JP4503091B2 - Superhydrophobic powder, structure having superhydrophobic surface using the same, and production method thereof - Google Patents

Description

  The present invention has a basic structure of an aggregate of silica-based nanofibers, a superhydrophobic powder in which a compound having a hydrophobic group is physically adsorbed on the silica surface, and a superhydrophobic surface using the same And a manufacturing method thereof.

  It is defined as superhydrophobic when a water droplet contacts with a solid surface and the contact angle of the water droplet is 150 ° or more. The range where the contact angle is 70 to 150 ° is defined as hydrophobic. In general, hydrophobicity is expressed by covering a surface with molecular residues having a low surface tension, but superhydrophobicity is difficult to express only with molecular residues having a low surface tension.

  On the other hand, many organisms in the natural world show superhydrophobicity. For example, leaves such as lotus, rice and cabbage have super hydrophobicity (super water repellency) that completely repels water droplets. It is known that the superhydrophobicity of lotus leaves is closely related to the surface structure of the leaves. That is, the surface layer is formed while the nanofibers are spread over the entire surface, and micron-sized protrusions such as nanofiber aggregates are formed on the outermost surface layer at a certain distance. It is known that hydrophobic wax exists on the surface. This suggests that the control of the surface roughness, that is, the surface structure / shape in the nano-dimension is the most important for developing the superhydrophobicity.

  The structural principle of superhydrophobic expression, also referred to as the effect of lotus, has become a guideline for the development of many artificial lotus-like structural design methods. I came. For example, it has been reported that the contact angle is increased to 170 ° or more by regularly arranging the carbon nanotubes on the surface of the substrate (see, for example, Non-Patent Document 1). In addition, it has been reported that polypyrrole nanofibers are grown on a platinum-coated silicon surface by an electrochemical process to increase the surface contact angle to 170 ° or more (for example, see Non-Patent Document 2). In addition, after forming a zinc oxide nanocrystal seeds film on the surface of the glass substrate at a temperature of 400 ° C. or higher, an infinite number of rod-shaped zinc oxide nanofibers are grown on the glass substrate surface. It is expressed (see, for example, Non-Patent Document 3).

  As a simple method, for example, a certain poor solvent is added to a solution of polypropylene, and it is cast on the surface of a substrate, and the temperature is adjusted, thereby forming a network structure composed of polypropylene nanoparticles, and thereby a contact angle. Has been reported to be increased to 160 ° (for example, see Non-Patent Document 4). In addition, a glass composed of oxides of silicon, boron, and sodium has a phase separation structure, and it is further etched by chemical treatment to induce a concavo-convex structure on the surface, and finally a fluorine compound is applied to the surface. Superhydrophobicity can be expressed by reacting (see, for example, Patent Document 1). Furthermore, after producing a laminated film of polyarylamine and polyacrylic acid, the surface is treated with a chemical method to induce a surface porous structure, and silica nanoparticles are fixed thereon, and finally a fluorinated alkyl. It is also known to construct a superhydrophobic surface by hydrophobizing with a silane coupling agent having a group (see, for example, Patent Document 2).

  Many known documents frequently discuss superhydrophobic films and methods for producing them, but they often correspond to techniques for processing roughness on the surface of a substrate (ie, roughness). The processing process tends to be complicated and the cost is high. Further, in the case of a superhydrophobic surface based on an organic polymer, the cost is low, but the solvent resistance and corrosion resistance of the obtained superhydrophobic surface are low, which causes a practical problem.

Research on making the powder itself superhydrophobic (superhydrophobic) or using the superhydrophobic powder to form a superhydrophobic film is extremely rare, but a recent example For example, it has been found that a powder of iron oxide (α-Fe ₂ 0 ₃ ) having a size of 2-3 μm exhibits superhydrophobicity by having a petal structure on the surface. (For example, refer nonpatent literature 5). However, the technique proposed in Non-Patent Document 5 has a narrow application range and is not based on an industrially simple technique.

  On the other hand, as a superhydrophobic powder in nature, it is understood that, for example, the feet of amembo correspond to an aggregate of superhydrophobic powder. The structure of the leg of Amembo is super-hydrophobic, and by adding the buoyancy and surface tension of the water generated due to it, the body more than 25 times the weight of the leg can be floated on the water surface. By adding elasticity, the Amoebo can run so as to fly over the water surface (see, for example, Non-Patent Document 6). The development of superhydrophobic powder has high industrial utility value, especially if it can be synthesized by a simple manufacturing method using silicon compounds existing in large quantities in nature as a raw material, the application will be further expanded. This is a highly anticipated issue.

