Angle-independent colloidal particles-based structure and method for producing the same

Abstract

One embodiment of the present disclosure provides a method for producing an angle-independent colloidal particles-based structure, the method having: preparing two or more types of hollow colloidal particles, wherein the types are distinguished based on a size of the hollow colloidal particles thereof, wherein the types have different particle sizes; and dispersing the at least two types of hollow colloidal particles to produce an amorphous structure, wherein the amorphous structure realizes the same color independently of an angle of an incident light thereto.

Claims

1. A method for producing a colloidal particle-based structure, the method comprising: preparing first and second hollow colloidal particles, wherein the first hollow colloidal particles are of a different particle size from the second hollow colloidal particles; dispersing the prepared first and second hollow colloidal particles to produce an amorphous structure, wherein the amorphous structure has a same structural color independent of an angle of an incident light thereto; and treating the amorphous structure with a polymer or an inorganic material to fill gaps between the first and second particles.

2. The method of claim 1, wherein preparing of the first hollow colloidal particles comprises: preparing a core particle; coating an inorganic shell on an outer face of the prepared core particle to form a core-shell particle; and heat-treating the core-shell particle to remove the core from the core-shell particle to hollow the particle.

3. The method of claim 2, wherein the core particle is made of a flammable organic material.

4. The method of claim 1, further comprising incorporating any one or any combination of any two or more of carbon nanotubes (CNT), carbon black, and Fe particles into the amorphous structure.

5. The method of claim 1, wherein preparing of the second hollow colloidal particles comprises: preparing a core particle; coating an inorganic shell on an outer face of the prepared core particle to form a core-shell particle; and heat-treating the core-shell particle to remove the core from the core-shell particle to hollow the particle.

6. The method of claim 5, wherein the core particle is made of a flammable organic material.

7. The method of claim 1, further comprising incorporating the treated amorphous structure into a cosmetic, a paint, or an optical fiber.

8. The method of claim 1, wherein the treated amorphous structure is a film that reflects ultraviolet light and reflects light in a portion of visible light spectrum.

9. The method of claim 1, wherein the structural color is of a wavelength equal to a period of a repeated refractive index in the structure.

10. A method for producing a colloidal particle-based structure, the method comprising: preparing first and second hollow colloidal particles, wherein the first hollow colloidal particles are of a different particle size from the second hollow colloidal particles; dispersing the prepared first and second hollow colloidal particles to produce an amorphous structure, wherein the amorphous structure has a same structural color independent of an angle of an incident light thereto, and treating the amorphous structure with a material having a refractive index the same as a refractive index of the first and second particles to fill gaps between the first and second particles.

11. The method of claim 10, further comprising incorporating any one or any combination of any two or more of carbon nanotubes (CNT), carbon black, and Fe particles into the amorphous structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated in and form a part of this specification and in which like numerals depict like elements, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the disclosure.

(2) FIG. 1 shows a flow chart of a method for manufacturing angle-independent colloidal particles-based structures according to one embodiment of the present disclosure.

(3) FIG. 2 shows a schematic diagram illustrating a method for manufacturing angle-independent colloidal particle-based structures according to one embodiment of the present disclosure.

(4) FIG. 3 is a SEM photograph of the particle prepared by the experimental example of the present disclosure.

(5) FIG. 4 are SEM images of hollow silica particles with 180 nm pore size as a core size and silica shell thicknesses of (a) 14 nm (b) 30 nm (c) and 38 nm (d) 44 nm, respectively.

(6) FIG. 5 shows an optical microscope photograph and a reflection graph of a colloidal particle-based structure using hollow particles of a specific size and a film produced by filling voids of the structure with TMPEOTA.

DETAILED DESCRIPTIONS

(7) For simplicity and clarity of illustration, elements in the figures are not necessarily drawn to scale. The same reference numbers in different figures denote the same or similar elements, and as such perform similar functionality. Also, descriptions and details of well-known steps and elements are omitted for simplicity of the description. Furthermore, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure.

