KR101033276B1 - Preparation of Superhydrophobic Polymer Fabrication - Google Patents

Abstract

Processes for producing superhydrophobic polymer fabrication, etched molds and superhydrophobic polymer structures have been developed. By using the above method, the superhydrophobic polymer structure can be produced easily and quickly, as well as the superhydrophobic surface can be repeatedly printed using a mold, so that the superhydrophobic polymer structure can be mass-produced in large area and economically.

Description

Preparation of Superhydrophobic Polymer Structures {Preparation of Superhydrophobic Polymer Fabrication}

The present disclosure generally relates to techniques for forming a superhydrophobic surface.

People are surrounded by and exposed to the surface of objects every day. Therefore, much research has been conducted on what phenomena occur on the surfaces that people frequently encounter and how they can be used to make life more comfortable. Superhydrophobicity refers to the physical properties of surfaces whose surfaces are extremely difficult to wet. For example, the leaves of plants, the wings of insects or the wings of birds have the property of preventing any external contaminants from being removed or contaminated from scratch without special removal. This is because the leaves of plants, the wings of insects, or the wings of birds are superhydrophobic (W. Barthloot and C. Neinhuis, Planta, 1997 , 202, pp. 1-8 ) .

Objects to which the superhydrophobic surface is applied may exhibit properties such as waterproofing and antifouling. Therefore, the technique of forming the superhydrophobic surface can be usefully used in various industrial fields. However, the formation of artificial superhydrophobic surface is still technically insufficient.

1 is a schematic diagram briefly showing a method of manufacturing a superhydrophobic polymer structure.
Figure 2 is a field emission-scanning electron microscope (FE-SEM) photograph of the aluminum surface without any treatment.
3 is a FE-SEM photograph showing the change in the surface structure of Al etched by the etchant during each time.
4 is a graph showing an aspect in which a reaction temperature during etching increases with etching time.
5 is a photograph showing the surface structure of Al etched for a short time at low and high temperatures, respectively.
6 is a FE-SEM photograph of a high-density polyethylene (HDPE) surface without any treatment.
FIG. 7 is an FE-SEM photograph showing the surface change of HDPE polymer structures made using Al template etched by etchant during each time.
8 is a graph showing the static contact angle of water droplets to the surface of HDPE polymer structures.
FIG. 9 shows static contact angle (θ _s ), advancing contact angle (θ _a ), receding contact angle (θ _r ) and contact angle hysteresis of water droplets to the surface of HDPE polymer structures. a graph showing the - (θ _a θ _r).
10 is a graph measuring the contact angle of water droplets to the surface of the HDPE polymer structure treated with various solvents.
FIG. 11 is a graph measuring the contact angle of water droplets to the surface of HDPE polymer structures exposed in solutions with various pHs.
12 is a sequential photograph showing the process by which activated carbon on the surface of the HDPE polymer structure is removed by water droplets.

A representative example of superhydrophobicity is the leaf surface of a plant that exhibits a lotus effect. In the present disclosure, techniques are studied in which the object has a biomimetic surface, such as the surface of a leaf of a plant, exhibiting a Lotus effect, in a way to make the surface of the object exhibit superhydrophobicity.

Methods of making superhydrophobic polymer structures, and thus etched molds and superhydrophobic polymer structures, have been developed.

In one embodiment, the method comprises micron-sized trace structures and nano-sized groove structures within the monolayer structures by chemical etching. Forming; Placing a polymer on the etched mold and applying heat and pressure to transfer the polymer structure from the etched mold; Removing the transferred polymer structure from the mold.

To apply a superhydrophobic surface in real life, the manufacturing process of the superhydrophobic surface is simple, inexpensive, and can be mass-produced in large areas, and such superhydrophobic surface can be applied to any object having various shapes. It is good to have physical properties.

In order for the superhydrophobic surface to have one or more of these properties, it is necessary to select a suitable material on which the superhydrophobic surface is formed. For example, if a superhydrophobic surface is to be formed on a hard ore or metal surface, the manufacturing process is difficult, expensive, difficult to produce in large areas, and not suitable for mass production. In addition, it will be difficult to apply or coat ores or metals with superhydrophobic surfaces to other objects. On the other hand, if a superhydrophobic surface is formed on the polymer structure, the polymer structure may be easily applied or coated on an object having various shapes because of its flexibility. Polymer structures are also easy to handle and require low manufacturing costs. Therefore, it is worth considering developing polymer structures with superhydrophobic surfaces.

