WO2017204529A1 - Magnetoplasmonic film, humidity sensor including same, and method for manufacturing same film and sensor - Google Patents

Abstract

The present invention relates to a magnetoplasmonic film, a humidity sensor including the same, and a method of manufacturing them. A magnetoplasmonic film according to an embodiment of the present invention comprises: a polymer filter membrane; and a core/shell nanoparticle layer of Ag/Fe₃O₄ formed on the polymer filter membrane under the application of an external magnetic field. The magnetoplasmonic film is sensitive to a change in a surrounding genetic environment allows observation of a change in the color due to a change in the genetic environment with naked eyes.

Description

Magnetoplasmonic film, humidity sensor comprising the same and method for manufacturing same

The present invention relates to a magnetoplasmonic film, a humidity sensor including the same, and a method of manufacturing the same, and more particularly, a magneto that is sensitive to a change in the surrounding dielectric environment and that the change in color according to the change in the dielectric environment is visually observed. The present invention relates to a plasmonic film, a humidity sensor including the same, and a manufacturing method thereof.

Metamaterials are materials designed to have properties that have not yet been found in nature and consist of a collection of composite elements formed from common materials such as plastics and metals.

These materials are usually arranged in a repetitive pattern, and the properties of metamaterials are due to their structure, not the properties of the base material. That is, the exact shape, geometry, size, orientation, and arrangement of the metamaterials determine the properties of the metamaterial.

Unlike bulk materials, nanoparticles are widely used in the manufacture of metamaterials because physical properties known as intrinsic properties of materials can be controlled according to particle size. In particular, silver (Ag) has the best electrical and thermal conductivity among all metals, and due to the optical properties of Ag, it has the highest Surface Plasmon Resonance (SPR) in the visible range, so that the nanostructured silver is a catalyst, SERS It can be applied to many fields such as surface enhanced raman scattering, photonic crystal, microelectronic device, biosensor, and plasmonic solar cell.

The plasmonic effect is a phenomenon in which free electrons in a metal vibrate collectively by external light, which is a photo-electron effect in a metal. This effect causes most of the light energy to be transferred to free electrons at a specific wavelength of incident light. It is due to resonance phenomenon. The plasmonic structure can alter the size and arrangement of metal particles, such as gold or silver, to control the plasmonic resonance frequency. At this time, maintaining the size of the thin film or particles to a few tens of nanometers very small, and the distance between the particles also to several tens of nanometers is an important factor in controlling the plasmonic resonance frequency. Accordingly, various studies have been conducted to control the size of metal nanoparticles and to maintain a constant distance between particles, and nanopatterning and nanolithography methods are mainly used.

Korean Unexamined Patent Publication No. 2016-0047818 discloses a three-dimensional plasmonic nanostructure and a method of manufacturing the same, which have a large-area nanostructure and can control light absorption properties and crystallinity.

Korean Patent Laid-Open No. 10-2016-0028564 discloses a multilayer dielectric thin film having a one-dimensional optical band gap structure having a defect, a metal thin film disposed on one surface of the multilayer dielectric thin film and having a predetermined surface plasmon resonance condition. A multi-layered thin film for detecting an optical signal emitted through the multi-layer dielectric thin film after entering the nano-particle structure layer having a two-dimensional optical band gap structure and the multilayer dielectric thin film formed on the metal thin film and reflected from the nano-particle layer Disclosed is a plasmonic sensor in which a structure and a nano structure are combined.

An object of one embodiment according to the present invention is sensitive to changes in the surrounding dielectric environment, and provides a magnetoplasmonic film, the humidity sensor including the same and a method of manufacturing the same that can be visually observed the change in color according to the change in the dielectric environment. It is.

In one aspect, the invention provides a membrane; And a core or shell nanoparticle layer of Ag / Fe ₃ O ₄ of a single layer or two or more layers formed by adjoining core / shell nanoparticles of Ag / Fe ₃ O _{4 on} or in the membrane, wherein the core / shell nano Provided is a magnetoplasmonic film, characterized in that the color changes in the visible region in accordance with the change in dielectric constant between the particles.

The membrane functions as a support for the nanoparticles. It can be a substrate that allows nanoparticles to be present as coated on a surface without entering the membrane.

On the other hand, the membrane may be a porous polar polymer, the membrane may be preferably characterized in that the pore size is 0.1 to 0.5㎛, the diameter is 30 to 60mm.

The core / shell nanoparticles may be a single layer or multiple layers of two or more. It is preferable to form a nanoparticle layer of 5 layers or less, preferably 3 layers or less. Depending on the monolayer or thin lamination structure of such five layers or less, the magnetoplasmonic effect can be provided according to the change of permittivity around the particle.

The nanoparticles may be magnetically bonded to each other to form a single layer or a stacked structure stably.

