KR20070044623A - Self-assembly of colloidal particles in confined geometry induced by microwave - Google Patents

Abstract

The present invention is a colloidal self-assembly method for self-assembly of particles of several hundred nm level present inside the droplet by removing the water of the droplet by using a microwave, thereby producing a spherical colloidal crystal, using the same, water dispersion on the pattern (aqueous) A colloidal particle is introduced and covered therein with oil, and then a photonic pattern manufacturing method for producing a line pattern of colloidal crystals controlled by microwave, that is, a photonic crystal pattern, and polymer particles of several hundred nm level in the same manner. The present invention relates to a photonic crystal manufacturing method of preparing a crystal using a combination of inorganic nanoparticles and selectively removing a polymer to produce a spherical photonic crystal having an inverted structure. In particular, the crystal proposed in the present invention exhibits optical properties as a photonic crystal by Bragg diffraction when the particle size is 200 ~ 300nm level.

Microwave, spherical colloidal crystal, spherical photonic crystal, droplet, micropipette

Description

Colloidal self-assembly in confined spaces using microwaves {SELF-ASSEMBLY OF COLLOIDAL PARTICLES IN CONFINED GEOMETRY INDUCED BY MICROWAVE}

1 is a schematic diagram of making spherical colloidal crystals from droplets using microwaves and a schematic diagram of a preparation of patterned colloidal crystals.

Figure 2 is a scanning electron micrograph of silica spherical colloidal crystals prepared in a uniform size according to Example 1.

3 is a photograph of silica spherical colloidal crystals prepared according to Example 1. FIG.

FIG. 4 is an optical micrograph showing the size of the droplets over time, eventually crystallized to form silica spherical colloidal crystals, as shown in Example 2. FIG.

FIG. 5 is a scanning electron micrograph of silica spherical colloidal crystals according to a change in microwave cycle shown in Example 3. FIG.

6 is a scanning electron micrograph of silica spherical colloidal crystals prepared according to Example 4. FIG.

7 is a reflectance graph according to silica particle size, as shown in Example 4. FIG.

8 is a reflectance graph according to the dispersion phase shown in Example 5. FIG.

9 is a scanning electron micrograph of the polystyrene spherical colloidal crystal prepared according to Example 6.

FIG. 10 is a scanning electron micrograph of an inverted structure of a silica spherical photonic crystal prepared according to Example 7. FIG.

FIG. 11 is an optical photomicrograph of patterned silica crystals prepared by a conventional method. FIG.

12 is an optical micrograph of the patterned silica crystals prepared by Example 8. FIG.

FIG. 13 is a scanning electron micrograph of the patterned silica crystals prepared by Example 8. FIG.

The present invention relates to a colloidal self-assembly method in a confined space using microwaves. More specifically, the present invention is a colloidal self-assembly method for self-assembling particles of several hundred nm level present inside the droplets by removing water from the droplets using microwaves, and thus producing spherical colloidal crystals. A method of manufacturing a photonic crystal pattern in which a pattern of colloidal crystals controlled by using microwaves, that is, a photonic crystal pattern is prepared by introducing an aqueous dispersion of colloidal particles on a pattern, and then covering the surface with an oil. The present invention relates to a photonic crystal manufacturing method of preparing a crystal using a high level of polymer particles and inorganic nanoparticles together, and selectively removing a polymer to produce a spherical photonic crystal having an inverted structure.

Photonic crystal refers to a material having a feature in which different materials having a period of several hundred nm to several μm are arranged in one, two, or three dimensions. This can be easily seen in nature, such as the wings of Morpho butterflies or opal gemstones. Observing them with a scanning electron microscope, the wing of the morpho butterfly is made in a regular pattern, the opal gemstones can be seen that the hundreds of nm level particles are stacked in a face centered cubic (FCC). The color of the colorful Morpho butterfly's wings and the beautiful opal gemstones are not chemical colors but are physical colors created by periodic patterns and particle crystals of hundreds of nm selectively reflecting light of a specific wavelength. In this case, the wavelength region of the reflected light that does not penetrate the photonic crystal structure is called a photonic bandgap. This optical bandgap is determined by the characteristic length of the crystal structure and the refractive index of the material constituting the photonic crystal.