Sun et al. , Acc. Chem. Res. 2005, 38, 644-652. Li et al. , J .; Mater. Chem. , 2008, 18, 2276-2280 Feng et al. , J .; Am. Chem. Soc. , 2004, 126, 62-63 Erbil et al. , Science, 2003, 299, 1377-1380 Cao et al. , Appl. Phys. Lett. , 2007, 91.034102 Gao et al. , Nature 2004, 432, 36 Special table 2008-508181 US Patent Application Publication No. 2006/029808

  The problem to be solved by the present invention is to make the powder containing silica as a main component itself superhydrophobic. More specifically, a physical adsorption of a compound having a hydrophobic group capable of reducing the surface free energy to an aggregate of organic-inorganic composite nanofibers in which a polymer filament having a linear polyethyleneimine skeleton is coated with silica. It is an object of the present invention to provide a superhydrophobic powder characterized by being formed and a simple method for producing the powder. Furthermore, a compound having a hydrophobic group is physically adsorbed to an aggregate of nanofibers mainly composed of silica, which is obtained by removing a polymer having a linear polyethyleneimine skeleton from the organic-inorganic composite nanofiber by baking. It is another object of the present invention to provide a superhydrophobic powder obtained by making it easy to produce the powder.

  Furthermore, it is providing the structure which has the superhydrophobic surface using said superhydrophobic powder, and its manufacturing method.

  As a result of intensive research to solve the above-mentioned problems, the present inventor formed an aggregate surface of organic-inorganic composite nanofibers in which an organic polymer and an inorganic silica are combined on the nanometer order. The silica surface of the nanofiber structure from which the organic portion of the silica or the organic-inorganic composite nanofiber is removed has the ability to physically adsorb compounds having hydrophobic functional groups, and the powder obtained after physical adsorption is The inventors have found that superhydrophobicity is expressed, and have completed the present invention.

  That is, the present invention is a superhydrophobic powder containing an association of organic-inorganic composite nanofibers, wherein the nanofiber is a compound in which a polymer filament having a linear polyethyleneimine skeleton has a hydrophobic group The present invention provides a superhydrophobic powder characterized in that it is coated with silica that has been physically adsorbed and a simple production method thereof.

  Furthermore, the present invention provides a superhydrophobic powder characterized in that a compound having a hydrophobic group is physically adsorbed on the silica surface of an aggregate of silica nanofibers and a method for producing the same.

  Furthermore, the present invention provides a structure having a superhydrophobic surface obtained by fixing the superhydrophobic powder obtained above on a solid substrate and a method for producing the structure.

  The superhydrophobic powder of the present invention can convert any solid surface to superhydrophobic by applying it to the surface of a base material of any material and shape. This can be applied to protective films for metals, metal oxides, fibers, wood, paper, leather, and plastics that can rust, rot, and get dirty with water. More specifically, structures such as buildings, car bodies, ship bodies, container structures, packages, glass products, pottery products (toilet bowls, entire bathrooms), pools, water pipes, electric wires, light bulbs, various covers, etc. It can be applied to the protective film. Furthermore, it can also be applied to the surface coating of household electrical appliances such as refrigerators, microwave ovens and washing machines, and electrical appliances for communication such as personal computers, televisions and mobile phones. It can also be applied to energy conversion-related fuel cell devices.

  The present inventors have already used a crystalline aggregate in which a polymer having a linear polyethyleneimine skeleton grows in an aqueous medium in a self-organizing manner as a reaction field, and hydrolyzes alkoxysilane on the surface of the aggregate in a solution. A silica-containing nanostructure (powder) having a complex shape with nanofibers as a basic unit and a method for producing them were provided by decomposing condensation and precipitating silica (JP 2005-264421, JP 2005-336440, JP-A-2006-063097, and JP-A-2007-051056.)

  The basic principle of this technique is to spontaneously grow a crystalline aggregate of a linear polyethyleneimine skeleton-containing polymer in a solution. Once a crystalline aggregate is formed, the crystalline aggregate is simply A silica source is mixed in the dispersion liquid, so that the deposition of silica only on the surface of the crystalline aggregate is naturally left (so-called sol-gel reaction). The silica-containing nanostructures obtained in this way basically have nanofibers as the unit for structure formation, and the spatial arrangement of these units induces the shape of the entire structure, so there are many nano-level gaps. A powder with a large surface area.

  Such a powder is very similar to the basic structure necessary for developing superhydrophobicity in nature, that is, nanofibers gather to form a micrometer dimension. Therefore, it is considered that superhydrophobicity can be expressed by modifying the powder surface with a chemical residue having a low surface tension.

  Based on this concept, the present inventors have developed a silica-containing nanostructure on the order of micrometer (a silica-containing nanostructure) having a basic structure of a nanofiber derived from a polymer having a linear polyethyleneimine skeleton. It was found that the powder itself can be made superhydrophobic by introducing a hydrophobic group into the powder surface, which is a structure composed of basic units in the metric order. Hereinafter, the present invention will be described in detail.

  In the present application, a filament is a polymer chain formed by crystallization of a plurality of linear polyethyleneimine skeleton portions in a polymer chain having a linear polyethyleneimine skeleton used in the present invention in the presence of water molecules. Are associated with each other and grow into a fibrous form. When a sol-gel reaction occurs on the surface of the filament, an organic-inorganic composite nanofiber in which the filament is coated with silica is formed. During this reaction, a plurality of organic-inorganic nanofibers are bonded or aggregated by silica. As a result, a silica-containing nanostructure (powder) that is an aggregate of organic-inorganic nanofibers is formed.

