KR102497998B1 - Humidity detecting method using nanowire and humidity detecting apparatus using nanowire - Google Patents

Abstract

The present invention discloses a method for measuring relative humidity using a nanowire. The method may include preparing an optical fiber having one end of a nanowire including a material whose volume changes by absorbing moisture; injecting a predetermined incident light into the other side of the optical fiber after disposing the nanowire in the humidity measurement target space; measuring an interference pattern by reflected lights emitted from the other side of the optical fiber - the reflected light is generated when the incident light is reflected from an end of the optical fiber and an end of the nanowire; and determining the humidity of the humidity measurement target space by comparing the interference pattern with a predetermined reference interference pattern.

Description

Method for measuring relative humidity using nanowires and apparatus for measuring relative humidity using nanowires

The present invention relates to a method and apparatus for measuring relative humidity, and more particularly, to a method and apparatus for measuring relative humidity using a nanowire formed at an end of an optical fiber.

Humidity measurement in the microscale area is very important in micro/nanoscale science and technology fields such as microfluidics, microrobots, and nanoprocesses, but most humidity sensors are difficult to access in the microscale area, so research is sluggish. do.

Humidity sensing plays an important role in various fields such as human health, smart electronic devices, and industrial processes. For example, transmission of viruses that cause viral infections, such as severe acute respiratory coronavirus 2 (SARS-CoV-2), is highly dependent on the relative humidity of the air [1-3]. In addition, human body humidity sensing is a key factor enabling human-machine interaction [4], information security protection [5] and clinical diagnosis [6]. Moreover, environmental humidity dictates the quality of technological processes in the semiconductor, pharmaceutical, textile, and food industries [7-10].

Recently, the importance of humidity has become more important at the microscale, where water evaporates rapidly due to its large surface area per unit volume [11]. In particular, studies on the evaporation of water meniscus in micro-scale space include microfluidic-based pumping [12, 13], cooling of electronic devices [14, 15], evaporation lithography [16, 17] has been continuously receiving attention in various physical application fields. Evaporation at the meniscus of the microcapillary strongly depends on the internal humidity around the meniscus. This is because ambient humidity is a key factor in controlling water evaporation at the microscale. Therefore, measuring the internal humidity of microstructures is an essential task in various technical applications.

In recent years, humidity based electronic or photonic materials such as graphene oxide [18], photonic crystals [19,20], polymers [6, 21–23], and fluorescent molecules [24] [0003] In the sensor, several attempts have been made to improve sensitivity, response speed and device configuration compatibility in order to measure humidity distribution on a micro scale.

However, despite continuous research, the sensing ability of humidity sensors is still limited to surfaces or open spaces, and the spatial-temporal resolution is still low. For this reason, investigating the internal humidity distribution of the capillary meniscus remains a long-standing task and still relies only on theoretical approaches [25–27].

Meanwhile, an attempt has been made to measure humidity by forming a nanowire at the end of an optical fiber and using the formed nanowire as a nanoprobe. As an example of this attempt, Patent Registration No. 10-2005058 (2019.07.23.) (Name: Humidity Sensor) (hereinafter referred to as prior art) may be cited.

In the prior art, a nanostructure minimizing light loss at a junction between an optical fiber and a nanowire by directly growing a nanowire at an end of an optical fiber is disclosed. In addition, the prior art provides a basic structure of a humidity sensor using this nanostructure. Since the humidity sensor can measure humidity as long as there is a space through which only optical fibers and nanowires pass, it is mentioned that humidity can be measured even in a place where it is generally difficult to measure, such as a narrow passage in the form of a tube or open only one side.

However, in the prior art, as a method for measuring humidity, it is only disclosed that the humidity can be measured by comparing the difference between the wavelength due to the interference of light before measuring the humidity and the wavelength due to the interference of light after measuring the humidity, Humidity measurement method is not provided. In addition, a method for setting a reference humidity for measuring a wavelength before measuring humidity is not provided. Furthermore, there is no evidence for the grounds and principles for measuring humidity using nanowires.

An object of the present invention is to provide a method and apparatus for measuring relative humidity using a nanowire capable of accurately measuring humidity by accessing a microspace.

A method for measuring relative humidity using a nanowire disclosed in the present invention includes preparing an optical fiber having a nanowire including a material whose volume changes according to an amount of moisture absorbed at one end thereof; injecting incident light into the other side of the optical fiber after disposing the nanowire in the humidity measurement target space; Measuring an interference pattern by reflected lights emitted from the other side of the optical fiber - the reflected lights include reflected light reflected from an end of the one side of the optical fiber and reflected light reflected from an end of the nanowire, and the interference pattern is changed by the volume change of the nanowire; and determining the humidity of the humidity measurement target space by comparing the interference pattern with a reference interference pattern.

Here, for the reference interference pattern, the nanowires are placed in a reference humidity space set to a specific reference humidity, the incident light is injected into the other side of the optical fiber, and the interference pattern by the reflected light emitted from the other side of the optical fiber is measured. It is characterized by being obtained by doing.

In particular, determining the humidity of the humidity measurement target space by comparing the interference pattern with the reference interference pattern: determining the wavelength (λ _m1 ) of a specific peak in the reference interference pattern, and determining the specific peak in the interference pattern. Determining the wavelength (λ _m ) of the peak corresponding to , determining the change amount (Δλ _m ) of the wavelength between the peaks, and determining the humidity of the humidity measurement target space based on the change amount. .

