KR20160060913A - Method for controlling aggregation of sol-gel nanoparticles by solvent relative permittivity, and fabrication of superhydrophobic surfaces using thereof - Google Patents

Abstract

The present invention relates to a fabrication method of a superhydrophobic surface. The fabrication method comprises the steps of: preparing a nanoparticle dispersion liquid; aggregating nanoparticles by adjusting dielectric constant values of the nanoparticle dispersion liquid through adding a solvent having solvent relative permittivity (ε) of 20 or less to the nanoparticle dispersion liquid; coating the aggregated nanoparticle dispersion liquid to the surface of an object to be coated; and treating the coated surface of the object to be hydrophobic. Through the method of the present invention, a surface exhibiting superhydrophobic properties can be obtained by adjusting the degree of aggregation of nanoparticles by adjusting the dielectric constant of the nanoparticle dispersion liquid and applying the same to the surface of the object to be coated.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sol-gel nanoparticle dispersed by a sol-gel nanoparticle,

The present invention relates to control of particle aggregation through controlling the dielectric constant of a dispersion solvent of a sol-gel nano-particle, and more particularly, to a method for controlling the aggregation of nanoparticles by controlling a dielectric constant of the nanoparticle dispersion, And a method of manufacturing a super water-repellent surface by applying the super-water-repellent surface to a surface to be coated to obtain a super-water-repellent surface.

The superhydrophobic phenomenon is a phenomenon in which water is repelled without absorbing water droplets. Such a super water repellent phenomenon is known in nature through the Lotus effect. It is understood that a material having a low surface energy has a micro or nano-sized surface roughness plays a very important role in forming such a super water-repellent surface, which is explained by Wenzel and Cassie-Baxter theory. Thereafter, various methods such as sol-gel method, physical vapor deposition method, template-based technique, lithography, electrospinning, and the like are applied to the artificial super water- Numerous studies are being conducted. In many cases, sol-gel based methods can be used in a variety of ways through relatively simple and low cost processes, compared to using complex processes, using expensive special materials, or using expensive equipment. . As a method of producing a super water-repellent surface using sol-gel nanoparticles, methods such as polymer blending, coagulant addition, self-assembly or repeated coating are known.

In the case of the conventional sol-gel technique, 'organic solvent-type silica sol and its preparation method' or 'Korean Patent Application No. 10-1454402' (Patent No. 10-0945198) are used from alkoxysilane at high temperature And the organic solvent-dispersed high-purity silica sol prepared by this method, the tetravalent alkoxysilane is subjected to hydrolysis and condensation using a precursor of silica as a silica precursor, A method of synthesizing a silica sol is known.

The dispersion stability of colloidal nanoparticles, ie, colloidal stability, is well known by the DLVO theory (Derjaguin-Landau-Verwey-Overbeek theory), and the van der Waals attraction and the electrostatic repulsion Electrostatic repulsion). For example, when the Van der Waals attractive force increases or the electrostatic repulsion decreases, the particle cohesion increases.

In addition, the polarity of the solvent of the dispersion medium also greatly influences the dispersion stability of the particles. For example, polarized silica nanoparticles tend to be well dispersed in highly polar solvents whereas they tend to aggregate in nonpolar solvents. In view of the DLVO theory, a low polarity solvent lowers the zeta-potential of the particles and reduces the electrostatic repulsion. It is also explained that the Van der Waals attraction increases due to the change of Hamarker constant of the particles. There are other types of interactions not covered by the DLVO theory. From the viewpoint of solvation due to strong interactions such as solvent-to-particle hydrogen bonding and the resulting particle stability, The degree of stabilization by the polar group and mutual attraction is reduced, and cohesiveness is increased.

In general, the above-described particle agglomeration has been solved only as a problem of stability degradation and has been studied based on a method for solving the problem. However, on the other side, it would be possible to produce a variety of scale roughness surfaces derived from this, if this particle aggregation could be controlled. It is expected that this method will be a new and easy method of producing super water - repellent by combining it with super water - repellent surface preparation.

