WO2009128588A1

WO2009128588A1 - Method for in-situ manufacturing monodisperse spherical photonic crystals with single or multi-colors using microfluidic devices

Info

Publication number: WO2009128588A1
Application number: PCT/KR2008/004542
Authority: WO
Inventors: Seung-Man Yang; Shin-Hyun Kim; Seog-Jin Jeon; Gi-Ra Yi; Woong-Chan Jeong
Original assignee: Korea Advanced Institute of Science and Technology KAIST
Current assignee: Korea Advanced Institute of Science and Technology KAIST
Priority date: 2008-04-15
Filing date: 2008-08-05
Publication date: 2009-10-22
Anticipated expiration: 2010-10-15
Also published as: KR20090109376A; KR100995383B1

Abstract

The present invention is a method for manufacturing monodisperse spherical photonic crystals with single or multi-colors with a uniform size, which comprises: preparing microfluidic devices consisting of glass tubes; treating a colloidal dispersion capable of being photo-polymerized to generate liquid drops with a uniform size in water using the prepared microfluidic devices; and passing the prepared liquid drops with a uniform size through a region exposed to the UV located downstream of the fluidic devices to carry out photo-curing. The present inventions include a method for in-situ manufacturing of monodisperse spherical photonic crystals with a uniform size using microfluidic devices consisting of glass tubes, a method for manufacturation of monodisperse spherical photonic crystals with single or multi-colors as well as evaluation of optical properties of the monodisperse spherical photonic crystals manufactured by the above method and electrical rotation of the monodisperse spherical photonic crystals. A monodisperse spherical photonic crystalline structure formed according to the present invention is preferably applied to a variety of applications including, pixels of reflex displays, labels for detection of biological molecules, etc.

Description

METHOD FOR IN-SITU MANUFACTURING MONODISPERSE SPHERICAL PHOTONIC CRYSTALS WITH SINGLE OR MULTI-COLORS

USING MICROFLUIDIC DEVICES

[Technical Field]

The present invention relates to a method for in-situ manufacturing monodisperse spherical photonic crystals with controlled shapes using microfluidic devices, and monodisperse spherical photonic crystals with single or multi-colors manufactured by the above method. More particularly, the present invention relates to a method for manufacturing monodisperse spherical photonic crystals in solid state which includes treating polymer solution capable of being photo-polymerized containing high concentration of colloidal particles to generate liquid drops with a uniform size using the microfluidic devices; and passing the prepared liquid drops through a region exposed to the UV during passing through a tube. Wherein, the high concentration of colloidal particles exhibit reflected colors via a regular arrangement of the colloidal particles inside of the liquid drop. The microfluidic devices may be modified to prepare Janus monodisperse spherical photonic crystals with multi-colors. Especially, the Janus monodisperse spherical photonic crystals have electrical anisotropy sufficient to alter their orientations via rotating by applying an electric field, so that the Janus monodisperse spherical photonic crystals are applied to color changeable pixels of displays.

[Background Art]

Photonic crystals mean a material with a periodical distribution of refractive indexes corresponding to light wavelengths. Light of a specific energy cannot exist inside a material, light incident of specific wavelength upon the photonic crystals will be highly reflected. Silica particles of the present invention may form a regular face centered cubic structure inside a liquid drop, which exhibit reflected colors as the photonic crystals. The photonic crystals have different reflection wavelengths depending on size or volume ratio of particles that make up the photonic crystals, the same principle may apply to opal jewerly exhibiting beautiful multiple colors. In particular, the present inventors developed a method for preparing a photonic crystal in a spherical form and controlling precisely a distribution of dimensions or colors of the photonic crystal.

Many studies and investigations in regard to methods for manufacturing spherical photonic crystals due to their optical isotropy. According to a document published in Advanced Materials as a famous materials journal (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)) and Korean Patent Registration No. 10-0466251, they proposed spherical crystals manufactured by preparing an aerosol using an electro-hydrodynamic injection device and evaporating a solvent portion of the aerosol. However, the aerosol system has a drawback in that evaporation of the solvent portion is too rapid to attain a favorable orientation of particles.