Alternatively, determining the humidity of the humidity measurement target space by comparing the interference pattern with the reference interference pattern is: the wavelength of a specific peak in the interference pattern measured in the reference humidity space maintained at the first reference humidity (λ _m1 ) Determining a wavelength (λ _m2 ) of a peak corresponding to the specific peak in the interference pattern measured in the reference humidity space maintained at the second reference humidity, and corresponding to the specific peak up to the nth reference humidity. performing a procedure for measuring the wavelength (λ _mn ) of the peak (where n is a natural number of 2 or more), determining a humidity calculation approximation equation fitting the measured wavelengths, and applying the interference pattern to the humidity calculation approximation equation. It may include calculating humidity by applying

로서 정의되고, 여기서, λ_m은 계측 간섭패턴의 상기 특정 피크의 파장이고, a, b, c는 상기 피팅에 의해 결정되는 상수이고, RH는 상기 습도측정대상공간의 상대 습도인 것을 특징으로 한다. In particular, the humidity calculation approximation is

where _λm is the wavelength of the specific peak of the measurement interference pattern, a, b, and c are constants determined by the fitting, and RH is the relative humidity of the humidity measurement target space. .

In addition, determining the wavelength of each of the specific peaks in the interference patterns determines the center wavelength of the specific peak by applying a Gaussian fitting approximation to the measured values around the specific peak of the interference pattern may further include

Further, preparing the optical fiber having the nanowire formed at the end thereof: preparing a nanopipette filled with a solution of a material forming the nanowire and having the same inner diameter as the diameter of the nanowire, and inserting the optical fiber with the end upward. and, after bringing the solution into contact with the end of the one side of the optical fiber through the end of the nanopipette, by raising the nanopipette below a predetermined critical speed, the end of the one side of the optical fiber Forming the nanowire may be further included.

(단,

)의 수식으로써 결정될 수 있는데, d_pt는 상기 나노피펫 말단의 내경, x는 습윤고체 영역의 축방향 길이, E는 상기 용액내 용매의 증발 속도, φ_wet는 상기 습윤고체 영역내 용질(즉, 상기 나노선을 형성하는 물질)의 부피 분율, φ₀는 상기 나노피펫내의 상기 용액에서 상기 용질의 부피 분율이고, 상기 습윤고체 영역은, 상기 용액이 상기 나노피펫 말단으로부터 인출된 후 적어도 일부가 응고되어 상기 나노선의 형상을 유지하고는 있지만 표면에서 상기 용매가 여전히 증발하고 있는 중인 구간을 나타낸다.Here, the critical speed (ν _c ) is,

(step,

), where d _pt is the inner diameter of the tip of the nanopipette, x is the axial length of the wet solid region, E is the evaporation rate of the solvent in the solution, and φ _wet is the solute in the wet solid region (i.e., A volume fraction of the material forming the nanowire), φ ₀ , is a volume fraction of the solute in the solution in the nanopipette, and at least a part of the wet solid region solidifies after the solution is withdrawn from the end of the nanopipette. This indicates a section where the solvent is still evaporating on the surface while maintaining the shape of the nanowire.

Meanwhile, an apparatus for measuring relative humidity using a nanowire disclosed in the present invention includes an optical fiber having a nanowire including a material whose volume changes according to an amount of moisture absorbed at one end thereof; a photoreceptor for injecting incident light into the other side of the optical fiber; an interferometer for measuring interference caused by reflected lights emitted from the other side of the optical fiber; and after disposing the nanowires in the humidity measurement target space, injecting the incident light into the other side of the optical fiber, and measuring an interference pattern by reflected lights emitted from the other side of the optical fiber - It includes the reflected light reflected from one end and the reflected light reflected from the end of the nanowire, and the interference pattern is changed by a change in the volume of the nanowire. It includes a controller that determines humidity.

Here, the reference interference pattern is obtained by arranging the nanowires in a reference humidity space set to a specific reference humidity, injecting the incident light into the optical fiber, and measuring the interference pattern by the reflected lights.

In particular, an end of the nanowire has a flat cross section perpendicular to the longitudinal direction of the nanowire.

Further, the optical fiber is implemented in a tapered shape in which the diameter decreases toward the end of the one side of the optical fiber, and the diameter of the end of the one side of the optical fiber is smaller than the diameter of the nanowire.

In particular, an end of the nanowire has a flat cross section perpendicular to the longitudinal direction of the nanowire.

The relative humidity measuring device may further include a moisture supply device for controlling the reference humidity space to a specific humidity, wherein the moisture supply device: injects an arbitrary pure gas into the reference humidity space. a first gas line; a reservoir for storing distilled water and having an upper space of the distilled water connected to the reference humidity space; a second gas line for injecting the pure gas into the distilled water stored in the reservoir; and a flow controller configured to control humidity in the reference humidity space by controlling gas injection amounts of the first gas line and the second gas line.

The present invention provides a scannable humidity nanoprobe capable of accurately measuring humidity at a predetermined point by accessing a microscopic space and mapping a humidity distribution in a three-dimensional space. In addition, a method and apparatus for measuring relative humidity using a humidity nanoprobe are provided.

The humidity nanoprobe of the present invention provides excellent humidity distribution mapping based on high spatial resolution and fast response.

The performance of the humidity nanoprobe is verified by experimentally measuring the microscopic humidity distribution and evaporation rate distribution in a water meniscus formed in micro-capillaries, which are the simplest microfluidic models.

Thus, the present invention makes it possible to explore problems related to microscopic evaporation dynamics by overcoming the geometrical constraints on the humidity measurable space.

1 is a diagram for explaining the configuration, manufacturing method, and interference pattern of a humidity nanoprobe according to the present invention.
FIG. 2 is a view showing each part, in particular, a wet solid region when a nanowire is formed using a fine pipette.
3 shows a schematic structure of a humidity measuring device based on a nanowire probe interferometer (NPI) using a humidity nanoprobe according to the present invention.
4 is a diagram showing measurement results of interference patterns measured at various humidities and fitting to wavelengths of specific peaks.
5 is a diagram for explaining a method of determining a peak in an interference pattern.
Fig. 6 is a diagram explaining a moisture supply device.
7 is a diagram showing measurement results and analysis results of reference interference patterns measured at various reference humidities.
8 is a diagram showing results and analysis of measurement of humidity distribution around microwells using the humidity nanoprobe according to the present invention.

