DECORATIVE AQUEOUS COMPOSITION AND METHOD FOR PRODUCING SAME

Abstract

[Object]

To provide a decorative aqueous composition that includes particles formed from opal-type colloidal crystals uniformly and stably dispersed in an aqueous dispersion medium, and exhibits a structural color due to interference of light, and to provide a method for producing the decorative aqueous composition.

[Solution]

The decorative aqueous composition of the present invention contains particles of opal-type colloidal crystals dispersed in an aqueous dispersion medium in which a polymer is dissolved. The particles of the opal-type colloidal crystals are made from hydrophilic colloidal particles having an average particle diameter ranging from 10 nm to 1000 nm with a variation coefficient of the particle diameter being within 20%. Therefore, the decorative aqueous composition of the present invention contains opal-type colloidal crystals uniformly and stably dispersed in an aqueous dispersion medium, and exhibits a structural color due to interference of light. As a result, the decorative aqueous composition can be suitably used in a cosmetic lotion or the like.

Claims

1.-9. (canceled)

10. A decorative aqueous composition comprising opal-type colloidal crystals dispersed in an aqueous dispersion medium, a polymer being dissolved in the aqueous dispersion, wherein colloidal particles constituting the opal-type colloidal crystals are dispersible in the aqueous dispersion medium and have an average particle diameter ranging from 10 nm to 1000 nm, and a variation coefficient of the particle diameter is within 20%.

11. The decorative aqueous composition according to claim 10, wherein a specific gravity of the colloidal particles is in a range from 0.9 times to 1.1 times a specific gravity of the aqueous dispersion medium.

12. The decorative aqueous composition according to claim 10, wherein the colloidal particles include a crosslinked polymer.

13. The decorative aqueous composition according to claim 10, wherein the colloidal particles include poly(N-isopropylacrylamide).

14. The decorative aqueous composition according to claim 10, wherein the colloidal particles include poly(N-isopropylacrylamide) and polyacrylamide.

15. The decorative aqueous composition according to claim 10, wherein the aqueous dispersion medium includes an alcohol in addition to water.

16. A decorative solidified body formed by solidifying the decorative aqueous composition of claim 10.

17. A method for producing a decorative aqueous composition, the method comprising mixing an aqueous dispersion medium, a polymer soluble in the aqueous dispersion medium, and colloidal particles having an average particle diameter ranging from 10 nm to 1000 nm with a variation coefficient of the particle diameter being within 20%, to form a dispersion of particles including opal-type colloidal crystals.

18. The method for producing a decorative aqueous composition according to claim 17, wherein the hydrophilic colloidal particles are a crosslinked hydrophilic polymer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 is a schematic diagram illustrating the formation of a charged colloidal crystal.

[0035] FIG. 2 is a schematic diagram illustrating a phase transition of a colloidal system.

[0036] FIG. 3 is a schematic diagram illustrating a depletion effect due to dissolution of a polymer in a colloidal system.

[0037] FIG. 4 is a schematic diagram of a decorative aqueous composition according to an embodiment of the present invention.

[0038] FIG. 5 is a schematic view of a colloidal particle made from a crosslinked polymer.

[0039] FIG. 6 is a process diagram illustrating a method for producing a decorative aqueous composition.

[0040] FIG. 7 is photographs of a decorative aqueous composition prepared in Example 1.

[0041] FIG. 8 is a graph showing measurement results for the decorative aqueous composition prepared in Example 1, the results being obtained by measuring the reflection spectrum at a different height from the bottom of a measurement cell.

[0042] FIG. 9 is a graph showing measurement results for a decorative aqueous composition prepared in Comparative Example 2, the results being obtained by measuring the reflection spectrum at a different height from the bottom of the measurement cell.

[0043] FIG. 10 is photographs showing the dispersed state when microgels prepared in Synthesis Examples 1 to 4 were dispersed in water-ethanol solutions at various temperatures.

[0044] FIG. 11 is a graph showing the measurement results of the reflection spectra of microgels prepared in Synthesis Example 4.

[0045] FIG. 12 is photographs of the decorative aqueous composition of Example 9.

[0046] FIG. 13 is photographs of the decorative aqueous compositions of Examples 11 to 13.

[0047] FIG. 14 is graphs showing the relationship between the concentration of the polymer dissolved in the decorative aqueous composition and the lattice spacings.