A method for manufacturing spherical colloidal crystals using a liquid drops was disclosed in a document published in the Advanced Materials (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)) and Korean Patent Registration No. 10-0717923 (2007). However, the proposed method has a drawback of demanding a complicated process and long period of time in that the method separates a step of generating liquid drops and a step of evaporating the liquid drops. On the other hand, Korean Patent Application No. 10-2007-0029989 proposed a method that comprises adding high concentration of silica particles to a polymer solution capable of being curable by the UV, forming liquid drops with irregular sizes from the mixed polymer solution and solidifying the liquid drops. However, the proposed method has limits that the method cannot control a size of the spherical photonic crystals and produce the spherical photonic crystals with multi-colors.

[Disclosure]

[Technical Problem]

The present invention is a method for manufacturing monodisperse spherical photonic crystals with single or multi-colors with a uniform size, which comprises : (a)preparing microfluidic devices consisting of glass tubes; (b)treating a colloidal dispersion capable of being photo-polymerized using the prepared microfluidic devices to generate liquid drops with a uniform size in water; and (c)passing the prepared liquid drops with a uniform size through a UV exposure region located downstream of the fluidic devices to carry out photo-curing of the prepared liquid drops with a uniform size.

The conventional aerosol system which prepares an aerosol using an electro- hydrodynamic injection device and evaporates a solvent portion of the aerosol into air to form the spherical crystals, has a drawback in that evaporation of the solvent portion is too rapid to attain a favorable orientation of particles. The method for manufacturing spherical colloidal crystals using liquid drops has a drawback of demanding a complicated process and long period of time in that the method separates a step of generating liquid drops and a step of evaporating the liquid drops. The method which comprises adding high concentration of silica particles to a polymer solution capable of being curable by the UV, forming liquid drops with irregular sizes from the mixed polymer solution and solidifying the liquid drops, has limits that the method cannot control a size of the spherical photonic crystals and produce the spherical photonic crystals with multi-colors. [Technical Solution]

In order to solve the problem of the conventional techniques as descripted above, the present invention provides a method for in-situ manufacturing monodisperse spherical photonic crystals with single color with a uniform size using microfluidic devices. Also, the present invention provides a method for in-situ manufacturing monodisperse spherical photonic crystals with multi-colors and altering their orientations via rotating by applying an electic field. The manufactured monodisperse spherical photonic crystals have a high utility as pixels of display devices.

[Advantageous Effects]

The method of manufacturing monodisperse spherical photonic crystals according to the present invention has an advantage in that the monodisperse spherical photonic crystals with single or multi-colors with a uniform size can be manufactured using a simple process in a short period of time. [Description of Drawings]

Fig. 1 is a schematic view illustrating a method for in-situ manufacturing monodisperse spherical photonic crystals with a uniform size according to the present invention;

Fig. 2 shows optical microscope photographs of liquid drops and the monodisperse spherical photonic crystals with blue, green and red color, respectively, manufactured according to Example 1 , each having a uniform size;

Fig. 3 shows reflectance spectra of the monodisperse spherical photonic crystals with blue, green and red color, respectively, illustrated in Fig. 2;

Fig. 4 is a schematic view illustrating a method for in-situ manufacturing the monodisperse spherical photonic crystals with multi-colors;

Fig. 5 shows optical microscope photographs of the monoperse spherical photonic crystals with multi-colors of red and green colors manufactured according to Example 2;

Fig. 6 shows optical microscope photographs of the monoperse spherical photonic crystals with multi-colors of green and black colors manufactured according to Example 3;

Fig. 7 shows scanning electron microscope photographs showing of surfaces of the monoperse spherical photonic crystals with multi-colors manufactured according to Examples 3 and 4, respectively; and Fig. 8 shows photographs showing alteration of orientation of the monoperse spherical photonic crystals with multi-colors via rotating driven as in Example 5. [Best Mode]

The present invention provides a method for manufacturing monodisperse spherical photonic crystals with single or multi-colors using microfluidic devices.

The present invention is a method for manufacturing monodisperse spherical photonic crystals with single or multi-colors with a uniform size using microfluidic devices, which comprises : (a)preparing microfluidic devices consisting of glass tubes; (b)treating a colloidal dispersion capable of being photo-polymerized to generate liquid drops with a uniform size in water using the prepared microfluidic devices; and (c)passing the prepared liquid drops with a uniform size through a region exposed to the UV located downstream of the fluidic devices to carry out photo-curing.