[Polymer (A) having linear polyethyleneimine skeleton (a)]
The polymer (A) having a linear polyethyleneimine skeleton (a) used in the present invention may be a homopolymer having a linear, star or comb structure, but may be a copolymer having other repeating units. There may be. In the case of a copolymer, the molar ratio of the linear polyethyleneimine skeleton (a) in the polymer (A) is preferably 20% or more from the viewpoint of forming a stable filament. It is more preferable that it is a block copolymer in which the number of repeating units in (a) is 10 or more.

  As the polymer (A) having the linear polyethyleneimine skeleton (a), the higher the ability to form a crystalline aggregate, the more preferable. Therefore, it is preferable that the molecular weight corresponding to the linear polyethyleneimine skeleton (a) portion is in the range of 500 to 1,000,000, whether it is a homopolymer or a copolymer. The polymer (A) having the linear polyethyleneimine skeleton (a) can be obtained from a commercially available product or a synthesis method already disclosed by the present inventors (see the above-mentioned patent document).

[Silica (B)]
The superhydrophobic powder provided by the present invention is a group of organic-inorganic composite nanofibers (I) in which the filament of the polymer (A) having the linear polyethyleneimine skeleton (a) is coated with silica (B). The basic structure of the aggregate or the aggregate of nanofibers (II) mainly composed of silica (B) obtained by removing the polymer (A) from the aggregate of the organic-inorganic composite nanofibers (I) by calcination And

  The silica (B) is obtained by a sol-gel reaction on the filament surface in the presence of the filament of the polymer (A). As a silica source necessary for the formation of the silica (B), for example, alkoxysilane , Water glass, hexafluorosilicon ammonium and the like can be used.

  As the alkoxysilanes, tetramethoxysilane, oligomers of methoxysilane condensates, tetraethoxysilane, oligomers of ethoxysilane condensates can be suitably used. Further, alkyl-substituted alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, iso-propyltrimethoxysilane, iso-propyltriethoxysilane, etc., 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycid Xylpropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptotriethoxysilane, 3,3 -Trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, p -Chloromethylphenyltrimethoxysilane, p-chloromethylphenyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane and the like can be used alone or in combination.

  In addition, other silica metal compounds may be mixed with the silica source. For example, tetrabutoxytitanium, tetraisopropoxytitanium, or an aqueous solution of titanium bis (ammonium lactate) dihydroxide stable in an aqueous medium, an aqueous solution of titanium bis (lactate), a propanol / water mixture of titanium bis (lactate), titanium (ethyl) Acetoacetate) diisopropoxide, titanium sulfate, hexafluorotitanium ammonium and the like can be used.

[Organic inorganic composite nanofiber (I)]
In the present invention, the size of the organic-inorganic composite nanofiber (I) is the molecular weight and shape of the polymer (A) used, the content of the linear polyethyleneimine skeleton (a), and the type and use ratio of the silica source used. In particular, the organic-inorganic composite nanofiber (I) having a thickness of 10 to 100 nm and an aspect ratio of 10 or more can be easily produced.

  The content of the polymer (A) in the organic-inorganic composite nanofiber (I) can be adjusted to 5 to 30% by mass, and the polymer (A) is included as a filament shape as described above.

The organic-inorganic composite nanofibers (I) are randomly arranged in a three-dimensional space during the production process (during sol-gel reaction) to form an aggregate (silica-containing nanostructure) having a size of 2 to 100 μm. The surface area of the powder composed of such an aggregate is in the range of 50 to ²⁰⁰ m ² / g.

  The method for producing the organic-inorganic composite nanofiber (I) and the aggregate thereof may be any method described in the patent literature already provided by the present inventors.

[Nanofibers (II) mainly composed of silica]
When the aggregate of the above-described organic-inorganic composite nanofiber (I) is heated and fired, the polymer (B) contained therein is removed while maintaining the shape, and the silica is the main constituent component. An aggregate of nanofibers (II) can be obtained. Normally, under the firing conditions, the polymer is completely removed, and 100% silica can be obtained. Here, using silica as the main constituent means that, for example, when the firing is insufficient, the carbide of the polymer (A) is included. In any case, the shape of the nanofiber is formed by silica (B), and the content of silica (B) is usually 95% by mass or more, preferably 98 to 100% by mass.

  The baking temperature should just be 500-800 degreeC, and baking time can be set suitably with temperature. It may be 1 to 3 hours at a temperature higher than 500 ° C., and it is desired to calcinate 2 to 6 hours or more near 500 ° C.

The structure of the aggregate obtained by firing is the same as before firing, and the nanofiber (II) has a thickness of 10 to 100 nm and an aspect ratio of 10 or more. The nanofiber of this thickness is random in a three-dimensional space. The aggregate formed by the arrangement still maintains a size of 2 to 100 μm. The specific surface area of the powder obtained after firing is larger than that before firing, and is generally 100 to 400 m ² / g.