Korean Patent Registration No. 10-0945198 Korean Patent Registration No. 10-1454402

Accordingly, an object of the present invention is to provide a super-water-repellent surface preparation method capable of controlling a degree of aggregation of nanoparticles by controlling a dielectric constant of a nanoparticle dispersion and applying the same to a surface of a coating object, will be.

The above object is achieved by a method for preparing a nanoparticle dispersion, comprising: preparing a nanoparticle dispersion; Adjusting a dielectric constant value of the nanoparticle dispersion by adding a solvent having a dielectric constant (竜) of 20 or less to the nanoparticle dispersion; and agglomerating the nanoparticles; Coating the agglomerated nanoparticle dispersion on a surface to be coated; And a step of surface-hydrophobizing the surface of the coated object to be coated.

Wherein adjusting the dielectric constant of the nanoparticle dispersion to coalesce the nanoparticles comprises adjusting the dispersion of the nanoparticles to have a dielectric constant of 30 or less, wherein the solvent is selected from the group consisting of nanosized and nanosized , A non-polar solvent having a dielectric constant of less than 5, a low polarity solvent having a dielectric constant of 5 to 20, and a mixture thereof.

In preparing the nanoparticle dispersion, it is preferable that the nanoparticles are formed by a sol-gel technique.

In addition, the step of surface-hydrophobizing the surface to be coated may include the steps of: impregnating the surface to be coated with a hydrophobic solvent containing hydrophobic silane; A step of performing hydrophobic reaction in a nitrogen atmosphere; And removing the surface to be coated from the hydrophobic solvent and washing the surface.

According to the structure of the present invention described above, the degree of aggregation of nanoparticles is controlled by controlling the dielectric constant of the nanoparticle dispersion, and the surface of the nanoparticle dispersion is applied to the surface of the coating object to obtain a surface causing super water repellency.

1 is a flow chart of a method for producing super water repellent surface,
Figure 2 is a photograph of a nanoparticle dispersion according to chloroform concentration,
3 and 4 are dynamic light scattering (DLS) graphs of nanoparticle dispersions according to chloroform concentration,
5 is an electron micrograph of the coating layer of the nanoparticle dispersion according to the chloroform concentration,
6 and 7 are graphs showing dielectric constant values according to the chloroform concentration,
8 is an electron micrograph of a substrate having a super water repellent surface.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method of manufacturing a super water-repellent surface according to an embodiment of the present invention will be described in detail with reference to the drawings.

First, a nanoparticle dispersion is prepared as shown in FIG. 1 (S1).

A nanoparticle dispersion in which the nanoparticles are uniformly dispersed in the dispersion is prepared. Since nanoparticles in powder form are strong in aggregation among the particles, it is difficult to redisperse the nanoparticles when they are applied to a substrate, and it is difficult to control the degree of coagulation of particles in various ranges. Thus, it is desirable to use a sol-gel technique to effectively apply nanoparticles to a substrate.

Here, the nanoparticles may be ceramic nanoparticles or metal oxide nanoparticles. The nanoparticles may be formed of silicon oxide (SiO ₂ ), titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), aluminum oxide (Al ₂ O ₃ ) It is preferable to use one selected from the group consisting of

The diameter of the nanoparticles is preferably 10 nm to 1 mu m. When the nanoparticles are less than 10 nm, there is a limitation in acquiring various sizes due to aggregation between the nanoparticles. If the nanoparticles are larger than 1 탆, only the micro-level roughness is formed without the nano-level roughness. .

The dispersion liquid for dispersing the nanoparticles is a mixture of water and a polar organic solvent to facilitate dispersion of the nanoparticles. The polar organic solvent is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, And mixtures thereof.

A low polarity solvent is added to the nanoparticle dispersion to agglomerate the nanoparticles (S2).