The liquid drops or the monodisperse spherical photonic crystals manufactured as above method may have a size ranging from lOμm to lmm.

The micro-fine inner glass tubes used herein may have an inner diameter in a range of 1 to l,000μm and the micro-fine outer glass tubes used herein may have an inner diameter in a range of 10 to 10,000μm.

The colloidal dispersion used herein may have a flow rate ranging from 0.1 to lOOM/min, and the flow rate of water may range from 10 to 10,000/^/min.

The transparent fluid tube used herein is exposed to UV at a light intensity ranging from 1 to 100mW/cm , and the liquid drops containing the colloidal dispersion may be photo-curable by being exposed to the UV for 0.1 to 10 seconds during flowing the fluid tube exposed to the UV using water.

The monodisperse spherical photonic crystals with single or multi-colors with a uniform size using microfluidic devices can be manufactured by removing the particles from the formed monodisperse spherical photonic crystals with single or multicolors with a uniform size.

The inner tube of the microfluidic device may consist of a pair of at least two glass tubes such that each colloidal dispersions with different color can be combined into a single liquid drop at ends of the inner tubes. In this regard, the dispersions of carbon black, carbon nano tubes or titania nanoparticles may be added to the inner tube to impart electrical anisotropy to the monodisperse spherical photonic crystals with single or multi-colors with a uniform size. Alternatively, the dispersions containing surface-treated silica particles may be added to the inner tube to impart electrical anisotropy to the monodisperse spherical photonic crystals with single or multi-colors with a uniform size.

The present invention can control colors of the monodisperse spherical photonic crystals with single or multi-colors by altering their orientations via applying an electric field to the monodisperse spherical photonic crystals with single and/or multi-colors manufactured as above method.

The present invention can control colors of the monodisperse spherical photonic crystals with single or multi-colors by altering their orientations via applying an electric field to the monodisperse spherical photonic crystals with single and/or multi-colors with electrical anisotropy manufactured as above method.

When the present inventors manufactures the monodisperse spherical photonic crystals with single or multi-colors with a uniform size using microfluidic devices, they may manufacture the monodisperse spherical photonic crystals with multi-colors, they may manufacture the monodisperse spherical photonic crystals with multi-colors in which one color occupies a larger area than that occupied by another color.

The present invention can control colors of the monodisperse spherical photonic crystals by altering their orientations via applying an electric field to the monodisperse spherical photonic crystals manufactured as above method, comprising a method controlling colors of the monodisperse spherical photonic crystals with single or multi-colors using a low power, that exhibit variation of the colors even at a monodisperse spherical photonic crystals' rotational angle of 180° or less.

The present invention will be described in more detail as below.

In an aspect of the present invention to accomplish the above purposes, the present invention relatets to a method for manufacturing monodisperse spherical photonic crystals with single or multi-colors with a uniform size comprising: (a) assembling micro-fine glass tubes to prepare a microfluidic device; (b) adding colloidal dispersions capable of being photo-polymerized and a water phase containing a surfactant to the microfluidic device so as to form liquid drops with a uniform size; and (c) passing the formed liquid drops through the tubes exposed to the UV so as to be solidified into the photonic crystals and, in addition, applications of the manufactured monodisperse spherical photonic crystals.

The micro-fine glass tubes used in Step (a) may have an inner diameter ranging from several micrometers to several hundreds micrometers, and preferably have a round polished ends. For preparation of the monodisperse spherical photonic crystals with single color, a smaller micro-fine tube is introduced into a larger micro-fine tube and the prepared micro-fine tubes are tightly sealed using a liquid adhesive capable of being photo-polymerized or other desired methods. The inner tube and the outer tube have separate openings, respectively, each being connected to an external fluid supply device through a pipe. For production of the monodisperse spherical photonic crystals with multi-colors, at least two smaller inner tubes are paired and each of the inner tube and outer tubes have separate openings. The sealing material used in the Step (a) may comprise at least one or two or more selected from adhesives based on photo-polymerizable polymers having acryl groups, however, the present invention is not particularly limited thereto so far as the adhesive is useable to seal the tubes.