The membrane is configured to be expandable and contractible, which can alter the spacing or arrangement between nanoparticles, thereby causing a change in dielectric constant between particles, which can cause visible color changes.

The core / shell nanoparticles of Ag / Fe ₃ O ₄ may be spherical particles having a diameter of 180 to 200 nm.

In another aspect, the present invention, the membrane; And a core or shell nanoparticle layer of Ag / Fe ₃ O ₄ of a single layer or two or more layers formed by adjoining core / shell nanoparticles of Ag / Fe ₃ O _{4 on} or in the membrane, wherein the core / shell nano Provided is a magnetic structure comprising a magnetoplasmonic film, characterized in that the color changes in the visible region in accordance with the change in dielectric constant between the particles.

In another aspect, the invention provides a membrane; And a core or shell nanoparticle layer of Ag / Fe ₃ O ₄ of a single layer or two or more layers formed by adjoining core / shell nanoparticles of Ag / Fe ₃ O _{4 on} or in the membrane, wherein the core / shell nano Provided is a humidity sensor, characterized in that the color changes in the visible region in accordance with the change in dielectric constant between the particles.

It may further include a hygroscopic inorganic salt doped around the core / shell nanoparticles to increase the moisture adsorption rate.

The hygroscopic inorganic salt may be a mixture of CaCl ₂ or KOH and K ₂ CO ₃ .

In another aspect, the present invention provides a method for producing a membrane comprising the steps of: preparing a membrane; Placing core / shell nanoparticles of Ag / Fe ₃ O ₄ in or on a membrane surface and applying a magnetic field to one side of the membrane; And it provides a method for producing a magnetoplasmonic film, comprising the step of drying the membrane.

The application of the magnetic field is characterized in that it is carried out by placing a magnetic block under the membrane.

Placing a core / shell nanoparticles of the Ag / Fe ₃ O ₄ is characterized in that the apply the core / shell nanoparticle dispersion of Ag / Fe ₃ O ₄ on the membrane.

The intensity of the applied magnetic field is characterized in that 30 to 100 mT.

In the manufacture of the magnetoplasmonic film according to an embodiment of the present invention, the nanoparticle layer may be formed under the application of an external magnetic field. As a result, a uniform and dense layer is formed by the strong magnetic response of the nanoparticles to the magnetic field and the high porosity of the membrane which accelerates the arrangement of the nanoparticles upon shrinkage of the polymer filter membrane.

One embodiment of the present invention can provide a humidity sensor (Humidity sensors) comprising a magnetoplasmonic film, the nanoparticle layer is very sensitive to the surrounding dielectric environment, the nano-scattering (Mie scattering) and It shows vivid color by Plasmon resonance scattering, ie it shows excellent detection ability that shows a vivid color change even when the surrounding minute dielectric environment changes, and this color change takes place in the visible region, so specialized equipment Can be observed with the naked eye.

1 is a schematic diagram schematically showing a method for producing a magnetoplasmonic film on a membrane according to an embodiment of the present invention.

2 is a scanning electron microscope (A) image and a transmission electron microscope (TEM) image of Ag @ Fe ₃ O ₄ nanoparticles according to an exemplary embodiment of the present invention.

3 is an extinction spectra (C) and a magnetic hysteresis curve (D) at 300K of Ag @ Fe ₃ O ₄ nanoparticles according to an embodiment of the present invention.

Figure 4 is a SEM (C) image of the magnetoplasmonic film prepared according to an embodiment of the present invention and the SEM image (D) of the magnetoplasmonic film prepared without the application of an external magnetic field.

5 is a reflection spectrum and a photograph of the magnetoplasmonic film according to the type of magnetic nanoparticles

6 is an SEM image (A) of a membrane to which PEG is added and a photograph thereof.

FIG. 7 is a graph (C) showing a correlation between λ _max and swelling values at a long wavelength peak according to the reflection spectrum (B) and PEG concentration of a PEG-doped membrane.

FIG. 8 is a color change photograph at various relative humidity levels of a CaCl ₂ doped humidity sensor and a KOH and K ₂ CO ₃ doped humidity sensor according to one embodiment of the present invention.

9 is a photograph showing color response to exhalation of a humidity sensor according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Accordingly, embodiments of the invention may be modified in many different forms and should not be construed as limited to the embodiments set forth herein.

Throughout the specification of the present invention, when a part is said to "include" a certain component, it means that it can further include other components, without excluding the other components unless otherwise stated.

Throughout the specification of the present invention, when a step is located "on" or "before" another step, it is not only when a step is in direct time series relationship with another step, but also after mixing with each step. Likewise, the order of the two stages may include the same rights as in the case of an indirect time series relationship in which the time series order can be reversed.