[Hydrophobic treatment and superhydrophobic powder production method]
In the present invention, in order to obtain a superhydrophobic powder, the free energy on the surface of the nanofiber (I) or nanofiber (II) aggregate must be reduced. In order to reduce the free energy of the surface, a compound (X) having a hydrophobic group, for example, a hydrophobic polymer (X1), an amphiphilic polymer (X2), a long-chain alkyl group-containing compound (X3), or fluorine Superhydrophobicity can be easily achieved by physically adsorbing the compound (X4) on the silica portion. In the present invention, the expression “compound having a hydrophobic group” means that the compound has a hydrophobic portion (group) or is hydrophobic as a compound. For example, there is no clear “hydrophobic group” in polypropylene oxide and the like to be described later, but it is a compound that exhibits hydrophobicity in that it does not mix with water at an arbitrary ratio. It is included as a compound having.

  As the hydrophobic polymer (X1), for example, poly (meth) acrylates can be suitably used. Specifically, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate, polybenzyl (meth) acrylate, polycyclohexyl (meth) acrylate, poly t-butyl (meth) acrylate, polyglycidyl (meth) Acrylates, polypentafluoropropyl (meth) acrylates, etc., and general-purpose polystyrenes, polyvinyl chlorides, polyvinyl acetates, epoxy resins, polyesters, polyimides, polycarbonates, and other polymers that do not dissolve easily in water. it can.

  Examples of the amphiphilic polymer (X2) include polyacrylamide such as poly N isobutyl acrylamide, poly N, N-dimethyl acrylamide, and the like, and polyoxazolines such as polymethyl oxazoline, polyethyl oxazoline, polyvinyl oxazoline, and polyphenyl. Oxazoline, polypropylene oxide and the like can be preferably used.

  As the long-chain alkyl group-containing compound (X3), alkylamine, alkylcarboxylic acid, alkylsulfonic acid, alkylphosphoric acid and the like, which are compounds having an alkyl group having 6 to 22 carbon atoms, can be suitably used.

  Examples of the fluorine-containing compound (X4) include 2,3,4-heptafluorobutyl methacrylate, FLUONATE K-700, K702, K703, K-704, K-705, K-707, K- manufactured by DIC Corporation. 708 etc. can be used suitably.

  In order to efficiently physically adsorb the compound (X) having a hydrophobic group, which can reduce the surface energy, onto the silica (B) on the surface of the nanofiber (I) or the aggregate of the nanofiber (II). Singly or several kinds of these compounds are dissolved in a solvent, and nanofiber (I) or nanofiber (II) is dispersed in the solution and stirred at room temperature, for example, 20 to 30 ° C. for 1 to 24 hours. That's enough.

  As the solvent, it is desirable that the compound (X) can be dissolved, and at the same time, the affinity with silica is maintained. Specific examples include toluene, furan tetrahydride, methylene chloride, chloroform, methyl ethyl ketone, cyclohexanone, xylene and the like.

  If the density | concentration of the said compound (X) is 1-5 mass% in the said solution, it can be used conveniently. In that case, it is preferable that mass ratio (X) / (I) or (II) of compound (X) and nanofiber (I) or (II) is 5/100 to 100/100. At this time, it is preferable to add the above-mentioned solvent appropriately so that the concentration of the nanofiber (I) or (II) is 1 to 10% by mass. Alternatively, nanofiber (I) or (II) is dispersed in a solvent miscible with the solvent in which compound (X) is dispersed in advance, and then added to the solvent of compound (X) and stirred. May be.

  After stirring and mixing for a certain period of time, the mixture is filtered or centrifuged, and the solid content is washed with a solvent such as toluene, chloroform, hexane, cyclohexane, etc., and dried at room temperature, whereby the superhydrophobic powder of the present invention Can be obtained.

  The superhydrophobic powder obtained by the above method has no water wettability and can only float on the water surface as a powder even when dispersed in water. This is completely different from completely sinking in water before the adsorption of the compound (X) having a hydrophobic group having a low surface free energy.

[Superhydrophobic surface using super water-repellent powder]
A structure having a superhydrophobic surface can be obtained by bonding and fixing the superhydrophobic powder of the present invention to the surface of a solid substrate. Adhesion fixation is easily achieved by mixing the powder with a polymer solution, silica sol solution, or commercially available paint, adhesive, etc., applying the mixture to the surface of the substrate, and drying it as necessary. it can.

  The superhydrophobic surface is a state in which the superhydrophobic powder is fixed on the surface of the base material, and a continuous film is formed using a polymer or silica sol as a binder, and the superhydrophobic powder of the present invention is formed on the continuous film surface. Are distributed at regular intervals.

  The polymer that can be used for the binder layer is not particularly limited as long as it is a hydrophobic polymer. Examples of the hydrophobic polymer include polystyrene, polyvinyl chloride, polymethacrylate, polyacrylate, polycarbonate, polyester, and epoxy resin.

  Moreover, as a binder layer of the said coating film, a commercially available coating material or a commercially available adhesive agent can also be used normally.