In the Step (b), the colloidal dispersions capable of being photo-polymerized as an oil phase and water as a continuous phase flow into the microfluidic device. Herein, the water phase may contain 0.1 to 5% (v/v), and preferably 1 to 2% (v/v) of a surfactant. The colloidal dispersion capable of being photo-polymerized may contain 5 to 40% (v/v), and preferably 10 to 30% (v/v) of colloidal particles with a uniform size. The size of the colloidal particles may range from 100 to 100,000nm, and preferably 150 to 3,000nm.

The flow rate may be regulated to form liquid drops with a uniform size. For the colloidal dispersions, the flow rate typically ranges from 1 to 10//#/min, but it is preferably varied depending on an inner diameter of the glass tube or the flow rate of water. Also, the flow rate of water typically ranges from 10 to 1,000/^/min, but it is preferably varied depending on the inner diameter of the glass tube or the flow rate of the colloidal dispersion.

In the Step (c), the liquid drops flowing through the tube are exposed to the UV and cured. UV irradiation is normally performed at a light intensity of 1 to 40mW/cm² for 1 to 10 seconds, but, it is determined depending on a length of the UV exposure region and a flow velocity of the water. The liquid drops passed through the UV exposure region become hard spherical photonic crystals by solidification, which exhibit higher reflected colors than those of the liquid drops of before passing through the UV exposure region.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The present invention proposes a method for in-situ manufacturation of monodisperse spherical photonic crystals with a uniform size using microfluidic devices without an alternative evaporation process, unlike conventional methods, and is favorably applied to fabrication of a applicable structure including reflection type displays, in particular manufacturing monodisperse spherical photonic crystals with multi-colors.

According to the conventional method, the inventors must wait until the water ingredients of the liquid drops are dissolved in an oil phase by leaving them for 12 hours at room temperature, or induce the water ingredients of the liquid drops to be evaporated for several tens of minutes using microwave, so as to remove the water ingredients from the liquid drops, however, the conventional method demands a very complicated and long process.

Meanwhile, when the liquid drops capable of photo-polymerized are prepared using an emulsion device to manufacture the spherical photonic crystals, a drawback is that only the spherical photonic crystals with single color with irregular sizes can be manufactured.

According to the present invention, it is possible to manufacture the liquid drops using the microfluidic devices and the monodisperse spherical photonic crystals with single or multi-colors with a uniform size in-situ using photo-curing techniques, wherein the liquid drops with a uniform size can be formed in two modes. One of the modes is a "dripping" mode such that the liquid drops are prepared by a balance between drag force of a water stream and capillary force of interfacial tension. The dripping mode normally happened when the flow velocity of water is higher than the flow velocity of the colloidal dispersion. The size of the liquid drops prepared by the balance of forces may be calculated by the following equation 1 : Equation 1

For the equation 1, d_d is a diameter of the prepared liquid drop, dj is an inner diameter of an inner glass tube, ■' is interfacial tension, ^' is a flow velocity of water, and η_c is a viscosity of water. Therefore, the size of the prepared liquid drops depends on the inner diameter of the inner glass tube and the flow velocity of water. As the inner diameter increases and the velocity of water decreases, larger liquid drops are prepared. On the other hand, the flow velocity of the colloidal dispersion determines a periodic cycle of preparing the liquid drops but has no influence on the size of the liquid drops. Thus, only increase in flow velocity of the colloidal dispersion while maintaining the flow velocity of water is need to prepare the liquid drops with a uniform size at a relatively high speed.

However, if the flow velocity of the colloidal dispersion is similar to the flow velocity of water, a mechanism of formation of liquid drops changes from the dripping mode to a jetting mode. The jetting mode means that the colloidal dispersions are jetted in a long cylinder form and the long extended cylinder form changes to a spherical form by being cut off due to unstable interfacial energy of the long extended cylinder. This is a well known phenomenon as "Plateau-Rayleigh instability" state, and this is the same principle as a water stream is cut into small water drops. The jetting mode has a merit of a high speed for formation of liquid drops.

Meanwhile, a microfluidic device comprising a pair of at least two inner glass tubes is used to prepare the spherical photonic crystals with multi-colors. In this case, the same conditions for preparation are maintained as above, the colloidal dispersions exhibiting two different reflected colors are just introduced into at least two inner tubes. The colloidal dispersions are formed into single liquid drops at ends of the inner glass tubes, which, in turn, each liquid drops can have at least two reflected colors.