In the present disclosure, a method of forming a superhydrophobic surface on a surface of a polymer structure is provided. In one embodiment, the method includes making a mold capable of transferring a superhydrophobic surface to the polymer structure, and imprinting the mold on the polymer structure. This method makes it possible to mass produce a superhydrophobic polymer structure because the mold can be repeatedly transferred to the superhydrophobic surface on the polymer structure.

In one embodiment, a superhydrophobic polymer structure is provided having a micron sized monolayer structure formed on a surface thereof. On the micron-sized monolayer structure, a nanostructured fiber structure is formed.

The term "monolayer structure" as used herein generally means a surface structure consisting of amorphous fragments that are irregularly distributed on the surface of the substrate.

As used herein, the term “fiber structure” generally refers to a surface structure in which amorphous fibrous shapes of grass-like shape are formed on the surface of a substrate.

The term "micro size" as used herein may be interpreted as, but not limited to, 1 to less than 1000 micrometers.

As used herein, the term "nano size is limited to, but may be interpreted as less than 1 to 1,000 nanometers.

To produce superhydrophobic polymer structures having micron-sized monolayer structures and nano-sized fiber structures on the surface, one can use a mold that enables the formation of such structures on the surface of the polymer structure by imprinting. .

The mold needs to have a structure corresponding to the superhydrophobic surface of the superhydrophobic polymer structure to be produced. Thus, the mold may have a form in which a micron-sized monolayer structure is formed on the surface. Nano-sized groove structure may be formed on the micron-sized monolayer structure. The term “groove structure” generally means a surface structure recessed by chemical etching, which corresponds to the fiber structure.

The micronized dendrite structures observed on the leaf surface of plants exhibiting the Lotus effect are relatively regular and formal. If a mold is made for the production of biomimetic surfaces, an etching method such as photolithography may be used. The biomimetic surface may have a regular and atypical protrusion structure. However, when using photolithography, not only the surface treatment area is limited, but also it is difficult to control the profile of the surface formed through photolithography, and in particular, it is technically very complicated and difficult to form a biomimetic hierarchical surface.

Regular and formal protrusion structures are not necessary to achieve superhydrophobicity. Even if they do not form a regular protruding structure, the presence of nano-sized fibrous structures on micron-sized ridges can be as effective as water molecules floating in the air. Thus, the micron size ridge structure need not be regular or formal.

In one embodiment of the present disclosure a micron-sized monolayer structure is formed by chemically etching the template instead of forming a regular or formal ridge structure in mimicking such a micron-sized ridge structure of the living body. This avoids the complicated process of making a mold that can occur to form a regular or formal ridge structure.

Chemically etching the mold forms micron-sized monolayer structures and nano-sized groove structures within the monolayer structures without the need for additional complicated processes.

Molds for the production of superhydrophobic surface polymer structures may be of any material as long as they can form micron-sized monolayer structures and nano-sized groove structures within the monolayer structures when chemically etched. It would be more advantageous to use a material that is easy to handle, inexpensive, and has one or more of the properties of a hierarchical structure in which the monolayer and groove structures are complex.

In one embodiment, the mold may be a mold made of metal. In the case of a metal mold, chemical etching may be easily performed within a short time, and a hierarchical structure may be easily formed. Although not limited thereto, any metal such as, for example, aluminum, tin, titanium, iron, copper, zinc, nickel, tungsten and alloys thereof may be used as the mold. Metals used as molds should be light, easy to handle and inexpensive to handle in the manufacturing process, and have a strength that does not wear out easily even after repeated impriting. For example, aluminum is very light, has adequate strength, is inexpensive, and is useful because it has a clear biomimetic layer formed upon chemical etching.

In one embodiment, chemical etching using a suitable etchant may be used to form monolayer and groove structures on the surface of the mold. The etchant may be an etchant that creates a monolayer texture on the surface. The etchant may comprise a mixture of one or more solutions of solutions such as HNO ₃ , H ₃ PO ₄ , H ₂ SO ₄ , H ₂ CrO ₄ , HCl, HF, NH ₄ OH, NaOH and KOH. The etchant may vary depending on the type of material used as the template. The composition of etchant that can be used for metals is illustrated in "Vander Voort, GF, Metallography: Principles and Practice, McGraw-Hill, New York, 1984", which is incorporated herein by reference in its entirety.