The terms "about", "substantially", and the like as used throughout the specification of the present invention are used at or near the numerical values when the manufacture and material tolerance unique to the meanings mentioned are given, and the present invention In order to facilitate the understanding of the agreement, accurate or absolute figures are used to prevent unscrupulous infringers from using the disclosures unfairly. As used throughout this specification, the term "step to" or "step of" does not mean "step for."

The present invention relates to a magnetoplasmonic film, a humidity sensor including the same, and a manufacturing method thereof. Magnetoplasmonic film according to an embodiment of the present invention is a membrane; And a core / shell nanoparticle layer of Ag / Fe ₃ O ₄ coated on the membrane under application of an external magnetic field.

Nanoparticle layer of the magnetoplasmonic film according to an embodiment of the present invention is a core / shell nanoparticles of Ag / Fe ₃ O ₄ (hereinafter referred to as 'nanoparticle', also referred to as Ag @ Fe ₃ O ₄ ) Planar particles may be contacted to form a single layer or two or more multilayers.

The nanoparticle layer may be formed under the application of an external magnetic field, thereby forming a uniform and dense layer due to the strong magnetic response of the nanoparticles to the magnetic field and the high porosity of the membrane to accelerate the arrangement of the nanoparticles upon shrinkage of the membrane. .

The nanoparticle layer is very sensitive to the surrounding dielectric environment, and displays vivid colors by Mie scattering and Plasmon resonance scattering of the nanoparticles. In other words, it shows a vivid color change in the change of the surrounding minute dielectric environment, and this color change occurs in the visible light region, so that it can be observed with the naked eye without specialized equipment.

By using these characteristics, the magnetoplasmonic film of the present invention can be utilized in various devices. Although not limited to this, the magnetoplasmonic film may be used as a magnet. Although not limited thereto, the magnetic field may be applied to the magnetoplasmonic film, and the magnet structure may be provided through a process of firing and aging.

One embodiment of the present invention provides a humidity sensor (Humidity sensors) including the magnetoplasmonic film (hereinafter also referred to as 'film').

More specifically, the humidity sensor according to an embodiment of the present invention comprises a membrane; A core / shell nanoparticle layer of Ag / Fe ₃ O ₄ formed on the membrane under application of an external magnetic field; And it may include a hygroscopic inorganic salt doped to the membrane, the magnetoplasmonic film may be used as a color indicator (color indicator).

As described above, the film exhibits a vivid color due to unscattering and plasmon resonance scattering of Ag / Fe ₃ O ₄ core / shell nanoparticles formed on the membrane. Due to the sensitivity to the high refractive index caused by plasmon resonance scattering of the nanoparticles and the excellent water absorption ability of the membrane, it shows excellent detection ability in both low humidity and high humidity conditions, and the clear color change of the film due to the difference in humidity is all visible. As it happens in, it can be checked with the naked eye without specialized equipment.

Hereinafter, the structure and characteristics of the magnetoplasmonic film according to an embodiment of the present invention and a method of manufacturing the same will be described in more detail. Magnetoplasmonic film according to an embodiment of the present invention can be more specifically specified and understood by the description of the manufacturing method.

According to one embodiment of the invention, the method for producing a magnetoplasmonic film comprises the steps of preparing a polymer filter membrane; Forming a core / shell nanoparticle layer of Ag / Fe ₃ O ₄ while applying a magnetic field to the polymer filter membrane; And removing the applied magnetic field and drying the polymer filter membrane.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows schematically the manufacturing method of the magnetoplasmonic film which concerns on one Embodiment of this invention.

Referring to FIG. 1, first, a polymer filter membrane 10 may be prepared.

The polymer filter membrane is made of a polymer of high polarity, has a high porosity, and may have a cross-linked structure. For example, but not limited to, nylon 66 filter membrane can be used.

Although not limited thereto, the pore size of the polymer filter membrane 10 may be 0.1 to 0.5 μm, and the diameter may be 30 to 60 mm.

Next, a core / shell nanoparticle layer of Ag / Fe ₃ O ₄ may be formed on the polymer filter membrane 10 while applying a magnetic field to the polymer filter membrane. The magnetic field is applied to one side of the membrane, so that the nanoparticles in the membrane are aligned with a minimum layer on the one side.

In general, the coffee-ring effect is often a useful patterning technique. However, there are times when this is an undesirable effect, for example, DNA microarrays, chemical recovery, and nanofabrication.

In the present invention, in order to suppress the coffee-ring effect, a method of applying a magnetic field has been devised, and thus a uniform and dense nanoparticle layer can be formed.

According to an embodiment of the present invention, the nanoparticle layer may be formed of a colloidal nanoparticle solution including a Ag / Fe ₃ O ₄ core / shell nanoparticle, more specifically, an aqueous colloidal suspension. It may be formed by dropwise in the form of droplets (droplet).