DESCRIPTION OF EMBODIMENTS

[0048] Hereinafter, embodiments that embody the present invention will be described with reference to the drawings.

[0049] FIG. 4 is a schematic diagram of a decorative aqueous composition according to an embodiment of the present invention. In this decorative aqueous composition, a polymer 2 having an average molecular weight of 100000 or higher is dissolved in an aqueous dispersion medium 1 such as water or water-ethanol (50% or more of water in terms of a weight ratio), and opal-type colloidal crystals 3 are further dispersed in the aqueous dispersion medium 1. Each opal-type colloidal crystal 3 has a structure in which colloidal particles 4 are close-packed. The average particle diameter of the colloidal particle 4 ranges from 10 nm to 1000 nm, and a variation coefficient of the particle diameter is within 20%.

[0050] In this decorative aqueous composition, the polymer 2 having an average molecular weight of 100000 or higher is dissolved in the aqueous dispersion medium 1, and therefore as illustrated in FIG. 3, a depletion region of polymer (depletant) is formed in the vicinity where colloidal particles 4 constituting the opal-type colloidal crystal 3 are in close proximity to each other. As a result, a difference in osmotic pressure (osmotic pressure difference) is produced between the depletion region and other regions, which causes the colloidal particles 4 to contact with each other, and thus the opal-type colloidal crystal 3 is formed. The average molecular weight of the polymer is preferably 200000 or greater, more preferably 300000 or greater, and even more preferably 500000 or greater. The osmotic pressure difference is mostly stable regardless of the concentration of the electrolyte. Therefore, even if the electrolyte concentration of the solvent is at 0.1 mM, the structure of the opal-type colloidal crystal does not collapse.

[0051] In addition, the variation coefficient of the particle diameter of the colloidal particles 4 constituting the opal-type colloidal crystals 3 is within 20%, and therefore it is possible to achieve an orderly colloidal crystal structure with few defects. Furthermore, since the average particle diameter of the colloidal particles 4 ranges from 10 nm to 1000 nm, electromagnetic waves of various wavelengths such as ultraviolet rays, visible light rays, and infrared rays can be diffracted. Therefore, a composition having decorative properties can be formed.

[0052] Accordingly, light interference occurs due to the opal-type colloidal crystals 3, and as a result, the decorative aqueous composition according to an embodiment of the present invention exhibits glittering structural color.

[0053] The variation coefficient of the particle diameter of the colloidal particles constituting the opal-type colloidal crystals is required to be within 20%, is preferably less than 15%, more preferably less than 10%, and even more preferably less than 5%.

[0054] In addition, the specific gravity of the colloidal particles constituting the opal-type colloidal crystal particles is preferably in a range of from 0.9 times to 1.1 times the specific gravity of the aqueous dispersion medium. When the specific gravity of the colloidal particles is in this range, the specific gravity of the colloidal particles is close to the specific gravity of the aqueous dispersion medium, and therefore the opal-type colloidal crystal particles do not easily precipitate and can be stably dispersed. The specific gravity of the colloidal particles constituting the opal-type colloidal crystal particles more preferably ranges from 0.99 times to 1.01 times, and most preferably from 0.995 times to 1.005 times.

[0055] Furthermore, the polymer dissolved in the aqueous dispersion medium of the decorative aqueous composition can be used as long as it is a polymer that dissolves in the aqueous dispersion medium. The average molecular weight of the polymer is preferably 10000 or greater. As described above, when the colloidal particles are in close proximity to each other, the region where the space is too small for the polymer to enter (that is, the depletion region) is formed, and this region increases in its size. This increase of the depletion region in size brings the particles to be close together due to the osmotic pressure difference, and thereby ensuring the formation of the opal-type colloidal crystals. A polymer having an average molecular weight of 100000 or greater is even more preferable. Furthermore, as a preferable characteristic of the polymer, the polymer preferably has a property of not easily being adsorbed to the colloidal particles dispersed in the aqueous dispersion medium. This is because in a case where the polymer is easily adsorbed to the colloidal particles, the polymer may act as an agglomerating agent, and there is a risk that the colloidal particles may aggregate and precipitate.

