KR101888130B1 - Smart-shield for gas sensor and manufacture method thereof - Google Patents

Abstract

The present invention relates to a gas sensor protection membrane fabricated from a fluoropolymer film that is double coated with a silica coating and a hydrophobic material coating through a dip coating process.
The dip coating method comprises the steps of: adding an adhesive to a solution in which SiO ₂ nanoparticles are dispersed in an organic solvent; immersing and drying the fluoropolymer film; repeating the step of coating the fluoropolymer film with SiO ₂ ; And immersing and drying the fluorine-based polymer film coated with the SiO ₂ -containing solution to coat the film with a hydrophobic substance to impart water repellency and oil repellency.

Description

TECHNICAL FIELD [0001] The present invention relates to a smart sensor for a gas sensor for detecting a gas component,

The present invention relates to chemical detectors, and more particularly to techniques for improving the material properties of chemical detectors.

The chemical detector is a gas sensor. It detects dangerous substances contained in the gas. Its various principles and structures have long been known. The present applicant has also continuously carried out various research and development activities for more than a decade with the achievements of Korean Patent No. 545455, Patent No. 609396, Patent No. 1068827, No. 10965350, and the like. The contents of these patent documents relate to gas detection principles, systems, mechanical structures and devices within the device housing. These prior arts also relate to techniques for accurately and efficiently sensing and treating gaseous particles while they are being drawn into the detector.

However, what if the gas particles are not properly trapped inside the chemical detector? No matter how good the device is, the gas detection function can not be performed properly. Such situations include, for example, disturbance caused by liquids such as rain, and oily dust which may contaminate the surface of a chemical detector.

The inventors of the present invention have completed the present invention after long research and development in order to fully control the situation and to operate the chemical detector anytime and anywhere.

It is therefore an object of the present invention to apply a means having a shielding function to liquids and oils to chemical detectors. The chemical detector should give the part that captures the gas a property that does not get wet and a property that does not absorb oil. The former characteristic is referred to as a water-repellent characteristic, and the latter characteristic may be referred to as a oil-repellent characteristic.

That is, an object of the present invention is to protect a portion where a chemical detector captures a gas, such as a membrane-like member having a surface imparted with water repellency and oil repellency. The inventors of the present invention named this R & D project as <smart shield>.

However, even if a smart shield (membrane with surface water repellency and oil repellency) is installed on a chemical detector, ie a gas sensor, the smart shield must ensure gas penetration. If the gas can not penetrate the membrane properly, it can not perform the essential function of the chemical detector. That is, another object of the present invention is to realize a characteristic that a gas can be selectively transmitted to a smart shield except a liquid (water and oil) in detecting a gas / liquid mixture composed of fine particles in air.

Another object of the present invention is to implement a smart shield simply and economically.

Yet another object of the present invention is to provide a chemical detector equipped with such a smart shield member.

On the other hand, other unspecified purposes of the present invention will be further considered within the scope of the following detailed description and easily deduced from the effects thereof.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein,

A step of adding an adhesive to a solution in which SiO ₂ nanoparticles are dispersed in an organic solvent, and immersing and drying the fluoropolymer film, and repeating the step of coating the fluoropolymer film with SiO ₂ ;

The step of immersing and drying the fluorine-based polymer film coated with SiO ₂ on a solution mixed with a hydrophobic substance to coat the hydrophobic substance on the film to impart water repellency and oil repellency; And

And forming a membrane for protecting the gas sensor with a fluoropolymer film having a double coating of the hydrophobic substance and SiO ₂ .

In the method for manufacturing a gas sensor protection membrane according to any one of the preferred embodiments of the present invention, the fluoropolymer film may be a polytetrafluoroethylene (PTFE) film.

The hydrophobic material may be at least one selected from the group consisting of alkyltrichlorosilane, alkyltrimethoxysilane, alkyltriethoxysilane, polytetrafluoroethylene (PTFE), polytetrafluoroethylene (PTFE), polytetrafluoroethylene , One of perfluoroalkoxyalkane (PFA), dichlorodimethylsilane (DDMS), perfluorodecyltrichlorosilane (FDTS), fluoroctyltrichlorosilane (FOTS) and octadecyltrimethoxysilane (OTMS) Or more.