Add a nonpolar or low polarity solvent with lower dielectric constant (ε) than water and polar organic solvent in the nanoparticle dispersion with water and polar organic solvent mixed. The dielectric constant indicates the polarity of the solution and the lower the dielectric constant, the lower the polarity of the solvent. Wherein the non-polar or low polarity solvent uses a solvent having a dielectric constant of 20 or less.

A preferred nonpolar solvent is a nonpolar solvent having a dielectric constant of less than 5 so that the dielectric constant can be easily controlled by mixing with the dispersion. The nonpolar solvent is a nonpolar solvent such as toluene, xylene, benzene, hexane, Chloroform, Carbon tetrachloride, and mixtures thereof.

If necessary, a low polarity solvent having a dielectric constant of 5 to 20 may be used to finely adjust the dielectric constant. The low polarity solvent may be isopropyl alcohol, butyl alcohol, t-butyl alcohol t-butyl alcohol, pentyl alcohol, benzyl alcohol, and mixtures thereof.

In the process of lowering the polarity of the dispersion solvent by injecting the nonpolar solvent alone into the silica nanoparticle dispersion, the polarities of the solvents are too different, and the solutions may be phase-separated without being mixed with each other. When a low polarity solvent having a polarity somewhat larger than that of a nonpolar solvent is used together as an intermediate solvent, the polarity of the nanoparticle dispersion medium solution can be controlled in various ways while suppressing the phase separation of the solution.

By using the dielectric constant value indicating the polarity of the solution, the dielectric constant value of the dispersion can be adjusted to various ranges, thereby controlling the degree of agglomeration of the particles. That is, when a non-polar or low-polarity solvent is added to the dispersion, the degree of coagulation of the particles is increased.

2 to 4, wherein FIG. 2 illustrates the addition of chloroform with a dielectric constant of 4.8 to the dispersion, where ref refers to pure dispersion and Chl 15% refers to the amount of chloroform added to the dispersion 15% is added. It can be seen that as the amount of chloroform added increases, the dispersion becomes cloudy, meaning that a large amount of coagulated particles are mixed.

FIGS. 3 and 4 are graphs showing dynamic light scattering (DLS) of nanoparticles in the dispersion. FIG. 3 shows DLS values when the nanoparticles are 10 nm and FIG. 4 shows DLS values when the nanoparticles are 40 nm. As a result, the degree of agglomeration of the nanoparticles increases with increasing the content of chloroform regardless of the size of the nanoparticles.

The nanoparticle dispersion is coated on the surface of the coating target (S3).

In step S2, the nanoparticle dispersion liquid with controlled degree of coagulation is coated on the surface of the coated object. Here, the surface to be coated is described as a substrate, and it can be applied to any surface for hydrophobic surfaces such as a film as well as a substrate.

The coating can be coated by various coating methods such as spin coating, dip coating and bar coating, and the thickness of the coating can be adjusted by repeated coating if necessary.

FIG. 5 is an electron micrograph (SEM) image obtained by coating a dispersion prepared by dissolving chloroform added in a dispersion solvent on a substrate. It is confirmed that nanoparticles are hardly aggregated when chloroform is 0% And the degree of aggregation of the nanoparticles increases as the amount of chloroform added to the dispersion solvent increases. Particularly, when the chloroform content is 45%, the diameter of the aggregated particles is about 1 탆, and when the chloroform content is 55% or more, the diameter is about 4 탆. At this time, the nanoparticles in the bundle do not aggregate to a uniform diameter but aggregate to an irregular diameter, so that the nanoparticle dispersion coated on the substrate is not uniform and particles having various diameters at nano- and micro-levels are distributed.

The substrate coated with nanoparticles is dried at a temperature where the nanoparticles are not denatured. Here, the drying temperature is preferably 50 to 200 DEG C at which the ceramic and metal oxide particles are not denatured.

The surface to be coated is surface-hydrophobized (S4).