For example, when using an etchant containing HCl and HF as an etchant for aluminum, HCl directly etches aluminum, and HF removes a small amount of impurities such as Fe and Si contained in aluminum. HCl helps to etch the mold surface evenly. If the material forming the mold is different, the components performing this role may be different.

In one embodiment, the formation of the monolayer structure and the groove structure of the mold can be controlled by adjusting the temperature or etching time. For example, when a metal is used as a template, when a metal is etched at a low temperature in the range of 0 ° C to room temperature, a single layer structure having a micron size is formed, and due to the exothermic reaction due to the reaction between the metal and the etchant over time, When etching is performed at a high temperature in the range of 60 to 100 ° C., the reaction temperature may rise to form a nano-sized groove structure. Thus, by appropriately adjusting the temperature or etching time, the desired hierarchical structure may be formed on the surface of the mold. The temperature at which the etching is performed may be adjusted within the range of 0 to 100 ° C., for example, and the time at which the etching is performed may be adjusted within the range of 1 second to 10 minutes.

As described above, the micron-sized monolayer structure and the nano-sized groove structure formed in the monolayer structure through chemical etching may be used to form a superhydrophobic polymer structure having a biomimetic surface.

To this end, a process of placing a polymer on the etched mold, applying heat and pressure to transfer the polymer structure from the etched mold, and detaching the transferred polymer structure from the mold may be performed.

The shape of the mold for printing out the polymer structure can be any. The shape of the mold may vary depending on the appearance of the polymer structure to be manufactured. Although not limited thereto, the shape of the mold may be, for example, a shape such as a plate or cylinder. In the case of transferring the polymer structure from the plate-shaped mold, by setting the plate shape appropriately, the polymer structure having the desired shape may be produced. In addition, the transfer of polymer structures from cylindrically shaped molds would allow for the mass production of large area polymer structures, such as the application of a roll-to-roll process.

The polymer structure manufactured by transferring from the mold in the above manner may have a nano-sized fibrous structure on the micron-sized monolayer structure on the surface. When the surface of a mold having recessed micron-sized monolayers and nanosized grooves is stamped onto the surface of the polymer by chemical etching, the surface of the polymer structure is in contrast to the raised micron-sized monolayer and nanosized structures. It will have a fiber structure of size.

It is preferable to use a polymer having physical properties that transfer from the mold to the surface of the polymer structure is easy and accurate, and also retain the structure formed after the transfer. Any polymer that is flexible and has the appropriate strength can be used.

In one embodiment, the polymer may be a thermoplastic polymer. The thermoplastic polymer is a polymer having a property of plastic deformation upon heating but reversibly hardening upon cooling. When the thermoplastic polymer is used for the transfer of the mold, the polymer becomes flexible through heating and pressurization, so that it is easy to transfer a structure such as a structure recessed in the mold, and when cooled, the structure formed through the transfer can be well maintained. do.

The thermoplastic polymers include, but are not limited to, polyesters including, for example, polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT) and polyethylene naphthalate (PEN); Polyalkylenes including polyethylene (PE) and polypropylene (PP); Vinyl polymers including polyvinyl chloride (PVC); Polyamides; Polyacetals; Polyacrylates including polymethyl methacrylate (PMMA); Polycarbonate; polystyrene; Polyurethane; Acrylonitrile-butadiene-styrene copolymer (ABS); Halogenated polyalkylenes; Polyarylene oxide, polyarylene sulfide, and the like.

The superhydrophobic polymer structure produced by the above method can be mass produced easily and quickly in large area. The superhydrophobic polymer structure can be applied to any field as long as superhydrophobicity is required. For example, the present invention can be widely used to prevent loss caused by water or to prevent or prevent contamination. Although not limited thereto, the superhydrophobic polymer structure may be coated or applied, for example, for waterproofing, antifouling, anti-freezing, anti-fogging, self-cleaning, and the like. For example, the superhydrophobic polymer structure may be coated on the surface of an automobile body to prevent contamination and to prevent steaming, or to be coated on the bottom of a ship to prevent smudges, or to the surface of a large antenna To prevent freezing of ice, to coat the inner surface of the water transport pipe to prevent corrosion and contamination, to improve water flow, or to apply to water-repellent systems in greenhouses.