The present invention also features a gas sensor protection membrane fabricated from a fluoropolymer film that is double coated with a silica coating and a hydrophobic material coating through a dip coating process.

According to the present invention, it is possible to produce a membrane for a gas sensor which not only has super-water repellency and oil repellency but also permits selective permeation of gas only. By allowing such a smart shield member to be used for a gas sensor, chemical weapons can be effectively detected in the air in any bad environment. This is not necessarily limited to military effects. A gas sensor that detects a variety of chemicals contained in air will naturally expand its effect.

On the other hand, even if the effects are not explicitly mentioned here, the effect described in the following specification, which is expected by the technical features of the present invention, and its potential effects are treated as described in the specification of the present invention.

FIG. 1 is an image showing the contact angle between water and hexadecane on the surface of a sample prepared by the examples and the comparative examples. FIG.
Fig. 2 is an image showing the wettability test of water and hexadecane on the surface of a sample prepared according to Examples and Comparative Examples. Fig.
FIG. 3 is a SEM and AFM photographs of the surface of a sample prepared according to Examples and Comparative Examples. FIG.
4 is a graph showing changes in superhydrophobicity / oil repellency of the samples prepared by the examples and the comparative examples after acid / base treatment.
Fig. 5 is a graph showing the results of the optical stability test of the samples produced by the examples and the comparative examples. Fig.
FIG. 6 is an image showing a method of inspecting the gas permeability of a film through a calcium carbonate precipitation reaction on a sample manufactured by the examples and the comparative examples.
FIG. 7 is a graph showing the gas permeation performance using the SPME method for the samples manufactured by the examples and the comparative examples.
FIG. 8 is a graph showing the gas permeation performance using the QCM method for the samples manufactured by the examples and the comparative examples.
* The accompanying drawings illustrate examples of the present invention in order to facilitate understanding of the technical idea of the present invention, and thus the scope of the present invention is not limited thereto.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for manufacturing a membrane used in a gas sensor including a chemical detector. The membrane of the present invention has water repellency and oil repellency.

The water repellency of the present invention means superhydrophobic. Hydrophobic, a water repellent in the general sense, means a property that can not be easily combined with water molecules. This is mainly achieved by eliminating water-soluble solutions such as water from the surface of the non-polar materials so that the water-soluble solutions aggregate and form water droplets. At this time, the contact angle of the surface is generally more than 90 °.

The contact angle refers to the angle at which the solid-liquid interface coincides with the liquid-gas interface. It is mainly used to measure the wettability of the solid surface, and the wettability of the solid surface can be evaluated by measuring the fixed contact angle and the roll angle hysteresis (difference between the maximum contact angle and the minimum contact angle).

The super water repellency in the present invention means a very high hydrophobic property. This refers to a case where the contact angle of water droplets formed on the surface exceeds 150 deg. And the hysteresis angle hysteresis is less than 10 deg. do. This characteristic is also called the Lotus effect. A hierarchical geometry structure is required to have these characteristics. Therefore, the present invention forms a dual scale rough surface with microroughness covered with nanoroughness on the membrane surface.

In addition, the membrane surface of the present invention has an oleophobic property. This refers to the surface properties excluding oily solutions.

The present invention was dip-coated to form a dual scale rough surface on the membrane surface. To form a precursor layer on the surface of the membrane, a dip coating is firstly performed, and a film consisting of the precursor is again dip coated secondarily.

A fluorine-based polymer film was used as the membrane base material. More preferably, the fluoropolymer film is a polytetrafluoroethylene (PTFE) film. It is well-known as DuPont Teflon ^TM . Polymeric fluoropolymer films capable of forming double-scale roughness through the coating process of the present invention are not limited to PTFE.

In the primary coating step, the process of immersing and drying the fluoropolymer film in the silica coating solution is repeated. The silica coating solution is obtained by adding an adhesive to a solution in which SiO ₂ nanoparticles are dispersed in an organic solvent. The repetition of the immersion and drying of the fluoropolymer film in the silica coating solution is preferably 1 to 5 times, preferably 20 seconds to 1 minute, and preferably 5 to 30 minutes. The fluoropolymer film is coated with SiO ₂ through this process.

In the second coating step, the SiO ₂ -containing fluoropolymer film obtained through the first step is immersed in a solution mixed with the hydrophobic substance and dried, and a hydrophobic substance is coated on the film to form a film on the surface of the substrate Form a double-scale roughness surface. Thereby imparting water repellency and oil repellency to the film.

