or more pairs of electrodes formed on the substrate, and a sensing layer formed between the electrodes and comprising the nanocomposite material according to the present invention as a sensing material. The insulating substrate may include a substrate having an oxide film (SiO₂) formed on a silicon wafer, a glass substrate, a ceramic substrate such as alumina, or a flexible plastic film such as polyethylene terephthalate (PET) or polyimide (PI). The electrodes may typically be formed using a material with excellent electrical conductivity and chemical stability, such as gold (Au), platinum (Pt), silver (Ag), or indium tin oxide (ITO), and may be formed in the form of one or more pairs of opposing electrode patterns, for example, interdigitated electrodes (IDE), by methods such as lithography, deposition, or printing. The above-described sensing layer can be formed by applying the prepared nanocomposite material solution or suspension onto a substrate on which the electrode is formed using thin film formation techniques such as spin coating, drop casting, inkjet printing, or spray coating, and then undergoing a drying or heat treatment process at an appropriate temperature, e.g., 60°C to 100°C, to remove the solvent. The thickness of the sensing layer can affect the response time and sensitivity of the sensor and can generally be controlled in the range of several hundred nanometers to several micrometers.

[0055] The operating principle of the sensor is as follows: When the sensor is exposed to an atmosphere containing target VOCs, the polymer matrix within the sensing layer selectively adsorbs specific VOC molecules based on their physical or chemical affinity. The adsorbed VOC molecules penetrate between the polymer chains, causing the polymer matrix to swell. This swelling phenomenon increases the average distance between the carbon black particles dispersed within the polymer matrix, resulting in the disruption of some existing conductive pathways or an increase in the resistance of these pathways. Consequently, the electrical resistance (R) measured between the two electrodes of the sensor... gas The resistance increases compared to the initial resistance (R0, resistance before VOC exposure). When VOCs around the sensor are removed, VOC molecules are desorbed from the polymer matrix, causing the polymer to shrink again and the carbon black network to be restored to its original state, and the sensor resistance also gradually returns to the initial state (R0).

[0056] The magnitude of the sensor's response is generally the rate of change in resistance relative to the initial resistance (ΔR / R0=(R gas It is quantified as -R0) / R0)), and the sensor's sensitivity (k) is the rate of change in resistance relative to the sensor's initial resistance (R0) due to exposure to a specific concentration of volatile organic compounds (VOCs) (ΔR / R0, where ΔR=R gas -R0 and R gas k = ((R) is the value obtained by dividing the stabilized resistance value after VOC exposure) by the concentration of the corresponding VOC (C), i.e., k = ((R gas It is defined as -R0) / R0) / C.

[0057] In the present invention, due to enhanced specific interactions between the carbon black surface and a nonpolar or low-polarity polymer matrix, carbon black particles are dispersed very uniformly and stably within the polymer matrix, forming an effective conductive network with low initial resistance (R0). In particular, a well-dispersed network near the percolation threshold concentration responds sensitively to even minute volume changes (swelling) of the polymer matrix, which can cause significant changes in the connectivity of the conductive pathways. Therefore, since the rate of change in electrical resistance (ΔR / R0) is large despite the slight swelling of the polymer due to VOC adsorption, consequently, very high sensitivity is exhibited, for example, for nonpolar VOCs such as toluene or n-hexane, 10 -3 ppm -1 Ideally, 5×10 -3 ppm -1 Sensitivity can be achieved. This can correspond to a significantly improved value compared to the sensitivity of conventional sensors that use untreated carbon black or rely on non-specific interactions.

[0058] Furthermore, as the entire sensor sensing layer is composed of a hydrophobic / non-polar environment, interactions with water molecules or polar VOC molecules are weak, while interactions with non-polar VOC molecules are strong, exhibiting high selectivity (particularly selectivity toward moisture / polar VOCs). The selectivity (A / B) of the sensor is the sensitivity (k) of the sensor to a specific target volatile organic compound (VOC) 'A'. A The sensitivity of the sensor to ) and other comparison target VOC 'B' (k B Defined as the ratio of ), or the sensor's response to VOC 'A' under specific identical concentration conditions ((ΔR / R0) A Sensor response to ) and VOC 'B' ((ΔR / R0) BIt is defined as the ratio of ). This high selectivity is achieved through hydrophobic surface modification and the use of a non-polar matrix. Specifically, this combination maximizes van der Waals interactions with non-polar VOC molecules, thereby significantly improving responsiveness to a level of tens to hundreds of times compared to conventional methods, while minimizing interactions with water molecules or polar VOCs, thereby suppressing the increase in responsiveness to them to a level of approximately 10 times or less. This significant difference in the magnitude of responsiveness manifests as the excellent selectivity of the sensor of the present invention.