In the following examples will be described in detail with respect to the manufacturing method of the superhydrophobic polymer structure. In addition, an experiment is disclosed to investigate whether the surface of the polymer structure exhibits superhydrophobicity by measuring the contact angle of water droplets to the surface of the polymer structure prepared through the examples. The experimental results show that the surface of the polymer structure with hierarchical structure shows excellent superhydrophobicity.

In addition, the following experimental example shows the stability of the surface of the polymer structure and the self-cleaning effect of the surface of the polymer structure in a solution having a variety of solvents and various pH.

The present disclosure provides a simple and easy method of forming a biomimetic superhydrophobic surface on a polymer structure. By using the above method, the superhydrophobic polymer structure can be produced easily and quickly, as well as the superhydrophobic surface can be repeatedly printed using a mold, so that the superhydrophobic polymer structure can be mass-produced in large area and economically. In addition, the superhydrophobic polymer structure made by this method maintains superhydrophobicity without changing the surface structure in a solution having various solvents and various pHs, and has a good self-cleaning effect.

The present disclosure will become more apparent with reference to the embodiments described below in detail. However, it will be understood that the present disclosure is not limited to the embodiments disclosed below, but may be embodied and implemented in various different forms.

Example : Superhydrophobic Polymer  Manufacture of structures

1 is a schematic diagram briefly showing a method of manufacturing a superhydrophobic polymer structure. As shown in Fig. 1, an Al plate is etched to produce an aluminum mold having a hierarchical structure. The polymer is placed on the prepared mold and subjected to heat and pressure. The polymer structure is transferred from the mold and the superhydrophobic polymer structure is produced.

(1) Fabrication of aluminum molds and structural change analysis of mold surfaces

Aluminum (Al) was used as a template for the production of superhydrophobic polymer structures.

A commercially available Al plate (99.0%, 2 × 3 × 0.3 cm) was immersed in an etchant containing HCl and HF (HCl: HF: H ₂ O = 40 ml: 2.4 ml: 12.5 ml), respectively 10s, 20s Etching was performed at room temperature for 30s, 40s, 50s, 60s, 120s, 240s, 480s without temperature control. After etching, the Al plate was washed several times with water, dried with N ₂ gas, and stored.

The surface of the Al plate was analyzed using FE-SEM (Hitachi, s-4300).

2 is an FE-SEM photograph of the aluminum surface without any treatment. It does not have a smooth structure throughout the surface, but it can be seen that it is substantially flat.

3 is a photograph showing the change in the surface structure of Al etched by the etchant during each time. As can be seen in Figure 3, the surface of Al etched for a short time it can be seen that the micro-sized single-layer structure is formed. However, as the etching time is gradually increased, the micro-sized monolayer structure formed at first may be deformed. Nano-sized groove structures are formed on the surface of the micron-sized monolayer structure, increasing the hierarchical structure.

(2) Correlation analysis of structural change and temperature of aluminum mold surface

The etchant performs etching by first attacking defects exposed on the Al surface and incomplete portions of Al crystals. In this case, an Al surface having a similar structure should always be obtained regardless of the etching time, but the result of FIG. 3 shows that the aluminum surface structure varies according to the etching time. The correlation with temperature was investigated to determine the reason for the change from micro-sized structure to nano-sized structure with increasing etching time.

4 is a graph showing an aspect in which a reaction temperature during etching increases with etching time. As can be seen in Figure 4, the initial etching starts at room temperature, and as the etching time increases, the reaction temperature gradually increases, and the reaction temperature rises to about 100 ° C. In view of this phenomenon, since the etching reaction is not active at room temperature, the microstructure is formed, but when the etching time elapses, the reaction temperature increases and the etching reaction is actively performed. It can be assumed that a structure is formed.

