Inorganic nanoparticles, inorganic nanoparticle film, and method for producing inorganic nanoparticle film

Abstract

The polymer shell-attached nanoparticles and nanoparticle films are designed to prevent direct contact between the nanoparticle cores, significantly suppressing the formation of dimers and clusters, and to produce brighter colors in the target wavelength range.The polymer shell is 20 to 200 nm thick and is formed around inorganic nanocrystals with a particle size of 40 to 300 nm and a refractive index of 3 or higher. of The polymer shell formed around the inorganic nanocrystals consists of the hydroxyl groups on the surface of the inorganic nanocrystals and surface-modified functional groups; for example, the hydrophilic OH groups (hydroxyl groups) on the silicon surface are replaced with hydrophobic groups, and the silicon surface is modified and coated with N-isopropylacrylamide (NIPAM).

Description

[Technical Field]

[0001] The present invention relates to nanoparticles and nanoparticle films made of high refractive index materials such as silicon. [Background technology]

[0002] Nanoparticles (100-200nm) made of high refractive index materials such as silicon emit color due to Mie resonance. face The present inventors have proposed a nanoparticle dispersion solution that does not discolor or fade, has high monochromaticity, and can achieve high resolution, as well as a method for producing the same (see Patent Document 1). This was based on the fact that silicon and other materials exhibit large light scattering in the visible wavelength range and can be used as color-developing nanostructures without using periodic array structures, and by forming a dispersion solution and controlling the average particle diameter, a single particle can generate highly scattered light in the visible or near-infrared range. The present inventors have also proposed a nanoparticle film and dispersion solution that can achieve high hiding power and adjust the hue with fewer coating cycles (see Patent Document 2). This was achieved by confirming that single-layer, two-layer, or three-layer particle films using nanoparticles (100 to 220 nm) such as silicon have high hiding power, and by using nanoparticles with different particle size distributions, high hiding power and adjustable hue were simultaneously achieved. However, there is an issue that when particles come into contact with each other in the nanoparticle film (coating film) and form dimers or clusters, the color changes. Therefore, there is a demand for technology that prevents particles from coming into contact with each other in the coating film.

[0003] On the other hand, Patent Document 3 describes nanosemiconductor particles having a core made of silicon particles and a surrounding shell made mainly of silicon oxide. The nanosemiconductor particles in Patent Document 3 have bulk properties when the sum of the core particle diameter and shell thickness exceeds 100 nm, making it impossible to obtain the quantum size effect. Therefore, the particle diameter of the shelled particles is set to 100 nm or less. It also describes that the shell thickness must be 0.2 nm or more to isolate the cores and prevent them from agglomerating. However, there is no description of suppressing the formation of dimers or clusters by forming a polymer shell on the surface of nanoparticles.

[0004] Furthermore, Patent Document 4 describes particles having a shell of a silicon compound, the surface of which is modified with a silane coupling agent. The silica-coated nanoparticles described in Patent Document 4 have high solvent dispersibility and are intended for immobilization on a substrate or the like, and are not intended for color development. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-025023 [Patent Document 2] Japanese Patent Application Publication No. 2024-027742 [Patent Document 3] International Publication Pamphlet No. WO2007 / 086321 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-001555 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, there was a problem in that particles in the nanoparticle film (coating film) came into contact with each other, and dimers and clusters were formed during drying, which changed the particle size and, accordingly, changed the color produced by Mie resonance. In view of this situation, the present invention aims to provide nanoparticles and nanoparticle films with polymer shells that prevent direct contact between nanoparticle cores, thereby significantly suppressing the formation of dimers and clusters and enabling brighter color development in the target wavelength range. [Means for solving the problem]

[0007] In order to solve the above problems, the nanoparticles with a polymer shell of the present invention have a particle size of 40 to 300 nm. death, Refractive index 3 or more Color development Inorganic nanoparticles in which a polymer shell with a thickness of 20 to 200 nm is formed around the inorganic nanocrystals in be. A polymer shell of a specified thickness is formed on the surface of nanoparticles made of high-refractive index materials such as silicon, which emit color through Mie resonance. This prevents the nanoparticle cores from coming into direct contact with each other in the nanoparticle film (coating), suppressing the formation of dimers and clusters and achieving bright color development. According to the above configuration, grain The nanoparticles with a polymer shell may be able to promote chemical bonding with binders, resulting in the formation of more stable coating films.