(8) Examples of various embodiments are illustrated and described further below. It will be understood that the description herein is not intended to limit the claims to the specific embodiments described. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure as defined by the appended claims.

(9) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms a and an are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes, and including when used in this specification, specify the presence of the stated features, integers, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, operations, elements, components, and/or portions thereof. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. Expression such as at least one of when preceding a list of elements may modify the entire list of elements and may not modify the individual elements of the list.

(10) Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(11) In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. The present disclosure may be practiced without some or all of these specific details. In other instances, well-known process structures and/or processes have not been described in detail in order not to unnecessarily obscure the present disclosure.

(12) As used herein, the term substantially, about, and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, the use of may when describing embodiments of the present disclosure refers to one or more embodiments of the present disclosure.

(13) In accordance with the present disclosure, in order to solve the problem of angle dependence of the existing crystalline structure using colloidal particles, two or more kinds of colloidal particles of different sizes are prepared, and an amorphous structure is prepared using the colloidal particles, thereby providing an angle-independent colloidal particle structure. In the following, the details of the present disclosure will be described with reference to the drawings.

(14) FIG. 1 shows a flow chart of a method for manufacturing angle-independent colloidal particles-based structures according to one embodiment of the present disclosure. FIG. 2 shows a schematic diagram illustrating a method for manufacturing angle-independent colloidal particle-based structures according to one embodiment of the present disclosure.

(15) A method of fabricating an angle-independent colloidal particles-based structure according to one embodiment of the present disclosure may include a step S 100 of preparing two or more kinds of hollow colloidal particles with different sizes and a step S 200 of dispersing the hollow colloidal particles to produce an amorphous structure amorphous structure.

(16) At step S100, two or more kinds of hollow colloidal particles having different sizes are prepared. These hollow colloidal particles are fabricated by the following S 110 to S 130 steps.

(17) Preparing the hollow colloidal particle comprises: preparing a core particle S 110; coating an inorganic shell on the outer face of the prepared core particle to prepare a core-shell particle S 120; and a step 130 of heat-treating the core-shell particle.

(18) In step S 110, an organic material is used as the core particle, and it is preferable that the organic material is a combustible organic material. This is because in the subsequent heat treatment step S 130, the core material is burned away to form a hollow colloidal particle.

(19) In step S 120, the core-shell particle is produced by coating a shell made of an inorganic material on the outer face of the core particle. As such an inorganic material, an inorganic material capable of forming a shell by a sol-gel process may be used. As such an inorganic material, any one of SiO.sub.2, TiO.sub.2, and Al.sub.2O.sub.3 is preferably used.

(20) In step S 130, the core-shell particle is heat-treated. Through this heat treatment process, the hollow particle may be produced by burning the core material away.

(21) In step S100, two or more kinds of hollow colloidal particles having different sizes are prepared. In step S 200, amorphous structure is prepared by dispersing the hollow colloidal particles. By fabricating the amorphous structure in this way, it is possible to fabricate the angle-independent colloidal particle-based structure independent of the angle of incidence of light.

(22) Further, after step S 130, a step of mixing at least one of carbon nanotubes (CNT), carbon black, and Fe particles may be further included.

(23) The carbon nanotubes (CNTs), carbon black, or Fe particles prevent scattering of light as may be otherwise generated by impurities. By removing the light scattering due to the impurity in this way, in the reflectance graph for the colloidal particles, the peak may be formed with a clear sharpness.

(24) The method for manufacturing angle-independent colloidal particle-based structures has been described above. Hereinafter, a method of manufacturing a film including the angle-independent colloidal particles-based structure will be described. The description of the parts overlapping with those described above will be omitted, and the description will be focused on the features.

(25) A method of producing a film including an angle-independent colloidal particles-based structure further includes, after the manufacturing of the angle-independent colloidal particles-based structure, the step S 300 in FIG. 1.