The SiO ₂ is a hydrophobic solution immersion and the repeating of drying of the coated fluorine-containing polymer film preferably may be once to five hoein, immersion time is preferably 20 seconds ~ 1 minute, the drying time is preferably from 5 to 30 Minute. The fluoropolymer film is coated with SiO ₂ through this process.

The hydrophobic material may be mixed with an alkene-based organic solvent to form the hydrophobic solution.

Specific examples of the hydrophobic substance include alkyl trichlorosilane, alkyltrimethoxysilane, alkyltriethoxysilane, polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), dichlorodimethylsilane (DDMS) But are not limited to, perfluorodecyl trichlorosilane (FDTS), fluoro octyl trichlorosilane (FOTS), and octadecyl trimethoxysilane (OTMS).

Thus, a gas sensor protection membrane is fabricated by using a fluoropolymer film coated with a hydrophobic substance. Making and packaging the membrane to the desired size.

<Examples>

(a) First, 0.2 g of SiO ₂ nanoparticles are dispersed in 29 mL of hexane. To this solution was added 1 ml of a fluidized polydimethylsiloxane (PDMS), a hardener, and a 1: 0.1: 8 volume ratio of hexane to the adhesive. The PTFE film was immersed in the SiO ₂ solution for about 30 seconds and then dried at room temperature for 10 minutes. This process was repeated three times to prepare a SiO ₂ -coated PTFE film.

(b) Next, 1 ml of FOTS was mixed with 29 ml of hexadecane to prepare a FOTS solution with a hydrophobic solution. A SiO ₂ -PTFE film coated with FOTS was prepared by repeating the process of immersing the SiO ₂ -coated PTFE film in this solution for 30 seconds and drying for 10 minutes three times.

&Lt; Comparative Example 1 &

A SiO ₂ -coated PTFE film obtained by the process (a) of Example was prepared.

&Lt; Comparative Example 2 &

2.0cm)안에 FOTS 500μL를 넣었다. 실리카(SiO₂)로 코팅된 PTFE을 세라믹 홀더 위에 스테인리스강 철망에 고정 시킨 후 반응기를 완전히 밀봉한다. 반응기를 120에서 4시간 정도 가열하여 FOTS로 코팅된 SiO₂-PTFE을 제조하였다. A comparative group is made using the vapor deposition method. (a) was the same as that of the example. Ceramic holder located at the center of the stainless steel reactor surrounded by a heating band (2.5 cm

2.0 &lt; / RTI &gt; cm). The silica (SiO ₂ ) coated PTFE is fixed to the stainless steel wire mesh on the ceramic holder and the reactor is fully sealed. The reactor was heated at 120 for 4 hours to produce FOTS coated SiO ₂ -PTFE.

<Experimental Example 1>

Fig. 1 shows the result of measuring the contact angle of the sample of the example and the sample of the comparative example 2. Fig. The contact angles of water and hexadecane of the FOTS-PTFE of the example were measured, respectively. c) and d) are the contact angles of water and hexadecane of the FOTS-PTFE of the comparative example 2 Respectively. The contact angle with water was more than 150 °.

In addition, it was confirmed that the contact angle of hexadecane was 94 ° in the case of the sample of the present invention and 124 ° in the case of the sample of Comparative Example 2, both of which had oil repellency.

<Experimental Example 2>

This time, we tested the stability of water repellency and oil repellency. 2 shows a PTFE photographic image coated with an uncoated PTFE specimen, a comparative PTFE specimen coated with a vapor deposition pattern, and an example dip coating method.

The blue solution is water and the red solution is hexadecane. Uncoated PTFE samples did not penetrate water due to their water repellency, but hexadecane penetrated. In the sample of Comparative Example 2, both water and hexadecane remained spherical in shape, but it was confirmed that hexadecane penetrated into the sample over time. In contrast, the contact angle of the initial hexadecane was smaller than that of the sample of Comparative Example 2 as shown in FIG. 1, but the hexadecane did not permeate into the membrane sample and retained the initial oil repellency even after a lapse of time .

<Experimental Example 3>

The structure of the super water repellent and oil repellent surface was measured by scanning electron microscope (SEM) and atomic force microscope (AFM). Figure 3 shows the result.