[0008] Here, Mie resonance refers to the phenomenon in which, when light of wavelength λ (nm) is incident on an inorganic nanoparticle (refractive index n), the effective wavelength within the nanoparticle is λ / n (nm), and when the effective wavelength λ / n (nm) of the light is equal to the diameter of the nanoparticle, a standing wave is formed, resulting in the lowest-order Mie resonance. Furthermore, the particle size of nanoparticles refers to the average particle size, and the distribution of a certain type of particle size is the range (e.g., 4 to 50%) obtained by dividing the standard deviation by the average particle size.

[0009] The particle size of the nanoparticles with a polymer shell of the present invention is preferably 100 to 300 nm, and more preferably 100 to 220 nm. By selecting a particle size of 100 to 220 nm, when color development due to Mie resonance occurs with visible light, the particle size is narrowed to the range of 100 to 220 nm.

[0010] Furthermore, examples of inorganic nanocrystals with a refractive index of 3 or more include silicon (Si), GaAs, GaP, and InP. The refractive index of silicon is 4.32, while the refractive index of the inorganic compound GaAs is 4.27, GaP is 3.6, and InP is 3.0. The refractive index depends on the wavelength, but is defined as the value at a wavelength of 500 nm. The inorganic nanocrystals are preferably made of silicon or GaAs, which have a refractive index of 4 or higher. Even more preferable is silicon, which is the second most abundant element on Earth after oxygen, is found in soil, rocks, natural water, trees, plants, etc., and is widely used in semiconductors.

[0011] inorganic nanoparticles to In this method, the polymer shell formed around the inorganic nanocrystals is preferably one of polystyrene, polyacrylic, polyethylene glycol, and N-isopropylacrylamide (NIPAM). Polymer materials can have both hydrophobic and hydrophilic groups, or can be either hydrophobic or hydrophilic.

[0012] Preferably, the polymer shell formed around the inorganic nanocrystal is formed by bonding or adsorption to the hydroxyl groups or surface-modified functional groups on the inorganic nanocrystal surface. For example, the hydrophilic OH (hydroxyl) groups on the silicon surface are replaced with hydrophobic groups, and the silicon surface is modified and coated with N-isopropylacrylamide (NIPAM).

[0013] inorganic nanoparticles teeth The particle size of the inorganic nanocrystals, which are the core of the inorganic nanoparticles, is 100 to 200 nm, and the wavelength of visible light is color Here, when the particle size is 100 to 110 nm, a pink color may be produced. color In the case of 115 to 125 nm, blue color In the case of 130 to 140 nm, the green color In the case of 145 to 160 nm, yellow color Between 165nm and 200nm, skin-colored colorIt can be prepared into a colorant.

[0014] In addition, inorganic nanoparticles teeth In the case of inorganic nanocrystals, particles with particle size distribution peaks of approximately 100 nm, approximately 130 nm, and approximately 200 nm are mixed, and white light color It is also possible to color the particles in white by mixing three types of particles: blue (particle size distribution with a peak of about 100 nm), green (particle size distribution with a peak of about 130 nm), and red (particle size distribution with a peak of about 200 nm). Note that the particle size distribution here refers to a distribution with a width of about ±10%.

[0015] In addition, inorganic nanoparticles teeth The particle size of the inorganic nanocrystals is 200 to 300 nm, and the wavelength is in the near infrared region. color It is also possible to produce a color in the near-infrared region. color The particle size is adjusted to produce the color. In addition, inorganic nanoparticles teeth The particle size of the inorganic nanocrystals is 40 to 99 nm, and the ultraviolet light range color It may also be possible to produce color in the ultraviolet range. color The particle size is adjusted to produce the color.

[0016] The inorganic nanocrystals are preferably selected from Si, GaAs, GaP, and InP, which are specific inorganic materials with a refractive index of 3 or greater.

[0017] The present invention inorganic The nanoparticle film is made of the above-mentioned inorganic nanoparticles. in The formed single layer film, multilayer film, or laminated film has a surface filling rate of nanoparticles in the single layer of 15 to 74%. this inorganic The nanoparticle film can be used to produce highly opaque nanoparticle films for cosmetics, such as foundation, lipstick, and eye shadow.