[0056] In an embodiment of the present invention, a water-soluble ionic polymer or water-soluble nonionic polymer can be used as the water soluble polymer (depletant) that is added to express depletion attraction force between colloidal particles. Examples of water-soluble nonionic polymers include polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyether, and polyvinylpyrrolidone. Furthermore, examples of water-soluble ionic polymers include cationic polymers such as polyvinyl pyridine, polyvinyl benzyl ammonium, and polypeptides; and anionic polymers such as polyacrylic acids, polyacrylamides, poly(N-isopropylacrylamide), polypeptides and other such biopolymers, and natural polymers such as hyaluronic acid, chondroitin sulfate, alginic acid and other such polysaccharides. In the selection of these polymers, a polymer having a charge opposite to the surface charge of the colloidal particles is not preferable because such polymer may be adsorbed to the colloidal particles to form a charged colloid. However, even with a polymer having a charge opposite to the surface charge of the colloidal particles, if the salt concentration is high, the electric double layer becomes extremely thin, and the colloidal particles can be brought close to each other. As a result, a difference in osmotic pressure due to the difference in concentration of the polymer is created, which induces a depletion attraction force. Thus, the opal-type colloidal crystal is formed, and such polymer can be used. Furthermore, this phenomenon may be advantageously employed; the concentration of the salt in the colloid is adjusted as appropriate to control the thickness of the electric double layer, the attraction force between colloidal particles can be controlled. And thus, the growth rate of the opal-type colloidal crystals, the half width at half maximum of the colloidal crystal with respect to light, and the like can be controlled. Examples of methods for controlling the salt concentration include controlling the content rate of ionic groups (such as carboxylic acid salts and amino groups) in the polymer, and adding salt. In addition, the polymer is not limited to a linear polymer, and various branched polymers, polymer assemblies, micelles, and spherical particles can also be used as long as they exhibit a depletion effect and an attractive force effect.

[0057] Furthermore, the colloidal particles forming the opal-type colloidal crystals are preferably particles made from a hydrophilic polymer. Such colloidal particles can facilitate a stable dispersion of the opal-type colloidal crystal particles in the aqueous dispersion medium. Examples of the polymer constituting such colloid particles include poly(N-isopropylacrylamide), polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyether, and polyvinylpyrrolidone. Mixtures or copolymers of these polymers can also be used as the colloidal particles.

[0058] Furthermore, examples of water-soluble ionic polymers include cationic polymers such as polyvinyl pyridine, polyvinyl benzyl ammonium, and polypeptides; and anionic polymers such as polyacrylic acids, polyacrylamides, polypeptides, hyaluronic acid, chondroitin sulfate, alginic acid and other such polysaccharides, and other such natural polymers.

[0059] More preferable is a hydrophilic colloid particle 10 made from a crosslinked polymer, as illustrated in FIG. 5. The colloid particle 10 has a structure in which the polymer 11 is crosslinked with a crosslinking agent, and the dispersion medium can freely pass through the crosslinked mesh structure. Therefore, the apparent specific gravity of the colloidal particles 10 becomes extremely close to that of the dispersion medium, the apparent specific gravity of the opal-type colloidal crystals made from the colloidal particles 10 also becomes extremely close to that of the dispersion medium, and the opal-type colloidal crystals are stably dispersed in the dispersion medium without precipitating. The water-soluble polymer described above is desirable as the polymer constituting such a gel.

[0060] On the other hand, even hydrophobic particles such as styrene can be used when a dissociable group is introduced on the surface, because the hydrophobic particles can be stably dispersed in the dispersion medium. Examples of such polymers include polystyrene that has been made hydrophilic through copolymerization of styrene sulfonic acid.

[0061] The decorative aqueous composition according to an embodiment of the present invention can also be made into a decorative solidified body that has been solidified using a solidifying agent. As a result, mechanical strength can be dramatically increased, and handling ease is highly improved. In addition, the lattice spacing of the colloidal crystals changes when pressure is applied to the solidified body, and therefore the solidified body can be used as a pressure sensor or the like by measuring the change in the reflection spectrum thereof.

[0062] Examples of the solidifying agent include solutions containing a gel monomer, a crosslinking agent and a photopolymerization initiator. Examples of the gel monomer include vinyl monomers such as acrylamide and derivatives thereof, examples of the crosslinking agent include N,N-methylene bisacrylamide, and examples of the photopolymerization initiator include 2,2-azobis[2-methyl-N-[2-hydroxyethyl]-propionamide]. In addition, a water-soluble photosensitive resin in which an azide-based photosensitive group is pendant to polyvinyl alcohol can also be used. Furthermore, the colloid crystals may be formed in the resin monomer and then solidified.

