WO2023129026A1

WO2023129026A1 - Mechanochemical preparation of superhydrophobic powders

Info

Publication number: WO2023129026A1
Application number: PCT/TR2022/051494
Authority: WO
Inventors: Esen DAGASAN BULUCU; Mustafa Serdar ONSES; Nusret CELIK; Serdar AKAY
Original assignee: Erciyes Universitesi Strateji Gelistirme Daire Baskanligi
Priority date: 2021-12-28
Filing date: 2022-12-13
Publication date: 2023-07-06

Abstract

The present invention relates to a method of preparing superhydrophobic powders by mechanochemical hydrophobization of hydrophilic nanoparticles. The objective of the invention is to produce superhydrophobic surfaces with high repellency without using solvents and silanes and without the need for any thermal treatment.

Description

MECHANOCHEMICAL PREPARATION OF SUPERHYDROPHOBIC POWDERS

Field of the Invention

The present invention relates to a method of preparing superhydrophobic powders by mechanochemical hydrophobization of hydrophilic nanoparticles.

Background of the Invention

Superhydrophobic coatings are low surface energy coatings with high liquid repellency. Coatings with a contact angle higher than 150 degrees and a roll off angle lower than 10 degrees are defined as superhydrophobic coatings. They have high liquid repellency and low surface energy, which provide many properties. These properties can be listed as follows: anti-icing, anti-fouling, anti-fogging, anticorrosion, etc. Since these properties provided by superhydrophobic coatings offer solutions to many problems encountered in industrial applications, they are promising and important. For example, to provide a detailed explanation regarding the anti-icing property; ice formation in winter not only affects life negatively, but also can cause loss of life and property and adversely affect energy and communication security. It is considered to be a serious problem especially in aircraft. Ice formation in aircraft is a major problem as it increases the weight of the vehicle and restricts wing movements. Since superhydrophobic coatings have high water repellency, the water coming onto a surface is removed from the surface before it has the possibility to form ice on the surface. Even if ice formation is partial, it can be removed with a very low force because the ice is bound to the surface with a weak force due to the low surface energy, which is a general characteristic of superhydrophobic coatings. These coatings have the potential to be used in many areas such as the glass industry, textile industry, energy industry, automotive industry, packaging industry and have the potential to help solve existing problems in these areas. Due to the advantages provided by superhydrophobic coatings, the number of studies carried out in this field is increasing day by day. In the production of conventional superhydrophobic coatings, hydrophilic nanoparticles are modified with silane and derivatives thereof and then dispersed in a solvent and applied to the surface by spray method. In order to increase the resistance of these traditional superhydrophobic coatings, resin or derivatives thereof and hydrophobic nanoparticles are mixed and applied to the surface or resin type polymers are first applied to the surface and then hydrophobic nanoparticles are applied to the surface as a second layer. Another problem is the use of fluorine-containing silanes. The use of fluorine-containing silanes also significantly limits the use of superhydrophobic coatings. Fluorine-containing silane and derivatives can persist and accumulate in the human body and the environment for a long time and are therefore thought to cause major problems. Therefore, the production of superhydrophobic coatings without using fluorine-containing silane has been performed using wax and its derivatives, silicone and its derivatives, and significant progress has been made in this field. By conducting studies of this type, the problem related to mechanical strength and the use of fluorine-containing silane is aimed to be overcome to some extent. Another problem associated with superhydrophobic coatings is that they are solvent-based. This means that toxic solvents are used when applying superhydrophobic coatings to the surface or when modifying nanoparticles with silanes. In this case, solvents can cause serious problems and damage to the environment and human health. There are no studies in the literature in which the superhydrophobic coating is applied to the surface without the use of solvent. This indicates the difficulty of producing such coatings. When the literature is examined in general, it will be found that there is a widespread use of solvents with toxic properties. These solvents are a serious problem and their disposal is also a major problem.