Many studies have already been made on the production of spherical photonic crystals. One is to produce an aerosol through an electrohydraulic atomizer and to form spherical crystals as the solvent in the aerosol evaporates into the air. This is Korean Patent Registration No. 0466251, which is a spherical colloidal crystal, a method for producing a porous structure and an electro-hydraulic spraying device and advanced materials (Jun Hyuk Moon, Gi-Ra Yi, Seung-Man Yang, David J. Pine and Seung) Bin Park, "Electrospray-Assisted Fabrication of Uniform Photonic Balls" Advanced Materials , 16 (7), 605-609 (2004). In addition, the preparation of spherical colloidal crystals using droplets is described in the same journal (Gi-Ra Yi, Vinothan N. Manoharan, Sascha Klein, Krystyna R. Brzezinska, David J. Pine, Frederick F. Lange and Seung-Man Yang, " Monodisperse Micrometer-Scale Spherical Assemblies of Polymer Particles " Advanced Materials, 14 , 1137-1140 (2002)). However, the above two methods have some problems. In the case of using an electro-hydraulic spraying device, the production time of the spherical colloidal crystals is fast but the crystallinity is poor, resulting in many defects. On the other hand, in the case of the method using droplets, the level of defects is reduced by using the method used in the conventional method, so that the optical characteristics are obvious, but it takes too much time to crystallize colloid from the droplets. There are disadvantages. In the conventional method, the time required to remove water from the droplets varies slightly depending on the method, but has a disadvantage of requiring more than 12 hours.

On the other hand, the present invention relates to a technique for producing a patterned colloidal crystal, the conventional method is a method of introducing a colloidal dispersion on the pattern to evaporate the dispersion using a convection oven or hot plate to make a colloidal crystal. In this case, however, many cracks occurred, the surface was not smooth, and the defect level was high.

Accordingly, one object of the present invention is to provide a colloidal self-assembly method of self-assembling particles of several hundred nm level present inside the droplets by removing water from the droplets using microwaves, and thereby producing spherical colloidal crystals. It is.

Another object of the present invention is to introduce the colloidal crystals controlled by using microwave after introducing aqueous colloidal particles on the pattern using the colloidal self-assembly as described above and covering them with oil. It is to provide a photonic crystal pattern manufacturing method for producing a pattern, that is, a photonic crystal pattern.

Another object of the present invention is to prepare a crystal using the same method and several hundred nm level polymer particles and inorganic nanoparticles together, and to selectively remove the polymer to produce a spherical photonic crystal of inverted structure To provide.

The present invention proposes self-assembly of colloids into spherical structures using microwaves to compensate for the disadvantages of existing spherical colloidal crystal manufacturing methods. In the present invention, while selecting a manufacturing method through the droplets with a low level of defects, the use of microwave which can be said to be much more efficient than the conventional method for reducing the process time.

In the conventional method, the water was left at room temperature for 12 hours or more to remove the water component of the droplets, or the water component was dissolved in the oil phase or heated to about 70 ° C. in a convection oven to remove the water component. The latter case also took several hours to process, and the problem was that the oil evaporated with water a lot. However, in the method using the microwave proposed in the present invention brought the efficiency of energy consumption with the reduction of time.

Microwaves transfer energy through dipole rotation or ionic conduction of matter. Therefore, it selectively transfers a lot of energy to the polar material, and transmits less energy to the nonpolar material, thereby rapidly localizing the polar material. Thus, when applied to water droplets, only water molecules are selectively localized, and oil molecules receive little energy. Therefore, the water molecules with high energy become active in molecular motion, the temperature rises and eventually diffuse into the oil layer and then evaporate to the outside. Applying this principle to a droplet system consisting of water inside the oil or to a system with a layer of water inside the pattern, water can be selectively removed, rather than using a conventional convection oven or hot plate. It's much more efficient.

In the conventional convection oven, the sample vessel is first heated and the temperature of the oil and the droplets is increased together by conduction heat. As a result, the temperature of the oil and the droplets rises simultaneously, and with the evaporation of water molecules, a large amount of oil evaporates. In addition, since the vessel and the oil are heated together, there is a lot of unnecessary energy loss, and the time taken to evaporate the water in the droplets is also quite long.

In the present invention, when the water / oil droplet or the water layer in the pattern contains colloidal particles, when exposed to microwaves, water is selectively superheated, and water molecules pass through the oil layer to evaporate to the outside. do. As a result, in the case of droplets, the particles contained are spherical to form spherical colloidal crystals, and in the case of the water layer inside the pattern, colloidal crystals are formed along the pattern to form a colloidal crystal pattern. It is characterized by the point.

In the method using the microwave proposed in the present invention, the crystallization time of the colloid containing the droplets is very short, about 10 minutes, and the defects of the resulting spherical colloidal crystal are produced at a very low level.