The present invention provides a nanowire-based humidity nanoprobe capable of scanning a microscopic space on a micro scale. Humidity measurement is based on real-time monitoring of the interferometric response of polymer nanowires to humidity.

In addition, the internal humidity distribution near the water meniscus is mapped by scanning the inside of the water-filled capillary at minute intervals using a humidity nanoprobe. Moisture distribution mapping allows high-resolution analysis of the evaporation rate near the water meniscus.

The humidity nanoprobe provided by the present invention provides 3D scan possibility, high resolution and high accessibility for mapping the internal humidity of microcapillaries, thereby enabling microscopic evaporation dynamics and microscopic evaporation dynamics in microscale geometric structures and devices. It can contribute to exploring various related issues.

On the other hand, in the present invention, it is described that a nanometer-sized structure is formed at the end of an optical fiber, and also referred to as a 'nanowire' or 'nanoprobe' and described. However, these structures are not necessarily limited to the nanometer size, and may be formed in the micrometer size. Accordingly, the 'nanowire' or 'nanoprobe' of the present invention may also be interchangeably referred to as a 'microwire' or 'microprobe'.

That is, the diameter of the nanowire according to the present invention may not only be between several nanometers and hundreds of nanometers, but may also be between several micrometers and hundreds of micrometers. In some cases, it may be implemented in a size of several millimeters.

1 describes the configuration, manufacturing method, and interference pattern of the humidity nanoprobe used in the present invention. The humidity nanoprobe (or, it may be referred to as 'nanowire') of the present invention is a nanowire having a nanoscale diameter at the end of an optical fiber having a tapered shape or a flat end that decreases in diameter toward the end. It is in an extended form.

로 근사될 수 있는데, 주변 습도에 의한 주어진 파장(λ)에 대한 나노선 형성 물질의 굴절률(n)의 변화 및 나노선의 길이(L)의 변화에 의존하여 변한다. The key principle of the humidity nanoprobe of the present invention is that when light of a predetermined wavelength is injected into an optical fiber having a nanowire formed at its end, the light is reflected at the end of the nanowire and at the end of the optical fiber, respectively, to form two reflected lights. It uses an interference pattern formed by two reflected lights interfering with each other (see FIG. 1(a)). Here, the phase difference (δ) of optical interference is

It can be approximated as , which changes depending on the change in the refractive index (n) of the nanowire-forming material for a given wavelength (λ) due to ambient humidity and the change in the length (L) of the nanowire.

The nanowire according to the present invention may be formed using a material whose volume changes by absorbing moisture. Such materials include poly(methyl methacrylate) (PMMA) or polystyrene (PS). In particular, poly(methyl methacrylate) (PMMA) (average Mw 996,000, Sigma-Aldrich), due to its ability to absorb water (~2wt%) and high refractive index (1.49) to confine light within the nanowire waveguide, has been shown to be highly effective in humidity nanoparticles. It is preferable as a material for the nanowire constituting the probe.

Additionally, as nanowire forming materials, Poly(lactic acid) (PLA), Poly(caprolactone) (PCA), PEDOT:PSS, Polystyrene-co-maleic acid, Poly(methyl methacrylate), Polycarbonate, Polyurethane, Polyvinylpyrrolidone (PVP ), a hydrophobic polymer selected from the group consisting of Polyvinylidene Fluoride (PVDF), or Poly(acrylic acid) (PAA), Polyacrylamide (PAM), Polystyrene, sulfonate (PSS), Poly(vinyl alcohol) (PVA), Alginate, and Dextran. A hydrophilic polymer selected from the group consisting of may be used. In addition, organic conductive polymers (π conjugated polymers) may also be used as nanowire-forming materials, and they are characterized in that electrical and optical properties can be freely controlled through chemical doping. Biopolymers may also be used as materials for forming nanowires. A nucleic acid selected from the group consisting of DNA and RNA, a protein selected from the group consisting of Bovine Serum Albumin (BSA), Gelatin, and Collagen, and a polysaccharide selected from the group consisting of Dextran and Glycogen correspond to this category. Meanwhile, all kinds of liquids capable of dissolving the nanowire-forming material may be used as a solvent for preparing a solution containing a nanowire-forming material, including DI water, DMSO, DMF, Toluene, Xylene, THF, Ethanol, Chloroform, etc. may be included.

Meanwhile, in the humidity nanoprobe according to the present invention using an interference pattern by reflected light, in order to improve the accuracy of humidity measurement, it is necessary to improve the intensity (or amplitude) of optical interference.

와 같이 표현될 수 있다[21],The strength of the interference is

It can be expressed as [21],

Here, I ₁ and I ₂ are the intensities of reflected light reflected from the end of the nanowire and the end of the optical fiber, respectively.

In order to obtain a clear peak from the interference pattern, strong reflected light is required, and in order to obtain strong reflected light, it is necessary to improve light coupling efficiency at the junction of the nanowire and the optical fiber. In order to improve light coupling efficiency, it is preferable that the nanowire and the optical fiber are coaxially aligned. In the present invention, in order to align the nanowires with respect to the optical fiber, nanowires are formed at the end of the tapered optical fiber through a 3D printing method using a nanopipette as shown in the optical micrograph shown in FIG. 1(b). grown directly.

In the case of forming the nanowire through the 3D printing method of manufacturing the nanowire disclosed in the present invention, even if the optical fiber and the nanowire are not precisely coaxially aligned, good photocombining efficiency is exhibited.

In addition, in order to obtain strong reflected light, the end of the nanowire may be formed flat (see FIG. 1(c)). As a result, as shown in FIG. 1(d), an interference pattern having a clear peak with high intensity can be obtained [32].