(26) A method of producing a film including an angle-independent colloidal particles-based structure may include preparing two or more kinds of hollow colloidal particles having different sizes from each other; the step S 200 of dispersing the hollow colloidal particles to prepare an amorphous structure; and filling gaps between the particles of the amorphous structure with a material having a refractive index similar to that of the particles S 300.

(27) The hollow particles were prepared in the same manner as described above. The core particles may be formed of flammable organic material. The inorganic material may not be particularly limited as long as the material is made into a shell by the sol-gel process.

(28) In step S 300, the gaps between the particles of the amorphous structure may be filled with a material having a refractive index similar to the particles. The material having a similar refractive index to the particles may be a polymer or an inorganic material. In this connection, the gaps may be filled through a reaction using a precursor. For example, in the case of using a SiO.sub.2 shell, the filling may be performed through a reaction using silica precursor such as TEOS or TMOS. Alternatively, when using TiO.sub.2 shell or Al.sub.2O.sub.3 shell, the gaps may be filled using the ALD method.

(29) By filling the gaps between the particles of the amorphous structure with the material having a refractive index similar to that of the particle, an inverse structure may be formed to allow a form of a film. When the film is formed in this manner, the resulting structure is not collapsed.

(30) The methods for producing the angle-independent colloidal particles-based structure, and the film containing the same have been described above. Hereinafter, the angle-independent colloidal particles-based structure and the film including the same will be described.

(31) The angle-independent colloidal particles-based structure according to one embodiment of the present disclosure includes the amorphous structure comprising two or more types of hollow colloidal particles with different sizes. This amorphous structure is characterized by independence from the angle of the incident angle.

(32) As for the angle-independent colloidal particle-based structure according to the present disclosure, by controlling the thickness of the shell of the hollow colloidal particle to adjust the structure factor thereof, the wavelength of the light reflected in the visible light region may be controlled, thereby changing the color rendered by the particles.

(33) Further, as for the angle-independent colloidal particle-based structure according to the present disclosure, by controlling the inner pore size of the hollow particle to adjust the form factor, the reflection of ultraviolet rays may be controlled, thereby enabling the reflection of ultraviolet rays.

(34) Further, as for the angle-independent colloidal particles-based structure according to the present disclosure, the amorphous structure may further include at least one of carbon nanotube (CNT), carbon black, and Fe particles. The scattering of light due to impurities may be suppressed by addition of such particles.

(35) The angle-independent colloidal particles-based structure according to the present disclosure may be used as a UV blocking agent by using the ultraviolet reflection effect. Alternatively, the angle-independent colloidal particles-based structure according to the present disclosure may be used in color cosmetics, paints, and optical fibers because the color may be controlled by the angle-independent colloidal particles-based structure.

(36) The film comprising the angle-independent colloidal particles-based structure according to one embodiment of the present disclosure may include the non-crystalline structure comprising two or more types of hollow colloidal particles having different sizes from one another. In order to form the film, the gaps between the colloidal particles of the amorphous structure may be filled with a material having a refractive index similar to that of the colloidal particles. Thus, the amorphous structure may be independent of the angles of the incident light.

(37) As for the film including the angle-independent colloidal particle-based structure according to the present disclosure, by controlling the thickness of the shell of the hollow colloidal particle to adjust the structure factor thereof, the wavelength of the light reflected in the visible light region may be controlled, thereby changing the color rendered by the particles.

(38) Further, as for the film including the angle-independent colloidal particle-based structure according to the present disclosure, by controlling the inner pore size of the hollow particle to adjust the form factor, the reflection of ultraviolet rays may be controlled, thereby enabling the reflection of ultraviolet rays.

(39) Further, as for the film including the angle-independent colloidal particles-based structure according to the present disclosure, the amorphous structure may further include at least one of carbon nanotube (CNT), carbon black, and Fe particles. The scattering of light due to impurities may be suppressed by addition of such particles.