As the water flow, so the formed liquid drops flow to downstream and pass through the region exposed to the UV, resulting in solidified photonic crystals while maintaining the original shape of the liquid drops. In this case, at the inner of solidified spherical photonic crystals, the colloidal particles with a uniform size form a face centered cubic structure to exhibit reflected colors. Especially, the colloidal particles form a (111) face of the face centered cubic structure along a surface of the liquid drop, so as to form an isotropic photonic crystal whose optical properties are unchangeable according to rotation. In this case, the reflected color may be expected by the following equation 2:

Equation 2

wherein n is a refractive index of a substance, n is a volume ratio of the colloidal particles and D is a diameter of the colloidal particle.

The system used in the present invention is an oil/water liquid drop system, wherein the water, for example, triply distilled water is used, and the oil may be Ethoxylated trimethylolpropane triacrylate monomer(ETPTA, MW 428, viscosity 60 cps, SR 454) capable of being cured by irradiating the UV, however, it is not particularly limited thereto so far as the oil is cured when exposed to UV.

Also, as a surfactant to stabilize the liquid drops, for example, Pluronic F108(Ethylene Oxide/Propylene Oxide Block Copolymer, BASF) may be used, which has at least 10% solubility at room temperature, and is sufficient to stabilize the oil phase as an HLB value of at least 24, however, the surfactant is not particularly limited thereto so far as it has an HLB value of at least 8.

The colloidal particles for example, the silica particles can be used, and the silica particles can be prepared using a so called Stober-Fink-Bohn method, however, the colloidal particle is not particularly limited thereto.

According to the present invention, porous spherical photonic crystals as well as the colloidal spherical photonic crystals may be prepared using the same system, and these may be prepared by selectively removing silica particles from the prepared spherical photonic crystals. In this case, the silica particles are removed by compounds such as sodium hydroxide solution or fluoric acid, and only cured ETPTA may maintain its structure.

Meanwhile, introduction of electrical anisotropy to the spherical photonic crystals with multi-colors may control orientation of the spherical photonic crystals in an electric field. As methods for introducing electrical anisotropy, there are a method of preparing spherical photonic crystals which comprises modifying a surface of each silica particle using APS(3-aminopropyltriethoxysilane) so as to use original silica particles at one side while using the modified silica particles at the other side; a method of using original silica particles at one side, while using material, which has different electrical characters from the original silica particles, such as carbon black nanoparticles at the other side, etc. However, the methods are not limited thereto, and all methods may be used so far as introduce the electrical anisotropy.

The spherical photonic crystals with multi-colors with electrical anisotropy may be utilized in a rotating ball typed display (Gyricon display), such that the spherical photonic crystals are introduced into a polymer film, followed by expanding the film by absorbing liquid to capture each of the spherical photonic crystals inside a spherical space of the film. If an electric field apply to the prepared polymer film using a transparent electrode, it is possible to control reflected colors by alterating of orientation of the spherical photonic crystals via rotating at the inner of the polymer film.

Hereinafter, the present invention will be described in more detail with examples, however the examples below are for the purpose of illustration, and the present invention is not limited thereto.

<EX AMPLE 1>: Preparation of spherical photonic crystals with single color

Silica particles with a uniform size of 145nm prepared by Stober-Fink-Bohn method were dispersed in ETPTA in a volume ratio of 1 :2. Also 1 wt% of Pluronic F 108 as a surfactant was dispersed in water. These dispersions were introduced into a microfluidic device, which was manufactured with a glass tube having an inner diameter of 1 OOμm and another glass tube having an inner diameter of 400μm, at flow rates of 5//l/min and 500/^/min, respectively, so as to prepare liquid drops with a uniform size in a dripping mode. As these liquid drops flow along water and passed through a region exposed to the UV at a light intensity of lOmW/cm² for 1 second, resulting in solidified crystals.

Fig. 2A is an optical microscope photograph showing liquid drops with a uniform size, which flow in a microfluidic tube, while Fig. 2B shows prepared blue spherical photonic crystals.

Meanwhile in order to prepare spherical photonic crystals having green color with a uniform size, silica particles having a diameter of 152 nm were added to ETPTA in a volume ratio of 1 : 3, as a result, the photonic crystals are prepared and shown in an optical microscope photograph of Fig. 2C.