3 (a), 3 (c) and 3 (e) are scanning electron micrographs, and b), d) and e) are atomic force microscope (AFM) image photographs. Also, a) and b) are samples of uncoated PTFE, c) and d) are PTFE samples of Comparative Example 2, and e) and f) are PTFE samples of the examples.

As can be seen from the photographic images of a) and b), in the case of uncoated PTFE specimens, there are many micropores in the microstructural level between the strands. As shown in the photographs of c) and d), in the case of Comparative Example 2, it was confirmed that a large amount of SiO ₂ and FOTS were attached to each strand. It is also confirmed that the existing pore structure is filled with SiO ₂ and FOTS deposited.

As can be seen from e) and f), it was confirmed that a larger amount of SiO ₂ and FOTS were deposited on each surface of the PTFE surface on the sample surface of the example. Also, it was confirmed that the deposited SiO ₂ and FOTS filled the pores and the existing pore structure almost disappeared.

<Experimental Example 4>

The elemental (F, Si, Cl) content of each sample was analyzed by energy dispersive spectroscopy (EDS) as shown in the following table.

Sample F Si Cl SiO2-coated PTFE 72.0 27.8 0.2 Vapor-deposited FOTS-PTFE 79.2 20.8 0.1 Dip-coated FOTS-PTFE 83.4 15.7 0.8

As in the case of Comparative Example 2 and Example, it was confirmed that the content of F was increased when FOTS was additionally deposited on the PTFE membrane sample. In addition, it was confirmed that the content of F was larger than that of Comparative Example 2 in the case of Examples. In other words, when dip-coating method was used, it was confirmed that a larger amount of FOTS was deposited on the surface of the PTFE membrane than in the vapor deposition method. This result is consistent with the results of the scanning electron microscopy and atomic force microscope analysis.

Based on the results of the analysis (FIG. 3), the characteristics of each of the sample samples shown previously (FIGS. 1 and 2) can be described. The hydrophobic properties of the PTFE specimens have SiO ₂ and FOTS coatings to provide a double-scale roughness structure that is hierarchical to the surface. As a result, the surface has a super-water-repellent property and also has a property of oil repellency. In the case of Comparative Example 2, it can be seen that even after the deposition, a part of the existing pore structure still remains, and the hexadecane penetrates gradually through the remaining pore structures, (Fig. 3).

On the other hand, in the case of the sample coated with FOTS by the method of the embodiment, most of the existing pore structure is filled with a large amount of FOTS, and most of the pore structure permeable to hexadecane disappears (FIG. 3) The oil repellency can be maintained over time (FIG. 2).

<Experimental Example 5>

The chemical durability of the samples of the examples was tested. Fig. 4 shows the result.

The samples of the examples were exposed to hydrochloric acid (pH = 1) and sodium hydroxide (pH = 10), respectively, and contact angles of water and hexadecane were measured. The contact angles of water and hexadecane were measured, increasing the exposure time to hydrochloric acid and sodium hydroxide, respectively. The contact angles of water and hexadecane were maintained at contact angles before exposure even after exposure to hydrochloric acid and sodium hydroxide I could.

As a result, it was confirmed that the super-water repellency and oil repellency of the gas sensor membrane samples developed through the present invention have excellent durability against acids and bases.

<Experimental Example 6>

The optical durability of the sample was tested. Figure 5 shows the result.

The sample of the example was irradiated with ultraviolet light (? = 254 nm) at atmospheric conditions and the contact angle of water and hexadecane was measured every 12 hours (120 hours). EXAMPLES The samples were maintained at the contact angle of water and hexadecane before exposure even when exposed to ultraviolet rays under atmospheric conditions. Through this, it was confirmed that the super water repellency and oil repellency of the PTFE membrane produced through the present invention were excellent in stability against ultraviolet irradiation As shown in Fig.

<Experimental Example 7>

Next, the gas permeability of the sample was tested. If gas permeability is not available, it can not be used as a membrane of a gas sensor. 6 is a photograph showing the evaluation method of the gas permeability of the sample made by the embodiment and the evaluation result thereof.

The evaluation method of Experimental Example 7 is based on the reaction that carbon dioxide (CO ₂ ) gas reacts with calcium hydroxide (Ca (OH) ₂ ) to convert to calcium carbonate (CaCO ₃ ) solid and precipitate as shown in the following reaction formula .