[0063] The decorative aqueous composition according to an embodiment of the present invention can be produced according to the processes illustrated in FIG. 6.

Microgel Preparation S1

[0064] First, as a microgel preparation S1, hydrophilic colloidal particles 10 made from a crosslinked polymer are prepared as illustrated in FIG. 5. That is, a monomer that serves as a material of a polymer, a crosslinking agent, a surfactant, and a polymerization initiator are dispersed and mixed in purified water, and then heated to thereby carry out emulsion polymerization. This results in a dispersed liquid in which the microgels formed from the crosslinked polymer illustrated in FIG. 5 are dispersed in the dispersion medium.

Dialysis S2

[0065] Furthermore, the microgel dispersion formed as described above is dialyzed against water, and the surfactant and polymerization initiator are removed (dialysis S2).

Colloidal Crystallization S3

[0066] A polymer aqueous solution is added to the microgel dispersion purified by dialysis, and then stirred. This immediately results in a decorative aqueous composition in which opal-type colloidal crystals are dispersed, with the entire sample uniformly exhibiting a structural color.

EXAMPLES

[0067] The present invention will be described below while comparing more specific examples according to an embodiment of the present invention with comparative examples.

Example 1

Preparation of a Microgel

[0068] N-isopropylacrylamide (NIPAM, Wako Pure Chemical Industries, Ltd.) was used as a monomer, N,N-methylenebisacrylamide (BIS, Wako Pure Chemical Industries, Ltd.) was used as a crosslinking agent, sodium dodecyl sulfate (SDS, Wako Pure Chemical Industries, Ltd.) was used as a surfactant, and potassium peroxodisulfate (KPS, Kanto Chemical Co., Inc.) was used as a radical polymerization initiator. NIPAM (3.93 g) was dissolved in 175 mL of pure water produced in a Milli-Q purification device (hereinafter, referred to as pure water), BIS (0.075 g) was dissolved in 10 mL of pure water, and SDS (0.075 g) was dissolved in 60 mL of pure water. The three solutions were mixed and then transferred to a 500 mL 4-neck round bottom flask and stirred for 1 hour at 850 rpm and 70 C. while circulating Ar. Separately, a solution in which KPS (0.15 g) was dissolved in 5 mL of pure water and held at 70 C. was added to the 4-neck round bottom flask described above, and the mixture was stirred for an additional 4 hours at 850 rpm and 70 C. while circulating Ar to carry out an emulsion polymerization reaction, and a dispersion of microgels, in which polyisopropylacrylamide (PNIPAM) was crosslinked by N,N-methylenebisacrylamide (BIS), was obtained.

Preparation of a Decorative Aqueous Composition

[0069] The microgel dispersion obtained as described above was purified by dialysis with pure water and diluted to approximately 2 wt. %. An aqueous solution of polyacrylamide (PAAm, average molecular weight of 400000) was added to the sample at an amount so as to become 2 wt. %, and the entire sample immediately exhibited a uniform structural color (FIG. 7, right). The entire sample immediately exhibited a uniform structural color even when the PAAm concentration was 0.2 wt. %, but with the passage of time, the material precipitated to the bottom of the container in which the sample was placed, and a structural color was observed in the precipitate (FIG. 7, left).

Comparative Example 1

[0070] In Comparative Example 1, PAAm was not added to the microgel dispersion described above. All other details were the same as those of Example 1, and thus a detailed description thereof is omitted.

Comparative Example 2

[0071] In Comparative Example 2, the microgels in the microgel dispersion of Comparative Example 1 were forcibly precipitated by centrifugation, and the microgel concentration was set to 40 wt. %.

Evaluation

[0072] The reflection spectrum of the decorative aqueous composition of Example 1 was measured using a fiber spectrometer. The reflection spectrum of a sample with a PAAm concentration of 2 wt. % was measured at different heights (h) from the bottom of the measurement cell. As a result, as illustrated in FIG. 8, the reflection spectrum was approximately the same shape regardless of the height from the bottom, and the distance between the particle centers determined by the Bragg equation at the peak position was approximately 250 nm. This value indicates that the microgels were in mutual contact, and very small opal-type colloidal crystals were formed, and suggests crystallization by depletion attraction force (see FIG. 3).