In addition, in the case of patterned colloidal crystals, the oil layer covers the pattern, resulting in a very smooth crystal surface and significantly less cracking than in conventional cases. In addition, by slowing down the crystallization, the level of defects can be significantly controlled. Thus, patterned colloidal crystals show a fairly high level of optical properties, which is a very important factor in practical applications of patterned colloidal crystals.

The present invention is a method for producing spherical colloidal crystals using microwave, more specifically, the water / oil droplets containing the colloidal particles after the process of making the colloid containing the droplets to determine the spherical structure using a microwave oven. There are two stages to get angry.

In addition, the present invention provides a method for producing a spherical colloidal crystal of inverted structure, more specifically, an aqueous solution in which several hundred nm level polymer particles and several tens nm level inorganic particles are dispersed as an oil phase, and the resulting droplets In addition, the present invention also proposes a method of making an inverted spherical colloidal crystal through three steps of crystallization by applying microwave and selectively removing polymer particles at high temperature.

Finally, in the method for producing a patterned colloidal crystal, a water-based colloidal solvent is introduced onto the pattern, covered with oil, and then crystallized using a microwave oven.

The spherical colloidal crystal proposed in the present invention is a kind of photonic crystal and has an optical characteristic to selectively reflect light of a specific wavelength. In particular, the photonic crystal produced in the present invention is spherical in shape. When the photonic crystal is produced in a spherical shape, the surface is all composed of the faces of the face-centered cubes (1, 1, 1) so that the wavelength band selectively reflecting exhibits a property irrespective of the direction.

In the methods of the present invention, a method of preparing droplets employs a micropipette using viscous stress in a coflowing stream. This is the same method as presented in the aforementioned paper (Gi-Ra Yi, et al. , Advanced Materials, 2002, 14, 1137-1140) and is not proposed as a new method in the present invention proposal. In addition, as a method of manufacturing a pattern, a silicone rubber solution is introduced into a photoresist pattern prepared by an etching process, and then cured, and an ultraviolet curable polyurethane precursor (trade name, NOA60) is introduced into the resulting silicone rubber. It is produced by irradiating and curing ultraviolet rays. This too is not a limitation as a new method.

A new method proposed by the present invention is the use of microwaves in the method of crystallizing colloidal particles contained in the generated droplets or inside the pattern. In the case of droplets, the manufacturing time and energy efficiency can be drastically reduced compared to the existing methods, which can be said to take advantage of microwave. In addition, when creating a pattern, it is possible to produce colloidal crystals with a lower defect level, which exhibits better optical properties than conventional methods.

As droplets containing colloidal particles or suspensions inside a pattern are exposed to microwaves, water molecules are energized with high energy due to their high energy. As a result, the water molecules pass through the oil layer and evaporate to the outside. As a result, the droplet size gradually decreases, and the suspension inside the pattern gradually changes to a high concentration. Initially, colloidal particles are well dispersed within the droplets to maximize free volume entropy. As the droplet size decreases or the concentration of the suspension in the pattern increases, the colloidal particles begin to crystallize, crystallizing into a face-centered cubic structure (FCC structure), known as the lowest energy state.

The time it takes for the droplets to evaporate to form crystals depends on the size of the droplets and the microwave output. If the droplet size is large, the time required will be longer because of the large amount of water molecules that need to be evaporated. If the microwave energy is high, the time required for the evaporation of water will be shorter. In the present invention, the time required according to the period of the microwave may vary, which may be shown in detail in the embodiment.

The point at which crystallization is completed is indicated by the change in color. The initial emulsion state appears white. However, as the water is removed and crystallization proceeds, a change of color appears. This color change is due to the bandgap as a photonic crystal. The appearance of color can be easily predicted by Bragg's law of scattering, which is about twice the size of colloidal particles. Therefore, the band gap of the spherical colloidal crystal can be obtained at a desired position by only changing the size of the colloidal particles.

The same applies to patterned colloidal crystals. The initial suspension will appear white, but will color as the crystallization progresses. Likewise, the reflected color can be predicted by Bragg's law of scattering. The related equation is shown in Equation 1 below.

Where n is the reflectance of the material, V is the volume fraction of the crystal, D is the size of the diameter of the particle, and φ is the angle of incidence of light.

In the case of spherical colloidal crystals formed, all surfaces are made of hexagonal dense structure unlike ordinary colloidal crystals. Therefore, when the angle between the incident direction of light and the field of view is constant, light of the same wavelength can be seen at all times. This is a phenomenon not found in ordinary colloidal photonic crystals and can be said to occur only when manufactured in spherical shape.