The method for preparing Ag @ Fe ₃ O ₄ core / shell nanoparticles is not particularly limited and can be synthesized by a generally known method.

The concentration of the colloidal aqueous dispersion is not limited thereto, but may be, for example, 3 to 10 mg / ml, and the loading amount may be appropriately adjusted according to the size of the membrane and the thickness of the film to be formed. But may be, for example, 5 to 30 μl. Although not limited thereto, the core / shell nanoparticles of Ag / Fe ₃ O ₄ may be spherical particles having a diameter of 180 to 200 nm dispersed alone.

According to one embodiment of the invention, the application of an external magnetic field may be applied by a magnet. Although not limited thereto, for example, a neodymium (NdFeB) block magnet 30 may be used, and the magnet 30 may be disposed under the polymer filter membrane to apply a magnetic field. For example, the strength of the applied magnetic field may be 30 to 100 mT.

A droplet 20 of the colloidal nanoparticle solution is dropped onto the polymer filter membrane 10 to which a magnetic field is applied, and the droplet spreads on the membrane. At this time, capillary flows of the nanoparticles are suppressed by an external magnetic field, and the nanoparticle layer may be coated on the membrane uniformly and densely. The nanoparticle layer may be formed as a single layer or two or more multilayers according to the amount of droplets, the strength of the magnetic field, the type of solution, and the like.

More specifically, since the polymer filter membrane 10 is composed of a highly polar polymer having a porous and cross-linked structure, when a polar solvent molecule, for example, water enters, it does not dissolve but instead expands. . The polymer filter membrane expands immediately after the aqueous solution drops and exhibits a maximum surface area. At the same time nanoparticles are randomly arranged and magnetically deposited on the surface of the polymer filter membrane. As the droplets seep and the solvent begins to evaporate, the polymer membrane shrinks to its original state and the nanoparticles gather together to form a dense layer. Because of the hydrophilicity and high porosity of the polymer filter membrane, the colloidal droplets can quickly dry after falling on the membrane.

That is, according to one embodiment of the present invention, the nanoparticles loaded under the application of an external magnetic field can form a uniform and dense layer without a coffee-ring effect.

When the nanoparticle layer is formed without the application of an external magnetic field, a strong coffee-ring effect may occur, and thus a thin ring in which most of the nanoparticles have a deep red reflection color does not appear in the central region. And the distance between the nanoparticles is not uniform and can be randomly dispersed on the surface of the membrane.

However, in the case of forming the nanoparticle layer under the application of an external magnetic field as in one embodiment of the present invention, it is possible to exhibit a vivid red reflectance in all regions and to have a uniform and dense monolayer / or multilayer between particles. The nanoparticle layer can be formed.

When the forming of the nanoparticle layer is completed, the applied magnetic field may be removed, and the polymer filter membrane may be dried to obtain a magnetoplasmonic film. According to one embodiment of the present invention, after drying is completed, it can be stored for a predetermined time at a predetermined temperature. Although not limited to this, for example, it can be stored for 30 minutes at 60 ℃ temperature.

In addition, another embodiment of the present invention provides a method of manufacturing a humidity sensor comprising the magnetoplasmonic film.

As described above, when the polymer filter membrane is formed of a polar polymer, the polymer filter membrane has excellent water absorption ability.

According to one embodiment of the invention, since the polymer filter membrane itself does not show excellent moisture absorption capability, it is possible to dope hygroscopic inorganic salts into the polymer filter membrane.

According to one embodiment of the present invention, after forming the nanoparticle layer, it may further include the step of doping hygroscopic inorganic salts (hygroscopic inorganic salts) on the membrane (10).

Although not limited thereto, the hygroscopic inorganic salt may be CaCl ₂ , or a mixture of KOH and K ₂ CO ₃ . For example, but not limited to, 1 to 5 M CaCl ₂ or 0.5 to 1 M KOH and K ₂ CO _{3, respectively.} Mixtures of these may be used. The amount of the salt solution to be doped is not particularly limited and may be, for example, 5 to 10 μl.

After doping the hygroscopic inorganic salt, it can be stored for a predetermined time at a predetermined temperature. Although not limited to this, for example, it can be stored for 30 minutes at 60 ℃ temperature.

It can be observed that during the manufacture of the magnetoplasmonic film according to one embodiment of the invention the reflected color changes from blue to red after the loading is complete and the film is completely dried. This color reaction may be due to swelling leading to a change in distance between nanoparticles and / or a change in dielectric constant around.

According to one embodiment of the present invention, the magnetoplasmonic film includes nanoparticles having a core / shell structure of Ag / Fe ₃ O ₄ , and exhibits strong reflection color. This is believed to be due to the electromagnetic interaction of the metal core particles with the dielectric shell. This feature responds to minute changes in the dielectric constant in comparison with other types and types of nanoparticles, and has a characteristic that the change in the reflection color occurs in the visible region.