[0073] In contrast, in Comparative Example 1 in which the polymer (PAAm) was not added to the microgels, the entire sample did not exhibit a structural color. Therefore, in Comparative Example 2, the microgels were forcibly precipitated using a centrifugal separator and the microgel concentration was set to approximately 40 wt. % or higher, and a structural color was observed. The reflection spectrum of Comparative Example 2 is illustrated in FIG. 9. At this time, the structural color was expressed only in the lower portion of the centrifuge cell (area where the microgels were concentrated to a high concentration). In addition, the reflection peak wavelength varied depending on the height (h) from the bottom of the measurement cell, and the distance between particle centers determined by the Bragg equation varied in a range of from 290 nm to 310 nm. From the above results, it was found that in Comparative Example 2, hard sphere-type colloidal crystals in which only hard sphere repulsion acted on the microgel particles were formed, and the microgels were not in contact with each other.

Example 2 and Example 3

[0074] In Example 2 and Example 3, sodium chloride (NaCl) was added to pure water serving as a dispersion medium, at an amount to arrive at a predetermined concentration (0.1 mM in Example 2 and 0.01 mM in Example 3). All other conditions were the same as those in Example 1 (polyacrylamide concentration of 2 wt. %), and thus a detailed description thereof is omitted.

Example 4

[0075] In Example 4, hydrochloric acid (HCl) was added to pure water serving as a dispersion medium, at an amount to arrive at a concentration of 0.01 mM. All other conditions were the same as those in Example 1 (polyacrylamide concentration of 2 wt. %), and thus a detailed description thereof is omitted.

Example 5

[0076] In Example 5, sodium hydroxide (NaOH) was added to pure water serving as a dispersion medium, at an amount to arrive at a concentration of 0.01 mM. All other conditions were the same as those in Example 1 (polyacrylamide concentration of 2 wt %), and thus a detailed description thereof is omitted.

Evaluation

[0077] With the decorative aqueous compositions of Example 2 to 5 prepared as described above, similar to the case of Example 1, the entirety of each sample immediately and uniformly exhibited the similar structural color as Example 1 after the addition of PAAm. In addition, the measurement results of the reflection spectra matched the case of Example 1 within the range of measurement error. From the foregoing, it was found that even in an aqueous solution with a salt concentration of 0.1 mM, the opal-type colloidal crystals were stably dispersed and exhibited a structural color. Therefore, the decorative aqueous compositions of Examples 1 to 5 can be sufficiently used in cosmetic lotions or the like that contains ionic additives or pH buffers.

Example 6

[0078] In Example 6, the decorative aqueous composition of Example 1 was purified by dialysis, and then subjected to lyophilization to obtain a powder. When this powder was added to a 2 wt. % PAAm aqueous solution, it was found that a structural color was observed when the gel concentration was 2 wt. % or higher, and a dispersion of the opal-type colloidal crystals was obtained.

Example 7

[0079] To 250 L of a purified PNIPA gel (3.56 wt. %) aqueous solution prepared in the same manner as in Example 1, 25 mg of a polyacrylic acid (PAA, average molecular weight of 1000000) aqueous solution (prepared with a PAA concentration=5 wt. %) was added, the entire sample immediately exhibited a uniform structural color, and it was found that a dispersion of opal-type colloidal crystals was formed.

Example 8

[0080] To 200 L of purified PNIPAM microgels (3.56 wt. %) prepared in the same manner as in Example 1, 5 to 30 mg each of a sodium polyacrylate (NaPAA, PAA average molecular weight of 1000000, neutralization degree of 50%) aqueous solution (prepared with an NaPAA concentration=5 wt. %) was added the entire sample uniformly exhibited a structural color, and it was found that a dispersion of opal-type colloidal crystals was formed.

Comparative Example 3 and Comparative Example 4

[0081] In contrast, to 250 L of purified PNIPAM microgels (3.56 wt. %) prepared in the same manner as Example 1, 25 mg of an aqueous solution (5 wt. %) of NaPAA (neutralization degree of 50%) having an average molecular weight of 25000 in Comparative Example 3 and a molecular weight of 5000 in Comparative Example 4 was added a structural color was not observed, and it was found that a dispersion of opal-type colloidal crystals was not formed. As a cause for the failure to form the dispersion, it is thought that, due to the low molecular weight of the NaPAA molecules, the NaPAA molecules were able to penetrate into the space that was formed when the PNIPAM microgels were in close proximity to each other, and therefore a depletion region was not formed, failing to create a difference in osmotic pressure.