[0018] The present invention inorganicThe method for producing the nanoparticle film is as follows: mosquito 1) a method for producing a particle film having a refractive index of 3 or more; Color development Inorganic Nano crystal 2) forming a polymer shell having a thickness of 20 to 200 nm on the inorganic nanoparticles. crystal and 3) coating the inorganic nanoparticles with a polymer shell. crystal of base and transferring the image to a material. Also, the above inorganic The method for producing a nanoparticle film preferably further comprises the step of washing the particle film on the substrate with an organic solvent or treating it with oxygen plasma to remove only the polymer shell. [Effects of the Invention]

[0019] The nanoparticles and nanoparticle film with polymer shells of the present invention can significantly suppress the formation of dimers and clusters by preventing direct contact between the nanoparticle cores, thereby achieving brighter color development in the target wavelength range. [Brief explanation of the drawings]

[0020] [Figure 1] Schematic diagram of Si nanoparticle dispersion [Figure 2] Schematic diagram of forming a polymer shell using functional groups on the surface of Si nanoparticles [Figure 3] Flowchart of Si nanoparticle film fabrication [Figure 4] Optical microscope image of Si nanoparticle film after particle size separation [Figure 5] Enlarged optical microscope image of Si nanoparticle film after particle size separation [Figure 6] Illustration of forming a polymer shell on the surface of Si nanoparticles (Example 1) [Figure 7] Schematic diagram of the Si nanoparticle film fabrication method [Figure 8] SEM image of Si nanoparticle film (after oxygen plasma treatment) [Figure 9]Dark-field image of Si nanoparticle film [Figure 10] Extinction spectrum of Si nanoparticle dispersion [Figure 11] Reflectance spectrum of Si nanoparticle film (after oxygen plasma treatment) [Figure 12] Color space obtained from the reflectance spectrum of Si nanoparticle films (with and without surface shell) DETAILED DESCRIPTION OF THE INVENTION

[0021] An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the scope of the present invention is not limited to the following examples and illustrated examples, and many modifications and variations are possible.

[0022] Figure 1 is a schematic diagram of the dispersion of Si nanoparticles, and the current issues will be explained using this figure. As shown in Figure 1, an isolated Si nanoparticle 2, which is an inorganic nanocrystal, emits color due to Mie resonance. However, when it becomes a dimer or cluster (multimer), the color changes, causing a decrease in saturation and brightness. Therefore, by forming a polymer shell of a specified thickness (20 to 200 nm) around the Si nanoparticle 2, the nanoparticles are prevented from coming into contact with each other. vinegar In this specification, nanoparticles refer to nanometer-sized particles, and Si nanoparticles are spherical particles made of crystalline Si with a nanometer-sized particle size (diameter), and Si nanoparticles have a positive real part of the dielectric constant and exhibit Mie resonance.

[0023] Figure 2 shows a schematic diagram of the formation of a polymer shell using functional groups on the surface of Si nanoparticles. First, Si nanoparticles are dispersed in a solvent, and a solution containing functional groups to be used to modify the surface of the Si nanoparticles is added to modify the surface of the Si nanoparticles with the functional groups (see Figure 2(1)). Polymers are bonded or adsorbed to the surface-modified functional groups to form a polymer shell (see Figure 2(2)). The functional groups modified on the surface of the Si nanoparticles are tightly cross-linked, while the polymers that are bonded or adsorbed to the functional groups are relatively loosely cross-linked.

[0024] Figure 3 shows a flow diagram for fabricating a Si nanoparticle film. First, Si nanoparticles are prepared to a particle diameter of 40 to 300 nm (step S01). For example, commercially available silicon monoxide powder is used as the raw material. The silicon monoxide powder is annealed for 30 minutes in a nitrogen (N2) atmosphere at a temperature lower than the melting point of silicon (1414°C) or higher than the melting point (1350 to 1700°C), for example, at 1450°C. The particle size of the crystalline Si nanoparticles can be controlled by controlling the annealing temperature. The powder obtained after the annealing process is silicon dioxide particles containing Si nanoparticles. The annealed powder is then etched using hydrofluoric acid (HF). By etching with hydrofluoric acid, only the silicon dioxide is etched, and the Si nanoparticles contained within the particles are extracted. After etching, the alcohol is replaced with methanol as a polar solvent. The mixture is then stirred with an ultrasonic homogenizer to disperse the Si nanoparticles in alcohol, and the particle size of the Si nanoparticles is made uniform by density gradient centrifugation (2000-3000G; 60 minutes). Through these processes, a dispersion of Si nanoparticles with controlled particle size is produced. Other methods for aligning the particle size of nanoparticles in a dispersion liquid include density gradient centrifugation and particle size selection by adding a poor solvent. When using density gradient centrifugation, it is recommended that the centrifuge tube containing the dispersion be placed on a horizontal surface to perform centrifugation with high particle size resolution. By placing the tube on a horizontal surface and centrifuging in the horizontal direction, the direction of the centrifugal force is aligned with the longitudinal direction toward the bottom of the centrifuge tube, and the sedimentation path length is increased, thereby improving the resolution of density gradient centrifugation.