[0059] Furthermore, the enhanced non-polar interfacial bonding force maintains structural stability even during repeated swelling and shrinking, providing excellent long-term stability and reproducibility with suppressed baseline drift and consistent response characteristics.

[0060] In particular, the introduction of mixed alkyl groups can improve the pattern recognition capability of the sensor array by controlling the microenvironment of the surface to fine-tune selectivity for specific non-polar VOCs (e.g., optimizing interaction energy with non-polar molecules of a specific size or structure by adjusting the ratio of short chains to long chains), and the use of low-structure carbon black can further improve sensor performance by improving dispersion stability and response dynamics (facilitating free swelling / shrinkage of polymer chains to induce rapid response / recovery and improving reproducibility with a uniform network).

[0061] electronic nose system

[0062] An electronic nose system according to another aspect of the present invention is characterized by comprising a sensor array including one or more nanocomposite material gas sensors according to one aspect of the present invention described above, and a pattern recognition unit that processes a response signal from the sensor array.

[0063] An electronic nose is a device that mimics the human olfactory system to identify and analyze complex odors or gas mixtures. It generally consists of a sensor array composed of multiple gas sensors designed to have different sensitivity characteristics, a data acquisition unit that collects multidimensional response signal patterns obtained from each sensor, and a pattern recognition unit (e.g., a microprocessor equipped with a specific algorithm) that processes and interprets the collected patterns to identify the type of specific VOC or estimate its concentration. Pattern recognition algorithms that can be used include Principal Component Analysis (PCA), Linear Discriminant Analysis (LDA), Support Vector Machine (SVM), and Artificial Neural Network (ANN).

[0064] Using the technology of the present invention, a sensor array can be constructed with sensors of various characteristics. For example, the sensor array can be constructed using (i) sensors that use the same hydrophobic surface-modified carbon black but are combined with different types of nonpolar or low-polar polymer matrices (e.g., EPDM, PIB, PS, etc.), (ii) sensors that use the same nonpolar or low-polar polymer matrix (e.g., EPDM) but are hydrophobically surface-modified carbon black in different ways or to different degrees (e.g., carbon black with different alkyl chain lengths, phenyl group-modified carbon black, mixed hydrophobic group-modified carbon black, etc.), or (iii) a combination thereof. Each sensor exhibits a unique sensitivity and selectivity profile, i.e., a 'fingerprint' of the response pattern, for a specific VOC or group of VOCs. When such a sensor array is exposed to a specific odor (a mixture of various VOCs), each sensor generates a response signal of a different magnitude for the corresponding odor component. By combining these multiple sensor response values ​​into a single vector (response pattern) and analyzing it using a pre-trained database and pattern recognition algorithm, it is possible to identify the type of odor or estimate the concentration of specific components. In particular, the hydrophobic surface-modified carbon black-based nanocomposite gas sensor according to the present invention exhibits high sensitivity, excellent selectivity (especially moisture selectivity), and stability for non-polar VOCs; therefore, when included in a sensor array along with other types of sensors, such as hydrophilic surface-modified sensors, the diversity and discriminability of the overall response pattern of the sensor array can be significantly improved. For example, since hydrophilic sensors react sensitively to polar VOCs and hydrophobic sensors react sensitively to non-polar VOCs, combining them is expected to comprehensively detect polar VOCs and non-polar VOCs and effectively distinguish them, thereby dramatically expanding the application range and identification capabilities of electronic nose systems.

[0065] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are merely illustrative of the present invention, and the scope of the present invention is not limited by the following embodiments.