(40) The film including the angle-independent colloidal particles-based structure according to the present disclosure may be used as a UV blocking agent by using the ultraviolet reflection effect thereof. Alternatively, the film including the angle-independent colloidal particles-based structure according to the present disclosure may be used in color cosmetics, paints, and optical fibers because the color may be controlled by the film including the angle-independent colloidal particles-based structure.

EXAMPLES

(41) In the following, the details of the present disclosure will be further described with reference to the present specific example.

Present Example 1

(42) In the present example of the present disclosure, an amorphous colloidal particles-based structure is fabricated using two types of hollow SiO.sub.2 particles having two sizes respectively. Then, the resin and polymer having a refractive index similar to 1.45, which is the refractive index of silica, are used to fill the gaps existing between the particles of the colloidal particles-based structure. As a result, a film is produced that reflects light in the UV region corresponding to the form factor and reflects only light in the visible light region corresponding to the structure factor. The specific experimental procedure is carried out according to the schematic diagram as shown in FIG. 2.

(43) The materials used in the present example are as follows: Styrene (>97%, Sigma-Aldrich), Potassium persulfate (KPS, Sigma-Aldrich), Sodium styrene sulfonate (NaSS, JUNSEI), Sodium hydrogen carbonate, NaHCO.sub.3, JUNSEI), Inhibitor removers (Sigma Aldrich), Vinyltrimethoxy silane (VTMS, 98%, Sigma-Aldrich) and ammonium hydroxide solution (NH.sub.4OH, 28?30%, Sigma-Aldrich), Trimethylolpropane ethoxy triacrylate (TMPEOTA, SK CYTEC), Darocur 1173 (SK CYTEC).

(44) (a) Preparing Polystyrene Particle

(45) To prepare a charged polymer particle, a solution of a negatively charged water-soluble polymer particle is prepared by emulsion polymerization. Specifically, in the state of maintaining the temperature of 450 g of water at 65 degree C., co-monomer (sodium styrene sulfonic acid, 0.5 g) for charge adjustment and pH adjusting salt (sodium bicarbonate, 0.5 g) are injected into the water to form a first mixture. Then, the mixture is stirred. Further, a monomer (styrene, 5.0 g) is injected into the first mixture to form a second mixture. Nitrogen is continuously fed into the second mixture for 30 minutes to lower the oxygen concentration therein. Thereafter, an initiator (potassium persulfate, 0.25 g) is injected into the second mixture. Thus, the reaction is carried out at a reaction temperature of 80 C. for 9 hours while maintaining the amount of the monomer and water evaporated by the condenser. As a result, a polymer (polystyrene) particle having a milky white color and negative charge and 200 nm or less particle size is obtained.

(46) The polymer particles thus obtained are cleaned by centrifugation to remove impurities. In this regard, the centrifugation is carried out using distilled water at 12,000 rpm for 10 minutes, three times in total.

(47) (b) Preparing Core-Shell Particles using the Polystyrene Particles and Silica Precursor

(48) PS-SiO.sub.2 core-shell particles with uniform sizes are synthesized by sol-gel method. First, 1 ml of 1 wt % PS particles (in water) to be used as a core material was mixed with 10 ml of distilled water and 0.7 ml of ammonia. On the other hand, 2.0 ml of VTMS, which is a silica precursor, and 20 ml of distilled water are mixed with each other for 30 minutes to hydrolyze the precursor. Thereafter, the hydrolyzed precursor solution is mixed with the PS solution. Then, they react each other at a room temperature for 8 hours. Then, the solvent is removed using a membrane filter having a 200 nm pore size and an aspirator, and then the particles are cleaned using ethanol and then are dispersed in distilled water.

(49) (c) Heat-Treating the Core-Shell Particle to Prepare Hollow Colloidal Particle

(50) The prepared PS-SiO.sub.2 colloidal particles are dried for 2 days using a freeze dryer and then heat-treated for 6 hours in an air atmosphere at 600 C. using a furnace.