According to one embodiment of the present invention, it can be used under low humidity or high humidity conditions depending on the absorption ability of the hygroscopic inorganic salt, for example, when using CaCl ₂ as the hygroscopic inorganic salt, it can be used under relatively low humidity conditions, When using a mixture of KOH and K ₂ CO ₃ it can be used in relatively humid conditions.

In addition, the CaCl ₂ -doped humidity sensor may exhibit a rapid color change response even with minute humidity differences such as human exhalation, and may have excellent sensitivity of humidity sensing.

Hereinafter, the present invention will be described in more detail with reference to one embodiment of the present invention, but these are not intended to limit the scope of the present invention.

Example 1

Reagent Preparation

Ferric nitrate nonahydrate (Fe (NO ₃ ) ₃ 9H ₂ O), sodium citrate (C ₆ H ₅ Na ₃ O ₇ 2H ₂ O), sodium acetate (CH3COONa, NaAc), silver nitrate (AgNO3), ethylene glycol (EG), diethylene glycol (DEG), polyethylene glycol (PEG, Mn 200), potassium hydroxide (KOH) ), Potassium carbonate (K ₂ CO ₃ ), lithium chloride (LiCl), magnesium chloride (MgCl ₂ ), magnesium nitrate hexahydrate (Mg (NO ₃ ) ₂ · 6H ₂ O), potassium chloride (KCl) and potassium nitrate (KNO3) were purchased from Sigma-Aldrich Inc., Yongin, Korea Glycol was obtained from Biosesang (Biosesang, Gyeonggi-do, Korea) Calcium chloride was obtained from Yakuri Pure Chemical Co. (Kyoto, Japan), Copper (II) chloride (CuCl). ₂ ) was purchased from Junsei (Tokyo, Japan) Citric acid (C ₆ H ₈ O ₇ ) was purchased from Hayashi Pure Chemical Ind., Ltd., Japan (Japan) Nylon filter membrane (0.2 μm pore size, 47 mm diameter) was purchased from Whatman, UK Deionized water (> 18 MΩcm-1) was used for all solution preparations and experiments. It was a reagent and was used without further purification.

Synthesis of Ag @ Fe3O4 Core / Shell Nanoparticles

Ag @ Fe ₃ O ₄ core / shell nanoparticles were synthesized by generally known methods. Iron nitrate hexahydrate (Fe (NO ₃ ) ₃ .9H ₂ O) (4 mmol) was dissolved in ethylene glycol (40 mL), and sodium acetate (35 mmol) and silver nitrate (AgNO ₃ , 0.59 mmol) were added. The mixture was stirred vigorously until all reactants were completely dissolved. The resulting mixture was transferred to a 50 mL Teflon-lined stainless-steel autoclave and heated at 210 ° C. for 4 hours. The black product was washed several times with ethanol and deionized water and then dried in vacuo at 60 ° C. for 6 hours. 15 mg of the prepared nanoparticles were dispersed in 15 ml of citric acid (0.6 mg / ml) to stabilize the nanoparticles. The solution was sonicated with an ultrasonic probe for 2 hours. Then, the nanoparticles were washed with deionized water using a magnet, and the washing process was repeated three times.

Formation of Magnetoplasmonic Films

The magnetoplasmonic film of Ag @ Fe ₃ O ₄ nanoparticles was uniformly formed on the membrane under the application of an external magnetic field. Aqueous colloidal suspension (5 mg / ml) was loaded onto a membrane placed on neodymium (NdFeB) block magnets (40 mm × 20 mm × 5 mm) ( B = 50 mT). Capillary flows of the nanoparticles were suppressed by an external magnetic field and a uniformly coated film was obtained. Colloidal droplets (10 [mu] l, droplets) rapidly dried after 12 seconds of falling onto the membrane. After drying completely, it was stored for 30 minutes in an oven at 60 ℃ temperature.

Manufacturing of Humidity Sensor

The humidity sensor was prepared by doping hygroscopic inorganic salts to the membrane. Two humidity sensors were fabricated to sense different humidity ranges. A mixture of 2M CaCl ₂ and 0.625M KOH and 0.625MK ₂ CO ₃ was used for the sensing of low humidity and high humidity, respectively. 6 μl of salt solution was loaded onto the membrane coated with nanoparticles and stored at 60 ° C. for 30 minutes. The humidity sensor was placed in a closed box (38 mm x 10 mm) containing 300 μl of saturated salt solution as a moisture source. Six humidity control salt solutions of LiCl, MgCl ₂ , Mg (NO ₃ ) ₂ , CuCl ₂ , KCl and KNO ₃ with humidity values of 11%, 33%, 52%, 68%, 85% and 95%, respectively The temperature of 25 degreeC was maintained.