[0066] Preparation Example 1

[0067] 10 mmol of maleic anhydride and 10 mmol of 1-dodecylamine were reacted in toluene to obtain the intermediate maleamide, and N-dodecylmaleimide was synthesized by dehydrating this by heating it in the presence of acetic anhydride and sodium acetate. 1 g of commercial carbon black (Vulcan XC-72, Cabot Corp., DBP approx. 174 cm³ / 100 g) and 0.5 g of the synthesized N-dodecylmaleimide were placed in 100 mL of toluene and dispersed using an ultrasonic disperser for 30 minutes. Subsequently, the mixture was subjected to a Diels-Alder reaction by vigorously stirring at 110°C (toluene reflux temperature) for 6 hours under a nitrogen atmosphere. After the reaction was complete, the mixture was cooled to room temperature, the product was filtered, and washed several times with an excess of acetone until no unreacted maleimide was detected. The final solid was filtered and completely dried in an 80°C vacuum oven for 12 hours to obtain hydrophobic carbon black (sCB-DA-C12) powder with C12 alkyl groups introduced. Thermogravimetric analysis (TGA) confirmed that approximately 15 wt% of organic matter (derived from N-dodecylmaleimide) was bound to the carbon black.

[0068] Preparation Example 2

[0069] First, 1 g of commercial carbon black (Vulcan XC-72) was treated with an aqueous solution of hydrogen peroxide, a weak acid, to introduce hydroxyl groups (-OH) capable of acting as silane coupling reaction sites on the surface (CB-OH). After thoroughly washing and drying 1 g of CB-OH, it was dispersed in 100 mL of anhydrous toluene, and then 3 mL of phenyltrimethoxysilane (C6H5Si(OCH3)3) was added. The silanization reaction was carried out by refluxing and stirring the mixture at 110°C for 24 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled and the solid was separated using centrifugation, and then washed several times with excess toluene and ethanol until unreacted silane and byproducts were removed. The final obtained solid was filtered and dried in a vacuum oven at 100°C for 12 hours to obtain hydrophobic carbon black (sCB-Sil-Phenyl) powder with introduced phenyl groups. The successful introduction of the silane coupling agent was confirmed through elemental analysis (Si content).

[0070] Preparation Example 3

[0071] 1 g of commercial carbon black (Vulcan XC-72), 1 g of di-n-dodecyl disulfide, and 0.1 g of azobis-isobutyronitrile (AIBN) as a radical initiator were added to 100 mL of xylene and sonicated. The mixture was vigorously stirred at 140°C (near xylene reflux temperature) for 12 hours under a nitrogen atmosphere to induce a radical reaction. After the reaction was complete, the mixture was cooled and washed several times with excess hexane to remove unreacted materials and byproducts. The final solid obtained was filtered and dried in a vacuum oven at 80°C for 12 hours to obtain hydrophobic carbon black (sCB-DS-C12) powder with an introduced C12 alkylthio group (-S-C12H25). The successful introduction of the alkylthio group was confirmed through elemental analysis (increase in sulfur content).

[0072] Preparation Example 4

[0073] N-butylmaleimide (C4 alkyl) and N-dodecylmaleimide (C12 alkyl) were synthesized, respectively. 1 g of commercial carbon black (Vulcan XC-72) was mixed with 0.15 g of N-butylmaleimide and 0.15 g of N-dodecylmaleimide (total 0.3 g, molar ratio approximately 1:1) and dispersed in 100 mL of toluene. Then, a Diels-Alder reaction was carried out under the same conditions as in Preparation Example 1 (nitrogen atmosphere, 110°C, 6 hours). After the reaction, the mixture was thoroughly washed with acetone and dried in a vacuum oven at 80°C to obtain hydrophobic carbon black (sCB-DA-Mix) powder with a mixture of C4 alkyl and C12 alkyl groups introduced.

[0074] Preparation Example 5

[0075] Except for using 1 g of commercial low-structure carbon black with a DBP absorption of 75 cm³ / 100 g as a starting material, the same method as in Preparation Example 1 (using 0.5 g of N-dodecyl maleimide, toluene solvent, 110°C, 6 hours Diels-Alder reaction) was performed to obtain low-structure carbon black-based C12 alkyl group functionalized hydrophobic carbon black (sCB-DA-C12-LowDBP) powder.

[0076] Example 1

[0077] 16.0 mg of sCB-DA-C12 powder (carbon black content 16.0 wt%) obtained in Preparation Example 1 and 84.0 mg of ethylene propylene diene monomer (EPDM) were added to 10 mL of toluene. The mixture was treated for 1 hour using a bath-type sonicator to prepare a black suspension in which carbon black particles were uniformly dispersed within the polymer solution. Approximately 10 μL of the suspension was drop-casted using a micropipette onto a pre-prepared gold (Au) interdigital electrode (IDE) substrate (electrode width 10 μm, electrode spacing 10 μm, electrode length 1 mm, 50 pairs, on a SiO₂ / Si substrate). After being left at room temperature for 30 minutes to allow the solvent to air dry, the mixture was further dried in an oven at 60°C for 2 hours to completely remove residual solvent and complete the gas sensor device having an sCB-DA-C12 / PS nanocomposite thin film formed thereon.