_{Ca (OH) 2 (aq)} + CO 2 (g) → CaCO 3 (s) + H 2 O

An aqueous solution of calcium hydroxide (Ca (OH) ₂ ) was placed in a small glass bottle, and the inlet portion was sealed with the membrane sample obtained in the example. The glass bottle was placed in a large glass bottle and carbon dioxide (CO ₂ ) gas was injected into the large glass bottle. As the carbon dioxide (CO ₂ ) gas was injected into the large glass bottle, precipitates were formed in the small glass bottle and the solution became cloudy. This means that carbon dioxide gas (CO ₂ ) injected into a large glass bottle permeates through the PTFE membrane and enters the small glass bottle to react with calcium hydroxide (Ca (OH) ₂ ) to form calcium carbonate (CaCO ₃ ) The results show the excellent gas permeability of the membrane obtained by the examples.

<Experimental Example 8>

Solid-phase micro extraction (SPME) was used to confirm gas permeation performance. This SPME method is a sampling technique using fibers coated with an extraction phase.

FIG. 7 shows the gas permeability performance of the PTFE membrane obtained in the examples compared with the SiO ₂ and PTFE membranes not coated with FOTS. The gas permeability was evaluated for the film-free state, the sample in which SiO ₂ and FOTS coating were not performed, and the sample in the examples, such three samples. The gas was dimethyl methylphosphonate (DMMP). The gas permeated through the membrane was partially extracted by the solid phase extraction (SPME) method and the amount of gas permeation was analyzed by gas chromatography (GC). Based on the DMMP permeation amount of the free film conditions, SiO ₂ and FOTS the case of the PTFE membrane is not coated sikyeotgo transmitted through the gas of about ~ 60%, a PTFE membrane coated with SiO ₂ and the FOTS to the embodiment of a dip coating method It was confirmed that the sample was permeable to ~ 20% gas.

<Experimental Example 9>

Next, the gas permeation performance was confirmed using a quartz crystal microbalance (QCM). Figure 8 shows the results.

The gas permeability performance of the PTFE membrane coated with SiO ₂ and FOTS sequentially by the dip coating method of the embodiment was analyzed using a quartz microbalance (QCM). FIG. 8 is a graph comparing the results with SiO ₂ and PTFE membranes not coated with FOTS. DMMP was used for the gas, and the amount of gas permeated through the membrane was analyzed using a quartz microbalance (QCM). The Y-axis of the graph is the value (ΔF / μg) measured on a quartz microbalance, and the value decreases as the amount of gas permeated through the membrane decreases. The measurements were made with Blank, SiO ₂ and FOTS uncoated PTFE (bare-PTFE), dip-coated SiO ₂ and FOTS coated FOTS-PTFE (Dip-coated FOTS-PTFE) . Based on the measured values in the film-free state, it was confirmed that ~ 72% of the gas permeated through the Bare-PTFE membrane and ~ 57% through the Dip-coated FOTS-PTFE membrane.

The scope of protection of the present invention is not limited to the description and the expression of the embodiments explicitly described in the foregoing. It is again to be understood that the present invention is not limited by the modifications or substitutions that are obvious to those skilled in the art.

Claims (6)

A step of adding an adhesive to a solution in which SiO ₂ nanoparticles are dispersed in an organic solvent, and immersing and drying the fluoropolymer film, and repeating the step of coating the fluoropolymer film with SiO ₂ ;
The step of immersing and drying the fluorine-based polymer film coated with SiO ₂ on a solution mixed with a hydrophobic substance to coat the hydrophobic substance on the film to impart water repellency and oil repellency; And
And forming a membrane for protecting the gas sensor with a fluoropolymer film having the hydrophobic substance and the SiO ₂ double coated. The method according to claim 1,
Wherein the fluorine-based polymer film is a polytetrafluoroethylene (PTFE) film. The method according to claim 1,
The hydrophobic substance may be at least one selected from the group consisting of alkyl trichlorosilane, alkyltrimethoxysilane, alkyltriethoxysilane, polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), dichlorodimethylsilane (DDMS) Wherein the membrane comprises at least one of decyltrichlorosilane (FDTS), fluoroctyltrichlorosilane (FOTS), and octadecyltrimethoxysilane (OTMS). delete delete delete

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