Here, the method of manufacturing the nanowire using the 3D printing method provided by the present invention will be described in detail.

In order to form a nanowire having a nanometer-scale diameter at the end of an optical fiber, first, a nanopipette having an end having an inner diameter substantially equal to the diameter of the nanowire to be formed is prepared.

The nanopipette is filled with a solution of a nanowire forming material.

The optical fiber is preferably arranged in a vertical direction, with the end facing upward. The nanopipette is placed above the optical fiber with its end pointing downward, also preferably in a vertical direction. The optical fiber can be fixed in its position, and the nanopipette can be configured to vertically lower-raise.

Here, the optical fiber and the nanopipette can be coaxially aligned by arranging both the optical fiber and the nanopipette vertically and adjusting the horizontal position so that the ends are positioned on the same vertical axis. In the present invention, vertically arranging both the optical fiber and the nanopipette and aligning them coaxially are not essential steps, but it is preferable to perform the coaxial alignment step in order to improve the light coupling efficiency and increase the intensity of the reflected light.

Subsequently, the nanopipette is lowered so that the end of the optical fiber and the end of the nanopipette come into contact with each other, so that the solution of the nanowire forming material comes into contact with the end of the optical fiber through the end of the nanopipette. At this time, the movement may be controlled to the extent that the tapered end of the optical fiber is at least partially inserted into the end of the nanopipette.

Next, by raising the nanopipette at a separation speed equal to or less than a predetermined critical speed (ν _c ), a nanowire having a diameter substantially equal to the inner diameter of the distal end of the nanopipette extends from the distal end of the optical fiber and is formed.

Here, the critical velocity (ν _c ) is the maximum limit value of the separation velocity that allows the nanowire to be formed to have the same diameter as the inner diameter of the distal end of the nanopipette, and when the separation velocity is lower than the critical velocity, the nanowire Nanowires having the same diameter as the inner diameter of the distal end of the pipette may be continuously and uniformly formed. On the other hand, when the separation speed is higher than the critical speed, nanowires having a diameter different from the inner diameter of the distal end of the nanopipette, in particular, smaller than the inner diameter, may be formed, and the diameter may also be irregular and uneven.

와 같은 방식으로 결정될 수 있다. 여기서, ν_wet은 습윤고체 영역의 성장 속도이고, x는 습윤고체 영역의 축방향 길이에 해당하고, E는 습윤고체 영역의 표면에서의 증발 플럭스(evaporation flux)이고, d_pt는 피펫 말단의 내경이고, φ_wet는 습윤고체 영역내 용질의 부피 분율(volume fraction)이고, φ₀는 미세 피펫의 용액내 용질의 부피 분율(volume fraction)에 해당한다. The critical speed (ν _c ) is,

can be determined in the same way. where ν _wet is the growth rate of the wet-solid region, x corresponds to the axial length of the wet-solid region, E is the evaporation flux at the surface of the wet-solid region, and d _pt is the inner diameter of the pipette tip , φ _wet is the volume fraction of the solute in the wet solid region, and φ ₀ corresponds to the volume fraction of the solute in the solution of the micropipette.

로써 정의될 수 있는데, 여기서, D는 용매의 확산 계수이고, c는 습윤고체 영역의 표면에 인접한 기체 영역에서의 용매의 증기 농도이다. In particular, E

where D is the diffusion coefficient of the solvent and c is the vapor concentration of the solvent in the gas region adjacent to the surface of the wet solid region.

On the other hand, the wet solid region means that, as shown in FIG. 2, when the micropipette is raised from the end of the optical fiber, the solution is withdrawn from the end of the micropipette and then at least partially solidified to maintain the shape of the fine wire. However, it refers to the region where the solvent drawn from the pipette by capillary flow is still evaporating on its surface.

3 shows a schematic structure of a humidity measuring device based on a nanowire probe interferometer (NPI) using a humidity nanoprobe according to the present invention.

Referring to the drawings, the humidity measuring device according to the present invention may include an optical fiber in which nanowires are formed, a light input device, an interferometer, and a controller.

An optical fiber has a structure in which a nanowire containing a material whose volume changes by absorbing moisture is formed at one end. Such a nanowire may be manufactured by the above-described manufacturing method.

The photoinjector injects predetermined incident light through the other side of the optical fiber (ie, the portion where the nanowire is not formed). Here, the incident light injected into the optical fiber may have any wavelength, but in the present invention, red light (wavelength: 625 nm) emitted from an LED or band-passed by an optical filter was used as an example for an experiment.

Incident light emitted from the light input device may be concentrated through an objective lens and injected into the other side of the optical fiber through a coupler.

An interferometer collects reflected light emitted from the other side of the optical fiber and measures an interference pattern. An interferometer may be coupled to the coupler. As shown, the interferometer may include a plurality of lenses, reflectors, prisms, detectors, and the like.

The controller injects incident light to the other side of the optical fiber by controlling the light input in a state where the end of the optical fiber (ie, the nanowire at the end) is inserted into the space to be measured for humidity. In addition, the interferometer is controlled to receive the measurement result of the interference pattern by the reflected light emitted from the other side of the optical fiber. Then, the humidity of the humidity measurement target space is determined by analyzing the received result.

The method for determining humidity in the present invention is as follows.

First, the nanowire is put into a reference humidity space maintained at a known reference humidity, and the interference pattern measured at this time is analyzed and maintained as a 'reference interference pattern'.

Subsequently, an interference pattern is measured in a target space in which humidity is to be measured (ie, a humidity measurement target space) (hereinafter referred to as 'measurement interference pattern').

Then, the humidity of the target space is determined by comparing the reference interference pattern with the measurement interference pattern.