One of the state of the art applications is described in an article by Huanjun Chang (Rsc Advances, 5(39), 30647-30653) et al. In this article, they added 0.55 g PDMS to 30 mL THF (tetrahydrofuran), and in another container, 0.055 of curing agent to 30 mL THF, and stirred for 30 minutes by means of a magnetic stirrer. They then mixed these two mixtures in a ratio of 1/1. Hydrophobic silica nanoparticles modified with hexadecyltrimethoxysilane were added to the prepared PDMS THF mixture and stirred with an ultrasonic stirrer for 1 hour. The prepared wood samples were then immersed in this mixture and then heated at a temperature of 103 °C for 1 hour. After this process, the same samples were again immersed in this mixture and cured again. This process was repeated 3 times and a superhydrophobic coating was obtained. In this way, a coating with a contact angle of 152 degrees was obtained. As can be understood, a solvent was used in this study. These materials significantly limit the use of the coating. In addition, as can be seen, the contact angle of the coating they obtained is low.

In the method described in the Chinese application document CN105694715A, 5 g PDMS, 0.25 g curing agent and 0.05 g catalyst converter were added to 50 mL hexane and mixed homogeneously. In a separate container, 0.5 g of octadecyl trichlorosilane alkane (OTS) modified silica nanoparticles were taken into 10 ml of hexane and mixed by means of an ultrasonic device and a homogeneous mixture was obtained. Then the spin coating method was used to obtain the superhydrophobic coating with transparent properties. The coating process was carried out by first coating the mixture prepared using PDMS and then spin coating the hydrophobic silica mixture on this layer. This process was repeated 3 times and the coated substrate was allowed to rest at room temperature for 24 hours. The contact angle of the superhydrophobic coating they obtained is 166.8 degrees. As in the above study, silane and solvent were used in this study and curing process was needed at the same time. In order to carry out the curing process of the coating they made here, they allowed it to rest at room temperature for 24 hours and then cured it.

During the production of superhydrophobic coatings, solvents are used at different stages. The use of solvents poses significant problems during both production and application. The use of solvents poses threats such as poisoning of workers and fires in production facilities. As a result of this, additional safety measures need to be taken in both production and storage areas. These measures have a negative impact on production costs. Disposal or reuse of excess solvents after production are also important problems.

An important disadvantage of solvents occurs during use. If used by untrained users, these chemicals containing organic solvents pose serious threats. Conditions such as inhalation of solvents and their contact with skin limit the use of these coatings by a wide range of consumers.

Another group of chemicals widely used in the production of superhydrophobic surfaces are silanes. Silanes react easily with surfaces such as silicon oxide, and their alkyl chains or fluorocarbon groups provide a low surface energy. Silanes have significant disadvantages in terms of production and commercialization. Silanes are known to be sensitive to moisture. Silane molecules react with each other in the presence of water and form oligomers. The formation of these oligomers creates problems such as reproducibility. Details such as storage in controlled environments (argon environment) at the laboratory scale and the use of silane bottles as soon as they are opened will pose challenges in large-scale production.

Silane production, which is monopolized by certain companies in the world, is not available in our country. There have been difficulties in supplying silanes for the commercialization of superhydrophobic coatings. The invention of the present application will provide great convenience in terms of the production of superhydrophobic coatings with domestic resources.

Summary of the Invention

The objective of the invention is to produce superhydrophobic surfaces with high repellency without the use of solvents. Another objective of the invention is to produce superhydrophobic surfaces with high repellency without the use of silanes.

A further objective of the invention is to provide a production method that allows the production of superhydrophobic surfaces without the need of any thermal treatment.

Another objective of the invention is to provide a production method for obtaining superhydrophobic coatings with different functionalities by the hydrophobization of nanoparticles of different compositions. The objective of the invention is to provide a production method that allows the production of surfaces with high mechanical strength and non-wetting properties in water by mechanochemically grafting polymer chains and surrounding the nanoparticles with them.