[0078] Example 2

[0079] A gas sensor element was prepared using the same method as in Example 1 (using toluene solvent), except that 16.5 mg of sCB-Sil-Phenyl powder (carbon black content 16.5 wt%) and 83.5 mg of EPDM obtained in Preparation Example 2 were used.

[0080] Example 3

[0081] A gas sensor element was prepared using the same method as in Example 1 (using toluene solvent), except that 16.3 mg of sCB-DS-C12 powder (carbon black content 16.3 wt%) and 83.7 mg of EPDM obtained in Preparation Example 3 were used.

[0082] Example 4

[0083] A gas sensor element was prepared using the same method as in Example 1 (using toluene solvent), except that 15.8 mg of sCB-DA-Mix powder (carbon black content 15.8 wt%) and 84.2 mg of EPDM obtained in Preparation Example 4 were used.

[0084] Example 5

[0085] A gas sensor element was prepared using the same method as in Example 1 (using toluene solvent), except that 15.5 mg of sCB-DA-C12-LowDBP powder (carbon black content 15.5 wt%) obtained in Preparation Example 5 and 84.5 mg of EPDM were used.

[0086] Comparative Example 1

[0087] A gas sensor element was prepared using the same method as in Example 1 (using toluene solvent), except that 22.0 mg of untreated commercial carbon black (Vulcan XC-72, DBP approx. 174 cm³ / 100 g) (carbon black content 22.0 wt%) and 78.0 mg of EPDM were used.

[0088] Comparative Example 2

[0089] A gas sensor element was prepared in a manner similar to Example 1, except that 16.0 mg of hydrophobic modified carbon black (sCB-DA-C12) obtained in Preparation Example 1 was used, but 84.0 mg of polar polymer PVP (Poly(vinylpyrrolidone)) (Mw=40,000) was used instead of non-polar polymer PS, and 10 mL of ethanol was used as the solvent.

[0090] Experimental Example 1: Measurement of Initial Electrical Resistance

[0091] Surface modification of carbon black improves dispersibility within a non-polar polymer matrix, enabling the formation of an effective conductive network with a lower content. To verify this, the target initial resistance (R0) was set to approximately 400 kΩ (with an error range of ± 40 kΩ, within the range of several hundred kΩ), and for each type of carbon black (Examples 1-5 and Comparative Example 1), the carbon black content (wt%) in the nanocomposite material (matrix: EPDM, solvent: toluene) satisfying this target resistance range was experimentally determined. For Comparative Example 2, it was difficult to obtain the corresponding resistance value at a carbon black content of 25% or less due to poor dispersion. The results are shown in Table 1.

[0092] division Carbon black content (wt%) Example 1 16.0% Example 2 16.5% Example 3 16.3% Example 4 15.8% Example 5 15.5% Comparative Example 1 22.0% Comparative Example 2 N / A

[0093] The results in Table 1 clearly show that the hydrophobic surface modification according to the present invention (Examples 1-5) significantly improved the dispersibility of carbon black within a non-polar polymer (EPDM). The carbon black content required to achieve a similar initial resistance (approx. 400 kΩ) within the same non-polar polymer (EPDM) matrix was 22.0 wt% for untreated carbon black (Comparative Example 1), whereas it was 15.5–16.5 wt% for hydrophobically modified carbon black (Examples 1-5), a reduction of approximately 25–30%. This implies that the modified carbon black can form an effective conductive network with a smaller amount, which is attributed to improved dispersibility and strong non-polar interactions with the polymer. The use of low-structure carbon black (Example 5) and mixed alkyl groups (Example 4) suggests that the effect of improving dispersibility is particularly pronounced as they require a low content.

[0094] Experimental Example 2: Evaluation of VOC Response Characteristics (Sensitivity and Selectivity)

[0095] For each sensor element (Examples 1-5 and Comparative Example 1) fabricated to have a similar initial resistance (approx. 400 kΩ), the sensor sensitivity (k, ppm) when exposed to n-hexane, a representative non-polar VOC, and ethanol, a polar VOC, vapors at a concentration of 50 ppm, respectively. - Basic sensitivity and selectivity were evaluated by measuring ¹). Sensitivity (k) is k=((R gas -R0) / R0) / C (where R0 is the initial resistance, R gas ε₀ is the resistance stabilized after VOC exposure, and C is the VOC concentration (ppm). The results are shown in Table 2 below.