The system used in the present invention is a water / oil droplet system, in which water was used tertiary distilled water, and hexadecane was used as an oil. In addition, as a surfactant for stabilizing droplets, Hypermer 2296 (ester-like polymeric surfactant with long-chain alkyl and OH-groups) was used. . The oil is not limited to hexadecane, and any oil having low solubility with water such as toluene can be used. Surfactant is not limited to this, but any surfactant that can stabilize water / oil droplet system such as SPAN80 can be used. Colloidal particles were used as silica (silica) and polystyrene particles, silica particles were prepared using the Stober-Pink-Bohn method, polystyrene particles are emulsifier without emulsifier polymerization using free emulsion polymerization). In addition, all particles that can be produced in a uniform size, such as polymethylmethacrylate, titania, can be used. 3 shows a photograph of spherical colloidal crystals obtained using 244 nm size silica particles. It can be seen that this represents a vivid color.

In the present invention, microwaves were used not only for spherical colloidal crystals but also for producing inverted spherical structures. Polystyrene particles and silica nanoparticles were dispersed together inside the droplets, and then crystallized through microwaves, and only polystyrene particles, which are polymers, were selectively removed at a high temperature of 500 ° C. As a result, only the silica nanoparticles remained in a spherical structure, and an inverted structure was formed in which the polymer was present in an empty form.

In the preparation of patterned colloidal crystals, silica particles prepared in the same manner as mentioned above were used by water dispersion. The pattern used a polyurethane pattern having a width of 50 μm, and a silica suspension was introduced thereto. Silicone oil was introduced so that the pattern and suspension were completely submerged in the oil. It was crystallized by exposure to microwaves for several ten minutes.

In the following examples, the present invention is described in more detail, but is not limited thereto.

<Example 1>

Silica particles having a uniform size of 244 nm prepared by the Stover-Pink- present method were water-dispersed at 1wt% and prepared as droplets in hexadecane using a micropipette apparatus. At this time, 1 wt% of a hypermer 2296 surfactant was used. 1020W of microwaves were operated for 5 seconds on the prepared droplets, and 20 minutes of treatment were performed repeatedly with ON-OFF resting for 25 seconds. 2 is a scanning electron micrograph of the resulting spherical colloidal crystals. 3 is an optical photograph selectively reflecting green in the state in which spherical colloidal crystals are dispersed in hexadecane.

<Example 2>

The droplets prepared in the same manner as in Example 1 were subjected to 8 minutes of repeated 10-W microwave operation for 9.8 seconds and resting ON-OFF for 20.2 seconds. The optical micrographs shown in FIG. 4 showed that the droplet size changes and spherical colloidal crystals formed after the initial, 3, 6, and 8 minutes, respectively.

<Example 3>

Droplets prepared in the same manner as in Example 1 were exposed while adjusting the period of the microwaves. The scanning electron micrographs shown in FIG. 5 show the ON-OFF cycles of 1020W microwaves using 5 seconds-25 seconds, 9.8 seconds-20.2 seconds, 16.5 seconds-13.5 seconds, 23.2 seconds-6.8 seconds, respectively. The result of treatment for 8 minutes, 5 minutes, and 3 minutes is shown. The longer the period of the microwave, the shorter the crystallization time was, and accordingly, the colloidal defect level tended to increase slightly. However, the level of defects did not increase significantly, indicating that the optical properties did not decrease significantly.

<Example 4>

 Silica particles having a uniform size of 250 nm prepared by the Stover-Pink- present method were dispersed in a concentration of 1 wt%, and droplets were prepared in hexadecane using 2.3 wt% of a hypermer 2296 surfactant. The prepared droplets were treated for 20 minutes by repeating ON-OFF running 1020W of microwave for 5 seconds and resting for 25 seconds. FIG. 6 shows a scanning electron micrograph of the prepared spherical colloidal crystal. FIG. 7 shows a reflectance graph in which the spherical colloidal crystals dispersed in hexadecane are changed in the position of the band gap according to the size of the colloidal particles.

Example 5

The spherical photonic crystals produced by the method of Example 1 exhibit bandgaps at different wavelengths when in different dispersion phases. Initially prepared spherical colloidal crystals are dispersed in hexadecane. It was heated to 500 ° C. in a stove to remove hexadecane and exposed to air. It was also dispersed in water to measure the reflectivity in each case. FIG. 8 shows a reflectance graph showing the band gap positions when the dispersed phases are hexadecane, water, and air, respectively.