[0025] Next, a polymer shell having a thickness of 20 to 200 nm is coated on the Si nanoparticles (step S02). The polymer-shell-coated Si nanoparticles are then floated on the liquid surface and transferred to a substrate (step S03). For example, the polymer-shell-coated Si nanoparticles are allowed to self-assemble on a glass substrate to form a film. Alternatively, a dispersion of the polymer-shell-coated Si nanoparticles may be spin-coated or drop-coated onto a substrate to form a film. Thereafter, only the polymer shell is removed from the particle film on the substrate (step S04).

[0026] This section compares the particle size distributions of Si nanoparticles and polymer-shell-coated Si nanoparticles. The particle sizes of the nanoparticles dispersed in solution were measured using DLS (dynamic light scattering). The average particle sizes of the uncoated Si nanoparticles and the two types of polymer-shell-coated Si nanoparticles (NIPAM: 50 mM and 25 mM) were 175 nm, 275 nm, and 399 nm, respectively, with the polymer shell coating increasing the particle size. From this, the shell thickness can be calculated as 224 ÷ 2 = 112 nm for 50 mM NIPAM and 100 ÷ 2 = 50 nm for 25 mM NIPAM.

[0027] Figure 4 shows an optical microscope image of the prepared Si nanoparticle film after particle size separation, and Figure 5 shows an enlarged view. In Figures 4 and 5, (1) shows the case without a polymer shell, and (2) shows the case with a polymer shell. As shown in Figure 5(1), in the case without a polymer shell, there are many clusters, as indicated by the arrows in the image, whereas in the case with a polymer shell, individual particles are clearly visible, as shown in Figure 5(2). [Example]

[0028] An example of an embodiment in which a polymer shell is formed on the surface of a Si nanoparticle will be described. Fig. 6 shows an explanatory diagram of forming a polymer shell on the surface of a Si nanoparticle, and Fig. 7 shows a schematic diagram of a method for producing a Si nanoparticle film. First, a dispersion of Si nanoparticles in alcohol is centrifuged to remove the alcohol, and then dried overnight at 70°C. Then, the Si nanoparticles are dispersed in DMF (N,N-dimethylformamide) (concentration: 0.04 wt%). This is then subjected to ultrasonic treatment, and MPS ((trimethoxysilyl)propyl methacrylate) is added (to a surface area of ​​1 nm of Si nanoparticles). 2 The reaction is then carried out with a solvent (more than 100 molecules per molecule), followed by ultrasonic treatment for 2 hours at 50°C. Afterwards, the mixture is washed with alcohol 4 to 5 times.

[0029] Next, 25 or 50 mM NIPAM, BIS as a crosslinker, and ammonium persulfate (APS) as a polymerization accelerator were added to a nitrogen-purged glass container, and the container was heated to 80°C. While stirring, the dispersion of MPS-modified Si nanoparticles was added little by little using a syringe to form a polymer (poly(N-isopropylacrylamide)) shell on the surface of the Si nanoparticles. In the laboratory, Si nanoparticle films were fabricated by dispersing Si nanoparticles coated with a polymer shell in alcohol, gently dropping the dispersion onto a water surface, and then floating the particles on the water surface, where they were transferred to the substrate, as shown in Figure 7.

[0030] Figure 8 shows an SEM image of the Si nanoparticle film after oxygen plasma treatment. The Si nanoparticles have an average particle diameter (D ave ) = 188.31 nm. As shown in Figure 8, the crystalline Si nanoparticles that make up the fabricated Si nanoparticle film have a circularity close to that of a perfect sphere.