[0096] division n-hexane sensitivity (k, ppm - ¹) Ethanol sensitivity (k, ppm - ¹) Selectivity (n-hexane / ethanol) Example 1 6.52×10 -3 4.13×10 -6 1579 Example 2 7.05×10 -3 3.78×10 -6 1865 Example 3 6.80×10 -3 4.49×10 -6 1515 Example 4 7.23×10 -3 3.51×10 -6 2060 Example 5 7.51×10 -3 3.17×10 -6 2369 Comparative Example 1 1.53×10 -5 9.85×10 -8 155

[0097] As shown in the results of Table 2, under similar initial resistance conditions, the hydrophobic modified CB / non-polar EPDM sensor (Examples 1-5) showed a significantly higher sensitivity (k) to n-hexane, a non-polar VOC, of ​​about 430 to 500 times compared to the untreated CB sensor (Comparative Example 1). This demonstrates that the combination of hydrophobic modification and non-polar polymer of the present invention greatly improves sensitivity to non-polar VOCs.

[0098] On the other hand, the sensitivity to ethanol, a polar VOC, was found to increase by about 30 to 50 times compared to Comparative Example 1, but was significantly smaller than the increase in sensitivity to n-hexane.

[0099] Consequently, the selectivity index of the sensors in the examples, calculated from the n-hexane / ethanol sensitivity ratio, was found to be significantly higher—approximately 10 times or more—than that of Comparative Example 1. This clearly demonstrates that the hydrophobic modified sensors of the present invention detect non-polar VOCs very selectively compared to polar VOCs. In particular, Example 5 using low-structure carbon black and the mixed alkyl group (Example 4) exhibited high selectivity.

[0100] Experimental Example 3: Selectivity Evaluation

[0101] In a manner similar to Experimental Example 2, various types of VOC vapors with different chemical properties (non-polar: n-hexane, toluene; polar: ethanol, acetone) and water vapor (50 ppm) with the same concentration (50 ppm) were each exposed to the sensor, and the sensor sensitivity (k, ppm) for each VOC was - 1) was measured and compared. The results are summarized in Table 3 below, and the ratios of (n-hexane sensitivity / ethanol sensitivity) and (n-hexane sensitivity / water vapor sensitivity) were calculated as selectivity indicators.

[0102] division Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 n-hexane (non-polar) 6.52×10 -3 7.05×10 -3 6.80×10 -3 7.23×10 -3 7.51×10 -3 1.50×10 -5 Toluene (tragic) 5.98×10 -3 6.51×10 -3 6.25×10 -3 6.88×10 -3 7.03×10 -3 1.18×10 -5 Ethanol (polar) 4.13×10 -6 3.78×10 -6 4.49×10 -6 3.51×10 -6 3.17×10 -6 9.85×10 -8 Acetone (polar) 5.52×10 -6 5.07×10 -6 5.88×10 -6 4.79×10 -6 4.45×10 -6 1.31×10 -7 Water vapor (polar) 2.03×10 -6 1.75×10 -6 2.19×10 -6 1.52×10 -6 1.23×10 -6 8.21×10 -8 Selectivity (n-hexane / ethanol) 1579 1865 1515 2060 2369 155 Selectivity (n-hexane / water vapor) 3212 4029 3105 4757 6106 186

[0103] The results in Table 3 clearly demonstrate the excellent selectivity of the sensors of the present invention, particularly their high resistance to polar interfering substances and moisture. All examples (1-5) showed high sensitivity to non-polar VOCs (n-hexane, toluene), while their sensitivity to polar VOCs (ethanol, acetone) and water vapor was significantly lower, exhibiting very high selectivity indicators. This strongly demonstrates that the combination of hydrophobically modified CB and non-polar polymer selectively detects non-polar VOCs and effectively excludes the influence of polar interfering substances.

[0104] In particular, Example 4 (mixed alkyl group) and Example 5 (low-structure carbon black based) exhibited overall superior n-hexane / ethanol and n-hexane / water vapor selectivity indicators compared to other simple alkyl group modifications (Examples 1 to 3), demonstrating that such structural modifications can contribute to improved selectivity. Notably, Example 5 showed overwhelmingly high n-hexane / water vapor selectivity with the lowest sensitivity to water vapor.