Since the surface of the nanoparticles is hydrophilic, the surface of the coated substrate coated by step S3 is superhydrophilic. Therefore, the nanoparticles of the coated substrate are surface-hydrophobized so that the substrate coated with nanoparticles can be super-water-repellent without absorbing water. In the surface hydrophobic treatment, a hydrophobic silane for surface hydrophobization is added to a solvent, and then a coating substrate is impregnated with the hydrophobic silane and a hydrophobic reaction is performed in a nitrogen atmosphere. The coated substrate is then removed from the solvent and washed, and the solvent is thoroughly dried at 100-150 < 0 > C.

The hydrophobic silane is preferably added in an amount of 0.01 to 0.1 part by weight based on 100 parts by weight of the organic solvent. Also, the hydrophobic silane may be at least one selected from the group consisting of octadecyltrichlorosilane, octyltrichlorosilane, hexyltrichlorosilane, octadecyltriethoxysilane, octyltrimethoxysilane, hexylsilane, It is preferable to use alkoxysilane, chlorosilane, and silane having a fluorine group, such as perfluorooctyltriethoxysilane and the like, such as hexyltriethoxysilane and perfluorooctyltriethoxysilane.

In some cases, when hydrophobic nanoparticles are used as the nanoparticles, additional hydrophobic processes may be omitted.

The substrate manufactured through the above steps can be confirmed the relationship between the dielectric constant and the super water-repellent phenomenon through the graphs of FIG. 6 and FIG.

FIG. 6 is a graph showing the contact angle and relative permittivity according to the amount of chloroform added when chloroform with a dielectric constant of 4.8 is added to the dispersion. FIG. It can be seen that the dielectric constant value decreases as the amount of addition of chloroform having a dielectric constant lower than that of the dispersion increases, and thus the contact angle of the water droplet increases.

The numbers in parentheses indicate the inclination angle of the cloud due to the inclusion of chloroform, which means the water droplet rolls when water droplets are dropped on the substrate and the substrate is tilted. The angle of cloud inclination becomes lower as the dielectric constant value decreases and becomes a super water repellent angle where the water droplet rolls even if the substrate is not tilted near 0 ° in the dielectric constant value of 25 to 30. Therefore, when the dielectric constant is less than 30, the water repellent angle becomes a super-water-repellent angle at which water droplets roll, even if the substrate is not tilted to about 0 °. Therefore, it is most preferable to apply the nanoparticles formed in the dispersion having a dielectric constant value of 30 or less to the substrate.

FIG. 7 shows the water droplet contact angle and dielectric constant value according to the concentration when adding a dichloromethane having a dielectric constant value of 8.9 to the dispersion. 7, when the dielectric constant is 30 or less as in the case of FIG. 6, agglomeration of particles occurs rapidly and super water repellent phenomenon occurs. Therefore, it can be confirmed that when the dielectric constant of the dispersion is adjusted to 30 or less, and more preferably the dielectric constant is adjusted to 25 to 30, nanoparticles for super water-repellent development are produced.

Nano- and micro-level roughness is naturally formed on the surface of the coating layer according to the degree of agglomeration of the nanoparticles coated on the substrate. The substrate having such a surface becomes a super water-repellent surface through hydrophobization as shown in Fig.

<Examples>

100 parts by weight of tetraethoxysilane (TEOS) and 250 parts by weight of methanol were mixed and stirred for about 30 minutes while raising the temperature to 50 캜. Then, an aqueous solution containing 50 parts by weight of distilled water and 10 parts by weight of ammonia water was added to react. Thereafter, sufficient reaction was carried out until there was no change in the solid content, and the solid content was 7 parts by weight. The particle size of the finally prepared silica sol increased with the ammonia water content, and the particle size range was 1 to 40 nm.

Chloroform having a melt dielectric constant (?) Of 4.8 was added to the silica nanoparticle solution dispersed in methanol and distilled water in various ranges from 15 parts by weight to 60 parts by weight. Thereafter, the dispersion of silica nanoparticles containing chloroform was spin-coated on a glass substrate and then heat-treated at 150 ° C for 1 hour.