[evaluation]

The morphology of Ag @ Fe ₃ O ₄ NPs nanoparticles was measured by HR-TEM (JEOL, JEM-3010, Japan) and FE-SEM (S-4700, Hitachi, Japan). Magnetic measurements were performed using a Superconducting Quantum Interference Device (SQUID) magnetometer (MPMS XL-7, Quantum Design, Inc., San Diego, CA). . Absorbance and reflectance of nanoparticles are determined by UV-Vis spectroscopy (SCINCO, S310, Korea) and UV-Vis-NIR spectrophotometer, Cary 5000, respectively. , Varian, USA).

Core / Shell Nanoparticles

Magnetoplasmonic nanoparticles with an Ag core and a Fe ₃ O ₄ shell were prepared by an easy one-step solvothermal route by reduction of Ag ⁺ , Fe ^{3 +} and EG. The nanoparticles were stabilized by adsorption of citric acid through one or more carboxylate functional groups, indicating that the surface is negatively charged.

Figure 2 (A) is an SEM image of the Ag @ Fe ₃ O ₄ nanoparticles prepared in the above example, referring to this, it can be seen that the spherical nanoparticles having a diameter of about 190nm is dispersed alone, FIG. The magnified SEM image of 2 (A) shows that the surface of the nanoparticles is rough and composed of many small nanoparticles.

2 (B) is a TEM image of the magnetoplasmonic core / shell nanoparticle, in which the Ag core appears black and Fe ₃ O ₄ appears brighter due to the higher electron density than the Ag metal. The Ag core has a nearly uniform size of about 65 nm and the shell has a thickness of 62 nm (thickness of ca.).

In Figure 3 (A) there are two peaks of core-shell nanoparticles which are clearly distinguished. Peaks around 400 nm and 697 nm are due to the Mie scattering resonance of the iron oxide shell and the localized surface plasmonic resonance (LSPR) of the Ag core, respectively. The characteristic SPR peak around 420 nm is due to the large red-shift of the SPR peak of the core / shell nanoparticles (high reflectance (2.42) of the dielectric Fe ₃ O ₄ surrounding the Ag core at 697 nm.) Porous core / shell The magnetic properties of the nanoparticles can be seen in magnetic hysteresis loops at 300 K in Fig. 2 (B) The nanoparticles exhibit high magnetization saturation (M _S = 64 emu / g) and coercivity. ) It shows high soft ferromagnetism with H _C ~ 3.5Oe.

Magnetoplasmonic film

4 is a SEM image (C) of the magnetoplasmonic film prepared according to an embodiment of the present invention and a SEM image (B) of the magnetoplasmonic film prepared without the application of an external magnetic field.

Referring to the inset of Figure 4 (A), strong coffee-ring effects are observed in films made without external magnetic fields, where the majority of the nanoparticles have a deep red reflection color, while the central region of the center does not exhibit a clear reflection color. Gathered in a thin ring to indicate. By SEM inspection, the nanoparticles were observed to have random distances on the surface of the membrane with a range of interparticle distances.

In contrast, as shown in FIG. 4 (B), films made under the application of an external magnetic field in accordance with an embodiment of the present invention exhibit vivid red reflectance in all regions, with uniform and dense distances between particles. It can be confirmed that a multilayer is formed.

Color reaction

During the preparation of the magnetoplasmonic film, it was observed that the reflection color changed to blue when the loading was completed and the film was completely dried. This interesting color reaction may be due to swelling leading to a change in distance between particles and / or a change in dielectric constant around.

In order to explain the exact mechanism of the color change, the morphology of the film produced and the drying after adding DEG were examined by SEM. The membrane can be swollen by the addition of DEG and then reversibly retracted.

Compared to the film produced in this example, there are many cracks that divide the film into small island regions after the membrane has swollen and shrunk. Because of the limitations of the fabricated structure, it was found that the distance between the particles in each island region remained the same, while the film split into separate island regions due to the expansion of the membrane.

To clarify that the surrounding dielectric environment is the cause of the color change, various solvents were applied to the film. Because of the high polar polymer of nylon 66, the polar solvent has an affinity with nylon 66, forming H-bonds with the polyamide chains. The strong interaction of nylon 66 with the polar solvent causes the membrane to expand. In contrast, nonpolar molecules do not have any polar interaction with nylon 66 and cannot swell the membrane. Regardless of the type of solvent, the film responds clearly to both polar and nonpolar solvents, with purple to dark violet, blue violet, blue violet, Color change was observed with dark blue and cyan.

Optical Properties of Magnetoplasmonic Films

In order to study the optical properties of magnetoplasmonic films, various kinds of Fe ₃ O ₄ nanoparticles were used, and the films were prepared on the membrane using the same coating technique, and then reflectance was measured. The reflectance of the sample was measured in two different states, dried and doped with PEG. PEG molecules enter the expanded membrane network when loaded and are retained therein after being dried. This increases the surrounding dielectric environment surrounding the film at equilibrium after complete drying.