  The contact angle of the superhydrophobic surface obtained above can be varied in the range of 150-179 °. The higher the density of superhydrophobic powder on the surface, the better the contact angle. In order to obtain a surface having a target hydrophobicity level lower than this, for example, a contact angle of 70 to 150 ° which is a general hydrophobicity level, the use ratio of the superhydrophobic powder of the present invention is decreased. Of course, the density of the powder may be lowered.

  The solid substrate can be selected according to the material used for the binder layer, and examples thereof include glass, metal, metal oxide, wood, paper, fiber, plastic, rubber, leather, etc. There is no particular limitation, and any shape that can be applied with a coating liquid in which superhydrophobic powder is dispersed may be used.

  The method for fixing and adhering the superhydrophobic powder to the surface of the solid substrate is not particularly limited, and the coating liquid containing the powder is appropriately applied by a usual coating method such as a spin coater, bar coater, brushing, spray or the like. What is necessary is just to apply.

  Further, in accordance with the properties of the binder layer forming the coating film, the film obtained by coating can be cured by a process such as UV curing, heat curing, or natural drying.

  The superhydrophobic powder of the present invention is easily wetted by organic solvents other than water and can be easily dispersed. Accordingly, the medium that can dissolve or disperse the binder may be any solvent other than water, and a mixed medium of an organic solvent and water can also be used.

  In the coating liquid for surface preparation, the ratio of the binder constituent part and the superhydrophobic powder part may be in the range of binder / powder = 60/50 to 99/1 (mass ratio), and the composition ratio. In this range, the powder concentration of the coating liquid can be determined appropriately.

  In particular, when preparing a hydrophobic surface, the superhydrophobic powder must be exposed to the surface of the coating film. Therefore, it is desirable that the thickness of the coating film is within a certain range, for example, 0.1 to 20 μm. The thinner the coating film, the more the powder will protrude on the surface of the coating film, and the contact angle of water can be increased.

  Further, the horizontal distance between the powder-derived structures exposed on the surface of the coating film is an important structural element for the expression of superhydrophobicity of the entire film. If the horizontal distance between the powder structures is 1 to 20 μm, the superhydrophobicity can be sufficiently expressed, but even at a distance longer than that, the water contact angle can be increased to about 150 °, and depending on the intended use, It is preferable to adjust appropriately.

  Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified, “%” represents “mass%”.

[Shape analysis of nanofiber aggregates and powders by scanning electron microscope]
The isolated and dried aggregates and powders were fixed to a sample support with a double-sided tape, and observed with a surface observation apparatus VE-9800 manufactured by Keyence.

[Observation of nanostructures by transmission electron microscope]
A powder sample was dispersed in methanol, placed on a copper grid, and observed with a transmission electron microscope “JEM-2200FS” manufactured by JEOL Ltd.

[Contact angle measurement]
The contact angle was measured by an automatic contact angle meter Contact Angle System OCA (manufactured by Dataphysics).

[Differential thermogravimetric analysis]
The content rate of the compound (X) which has the hydrophobic group adsorb | sucked to the silica nanofiber was measured by TG-DTA6300 (made by SII Nano Technology Inc).

[Specific surface area measurement]
The specific surface area was measured by Flow Sorb II 2300 (manufactured by Micrometrics).

Synthesis example 1
[Preparation of powder composed of aggregate of organic-inorganic composite nanofiber (I)]
Powders having different shapes were produced by the methods disclosed in patent documents (Japanese Patent Application Laid-Open Nos. 2005-264421, 2005-336440, 2006-063097, and 2007-051056).

<Synthesis of linear polyethyleneimine (P5K)>
100 g of commercially available polyethyloxazoline (number average molecular weight 500,000, average polymerization degree 5,000, manufactured by Aldrich) was dissolved in 300 mL of 5M aqueous hydrochloric acid. The solution was heated to 90 ° C. in an oil bath and stirred at that temperature for 10 hours. Acetone 50 mL was added to the reaction solution to completely precipitate the polymer, which was filtered and washed three times with methanol to obtain a white polyethyleneimine powder. When the obtained powder was identified by ¹ H-NMR (heavy water), peaks 1.2 ppm (CH ₃ ) and 2.3 ppm (CH ₂ ) derived from the side chain ethyl group of polyethyloxazoline completely disappeared. It was confirmed that That is, it was shown that polyethyloxazoline was completely hydrolyzed and converted to polyethyleneimine.

  The powder was dissolved in 100 mL of distilled water, and 500 mL of 15% aqueous ammonia was added dropwise to the solution while stirring. The mixture was allowed to stand overnight, the precipitated powder was filtered, and the powder was washed 3 times with cold water. The washed powder was dried in a desiccator at room temperature (25 ° C.) to obtain linear polyethyleneimine (P5K). The yield was 94 g (containing crystallization water). In polyethyleneimine obtained by hydrolysis of polyoxazoline, only the side chain reacts and the main chain does not change. Therefore, the polymerization degree of P5K is the same as 5,000 before hydrolysis.