Based on these assumptions, structural changes were observed by adjusting the reaction temperature. 5 shows a photograph of the surface structure of Al etched for a short time at low and high temperatures, respectively. As can be seen in Figure 5, etching at low temperature for a short time to obtain a microstructure, and etching at a high temperature for a short time to obtain a nanostructure. Experiments show that etching at high reaction temperatures (above about 70 ° C) for short periods of time (1 to 10 seconds) yielded nanostructures that are not microstructures, while at low temperatures (about 0 ° C) for a long time ( When the etching was performed for about 30 seconds or more, the nanostructure was not formed and the microstructure was continuously maintained. In addition, when the Al template with microstructures is etched at a high temperature (about 70 ° C.) for a short time (5 to 10 seconds), nanostructures are formed. When the etching was carried out at ℃) it was confirmed that the microstructure is formed again and the same phenomenon was observed even if repeated several times. Therefore, it was confirmed that by controlling the temperature or the etching time, it is possible to control the formation of the microstructure or the nanostructure.

In addition, experiments were conducted on how the constituents of etchant affect the etching of Al. Experiments showed that it was HCl that directly etched Al and HCl alone could not etch Al surface evenly over the entire surface. However, Al was hardly etched when only HF was etched. In fact, for Al, even traces of Fe and Si are evenly mixed. Therefore, it was confirmed that HF removes these evenly dispersed impurities and plays a role in helping HCl to evenly etch the Al surface.

(3) Preparation of polymer structures and analysis of structural changes on the surface of polymer structures

Polymer replication of HDPE was performed for about 20 minutes by heat and pressure using Al molds prepared above. In the case of HDPE, the polymer transfer was performed at about 150 ° C. After the polymer transfer, the polymer was cooled to room temperature and the template and the transcript were separated by stripping.

Surfaces of all polymer transcripts were analyzed using FE-SEM (Hitachi, s-4300).

6 is a FE-SEM photograph of the HDPE surface without any treatment. It can be seen that it is almost flat throughout the surface.

7 is a FE-SEM photograph of the structural change of HDPE polymer structures made using Al template etched by etchant during each time.

As shown in FIG. 7, when the Al mold (ie, the Al template etched for 10s to 30s) using the micro-sized single-layer structure is used, the shape of the transferred polymer structure can be seen to be correspondingly transferred. . However, from the Al template (Al template etched for 40s ~ 480s) gradually began to form nanostructures, it can be seen that the nanostructure of the template was transferred to grass-like nano-sized fiber structure. As the etching time increases, not only the nanostructure is formed as the reaction temperature increases, but also the hierarchical structure of the Al surface increases. During the polymer transfer process, the melted polymer enters every corner of the mold and cools down. When the polymer transcript is separated using a stripping method, the polymer is stretched and separated to form a grass-shaped nano-sized fiber structure.

(4) Confirmation of the superhydrophobicity of the transferred polymer structure

In order to confirm that the surface of the transferred polymer structure exhibits superhydrophobicity, the contact angle of water droplets to the surface of the polymer structure was measured. The measuring method is Florian Exl et. al, Proceedings of the XIVth International Symposium on High The method disclosed in Voltage Engineering , 2005, D-47 was used. The average contact angles measured at nine different points for each polymer structure are shown in FIGS. 8 and 9.

FIG. 8 is a graph showing the static contact angles of the HDPE polymer structures having the various transferred structures, and Tables 1 and 9 below show the static contact angles (θ _s ) and the advancing contact angles of these HDPE polymer structures. The angle (θ _a ), the rearing contact angle (receding contact angle) θ _r and the contact angle hysteresis (θ _a -θ _r ).

TABLE 1

The polymer structure has a superhydrophobic surface when it has a static contact angle of about 150 ° and a contact angle hysteresis below 5 °. As can be seen in FIG. 8, it can be seen that the HDPE polymer structure can exhibit a superhydrophobic surface when produced using a template of Al template etched for longer than 30 s. In addition, the HDPE polymer structure having a superhydrophobic surface has a θ _s synergistic effect of about 65% compared to the flat HDPE polymer plate. In the case of the HDPE polymer structure, the contact angle hysteresis was also less than 3 ° in the transcript (30s to 60s) having a superhydrophobic surface, and as a result, the superhydrophobic surface was found. 8 and 9, it can be seen that when the structure of the polymer surface is changed to form a hierarchical structure, superhydrophobicity is increased regardless of the material.