In particular, determining the humidity of the humidity measurement target space by comparing the reference interference pattern with the measurement interference pattern measured in the humidity measurement target space is the wavelength of an arbitrary peak in the reference interference pattern (for example, the peak representing the maximum value). The wavelength (λ _m1 ) of is determined, and the wavelength of the peak corresponding to the wavelength of an arbitrary peak of the reference interference pattern in the measurement interference pattern (for example, the wavelength of the peak representing the maximum value of the measurement interference pattern (λ _{m )} )), determining the amount of change (or wavelength shift) between the wavelengths of the determined peak (Δλ _m ), and determining the humidity of the humidity measurement target space based on the determined amount of change (Δλ _m ). can

That is, since the wavelength shift of a specific peak appearing in the interference pattern of the humidity nanoprobe according to the present invention is proportional to the relative humidity of the space where the nanowire is placed, if the wavelength of the specific peak in the reference interference pattern can be known, the amount of change Relative humidity can be determined from the relationship of

Here, the specific peak may be the peak having the greatest intensity as described above in the interference pattern, or the peak appearing mth from a specific wavelength, the shape of the peak best fitting as a mathematical function, the specific peak It can be determined arbitrarily from a peak closest to the wavelength of , a peak that can be analyzed most rapidly and accurately in a humidity measuring device, and the like.

Meanwhile, FIG. 4 is a diagram showing measurement results of reference interference patterns measured at various reference humidities and fitting to wavelengths of specific peaks.

The reference interference pattern may be measured for one specific reference humidity, or preferably, may be measured for a plurality of different reference humidity. For example, the reference interference pattern may be measured for a plurality of types of reference humidity, such as 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc. (see FIG. 4(a)). ). It is preferable that the reference interference pattern be measured and maintained for each of as many types of reference humidity as possible. However, a method of measuring each reference interference pattern for several types of reference humidity, determining the optimal humidity calculation approximation formula using the measurement results, and calculating humidity using the determined humidity calculation approximation formula should also be considered. can

The method for determining the humidity calculation approximation may proceed as follows.

First, an interference pattern is measured in a space maintained at a first reference humidity, and a wavelength (λ _m1 ) of a specific peak is determined in the measured interference pattern. Subsequently, an interference pattern is measured in a space maintained at the second reference humidity, and a wavelength (λ _m2 ) of a specific peak (must be a peak corresponding to the specific peak) is determined in the measured interference pattern. By repeating the procedure for determining the wavelength in this way for n types of reference humidity, wavelength measurement values for n types of humidity are obtained (where n is a natural number of 2 or more). The measured result is the same as the red dots in FIG. 4(b), for example.

Subsequently, an approximate expression capable of expressing the acquired wavelength measurement values as a mathematical function is determined. An approximate formula may be, for example, a blue dotted line in FIG. 4(b).

로서 정의될 수 있다. 여기서, 최적의 피팅을 통해 상수인 a, b 및 c를 결정할 수 있다. The approximation is,

can be defined as Here, the constants a, b, and c can be determined through optimal fitting.

The approximation equation thus determined is used as an approximation equation for calculating humidity by using the wavelength of a specific peak appearing in the interference pattern measured using the humidity nanoprobe to determine the relative humidity of the target space.

That is, for example, if the wavelength of a specific peak is measured at 624.5 nm, the relative humidity can be calculated as any value between 60 and 70% by applying a predetermined humidity calculation approximation equation.

Meanwhile, a method for determining the wavelength value of the center (or maximum value) of a specific peak when a reference or measurement interference pattern is measured will be described with reference to FIG. 5 . The method includes determining an optimal approximation equation by Gaussian fitting measurement values appearing in the periphery of the peak.

로 정의될 수 있다. 가우시안 피팅은 공지된 방법을 활용할 수 있으므로, 상세한 설명은 생략한다. The approximation of Gaussian fitting is,

can be defined as Gaussian fitting can utilize a well-known method, so a detailed description will be omitted.

A central value (or maximum value) of a specific peak may be determined using this approximation formula, and a wavelength shift may be determined using the determined value.

On the other hand, the present invention provides a moisture supply device capable of supplying a controlled amount of moisture and maintaining a set humidity in order to form a reference humidity space. Referring to FIG. 6, the moisture supply device in the present invention includes a reference humidity space, a first gas line for injecting any pure gas into the reference humidity space, and a space above the distilled water for storing distilled water. A water tank connected to one gas line or the reference humidity space, a second gas line for injecting the pure gas into the distilled water stored in the water tank, and introducing the pure gas into the reference humidity space by controlling the first gas line and the second gas line, respectively. It may include a flow controller for controlling the amount of pure gas and / or moisture to be.

In this structure, when pure gas is injected into the second gas line, the pure gas evaporates the distilled water in the water storage tank, and the gas containing moisture is introduced into the reference humidity space.

Humidity inside the reference humidity space may be controlled by controlling the amount of pure gas in the first gas line and the amount of moisture-containing gas from the water storage tank. The flow rate of the gas containing moisture can be controlled by controlling the flow rate of the pure gas flowing into the reservoir.

Here, the pure gas may be nitrogen.

In the reference humidity space, a specific reference hygrometer for measuring humidity inside the space may be disposed. An operation of the flow controller may be controlled based on the measurement value of the reference hygrometer. At one side of the reference humidity space, an insertion portion into which the humidity nanoprobe of the present invention can be inserted may be formed.

It is possible to maintain the humidity of the reference humidity space at an arbitrary reference value using such a humidity supply device, and measure the reference interference pattern using the humidity nanoprobe of the present invention.

7 shows the wavelength shift of a specific peak of the interference pattern measured at various relative humidities.

Absorption of water molecules by the PMMA nanoprobe in air changes both the refractive index (n) and the length (L), resulting in a shift of a specific peak of the interference pattern (see Fig. 4(a)). In the figure, it is shown that the wavelength of a specific peak of the interference pattern gradually moves in a direction from black (relative humidity 30%) to yellow (relative humidity 90%).