To hydrophobize the coating layer, octadecyltrichlorosilane (OTS) was impregnated with a substrate coated with dissolved toluene (toluene) solution at a concentration of 0.5 parts by weight for about 10 hours, followed by washing and drying, Followed by heat treatment for 30 minutes.

The hydrophobicity of the coated surface of the substrate increased as the amount of chloroform added to the silica nanoparticle dispersion increased, and it was confirmed that the water repellency of the chloroform was such that the water contact angle after 45 parts by weight could not be measured.

If a nonpolar or low polarity solvent is added to the dispersion containing nanoparticles and polarity and the dielectric constant is controlled to be within 30, nanoparticles will be agglomerated into nano-sized and micro-sized particles. When this is applied to a substrate and subjected to hydrophobic treatment, the substrate has nano- and micro-roughness, which results in a super water-repellent phenomenon in which the tilt angle of the cloud approaches 0 °. That is, when the value of the dielectric constant of the dispersion is adjusted, a super water-repellent surface can be manufactured, and thereby a substrate exhibiting super-water-repellency can be manufactured.

Claims (10)

In the method for producing super water repellent surface,
Preparing a nanoparticle dispersion;
Adjusting a dielectric constant value of the nanoparticle dispersion by adding a solvent having a dielectric constant (竜) of 20 or less to the nanoparticle dispersion; and agglomerating the nanoparticles;
Coating the agglomerated nanoparticle dispersion on a surface to be coated;
Characterized by comprising the step of surface-hydrophobizing the surface of the coated object to be coated. The method according to claim 1,
The step of adjusting the dielectric constant of the nanoparticle dispersion to agglomerate the nanoparticles comprises:
Wherein the nanoparticle dispersion is adjusted to have a dielectric constant of 30 or less. The method according to claim 1,
The solvent may be,
Wherein the nanoparticles are selected from the group consisting of a nonpolar solvent having a dielectric constant of less than 5, a low polarity solvent having a dielectric constant of 5 to 20, and a mixture thereof so that the nanoparticles aggregate irregularly in nanosize and microsize. The method of claim 3,
The non-
And is selected from the group consisting of toluene, xylene, benzene, hexane, chloroform, carbon tetrachloride, and mixtures thereof,
The low-
Is selected from the group consisting of isopropyl alcohol, butyl alcohol, t-butyl alcohol, pentyl alcohol, benzyl alcohol, and mixtures thereof. Wherein said water-repellent surface is a water-soluble polymer. The method according to claim 1,
In preparing the nanoparticle dispersion,
Wherein the nanoparticles are formed by a sol-gel technique. The method according to claim 1,
Wherein the nanoparticles are selected from the group consisting of silicon oxide (SiO ₂ ), titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), aluminum oxide (Al ₂ O ₃ ) . The method according to claim 6,
Wherein the nanoparticles have a diameter of 10 nm to 1 占 퐉. The method according to claim 1,
In preparing the nanoparticle dispersion,
Wherein the dispersion is a mixture of water and a polar organic solvent,
Wherein the polar organic solvent is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, and mixtures thereof. The method according to claim 1,
Wherein the step of surface-hydrophobizing the surface to be coated comprises:
Impregnating the surface to be coated with a hydrophobic solvent containing hydrophobic silane;
A step of performing hydrophobic reaction in a nitrogen atmosphere;
And removing the surface to be coated from the hydrophobic solvent and washing the surface. 10. The method of claim 9,
The hydrophobic silane,
Octadecyltrichlorosilane, octyltrichlorosilane, hexyltrichlorosilane, octadecyltriethoxysilane, octyltrimethoxysilane, hexyltriethoxysilane (hexyltrimethoxysilane), octyltrimethoxysilane, octyltrimethoxysilane, octyltrimethoxysilane, Hexyltriethoxysilane, perfluorooctyltriethoxysilane, and mixtures thereof. &Lt; Desc / Clms Page number 19 &gt;

Images