In order to prepare spherical photonic crystals having red color, silica particles having a diameter of 190 nm were added to ETPTA in a volume ratio of 1 :2, the result is shown in Fig. 2D. In addition, Fig. 3 illustrates reflectance spectra of the spherical photonic crystals with blue color, green color and red color, respectively.

<EXAMPLE 2>: Preparation of spherical photonic crystals with multi-colors

Conditions of preparation used in Example 1 was maintained, Janus spherical photonic crystals having multi-colors using the microfluidic device consisted of a pair of two inner tubes. Fig. 4 shows a schematic view describing Example 2. In this case, in order to express red color silica particles having a diameter of 190 nm were mixed with ETPTA in a volume ratio of 1 :4 and, in order to express green color silica particles having a diameter of 145 nm were mixed with ETPTA in a volume ratio of 1:4. As a result, the Janus spherical photonic crystals were prepared, having red color at one hemisphere and green color at the other hemisphere. Fig. 5 shows optical microscope photographs showing the formed spherical photonic crystals. Wherein, Fig. 5A is a low magnification photograph and Fig. 5B is a high magnification photograph.

<EXAMPLE 3>: Preparation of spherical photonic crystals with multi-colors having electrical anisotropy

The spherical photonic crystals was prepared by the same method as Example 2, the dispersions which are mixed with silica particles having a diameter of 182nm in volume ration of 1 :2 were introduced to one of the inner tubes, and the dispersions which are mixed with silica particles having a diameter of 300nm in volume ration of 1 :2 additionally, are mixed with 3 wt% of carbon black nanoparticles, were introduced to the other of the inner tubes, so as to introduce electrical anisotropy. As a result, the spherical photonic crystals with multi-colors of green color and black color were prepared, and the electrical anisotropy was generated in the spherical crystals. Fig. 6 shows optical microscope photographs of the Janus spherical photonic crystals with multi-colors of green color and black color wherein Fig. 6A is a low magnification photograph and Fig. 6B is a high magnification photograph.

<EX AMPLE 4>: Preparation of porous spherical photonic crystals

The spherical photonic crystals with multi-colors of red color and black color was prepared by the same method as Example 3, using the dispersions which are mixed with silica particles having a diameter of 198nm in volume ratio of 1 :2 and the dispersions which are mixed with silica particles having a diameter of 300nm in volume ratio of 1 :2 and the dispersions which are mixed with 3wt% of carbon black nanoparticles. Fig. 7A shows a scanning electron microscope photograph of a surface of an interfacial part between colors of the prepared spherical photonic crystal with multicolors; An inner image of Fig. 7A shows an optical microscope photograph of the spherical photonic crystal with multi-colors of red color and black color. Meanwhile, immersing the spherical photonic crystals in 5 wt% fluoric acid for 12 hours selectively removed silica particles from the crystals, thereby preparing the porous spherical photonic crystals with multi-colors. Fig. 7B shows an optical microscope photograph of a surface of the spherical photonic crystal with multi-colors having a porous structure. An inner image of Fig. 7B shows an optical microscope photograph of the same thing.

<EXAMPLE 5>: Controlling colors using spherical photonic crystals with multi-colors

The spherical photonic crystals with multi-colors prepared in Example 3 were impregnated in an inner part of a PDMS(polydimethylsiloxane) film of a thickness of lmm and the impregnated PDMS film was dipped in hexadecane for 2 days so as to allow the PDMS film to absorb hexadecane, thus volume of the PDMS film was expanded. As a result, the PDMS film having each of the spherical photonic crystals encapsulated in a spherical space of the film was formed. Application of an electric field of 500V and 1 Hz to the PDMS film using an ITO transparent electrode resulted in control of reflected color via rotation of the spherical photonic crystals depending on variation of the electric field. Fig. 8 A shows a photograph that green hemispheres of the crystals directed upward, while Fig. 8B shows a photograph that black hemispheres of the crystals directed upward.