<Synthesis of Powder A Composed of Aggregates of Organic-Inorganic Composite Nanofiber (I)>
A certain amount of P5K was mixed in distilled water, heated to 90 ° C. to obtain a clear solution, and then the whole was prepared in 3% aqueous solution. The aqueous solution was naturally cooled at room temperature to obtain a pure white P5K aggregate solution. While stirring, 70 mL of an MS 51 (methoxysilane pentamer) ethanol solution (volume concentration: 50%) was added to 100 mL of the aggregate solution, and stirring was continued at room temperature for 1 hour. The deposited precipitate was filtered, washed with ethanol three times, and then dried under heating at 40 ° C. to obtain 16 g of aggregate as powder A. FIG. 1 shows an SEM photograph of the powder A obtained. It was confirmed to be an assembly of nanofibers.

From the thermogravimetric loss analysis of the powder A obtained above, it was confirmed that the polyethyleneimine content was 7%. Moreover, it was 132 m < ² > / g as a result of measuring a specific surface area.

Synthesis example 2
[Preparation of powder B composed of aggregates of nanofibers (II) containing silica as a main component]
The powder A (5 g) obtained in Synthesis Example 1 was heated in an electric furnace at 600 ° C. for 2 hours under air introduction conditions to remove polyethyleneimine contained in the powder A to obtain a white powder B. . The specific surface area was 208 m ² / g. FIG. 2 shows an SEM photograph of powder B. It was suggested that there was no change in the nanofiber structure after firing.

Example 1
[Synthesis of superhydrophobic powder 1 adsorbed with polybutyl acrylate]
200 mg of polybutyl acrylate was dissolved in 20 mL of toluene, 200 mg of powder A was added to the solution, and the mixture was stirred at room temperature for 3 hours. After filtering the mixed solution, the obtained powder was washed with toluene three times. The powder after drying did not sink in water, but floated on the water surface. This was completely different from the tendency of powder A before hydrophobization treatment to completely sink in water.

  After the obtained powder was adhered to a double-sided tape to form a surface made of powder, the contact angle of water was measured, and the contact angle of water was 178.4 °. It was strongly suggested that the membrane state of the powder was superhydrophobic. This is designated as superhydrophobic powder 1.

Example 2
[Synthesis of superhydrophobic powder 2 adsorbed with polymethyl methacrylate]
A powder was obtained in the same manner as in Example 1 except that polymethyl methacrylate was used instead of polybutyl acrylate. The powder after drying did not sink in water, but floated on the water surface.

  When the contact angle of water was measured in the same manner as in Example 1 using the obtained powder, it exceeded 174 °. It was strongly suggested that the membrane state of the powder was superhydrophobic. This is designated as superhydrophobic powder 2.

Example 3
[Synthesis of superhydrophobic powder 3 adsorbed with polyethyl methacrylate]
A powder was obtained in the same manner as in Example 1 except that polyethyl methacrylate was used instead of polybutyl acrylate and powder B was used instead of powder A. The powder after drying did not sink in water, but floated on the water surface. This was completely different from the tendency of powder B before hydrophobization treatment to completely sink in water. As a result of analysis of thermogravimetric loss, the polymer adsorption rate was 12.9%.

  Using the obtained powder, the contact angle of water was measured in the same manner as in Example 1. As a result, the contact angle of water was 179.7 ° (see FIG. 3). It was strongly suggested that This is designated as superhydrophobic powder 3.

  FIG. 4 shows a TEM photograph of the powder 3. Although the silica surface of the powder B before polymer adsorption was smooth, it was observed that particles having a size of several nanometers spread over the silica surface after polymer adsorption. That is, it was confirmed that the polymer was in a state of forming a nanometer order thin film on the surface of the nanofiber.

  FIG. 5 shows a thermal analysis chart of this powder. Although the thermal decomposition temperature of the polymer alone was around 327 ° C., the heat resistance of the polymer adsorbed on the powder 3 was improved, and the thermal decomposition temperature was shifted to 409 ° C. The polymer adsorbed on the nanofiber surface in the form of a nano thin film is considered to have formed a hybrid structure with silica on the nanometer order.

  After this powder 3 was immersed in various solvents for 1 week, the powder was filtered and dried at room temperature. After the treated powder was adhered to the double-sided tape, water droplets were dropped on it and the wettability was examined. FIG. 6 shows a wet state of water droplets. On the surface where the powder obtained after soaking in water, hexane and toluene was bonded to a double-sided tape, the water droplets were spherical and there was no wettability. However, on the surface where the powder obtained after being immersed in methanol, ethanol, chloroform, acetone, and THF was adhered to the double-sided tape, all were wet.

  The tape after checking the wettability was left in a dryer and heated at 80 ° C. for 2 hours. It was taken out and examined for wettability again at room temperature. FIG. 7 shows the wet state. In the system after immersion in water, hexane, and toluene, there was still no tendency to get wet, and the water droplets were in a round shape. Even in the system after immersion in methanol, ethanol, chloroform, acetone, and THF, the surface was not easily wetted by water droplets, the water droplets did not spread as seen in FIG. 6, and the water droplets remained elliptical or spherical.