FIG. 5 shows reflection spectra of magnetoplasmonic films coated with four kinds of magnetic nanoparticles and photographs thereof (250 nm hollow Fe ₃ O ₄ (A), 250 nm solid Fe ₃ O ₄ (B)). , 350 nm solid Fe ₃ O ₄ (C) and 190 nm Ag @ Fe ₃ O ₄ (D)).

Referring to FIG. 5, it was observed that the 250 nm solid Fe ₃ O ₄ sample appeared black in the dried state, while the hollow Fe ₃ O ₄ and core / shell Fe ₃ O ₄ samples clearly showed strong reflection colors. Could. 350nm Solid Fe ₃ O ₄ The sample shows dim blue-green. The reason for the relatively strong reflection color of the hollow sample may be due to the nonuniformity of the spherical hollow and the Mie scattering of the low density structure. Particle geometry, which can strongly affect electron and magnetic resonance, and their interactions, is known to play an important role in controlling the scattering direction of the sphere. The geometrical parameters of the hollow sample in the dried state are likely to satisfy the conditions indicative of backscattering to cyan (see FIG. 5 (A)). The reflected color also matches the spectra representing two peaks of 451 nm and 564 nm. In contrast, the conditions for directional scattering are not satisfied for 250 nm and 350 nm solid samples (FIGS. 5 (B), (C)). Obvious peaks are observed in the reflection spectra of the 350 nm solid sample (FIG. 5C), but the picture of the sample shows very dark cyan. This is very weak for the human eye but can be evidence of un-directional scattering that can be effectively collected by diffuse reflectance measurement. After doping of PEG, only the core / shell sample showed a strong reflection color. The 250 nm hollow Fe ₃ O ₄ sample was black while the weak yellow and green colors were observed in the 250 nm hollow and 350 nm solid samples, respectively.

Referring to FIG. 5D, in the case of the magnetoplasmonic film according to one embodiment of the present invention, there are two distinct peaks in the visible region (420 nm and 720 nm) in the reflection spectrum of the dried film. However, the high intensity ratio of the long wavelength peak to the short wavelength peak causes the film to appear red. After PEG doping, the long wavelength peak shifts significantly to 750 nm, which is invisible to the human eye, and the film shows a deep blue color that matches the short-wavelength peak of 430 nm.

Refractive Index and Sensitivity of Film

PEG was used to study the refractive index and sensitivity of the film.

6 is an SEM image (A) and a photograph (B) of the membrane to which PEG was added.

As shown in the SEM image of FIG. 6 (A), the network of the membrane is filled with PEG, and it can be seen that the porosity is clearly reduced as the concentration of PEG increases.

FIG. 7 is a graph (B) showing the correlation between λ _max and swelling values at a long wavelength peak according to the reflection spectrum (A) and PEG concentration of a PEG-doped membrane.

Referring to FIG. 7 (B), the short-wavelength peak caused by Mie scattering resonance is slightly red-shifted, 20% at 420 nm of the membrane to which 0% PEG is added and The membrane with 30% PEG added slightly shifted to 426 nm and 428 nm, respectively. This peak is fixed at 431 nm with increasing PEG concentrations of 50, 75 and 100%. Together with the red-shift properties, the peaks noticeably widen as PEG concentration is increased. On the other hand, the long-wavelength peak red-shifts from 731 nm to 792 nm when the PEG concentration increases from 0 to 30%, and the mass swelling value increases from 0 to 49%. As PEG concentration increases by 100%, mass expansion increases linearly by 173%. Long-wavelength peaks cannot be determined at PEG concentrations above 50% due to the limitation of the monochromator.

Referring to FIG. 6 (B), the droplets dried after various PEG concentrations were added are deep red, violet and blue-violet to deep blue. strongly reflects the color up to -blue). This change in color may be due to a bi-color characteristic as mentioned above (see FIG. 7 (A)). The film with 0% PEG added showed a dark red reflection due to the dominance of plasmon resonance scattering to Mie scattering. When the PEG concentration increased by 10%, the long-wavelength peak shifted significantly to 749 nm, which is invisible to the human eye, and the film showed violet color (426 nm). At higher PEG concentrations, the contribution of the reflection color of the long-wavelength peak is not significant. Indeed, the film appears dark blue according to the color of the 431 nm wavelength when the PEG concentration at which the refractive index of the media around the film is saturated (n = 1.46) is at least 50%.

Humidity sensor

The reaction of the salt-doped film to relative humidity (RH) is a closed petri dish containing saturated salts to control the range from low humidity (11%) to high humidity (95%). (closed petri dishes).