<EXAMPLE 6>: Preparation of spherical photonic crystals having asymmetric structure and control of colors

Spherical photonic crystals with multi-colors having an asymmetric structure were prepared using the dispersions which are mixed with silica particles having a diameter of 182nm in volume ratio of 1 :2 and the dispersions which are mixed with silica particles having a diameter of 300nm in volume ratio of 1 :2, additionally, the dispersions which are mixed with 3 wt% of carbon black nanoparticles, by the same method as Example 3, except that both dispersions have different flow rates in a ratio of 1:2. More relative flow rates of the dispersions flow, wider color area occupies. Color of the prepared photonic crystals with multi-colors were controlled using the same method as Example 5. A variation in colors was clearly observed even at a rotational angle of 180° or less of the spherical photonic crystals and low driving voltage was detected.

As described above, while the present invention has been described with reference to the accompanying desirable exemplary embodiments, it will be understood by those skilled in the art that various modifications and variations may be made therein without departing from ideas and the scope of the present invention as defined by the appended claims. [Industrial Applicability]

The present invention is useful for manufacturing monodisperse spherical photonic crystals with single or multi-colors with a very uniform size in a simple process in a short period of time. In addition, the spherical photonic crystals of the present invention may have electrical anisotropy allowing orientation control of the crystals via an electric field, so that they are preferably applied to variable applications such as pixels of reflection typed displays and key components of portable e-papers of future. Also, if monodisperse spherical photonic crystals with a variety of colors with a uniform size are used by being combined with biological molecules such as various proteins or DNA, they may be applied as useful particles detectable of biological molecules even only as a single fluorescence.

Claims

[CLAIMS] [Claim 1 ]

A method for manufacturing monodisperse spherical photonic crystals with single or multi-colors with a uniform size using microfluidic devices comprising:

(a) preparing microfluidic devices consisting of glass tubes;

(b) treating a colloidal dispersion capable of being photo-polymerized to generate liquid drops with a uniform size in water using the prepared microfluidic devices; and

(c) passing the prepared liquid drops with a uniform size through a region exposed to the UV located downstream of the fluidic devices to carry out photo-curing of the prepared liquid drops with a uniform size.

[Claim 2]

The method according to claim 1 , wherein the generated liquid drops or the prepared monodisperse spherical photonic crystals have a size ranging from lOjum to lmm. [Claim 3]

The method according to claim 1 , wherein the glass tubes comprise micro-fine inner glass tubes having an inner diameter in a range of 1 to 1 ,000μm and micro-fine outer glass tubes having an inner diameter in a range of 10 to 10,000/im. [Claim 4]

The method according to claim 1 , wherein the colloidal dispersion has a flow rate ranging from 0.1 to 100/^£/min and water has a flow rate ranging from 10 to 10,000/^/min. [Claim 5] The method according to claim 1 , wherein the microfluidic devices are transparent tubes and are exposed to the UV at a light intensity ranging from 1 to 100 mW/cm², while the prepared liquid drops are exposed to the UV for 0.1 to 10 seconds during passing through a UV exposure region. [Claim 6]

The method according to claim 1 , wherein the inner tubes of the microfluidic device consists of a pair of at least two glass tubes such that each colloidal dispersion with different color is formed into a single liquid drop at ends of the inner tubes. [Claim 7]

The method according to claim 6, wherein the dispersions of carbon black, carbon nano tubes or titania nanoparticles are added to the inner tube to introduce electrical anisotropy. [Claim 8]

The method according to claim 6, wherein a dispersion containing surface treated silica particles is introduced into the inner tube to introduce electrical anisotropy. [Claim 9]

The method according to claim 1 , wherein the prepared monodisperse spherical photonic crystals with single or multi-colors are treated to remove silica particles from the prepared monodisperse spherical photonic crystals with single or multi-colors with a uniform size. [Claim 10]

A method for controlling colors of the monodisperse spherical photonic crystals with multi-colors, comprising applying an electric field to the monodisperse spherical photonic crystals with multi-colors with a electrical anisotropy prepared by a method of claim 1 so as to alter their orientations. [Claim 11 ]

The method according to claim 1 , wherein the colloidal dispersions are provided into the paired glass tubes at different flow rates such that one color occupies a larger area than that occupied by another color in the monodisperse spherical photonic crystals with single or multi-colors. [Claim 12]

A method for controlling colors of the monodisperse spherical photonic crystals with single or multi-colors using a low power, comprising applying an electric field to the monodisperse spherical photonic crystals with single or multi-colors prepared by a method of claim 11 so as to alter their orientations at a rotational angle of 180° or less.