Changes in n and L according to humidity depend on the equilibrium amount (w) of water inside the nanowire. Therefore, it is possible to investigate the local relative humidity (RH) according to the w-RH relationship estimated in the multi-molecular theory, as follows [29].

... (1)

... (One)

where w is the wt% of H ₂ O per PMMA, and w ₁ is a polymeric material dependent proportionality constant known to be 6.25 for PMMA [29].

In the physical absorption process, w changes reversibly according to the relative humidity, and real-time measurement is possible. The wavelength shift of a specific interference peak due to the change of n and L, as a function of w, can be summarized as follows [29-31].

... (2)

... (2)

Here, λ _m is the wavelength of a specific interference peak. The Δλ-RH relationship can be inferred from equations (1) and (2).

First, in the reference humidity space including the humidity supply device as shown in FIG. 6, the Δλ-RH relationship was experimentally investigated. In FIG. 7 , the measured wavelength shifts (Δλ _p ) at various relative humidities are indicated by red dots.

The Δλp-RH relationship can be calculated theoretically by calculating the contributions of the refractive index change (Δn=(δn/δw)Δw) and the length change due to swelling (ΔL=(δL/δw)Δw) in equations (1) and (2). can be checked with The theoretical refractive index change (Δn) with humidity is shown as a blue dotted line (a dotted line with a weak slope at the bottom) in the figure. The change in length (ΔL) due to theoretical swelling with humidity is indicated by a green dotted line (second dotted line from the top) in the drawing. The sum of the refractive index change (Δn) and the length change (ΔL) can be estimated as the wavelength shift of the interference pattern that actually occurred as the properties of the humidity nanoprobe changed, and it appears as a red dotted line (uppermost dotted line). .

Referring to the drawing, it can be seen that the actual measured value (red dot) and the theoretical calculation result (red dotted line) substantially coincide, which means that the measured value measured by the humidity nanoprobe according to the present invention is the actual relative humidity prove that it can accurately reflect

In particular, in relation to Δλ _p -RH, it can be confirmed that the contribution of length change (ΔL) is much greater than the contribution of refractive index change (Δn).

8 is a view showing the results and analysis of measuring the humidity distribution inside the microcapillary using the humidity nanoprobe according to the present invention.

The Δλ _p -RH relationship can be verified by quantitatively probing the humidity inside the microcapillary. Here, the sensitivity of the humidity nanoprobe was confirmed to be 0.029 nm/% RH at 30 to 90% RH. The λp- _RH association was globally characterized over a wide range of humidity from 10 to 90%.

In the present invention, the improved resolution of the humidity nanoprobe was demonstrated with high reliability by measuring the spatial humidity distribution by water evaporating from the water meniscus inside the microcapillary tube. Humidity mapping is measured and analyzed by scanning the humidity nanoprobe vertically (z) and horizontally (x).

As shown in FIG. 8(a), in a microcapillary with a diameter of 750 μm filled with water, the line connecting the maximum position of the water meniscus was set as the X-Y surface (i.e., z = 0), and the cross-section of the capillary Set the center as the origin.

At laboratory conditions of 23° C. and 34% RH, the capillary was filled with water and one end of the capillary was plugged to allow the water to evaporate in only one direction.

8(b) shows the measurement of relative humidity measured while changing the distance (z) from 25 to 600 μm at 25 μm intervals and also changing the horizontal position (x) from -300 to 300 μm at 25 μm intervals. values are indicated by dots. In addition, simulation results of relative humidity calculated under the same scanning conditions are displayed as a 3D surface plot.

The humidity distribution measured around the meniscus showed a maximum of 92% RH depending on the distance (z), and showed a decreasing tendency as the distance increased.

Simulations, represented by surface plots, are performed by numerical calculation of the Laplacian equation (COMSOL Multi-physics 5.4). The result of further investigation of the evaporation of the water meniscus is shown in Fig. 8(c). The humidity distribution measured at z = 25 μm was highest at the center and rather low at the edges. However, as z increases, the humidity distribution starts to reverse. That is, the humidity distribution measured at z = 185 μm is maintained almost constant along the horizontal direction. However, at a location far from the meniscus (z = 585 μm), the humidity distribution is lowest at the center (x = 0) and increases toward the edge.

In this way, using the humidity nanoprobe according to the present invention, it was possible to successfully measure the internal humidity distribution of the microscopic space based on the evaporation of the water meniscus.

On the other hand, the microscale distribution of humidity near the meniscus is affected by the ambient humidity. 8(d) shows vertical humidity profiles from 25 μm to 1.35 mm when the ambient humidity is 27% (red dot) and when the ambient humidity is 43% (blue dot). The measured values (dots) agree well with the calculated values (solid lines) based on the Laplacian equation. z = 25 μm In this case, the measured humidity reached 90% regardless of the ambient humidity. However, it can be seen that the decrease slope according to the distance of the measured humidity is greatly influenced by the surrounding conditions, and converges to the ambient humidity when the distance is sufficiently far.

On the other hand, when the ambient humidity is low, it can be seen that the humidity near the meniscus decays more rapidly (the decreasing slope with distance is steeper).

Based on the obtained humidity distribution, the evaporation rate (Q _e ) at the meniscus can be estimated as follows [33].

... (3)

... (3)

where p is the pressure of the system, M _w is the molecular weight, D is the diffusion coefficient of water in air, ρ is the density of water, R is the gas constant, A is the cross-sectional area of the microcapillary, and x _a is the mole fraction of water vapor.

In the present invention, the evaporation rate of the meniscus according to the ambient humidity was experimentally estimated and verified experimentally. At an ambient humidity of 27%, Q _e was 0.22 nL/s, whereas at an ambient humidity of 43%, Q _e was calculated to be 0.17 nL/s.

With the present humidity nanoprobe, it has been demonstrated quantitatively and experimentally that varying ambient humidity can be an effective strategy to control microscale evaporation in open fluidic systems.