Preparation of a Copolymerized Microgel Dispersion

[0082] NIPAM-AAm copolymer gel dispersions of Synthesis Examples 1 to 4 described below were synthesized as microgel dispersions.

Synthesis Example 1

[0083] A NIPAM-AAm copolymer microgel dispersion was prepared by using, as monomers, 85 mol % of NIPAM, 10 mol % of acrylamide, and 5 mol % of BIS, and then adding SDS at a ratio of 1.5 wt. % and KPS at a ratio of 0.6 wt. %, with the other conditions being the same as in Example 1.

Synthesis Example 2

[0084] A NIPAM-AAm copolymer microgel dispersion was prepared by using, as monomers, 75 mol % of NIPAM, 20 mol % of acrylamide, and 5 mol % of BIS, and then adding SDS at a ratio of 3.0 wt. % and KPS at a ratio of 0.6 wt. %, with the other conditions being the same as in Example 1.

Synthesis Example 3

[0085] A NIPAM-AAm copolymer microgel dispersion was prepared by using, as monomers, 85 mol % of NIPAM, 10 mol % of acrylamide, and 5 mol % of BIS, and then adding SDS at a ratio of 1.0 wt. % and KPS at a ratio of 0.6 wt. %, with the other conditions being the same as in Example 1.

Synthesis Example 4

[0086] A NIPAM-AAm copolymer microgel dispersion was prepared by using, as monomers, 75 mol % of NIPAM, 20 mol % of acrylamide, and 5 mol % of

[0087] BIS, and then adding SDS at a ratio of 2.0 wt. % and KPS at a ratio of 0.6 wt. %, with the other conditions being the same as in Example 1.

[0088] The particle diameters of the NIPAM-AAm copolymer microgel dispersions of Synthesis Examples 1 to 4 prepared as described above were determined by measuring the diffusion coefficient by dynamic light scattering, and then entering the value thereof into the Stokes-Einstein equation. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Synthesis Particle Example NIPAM AAm Bis SDS KPS Diameter 1 85 10 5 1.5 0.6 271 mol % mol % mol % wt % wt % 27.3 nm 2 75 20 3.0 291 mol % mol % wt % 53.7 nm 3 85 10 1.0 320 mol % mol % wt % 36.1 nm 4 75 20 2.0 335 mol % mol % wt % 21.1 nm

Dispersion Test in an Aqueous Solvent of Microgel and Measurement of the Reflection Spectrum

[0089] The microgel dispersions prepared in Synthesis Examples 1 to 4 were lyophilized into a powder, and the microgels were dispersed in ethanol aqueous solutions each having concentrations of 0, 10, 20, 30, 40 and 50 wt. % such that the concentration of the microgels became 2 wt. %. As a result, as shown in FIG. 10, with all of the dispersions, in a temperature range of from 20 C. to 50 C., the microgels were dispersed without aggregating, and color development due to interference of the opal-type colloidal crystals was observed. Furthermore, when the reflection spectrum of the dispersion of Synthesis Example 4 was measured at different temperatures, as illustrated in FIG. 11, reflection peaks were observed up to at least 50 C., and the appearance maintained its color development as well.

Example 9

[0090] In Example 9, the microgel dispersions of Synthesis Example 1 and Synthesis Example 2 were lyophilized into powders and then dispersed in water to a concentration of 2 wt. % to form dispersions. Next, PAA was added at room temperature to these dispersions such that the PAA concentration was 10 mmol/L or 20 mmol/L. As a result, as shown in FIG. 12, interference colors associated with the formation of opal-type colloidal crystals were observed. Note that when the ethanol concentration was 30 wt. % or higher, the volume of the crystalline portion was reduced due to the shrinkage of the microgels, and a supernatant was observed. Thus, it was possible to maintain color development even when ethanol was added. In cases in which the ethanol concentration was 60 wt. % or higher, the PAAm did not dissolve. Regarding temperature resistance, microgels that could withstand 50 C. were successfully synthesized. The sample ultimately exhibited white turbidity at 54 C. Regarding ethanol, the microgels were not able to withstand 50 wt. % ethanol, but tolerability was improved to 30 wt. %. Only samples of 30 wt. % ethanol exhibited dramatic precipitation. Microgels were dispersed in 60 wt. % to 100 wt. % ethanol, but the PAAm added as a polymer is a poor solvent with respect to ethanol and did not dissolve.

Example 10

[0091] A decorative aqueous composition of Example 10 was prepared by the following operations.