8 is a photograph of reaction in various relative humidity environments of a CaCl ₂ doped humidity sensor and a KOH and K ₂ CO ₃ doped humidity sensor prepared according to one embodiment of the present invention.

Referring to FIG. 8, for CaCl ₂ -doped films, fast color change was observed when the film was placed in a dish. In addition, noticeable color change was observed when the relative humidity changed from 11% to 85%.

In contrast, the color reaction of KOH, K ₂ CO ₃ -doped films to relative humidity proceeded relatively slowly compared to CaCl ₂ -doped films. In addition, KOH, K ₂ CO ₃ -doped films showed no color change at low relative humidity (11% to 52%), but large changes were observed at 52% to 95%. The difference between the two types of humidity sensors is believed to be due to the moisture absorption capacity of the mixture of CaCl ₂ and KOH and K ₂ CO ₃ .

9 is a photograph showing color response to exhalation of a humidity sensor according to an embodiment of the present invention.

CaCl ₂ -doped films were used to sense humidity changes due to human exhalation. The humidity sensor showed a fairly fast color response to exhalation. At the peak of exhalation, the color changed from dry red to red-violet, violet blue and blue green in 2.7 seconds, and within 1.9 seconds after the exhalation stopped. It quickly returned to dark red.

Although the present invention has been described in detail above with reference to embodiments and examples, the present invention is not limited to the above embodiments, and may be modified in various forms, and is common in the art within the technical spirit of the present invention. It is clear that many variations are possible by the knowledgeable. In addition, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

Claims (14)

1. Membrane; And

   Ag / Fe ₃ O ₄ core / shell nanoparticles of Ag / Fe ₃ O ₄ formed on or in the membrane adjacent to each other comprises a single layer or two or more layers of Ag / Fe ₃ O ₄ core / shell nanoparticle layer,

   The color is changed in the visible region according to the change in dielectric constant between the core / shell nanoparticles,

   Magnetoplasmonic film.
2. The method of claim 1,

   The membrane is characterized in that the porous polar polymer,

   Magnetoplasmonic film.
3. The method of claim 2,

   The membrane has a pore size of 0.1 to 0.5㎛, characterized in that the diameter of 30 to 60mm,

   Magnetoplasmonic film.
4. The method of claim 1,

   The core / shell nanoparticles are characterized in that they are magnetically bonded to each other,

   Magnetoplasmonic film.
5. The method of claim 1,

   The membrane is configured to be expandable and contractible, characterized in that changing the spacing or arrangement between nanoparticles,

   Magnetoplasmonic film.
6. The method of claim 1,

   The core / shell nanoparticles of Ag / Fe ₃ O ₄ is characterized in that the spherical particles having a diameter of 180 to 200nm,

   Magnetoplasmonic film.
7. Membrane; And

   Ag / Fe ₃ O ₄ core / shell nanoparticles of Ag / Fe ₃ O ₄ formed on or in the membrane adjacent to each other comprises a single layer or two or more layers of Ag / Fe ₃ O ₄ core / shell nanoparticle layer,

   The color is changed in the visible region according to the change in dielectric constant between the core / shell nanoparticles,

   Magnetic structure comprising a magnetoplasmonic film.
8. Membrane; And

   Ag / Fe ₃ O ₄ core / shell nanoparticles of Ag / Fe ₃ O ₄ formed on or in the membrane adjacent to each other comprises a single layer or two or more layers of Ag / Fe ₃ O ₄ core / shell nanoparticle layer,

   The color is changed in the visible region according to the change in dielectric constant between the core / shell nanoparticles,

   Humidity sensor.
9. The method of claim 8,

   Further comprising a hygroscopic inorganic salt doped around the core / shell nanoparticles,

   Humidity sensor.
10. The method according to claim 9,

    The hygroscopic inorganic salt is a humidity sensor, characterized in that the mixture of CaCl ₂ or KOH and K ₂ CO ₃ .
11. Providing a membrane;

    Placing core / shell nanoparticles of Ag / Fe ₃ O ₄ in or on a membrane surface and applying a magnetic field to one side of the membrane; And

    Drying the membrane;

    Method for producing a magnetoplasmonic film.
12. The method of claim 11,

    The application of the magnetic field is characterized in that it is performed by placing a magnetic block below the membrane,

    Method for producing a magnetoplasmonic film.
13. The method of claim 11,

    Placing a core / shell nanoparticles of the Ag / Fe ₃ O ₄ is applied, which method comprises the core / shell nanoparticle dispersion of Ag / Fe ₃ O ₄ on the membrane,

    Method for producing a magnetoplasmonic film.
14. The method of claim 11,

    Characterized in that the intensity of the applied magnetic field is 30 to 100 mT,

    Method for producing a magnetoplasmonic film.

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