Experimental Example  1: transcribed Superhydrophobic Polymer  Check the stability of the structure

In order for the superhydrophobic polymer structure to be applied in real life, the superhydrophobicity of the polymer structure should have stability that is not damaged by external environment or pollutants. Therefore, an experiment was conducted to determine whether the superhydrophobic polymer structure maintains stability in a solution having various pH and stability in various solvents.

First, to test the stability of various superhydrophobic polymer structures in various solvents, HDPE polymer structures made using Al templates etched for 60 s in an etchant were prepared using hexane, petroleum ether, and toluene. Soak for 5 days in Cl-Benzene, methylene chloride, methylene chloride, chloroform, THF, EtOH, acetone, MeOH or water and observe the surface shape of the polymer structure Was measured.

After treatment with various solvents, the surface of the HDPE polymer structure was analyzed by FE-SEM, and it was confirmed that there was no change in the surface of the polymer structure when it was not treated.

10 is a graph measuring the contact angle of water droplets to the surface of the HDPE polymer structure treated with various solvents. As can be seen in FIG. 10, all HDPE polymer structures exposed to various solvents have a contact angle near about 160 °. Therefore, it can be seen that despite the treatment of various solvents, the structure of the surface of the polymer structure does not change and has stable superhydrophobic properties.

Then, to test the stability of the superhydrophobic polymer structure in the solution with various pHs, the HDPE polymer structure made using Al template etched in the etchant for 60 s was soaked in the solution having pH 1-13 for 3 days. After washing several times with water and the contact angle was measured.

As a result of analyzing the surface of the HDPE polymer structure exposed to the solution having a pH of 1 to 13 by FE-SEM, it was confirmed that there was no change compared to the surface of the polymer structure when it was not treated.

FIG. 11 is a graph measuring the contact angle of water droplets to the surface of HDPE polymer structures exposed in solutions with various pHs. As can be seen in Figure 11, even after exposure to a solution having a variety of pH for three days it can be seen that there is little change in the contact angle of the water droplets. Accordingly, it can be seen that despite the treatment of solvents having various pHs, the structure of the surface of the polymer structure does not change and has stable superhydrophobic properties.

Experimental Example  2: deceased Superhydrophobic Polymer  Midnight of the structure self - cleaning ) Check the effect

Superhydrophobic surfaces have a self-cleaning effect that can remove contaminants on their own. In order to confirm that the surface of the produced polymer structure exhibits a self-cleaning effect, an experiment was performed in which an activated carbon was placed evenly on the surface of the HDPE polymer structure, and then droplets were dropped by using a syringe. As a result, activated carbon was removed by water droplets on the surface of the polymer structure set at an angle (2 to 5 ^o ). The process was recorded with a digital camera.

FIG. 12 is a sequential photograph showing a process in which activated carbon placed on the surface of an HDPE polymer structure is removed by water droplets. As can be seen in Figure 12, it can be seen that the superhydrophobic surface of the HDPE polymer structure prepared through the above example exhibits a self-cleaning effect.

Claims (4)

Chemical etching to form a micron-sized trace structure and a nano-sized groove structure in the monolayer structure on the surface of the mold,
Placing a polymer on the etched mold and applying heat and pressure to transfer the polymer structure from the etched mold,
Formed by a method comprising stripping the transferred polymer structure from a mold,
Superhydrophobic polymer fabrication in which nano-sized fibrous structures are formed on the surface on micron-sized monolayer structures. A superhydrophobic polymer structure in which a nano-sized fibrous structure is formed on a surface on a micron-sized single layer structure, and the single layer structure and the fibrous structure have irregular and atypical shapes. The superhydrophobic polymer structure according to claim 1 or 2, wherein the polymer is a thermoplastic polymer. The method of claim 3, wherein the thermoplastic polymer comprises a polyester comprising polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT) and polyethylene naphthalate (PEN); Polyalkylenes including polyethylene (PE) and polypropylene (PP); Vinyl polymers including polyvinyl chloride (PVC); Polyamides; Polyacetals; Polyacrylates including polymethyl methacrylate (PMMA); Polycarbonate; polystyrene; Polyurethane; Acrylonitrile-butadiene-styrene copolymer (ABS); Halogenated polyalkylenes; A superhydrophobic polymer structure selected from the group consisting of polyarylene oxides and polyarylene sulfides.

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