  The results shown in FIGS. 6 and 7 strongly suggest that the surface-adsorbed polyethyl methacrylate does not desorb even when the powder 3 is immersed in a nonpolar or polar solvent. When dipped in a polar solvent and then dried at room temperature, the polar solvent causes a slight change in the surface energy of the microstructure domain of the polymer adsorbed on the silica nanofiber surface, which increases wettability, but heat-treats it. This strongly suggests that the surface energy is restored to its original reduced state and prevents wettability.

Example 4
[Synthesis of super water-repellent powder 4 adsorbed with fluorine-containing compound]
A powder was obtained in the same manner as in Example 3 except that 200 mg of poly (2,3,4-heptafluorobutyl methacrylate) was used instead of polyethyl methacrylate. The powder after drying did not sink in water, but floated on the water surface. As a result of the analysis of thermogravimetric loss, the polymer adsorption rate was 9.8%. This is designated as superhydrophobic powder 4.

  When the contact angle of water was measured in the same manner as in Example 1 using the obtained powder 4, it was 179.6 °. Further, the contact angle was 168 ° even in an aqueous alcohol solution containing 30% ethyl alcohol. Furthermore, the surface did not get wet even with a 50% alcohol aqueous solution. Incidentally, in the powder 3 obtained in Example 3, the contact angle of a 30% aqueous alcohol solution is 48 °. The surface free energy lowering ability by the fluorine atom is also expressed for alcohol, which is considered to be a result of showing a flipping effect.

Example 5
[Synthesis of super water-repellent powder 5 adsorbed with tetradecylamine]
In Example 3, a powder was obtained in the same manner as in Example 3 except that tetradecylamine was used instead of polyethyl methacrylate and the stirring time at room temperature was 6 hours. The powder after drying did not sink in water, but floated on the water surface. As a result of thermal weight loss analysis, the adsorption rate of tetradecylamine was 10.5%. This is designated as superhydrophobic powder 5.

  When the contact angle of water was measured in the same manner as in Example 1 using the obtained powder 5, it was 175 °. It was strongly suggested that the membrane state of the powder was superhydrophobic.

Example 6
[Synthesis of super water-repellent powder 6 adsorbed with poly (ethyloxazoline)]
A powder was obtained in the same manner as in Example 3 except that poly (ethyloxazoline) was used instead of polyethyl methacrylate. The powder after drying did not sink in water, but floated on the water surface. As a result of the analysis of thermogravimetric loss, the adsorption rate of poly (ethyloxazoline) was 11.3%. This is designated as superhydrophobic powder 6.

  When the contact angle of water was measured in the same manner as in Example 1 using the obtained powder 6, it was 167 °. It was strongly suggested that the membrane state of the powder was superhydrophobic. Poly (ethyloxazoline) is an amphiphilic polymer that dissolves in both water and organic solvents. However, when adsorbed on the powder B, the polar part of the polymer is strongly bonded to silica, and the ethyl groups in the side chain face the surface. Therefore, it is thought that superhydrophobicity will be expressed.

Example 8
[Superhydrophobic membrane on filter paper using superhydrophobic powder 3 (dipping method)]
After adding the super-hydrophobic powder 3 (10 mg) obtained in Example 3 to 500 mg of an aqueous polyurethane resin (manufactured by DIC Corporation, nonionic, prepared by adding water to a nonvolatile content of 10%) and uniformly dispersing The filter paper was immersed in the dispersion for 15 minutes. After removing the filter paper and drying at room temperature, water drops were dropped on the filter paper, but the water drops blew completely.

Example 9
[Superhydrophobic membrane on filter paper using superhydrophobic powder 3 (brush method)]
The same dispersion used in Example 8 was brushed on the filter paper. When the surface contact angle was measured after drying at room temperature, the contact angle was 154 °. The filter paper did not get wet.

Example 10
[Superhydrophobic film on glass using superhydrophobic powder 3 (casting method)]
A dispersion similar to that in Example 8 was cast on a glass slide using a bar coater. The cast film thus obtained was dried at room temperature and then the surface contact angle was measured. The contact angle was 166 °.

Example 11
[Superhydrophobic membrane on wood using superhydrophobic powder 3 (brush method)]
The same dispersion used in Example 8 was brushed on a wooden board that had not been surface-treated. After drying it at room temperature and dropping water drops, the water was completely repelled and the wood surface did not get wet.

Example 12
[Superhydrophobic film on cowhide using superhydrophobic powder 6 (dipping method)]
In Example 8, a dispersion was prepared in the same manner as in Example 8, except that the superhydrophobic powder 6 obtained in Example 6 was used instead of the superhydrophobic powder 3. A cut-off piece of cowhide that was not surface-treated was immersed in the dispersion for 1 hour. After removing the cowhide and drying at room temperature, water droplets were dropped on it, but the water droplets completely repelled and the wettability was lost.

Example 13
[Superhydrophobic membrane on the inner wall of glass tube using superhydrophobic powder 2 (dipping method)]
In Example 8, a dispersion was obtained in the same manner as in Example 8 except that the superhydrophobic powder 2 obtained in Example 2 was used instead of the superhydrophobic powder 3. The dispersion was sucked into a glass pipette (inner diameter 6 mm, length 8 cm) and held for 2 hours, and then the liquid was extruded. After the glass pipette was dried at 60 ° C., the test was performed by sucking water into the glass pipette and pushing out the water again. No water droplets adhered to the glass wall, and the absorbed water could be completely transferred to another container without reducing its weight.