<Example 6>

The polystyrene particles prepared in 320 nm size were water-dispersed at a concentration of 2 wt% using an emulsion polymerization without an emulsifier. This was prepared as a droplet in hexadecane using 1 wt% of the surfactant hypermer 2296, and then 20 minutes of the 1020W microwave was operated for 5 seconds and the ON-OFF was rested for 25 seconds. 9 shows a scanning electron micrograph of a polystyrene spherical crystal.

<Example 7>

By dispersing the polystyrene particles prepared in 320nm size by 3.8wt% by using emulsion polymerization without emulsifier, and by dispersing 3.8wt% of 30nm silica nanoparticles in a ratio of 7: 3. This was prepared as a droplet in hexadecane using 1 wt% of a surfactant hypermer2296. 1020W microwave for 5 seconds, 25 seconds to turn on and off repeatedly for 20 minutes to crystallize, and then maintained in 500 ℃ oven for 5 hours to selectively remove the polymer. 10 is a scanning electron micrograph of the resulting inverted spherical photonic crystal.

<Example 8>

0.5 ml of a 5 wt% aqueous silica solution was administered to a NOA 60 pattern having a width of 50 μm. Carefully introducing it into the silicone oil will evenly distribute the suspension over the pattern. The pattern was crystallized by maintaining the ON-OFF cycle of 1020W microwave for 5 minutes to 25 seconds for 30 minutes, and the silicone oil was washed with hexane and observed with an optical microscope and a primary premicroscopic microscope. Fig. 11 (conventional method) and Fig. 12 (method of the present invention) show optical micrographs thereof, and Fig. 13 show scanning electron micrographs. In particular, Figures 11 and 12 introduced the silica suspension on the PDMS pattern of the conventional method, it is shown in contrast to the pattern dried in a convection oven.

In the present invention, microwaves were used to prepare spherical colloidal crystals from droplets. As a result, the time required was shorter than that of the conventional method, and crystals having a low level of defects could be prepared. This is a very important factor in the industrial production of spherical colloidal crystals. While the conventional method takes about 12 hours to crystallize the colloidal particles inside the droplets, the present method consumes about 10 minutes, resulting in a reduction of about 60 times, which greatly improves productivity. . In addition, by using microwaves, only water molecules can be selectively heated to use energy efficiently, which significantly lowers production costs. In addition, the problem of evaporation of oil, which is a problem in the conventional method, has been greatly reduced, which has a positive effect in three aspects. Spherical colloidal crystals are currently being investigated for many applications, and provide effects that can be applied to pigments, biosensors, and the like of reflective display devices. Mass production is essential for this application, which requires shortening of the process time and energy efficient use, and the present invention can be said to have a great contribution in this regard.

In addition, when preparing a patterned colloidal pattern, oil is introduced onto the pattern and the suspension and crystallized using microwaves to create a structure that is much less cracked, has a lower level of defects, and has a smoother surface than conventional methods. Could confirm. As a result, the optical characteristics have been remarkably improved, and when it is used as a pigment of a reflective screen display device, it is expected to provide improved color.

Claims (9)

A method of inducing self-assembly of particles by crystallizing a colloidal dispersion within a limited space, wherein the method uses a microwave. The method of claim 1, Colloidal self-assembly, which uses microwaves to remove water from water / oil droplets, resulting in spherical colloidal crystals. The method of claim 1, A colloidal self-assembly method in which microwaves are used to remove water from a suspension using a pattern as a confined space, thereby producing patterned colloidal crystals. In the method for producing a spherical colloidal crystal of inverted structure, Colloidal self-assembly using microwaves to remove water from water / oil droplets. The method according to claim 2 or 3, Colloidal self-assembly, which determines the completion of crystallization by the disappearance of the white of the droplet or the disappearance of the white on the pattern and the appearance of the bandgap wavelength of the photonic crystal, depending on the colloid size and the type of the dispersed phase. The method of claim 2 or 3, Colloidal self-assembly to control the level of defects through the control of microwave intensity. The method of claim 6, Colloidal self-assembly method characterized in that the control of the intensity of the microwave by using a constant power, but by changing the period. A colloidal self-assembly method, characterized in that the bandgap of the spherical colloidal crystal produced by the method of claim 1 or 2 is controlled by the size of the colloidal particles used. A colloidal self-assembly method, characterized in that the bandgap of the spherical colloidal crystal produced by the method of claim 1 or 2 is controlled by the type of dispersed phase.

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