[0031] Figure 9 shows a dark-field image of the Si nanoparticle film. Figures 9(1) to (8) show the average particle size (D ave The dark-field images of the Si nanoparticle films of samples (F1 to F8) whose standard deviation (CV) and standard deviation divided by average particle size (CV) are shown in Table 1 below. The average particle size was controlled to about 110 to 200 nm ±10%, and the differences in the hues of each were confirmed.

[0032] [Table 1]

[0033] The extinction spectrum of the Si nanoparticle dispersion is shown in Figure 10. It can be seen that the spectral peak shifts to longer wavelengths as the average particle size increases.

[0034] Figure 11 shows the total reflectance spectrum of the Si nanoparticle film (after oxygen plasma treatment). Reflecting the extinction spectrum of the dispersion in Figure 10, Figure 11 shows that as the nanoparticle size increases, the reflectance spectrum changes in the range of approximately 450 to 800 nm. Total reflectance is expressed as the ratio of the sum of specularly reflected light and diffusely reflected light to the incident light.

[0035] Figure 12 shows the color space obtained from the reflectance spectra of Si nanoparticle films with and without a surface shell. Figure 12 shows the CIE1931 color space. The CIE1931 color space quantitatively represents the relationship between visible light and the color of human color vision. Figure 12 shows that Si nanoparticles with a polymer shell formed on their surface have a wider range of color variation than Si nanoparticles without a polymer shell formed on their surface. This shows that the polymer shell expands the color gamut by suppressing cluster formation. [Industrial Applicability]

[0036] The present invention is useful for cosmetics, particularly foundations that are effective in small amounts, and highly opaque inks. [Explanation of symbols]

[0037] 1 color Material 2. Si nanoparticles 3. Polymer shell 4. Air 5 water 6. Glass substrate 7 Beaker 8 Dropper 9 glass rods

Claims

1. The inorganic nanoparticles for coloring material are characterized in that a polymer shell having a thickness of 20 to 200 nm is formed around color-developing inorganic nanocrystals having a particle size of 40 to 300 nm and a refractive index of 3 or more.

2. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the polymer shell is any one of polystyrene, polyacrylic, polyethylene glycol, and N-isopropylacrylamide (NIPAM).

3. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the polymer shell is formed by bonding or adsorbing to a hydroxyl group or a surface-modified functional group on the surface of the inorganic nanocrystal.

4. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the inorganic nanocrystals have a particle size of 100 to 200 nm and exhibit a color in the visible light region.

5. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the inorganic nanocrystals contain a mixture of particles having particle size distribution peaks of approximately 100 nm, approximately 130 nm, and approximately 200 nm, respectively, and emit the color of white light.

6. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the inorganic nanocrystals have a particle size of 200 to 300 nm and exhibit a color in the near-infrared region.

7. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the inorganic nanocrystals have a particle size of 40 to 99 nm and emit a color in the ultraviolet light region.

8. 2. The inorganic nanoparticles for coloring material according to claim 1, wherein the inorganic nanocrystals are selected from the group consisting of Si, GaAs, GaP, and InP.

9. 9. An inorganic nanoparticle film, which is a single-layer film, a multi-layer film, or a laminate film formed from the inorganic nanoparticles for coloring material according to any one of claims 1 to 8, and which is characterized in that the surface filling rate of the nanoparticles in the single layer is 15 to 74%.

10. A cosmetic product using the inorganic nanoparticle film of claim 9.

11. A highly opaque nanoparticle film comprising the inorganic nanoparticle film of claim 9.

12. A method for producing a particle film made of the inorganic nanoparticles for coloring material according to any one of claims 1 to 8, comprising: A step of preparing color-forming inorganic nanocrystals having a refractive index of 3 or more to have a particle size of 40 to 300 nm; coating the inorganic nanocrystals with a polymer shell having a thickness of 20-200 nm; transferring the polymer shell coated inorganic nanocrystals to a substrate; A method for producing an inorganic nanoparticle film, comprising:

13. The method for producing a nanoparticle film according to claim 12, further comprising the step of washing the particle film on the substrate with an organic solvent or performing oxygen plasma treatment to remove only the polymer shell.

14. The method for producing an inorganic nanoparticle film according to claim 12 or 13, wherein in the step of transferring to the substrate, the inorganic nanoparticles coated with the polymer shell are floated on a liquid surface and transferred to the substrate.

Images