In conclusion, using the present invention, it was possible to suggest internal humidity mapping in a microscopic space through 3D scanning of an interferometric humidity nanoprobe. The humidity nanoprobe disclosed in the present invention provides a non-invasive and highly accurate measurement method capable of accessing and exploring the minute humidity distribution and evaporation dynamics inside a micro-channel. Applicants anticipate that this invention will open up interesting applications in evaporation-related physics and engineering.

[references]

[1] J. Shaman, M. Kohn, Proc. Natl Acad. Sci. U.S.A. 2009, 106, 3243-3248.

[2] A. C. Lowen, S. Mubareka, J. Steel, P. Palese, PLoS Pathog. 2007, 3, 1470-1476.

[3] Y. Ma, Y. Zhao, J. Liu, X. He, B. Wang, S. Fu, J. Yan, J. Niu, J. Zhou, B. Luo, Sci. Total Environ. 2020, 724, 138226.

[4] J. Yang, R. Shi, Z. Lou, R. Chai, K. Jiang, G. Shen, Small 2019, 15, 1902801.

[5] L. Ju, W. Gao, J. Zhang, T. Qin, Z. Du, L. Sheng, S. X. A. Zhang, J. Mater. Chem. C 2020, 8, 2806-2811.

[6] J. Dai, H. Zhao, X. Lin, S. Liu, Y. Liu, X. Liu, T. Fei, T. Zhang, ACS Appl. Mater. Interfaces 2019, 11, 6483-6490.

[7] D. Li, E. J. Borkent, R. Nortrup, H. Moon, H. Katz, Z. Bao, Appl. Phys. Lett. 2005, 86, 024105.

[8] N. Zheng, X. Bu, P. Feng, Nature 2003, 426, 428-432.

[9] Z. Chen, C. Lu, Sens. Lett. 2005, 3, 274-295.

[10] L. Ruiz-Garcia, L. Lunadei, P. Barreiro, J. I. Robla, Sensors 2009, 9, 4728-4750.

[11] N. Scott Lynn, C. S. Henry, D. S. Dandy, Lab Chip 2009, 9, 1780.

[12] N. Scott Lynn, D. S. Dandy, Lab Chip 2009, 9, 3422-3429.

[13] R. Crawford, T. E. Murphy, A. K. Da Silva, H. Berberoglu, Exp. Therm. Fluid Sci. 2013, 51, 183-188.

[14] R. Xiao, S. C. Maroo, E. N. Wang, Appl. Phys. Lett. 2013, 102, 123103.

[15] D. Li, G. S. Wu, W. Wang, Y. D. Wang, D. Liu, D. C. Zhang, Y. F. Chen, G. P. Peterson, R. Yang, Nano Lett. 2012, 12, 3385-3390.

[16] S. Lone, J. M. Zhang, I. U. Vakarelski, E. Q. Li, S. T. Thoroddsen, Langmuir 2017, 33, 2861-2871.

[17] P. Kolliopoulos, K. S. Jochem, R. K. Lade, L. F. Francis, S. Kumar, Langmuir 2019, 35, 8131-8143.

[18] S. Borini, R. White, D. Wei, M. Astley, S. Haque, E. Spigone, N. Harris, J. Kivioja, T. Ryhanen, ACS Nano 2013, 7, 11166.

[19] J. H. Kim, J. H. Moon, S. Y. Lee, J. Park, Appl. Phys. Lett. 2010, 97, 103701.

[20] Y. Y. Diao, X. Y. Liu, G. W. Toh, L. Shi, J. Zi, Adv. Funct. Mater. 2013, 23, 5373-5380.

[21] C. Bian, M. Hu, R. Wang, T. Gang, R. Tong, L. Zhang, T. Guo, X. Liu, X. Qiao, Appl. Opt. 2018, 57, 356-361.

[22] C. Meng, Y. Xiao, P. Wang, L. Zhang, Y. Liu, L. Tong, Adv. Mater. 2011, 23, 3770-3774.

[23] P. Wang, L. Zhang, Y. Xia, L. Tong, X. Xu, Y. Ying, Nano Lett. 2012, 12, 3145-3150.

[24] Y. Cheng, J. Wang, Z. Qiu, X. Zheng, N. L. C. Leung, J. W. Y. Lam, B. Z. Tang, Adv. Mater. 2017, 29, 1703900.

[25] Y. Akkus, A. Koklu, A. Beskok, Langmuir 2019, 35, 4491-4497.

[26] H. K. Dhavaleswarapu, P. Chamarthy, S. V. Garimella, J. Y. Murthy, Phys. Fluids 2007, 19, 082103.

[27] K. Bellur, E. F. Medici, C. K. Choi, J. C. Hermanson, J. S. Allen, Phys. Rev. Fluids 2020, 5, 024001.

[28] J. Lee, H.-R. Lee, J. Pyo, Y. Jung, J.-Y. Seo, H.G. Ryu, K.-T. Kim, J. H. Je, Adv. Mater. 2016, 28, 4071-4076.

[29] A. M. Thomas, J. Appl. Chem. 1951, 1, 141-158.

[30] T. Watanabe, N. Ooba, Y. Hida, M. Hikita, Appl. Phys. Lett. 1998, 72, 1533-1535

[31] W. Zhang, D. J. Webb, Opt. Lett. 2014, 39, 3026-3029

[32] N. Kim, J. Lee, M. J. Yong, U. Yang, J. T. Kim, J. Kim, B. M. Weon, C. C. Kim, J. H. Je, Adv. Mater. Technol. 2020, 5, 1900937.

[33] N. S. Lynn, C. S. Henry, D. S. Dandy, Lab Chip 2009, 9, 1780-1788.