(51) (d) Producing Amorphous Structure Using the Hollow Particles

(52) Two kinds of hollow colloidal particles having different sizes are dispersed in ethanol at 30 wt % to produce a first dispersion. CNT particles are dispersed in ethanol at a concentration of 0.1 wt % to produce a second dispersion. The first dispersion and the second dispersion are mixed at a ratio of 10:1 v/v to form a mixture. This mixture was dried in an oven at 40 degree C. to produce a closely packed structure.

(53) Conventionally, an amorphous structure may be self-assembled into a non-close packed form by reducing the stability between particles using particles with the same size and salts. In such a self-assembled state, the solvent is evaporated to produce the random structure. However, in the case of this conventional approach, even when the particles having the same single size are used, the reflectance of the structure slightly differs each time the structure is manufactured.

(54) Accordingly, the present inventors have attempted to fabricate a structure having a closely packed form but a random dispersion of the particles, unlike the conventional method. For this purpose, two types of hollow SiO.sub.2 particles with different particle diameters are prepared. Then, the amorphous structures is prepared by mixing them.

(55) When particles with the same size are mixed, the particles are arranged in a regular manner, thereby forming a photonic crystal structure with a long range order. To the contrary, when an amorphous structure is produced by mixing two types of particles having two different sizes, the particles are randomly arranged, whereby a photonic crystal structure having a short range order by this random arrangement may be realized. Further, when the average sizes of the particles produced by the close packing are substantially the same, the average distances between the particles are substantially the same, thereby achieving a constant reflectivity. Further, as described in step (e) below, the gap between the particles present in the fabricated structure is filled with TMPEOTA. This maintains the shape of the structure without changing the distance between the particles.

(56) (e) Fabricating an Inverse Structure Using a Polymer Having the Same Refractive Index as the Hollow Particle

(57) A polymer and resin (TMPEOTA 100 ul) having a refractive index similar to that of the shell are dropped onto the colloidal particles-based structure prepared in step (d). This causes the polymer and resin to penetrate into the air gap in the structure. This allows the gap between the hollow colloidal particles to be filled by TMPEOTA, resulting in a film-like structure.

(58) FIG. 3 is a SEM photograph of the particle prepared by the experimental example of the present disclosure. FIG. 3(a) shows a PS particle of 200 nm, and FIG. 3(b) shows the change after the heat treatment thereof.

(59) FIG. 4 are SEM images of hollow silica particles with 180 nm pore size as a core size and silica shell thicknesses of (a) 14 nm (b) 30 nm (c) and 38 nm (d) 44 nm, respectively.

(60) FIG. 5 shows an optical microscope photograph and a reflection graph of a colloidal particle-based structure using hollow particles of a specific size and a film produced by filling voids of the structure with TMPEOTA.

(61) Referring to FIG. 5, when the pore size is 180 nm and the shell thickness is 30 nm and 44 nm respectively (corresponding to particle sizes 240 nm and 268 nm), the structure only including the particles exhibits cyan color as in FIG. 5(a), while the inverse structure shows a red color as shown in FIG. 5(b).

(62) Based on the calculation results according to the calculation formula, the structure including only the particles has a scattering wavelength of 591 nm, and the inverse structure has a scattering wavelength of 687 nm. Further, when the actual reflectance was measured, reflectance values of about 579 nm and 682 nm were obtained, respectively, as shown FIG. 5(e).

(63) As for the structure including only the particles, it is confirmed that a form factor having a value near 300 nm is measured as in the black graph of FIG. 5(e). Thus, it is confirmed that the effect of ultraviolet ray blocking by the structure is achieved.

(64) While the foregoing description of the present disclosure has been provided with reference to preferred embodiments of the present disclosure, those skilled in the art will appreciate that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure set forth in the claims that follow.