[0092] First, the microgel dispersion prepared in Synthesis Example 3 was lyophilized into a powder, and then dispersed in ethanol aqueous solutions having concentrations of 0, 10, 20, 30, 40 and 50 wt. % such that the microgel concentration was 2 wt. %. Hydroxyethyl cellulose (molecular weight: 500000, product name: SE550, available from Daicel Corporation) was added to the dispersion at a concentration of 0.5 wt. %.

Examples 11 to 13

[0093] For the decorative aqueous composition of Example 11, hydroxyethyl cellulose having a different molecular weight than that of Example 10 was used (in Example 11, product of the trade name SE600, available from Daicel Corporation, having a molecular weight of 1020000 was used, in Example 12, product of the trade name SE850, available from Daicel Corporation, having a molecular weight of 1480000 was used, and in example 13, product of the trade name SE900, available from Daicel Corporation, having a molecular weight of 1560000 was used). Examples 11 to 13 were prepared with the other details being the same as those of Example 10. As a result, as shown in FIG. 13, interference colors associated with the formation of opal-type colloidal crystals were clearly observed.

Example 14

[0094] To 500 L of a purified PNIPAM gel (diameter of 193 nm, 3.56 wt. %) prepared in the same manner as in Example 1, 0.05 g of a 20 wt. % solution of polyethylene glycol (average molecular weight of 500000) was added, the entire sample exhibited a uniform structural color, and it was found that a dispersion of opal-type colloidal crystals can be prepared even when using polyethylene glycol as a water-soluble polymer.

Relationship Between the Concentration of the Polymer Dissolved in the Decorative Aqueous Composition and the Lattice Spacing

[0095] In order to examine the relationship between the concentration of the polymer dissolved in the decorative aqueous composition and the lattice spacing, the following experiment was conducted.

[0096] First, a water dispersion of the NIPAM microgels produced by the method of Example 1 was prepared, and PAAm having a molecular weight of 400000 (or PEG having a molecular weight of 1000000) was added thereto, and the lattice spacing was determined from a measurement of the Bragg diffraction wavelength. Meanwhile, the inter-particle distance for a case in which the size of the microgels was constant was determined through calculations. The results are shown in FIG. 14. From the graphs of FIG. 14, it was found that as the concentration of PAAm (or PEG) increased, the lattice spacing became smaller.

Solidification of Dispersion of Opal-Type Colloidal Crystals

[0097] The dispersions of the opal-type colloidal crystals of each of the examples described above can be immobilized by a known method (JP 2006-182833: Gel immobilized colloidal crystals). A specific example thereof is presented below.

[0098] The following chemical agents are added and dissolved in the dispersion of the opal-type colloidal crystals of each example.

[0099] Gel monomer: N,N-dimethylol acrylamide (N-MAM)

[0100] 0.67 mol/L

[0101] Crosslinking agent: methylenebisacrylamide (BIS) 10 mmol/L

[0102] Photopolymerization initiator: 2,2-azobis[2-methyl-N-[2-hydroxyethyl]-propionamide

[0103] 4 mg/mL

[0104] Sodium dodecyl sulfate: 10 mol/L

[0105] Then, the gel monomer is polymerized by irradiating the dispersion of the above-described composition with ultraviolet light, and a solidified body of the dispersion of opal-type colloidal crystals is obtained.

[0106] The present invention is not limited in any way to the description of the embodiments and examples of the invention described above. Various modified aspects that are within a scope that could be readily conceived of by a person skilled in the art are also included in the present invention without departing from the scope of the claims.

INDUSTRIAL APPLICABILITY

[0107] The decorative aqueous composition according to the present invention contains opal-type colloidal crystals dispersed in an aqueous dispersion medium, and exhibits a glittering, aesthetically excellent structural color through Bragg diffraction. In addition, because the structural color thereof does not change at a salt concentration of about 0.1 mM, the decorative aqueous composition can be suitably used in cosmetic products such as cosmetic lotions.

REFERENCE SIGNS LIST

[0108] 1 Aqueous dispersion medium [0109] 2 Polymer [0110] 3 Opal-type colloidal crystal [0111] 4,10 Colloidal particle [0112] 11 Polymer [0113] 12 Crosslinking agent [0114] 13 Crosslinking point [0115] S1 Microgel preparation [0116] S2 Dialysis [0117] S3 Colloidal crystallization