Claims (14)

preparing an optical fiber in which a nanowire containing a material whose volume changes according to the amount of moisture absorbed is formed at one end;
injecting incident light into the other side of the optical fiber after disposing the nanowire in the humidity measurement target space;
Measuring an interference pattern by reflected lights emitted from the other side of the optical fiber - the reflected lights include reflected light reflected from the end of the one side of the optical fiber and reflected light reflected from the end of the nanowire, and the interference pattern is changed by the volume change of the nanowire; and
A method of measuring relative humidity using nanowires, comprising comparing the interference pattern with a reference interference pattern to determine the humidity of the humidity measurement target space. According to claim 1,
The reference interference pattern,
Disposing the nanowire in a reference humidity space set to a specific reference humidity, and injecting the incident light into the other side of the optical fiber;
Relative humidity measuring method using a nanowire, characterized in that obtained by measuring the interference pattern by the reflected light emitted from the other side of the optical fiber. According to claim 2,
Comparing the interference pattern with the reference interference pattern to determine the humidity of the humidity measurement target space:
Determining the wavelength (λ _m1 ) of a specific peak in the reference interference pattern,
Determining the wavelength (λ _m ) of a peak corresponding to the specific peak in the interference pattern, and
A method for measuring relative humidity using nanowires, comprising determining a change amount (Δλ _m ) of the wavelength between the peaks and determining the humidity of the humidity measurement target space based on the change amount. According to claim 2,
Comparing the interference pattern with the reference interference pattern to determine the humidity of the humidity measurement target space:
Determining the wavelength (λ _m1 ) of a specific peak in the interference pattern measured in the reference humidity space maintained at the first reference humidity,
Determining the wavelength (λ _m2 ) of the peak corresponding to the specific peak in the interference pattern measured in the reference humidity space maintained at the second reference humidity,
Performing a procedure for measuring the wavelength (λ _mn ) of the peak corresponding to the specific peak up to the nth reference humidity (wherein n is a natural number of 2 or more);
determining a humidity calculation approximation that fits the measured wavelengths; and
A method for measuring relative humidity using nanowires, comprising calculating humidity by applying the interference pattern to the humidity calculation approximation formula. According to claim 4,
The humidity calculation approximation is

is defined as,
Here, λ _m is the wavelength of the specific peak of the interference pattern, a, b, and c are constants determined by the fitting, and RH is the relative humidity of the humidity measurement target space. How to measure relative humidity. According to claim 3 or 4,
Determining the wavelength of each of the specific peaks in the interference pattern and the reference interference pattern,
Relative humidity measurement using nanowires, further comprising determining a central wavelength of the specific peak by applying a Gaussian fitting approximation to measured values around the specific peak of the interference pattern or the reference interference pattern. method. According to claim 1,
Preparing an optical fiber having a nanowire formed at the end thereof is:
Preparing a nanopipette filled with a solution of a material forming the nanowire and having the same inner diameter as the diameter of the nanowire;
Fixing the optical fiber with the end facing upward, and
Forming the nanowire at the one end of the optical fiber by bringing the solution into contact with the one end of the optical fiber through the end of the nanopipette and then raising the nanopipette below a predetermined critical speed. A method for measuring relative humidity using nanowires, further comprising: According to claim 7,
The critical speed (ν _c ) is,

(step,

) is determined by the formula,
Here, d _pt is the inner diameter of the distal end of the nanopipette, x is the axial length of the wet solid region, E is the evaporation rate of the solvent in the solution, φ _wet is the volume fraction of the solute in the wet solid region, and φ ₀ is the The volume fraction of the solute in the solution in the nanopipette - the wet solid region, after the solution is withdrawn from the end of the nanopipette, at least partially solidifies to maintain the shape of the nanowire, but the solvent on the surface Represents a section that is still evaporating -, Relative humidity measurement method using nanowires. an optical fiber having a nanowire including a material whose volume changes according to an amount of moisture absorbed at one end of an optical fiber;
a photoreceptor for injecting incident light into the other side of the optical fiber;
an interferometer for measuring interference caused by reflected lights emitted from the other side of the optical fiber; and
After the nanowire is placed in the humidity measurement target space, the incident light is injected into the other side of the optical fiber, and an interference pattern by reflected lights emitted from the other side of the optical fiber is measured - includes the reflected light reflected from the end of the nanowire and the reflected light reflected from the end of the nanowire, and the interference pattern is changed by a change in the volume of the nanowire -, the interference pattern is compared with a reference interference pattern to measure the humidity of the target space A controller that determines; Relative humidity measuring device using a nanowire comprising a. According to claim 9,
The reference interference pattern,
Relative humidity measuring device using nanowires, characterized in that obtained by arranging the nanowires in a reference humidity space set to a specific reference humidity, injecting the incident light into the optical fiber, and measuring an interference pattern by reflected lights. According to claim 9,
The nanowire is characterized in that the nanowire is formed along the longitudinal direction of the optical fiber at the end of the one side of the optical fiber, relative humidity measuring device using a nanowire. According to claim 9,
The optical fiber is implemented in a tapered shape in which the diameter decreases toward the end of the one side of the optical fiber, and the diameter of the end of the one side of the optical fiber is smaller than the diameter of the nanowire. measuring device. According to claim 9,
An end of the nanowire has a flat cross section perpendicular to the longitudinal direction of the nanowire. According to claim 10,
The relative humidity measuring device further includes a moisture supply device for controlling the reference humidity space to a specific humidity,
The moisture supply device:
a first gas line injecting an arbitrary pure gas into the reference humidity space;
a reservoir for storing distilled water and having an upper space of the distilled water connected to the reference humidity space;
a second gas line for injecting the pure gas into the distilled water stored in the reservoir; and
a flow controller controlling the humidity inside the reference humidity space by controlling the amount of gas injected into the first gas line and the second gas line; Relative humidity measuring device using a nanowire, characterized in that consisting of.

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