  For comparison, when an untreated glass pipette was used, it was confirmed that water droplets adhered to the wall whenever water was pushed out after sucking out water.

[Stability evaluation 1]
Using the superhydrophobic powders 1, 3, 4, and 6 obtained in Examples 1, 3, 4, and 6, the stability was evaluated by the following method. Add 30 mL of distilled water to a glass bottle and add 20 mg of each powder. Stirrer chips were placed here and stirring was continued for 7 days at room temperature (25 ° C.), and then the state of the powder was observed. When stirring was stopped, any powder would float on the water surface and will not sink into water again. It was confirmed.

  Further, the contact angle in the film state was measured in the same manner as in the Examples, and it was confirmed that all the powders had the same contact angle before stirring in water and maintained superhydrophobicity.

  Furthermore, the superhydrophobic powder 4 after stirring in water was measured for the contact angle with an aqueous alcohol solution containing 30% ethyl alcohol in the same manner as in the example, and it was 167 °, indicating that the performance was maintained. confirmed.

[Stability evaluation 2]
The dispersion obtained in Example 8 was held in a thermostatic bath at 30 ° C. for 7 days, and then applied to filter paper and dried in the same manner as in Example 9. When the contact angle of water was measured after drying, it was 156 °, and it was confirmed that superhydrophobicity was maintained even in the aqueous paint.

3 is a SEM photograph of powder A obtained in Synthesis Example 1. Above: Low magnification. Below: High magnification. 4 is a SEM photograph of powder B obtained in Synthesis Example 2. Above: Low magnification. Below: High magnification. It is a water contact angle photograph in Example 3. 4 is a TEM photograph of superhydrophobic powder 3 obtained in Example 3. Left figure: Before polyethyl methacrylate is adsorbed, Right figure: After adsorption 4 is a thermal analysis (TG-DTA) chart of superhydrophobic powder 3 obtained in Example 3. FIG. It is the wettability photograph in the film | membrane surface produced after processing the powder obtained in Example 3 in various solvents. It is the photograph which observed the wettability of water again after drying the powder film of FIG. 6 at 80 degreeC for 2 hours.

Claims (9)

A powder composed of an association of an organic-inorganic composite nanofiber (I) in which a filament of a polymer (A) having a linear polyethyleneimine skeleton (a) is coated with silica (B) is dispersed in a solvent. a step of compounds having a hydrophobic group and (X) are mixed, Ru compound to silica (B) to (X) by physically adsorbed liquid,
Isolating the treated powder obtained in the step;
A process for producing a superhydrophobic powder characterized by comprising: (1) firing an association of organic-inorganic nanofibers (I) in which a filament of polymer (A) having a linear polyethyleneimine skeleton (a) is coated with silica (B);
(2) A powder comprising an aggregate of nanofibers (II) having silica (B) obtained in step (1) as a main constituent is dispersed in a solvent, and a compound having a hydrophobic group in the dispersion ( X) were mixed, a step of Ru compound to silica (B) to (X) is physically adsorbed,
(3) a step of isolating the treated powder obtained in step (2);
A process for producing a superhydrophobic powder characterized by comprising: The compound (X) having a hydrophobic group is a hydrophobic polymer (X1), an amphiphilic polymer (X2), a long-chain alkyl group-containing compound (X3) having 6 to 22 carbon atoms, and a fluorine-containing compound (X4). The method for producing a superhydrophobic powder according to claim 1 or 2, which is one or more compounds selected from the group consisting of : The hydrophobic polymer (X1) is poly (meth) acrylate, polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyester, polyimide or polycarbonate, and the amphiphilic polymer (X2) is polyacrylamide, polyoxazoline or The method for producing a superhydrophobic powder according to claim 3, which is polypropylene oxide, and the long-chain alkyl group-containing compound (X3) is an alkylamine, alkylcarboxylic acid, alkylsulfonic acid or alkylphosphoric acid. The organic-inorganic nanofiber thickness of (I) is not less 10 to 100 nm, an aspect ratio of 2 or more, according to claim 1 and the magnitude of the aggregate of the organic-inorganic nanofiber (I) is in the range of 2~100μm The manufacturing method of the super-hydrophobic powder of any one of -4 . The thickness of the nanofiber (II) is 10 to 100 nm, the aspect ratio is 2 or more, and the size of the aggregate of the nanofiber (II) is in the range of 2 to 100 µm. A method for producing the superhydrophobic powder according to claim 1. Superhydrophobic powder obtained by the production method according to any one of claims 1 to 6. A structure having a superhydrophobic surface, wherein the superhydrophobic powder according to claim 7 is fixed to the surface of a solid substrate. A method for producing a structure having a superhydrophobic surface, comprising the steps of dispersing a superhydrophobic powder obtained by the production method according to claim 7 in a solution, applying the dispersion, and drying.