[0105] Experimental Example 4: Evaluation of Long-term Stability and Reproducibility

[0106] To evaluate the long-term performance stability and response reproducibility of the sensor, a process of exposing the sensor to n-hexane vapor at a specific concentration (50 ppm) for 5 minutes, followed by recovery by flowing dry air for 10 minutes, was repeated 100 times. The baseline resistance (R0) value at the start of each cycle (dry air exposure state) was recorded, and the baseline resistance drift (%) over 100 cycles was calculated. In addition, the response reproducibility was evaluated by calculating the relative standard deviation (RSD, %) of the maximum resistance drift (ΔR / R0) values ​​measured in each cycle. The measurement results are summarized in Table 4 below.

[0107] Example 1 Example 2 Example 4 Example 5 Comparative Example 1 Base resistance drift(% @ 100 cycles) 4.5% 4.3% 4.2% 4.0% >30% Response reproducibility (△R / R0RSD @ 100 cycles) 5.3% 5.1% 4.9% 4.7% >15%

[0108] Referring to Table 4, all embodiments exhibited significantly lower base resistance drift and small response RSD values ​​compared to Comparative Example 1, demonstrating excellent long-term stability and reproducibility. This is attributed to the strong nonpolar interactions and interfacial bonding forces between the hydrophobically modified carbon black surface and the nonpolar polymer matrix, which maintain the structural stability of the sensor even under repeated swelling / shrinkage stress. The base resistance of all sensor embodiments stabilized, with a very small drift within + / - 5%, and the response reproducibility (RSD) was also excellent at less than 6%, with almost no decrease in sensitivity observed even with repeated measurements. Therefore, it can be seen that the present invention provides a qualitative improvement effect that goes beyond merely excellent initial performance to provide stable and reliable nonpolar VOC measurement results even with long-term use.

[0109] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form. The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A nanocomposite gas sensor comprising: carbon black particles having hydrophobic functional groups introduced on their surface; and a non-polar or low-polarity polymer matrix capable of non-polar interaction with the hydrophobic functional groups; wherein the carbon black particles are dispersed within the polymer matrix to form a conductive network, the content of the carbon black particles is 2% to 25% by weight relative to the total weight of the nanocomposite material comprising the carbon black particles and the polymer matrix, and the electrical resistance changes according to the swelling of the polymer matrix upon exposure to volatile organic compounds (VOCs). Claim 2 A nanocomposite gas sensor according to claim 1, characterized in that the hydrophobic functional group comprises a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms. Claim 3 A nanocomposite gas sensor according to claim 1, characterized in that the hydrophobic functional group is introduced onto the surface of the carbon black through a Diels-Alder reaction with a maleic acid derivative comprising a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms. Claim 4 A nanocomposite gas sensor according to claim 1, characterized in that the hydrophobic functional group is introduced through a silanization reaction with the carbon black surface or a reaction with hexamethyldisilazane (HMDS) with a hydrophobic silane coupling agent comprising a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms. Claim 5 A nanocomposite gas sensor according to claim 1, characterized in that the hydrophobic functional group is introduced onto the surface of the carbon black through a radical reaction with a dialkyl disulfide compound comprising a phenyl group, an alkylphenyl group, or an alkyl group having 1 to 30 carbon atoms. Claim 6 In claim 1, the non-polar or low-polarity polymer matrix has a solubility parameter value of 19 MPa 0.5 A nanocomposite gas sensor characterized by being selected from ethylene propylene diene monomer (EPDM), polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polystyrene (PS), polymethyl methacrylate (PMMA), polybutyl methacrylate (PBuMA), and copolymers or blends thereof. Claim 7 A nanocomposite gas sensor according to claim 1, characterized in that two or more hydrophobic alkyl groups with different carbon numbers are introduced together on the surface of the carbon black. Claim 8 A nanocomposite gas sensor according to claim 1, characterized in that the carbon black particles before the introduction of the hydrophobic functional group have a DBP (Dibutyl Phthalate) absorption amount of less than 110 cm³ / 100g. Claim 9 delete Claim 10 A nanocomposite gas sensor according to claim 1, characterized in that the nanocomposite material has an initial electrical resistance of 1 kΩ or more and 5 MΩ or less before exposure to volatile organic compounds (VOCs). Claim 11 An electronic nose system comprising a nanocomposite material gas sensor according to any one of claims 1 through 8 and 10.