Detailed Description of the Invention

The “ Mechanochemical Preparation of Superhydrophobic Powders'" developed to fulfill the objective of the present invention is illustrated in the accompanying figures, in which:

Figure 1- is the graphical representation of a) the effect of the viscosity of methyl-terminated polysiloxane on superhydrophobic coating, and b) the effect of particle size on superhydrophobic coating.

Figure 2- is the representation of the amount of organic solvent used to make 1 gram of hydrophilic silica superhydrophobic by using alkyl silane and fluorinated silane. In the present invention, production is made without using solvents.

The method for the mechanochemical preparation of the superhydrophobic powders of the present invention, which is developed for the purpose of making hydrophilic nanoparticles hydrophobic, comprises the following process steps: - adding the polymer with low surface energy and nanoparticles into the chamber,

- placing the balls into this chamber and performing the mixing process,

- obtaining the superhydrophobic nanoparticles, which are the final product.

In one embodiment of the invention, inorganic nanoparticles are preferably used as nanoparticles. These inorganic particles have a particle size of 250 microns or less, and nanoparticles selected from a group including silica, titanium dioxide, zinc oxide, aluminum oxide, silicon carbide, silicon carbide, magnesium oxide, boron carbide, copper oxide, boron nitride, calcium oxide, iron oxide, silver and mixtures thereof are used. Considering the optimized ratios, the size of the nanoparticle used is at most 250 pm.

In one embodiment of the invention, a polymer selected from the group comprising vinyl-terminated polysiloxane, paraffin wax, beeswax, methyl-terminated polysiloxane and mixtures thereof may be used as a low surface energy material.

In one embodiment of the invention, the grinding time of the chamber at a rotational speed of 200 rpm is at least 30 minutes. When the chamber is operated at rotational speed (100 rpm) lower than 200 rpm, the duration is at least 60 minutes.

In one embodiment of the invention, the methyl-terminated poly siloxane used must have a viscosity above 100 cSt. As can be seen in Figure la, when methyl- terminated polysiloxane with a value of 10 cSt is used, the contact angle is 0 degree. In other words, the surface absorbs water completely. As can be seen from the graph, superhydrophobic property is obtained when silicone with a value of 100 cSt and above is used. Another parameter that has an impact on the superhydrophobic coating is the effect of the size of the particle used. As can be seen in Figure lb, when silica nanoparticles with particle size between 149-250 pm are used, a contact angle of 159 degrees and a roll off angle of 8 degrees are obtained. Surfaces with a roll off angle higher than 10 degrees are not characterized as superhydrophobic coatings. As can be seen, the surface obtained with particles of 250 pm size is at the limit in terms of rolling angle. Based on this data, it can be said that the size should not exceed 250 pm. In addition, when particles with a size larger than 841 pm are used, it is seen that powder material is not obtained when particles with much higher sizes are used. A pellet-shaped material is obtained. It also does not show superhydrophobic properties (<150°). It is seen in the graph that as the particle size decreases, the repellency of the superhydrophobic coating increases further, that is, the contact angle increases, and the rolling angle decreases.

No solvents are used at any stage of the invention. However, solvent is used to make nanoparticles hydrophobic with fluorinated silane and alkyl silane. As can be seen in Figure 2, 20 mL of solvent is used to modify 1 gram of hydrophilic silica nanoparticle with alkyl silane and impart superhydrophobic properties, while 1 gram of hydrophilic silica nanoparticle is modified with fluorinated silane and approximately 130 mL of solvent is used to impart superhydrophobic properties. When the related literature is examined, solvents are used to modify the silica as well as to apply it to the surface. (Chemical Engineering Journal 396 (2020): 125230; Macromolecules 51.23 (2018): 10011-10020)

Within the scope of the invention, polysiloxane (methyl-terminated siloxane or vinyl-terminated siloxane) is used to make hydrophilic nanoparticles hydrophobic. 2 grams of silica nanoparticles and 1 gram of polysiloxane are added into the chamber made of tungsten carbide. Then 20 balls made of tungsten carbide are placed in this chamber and the system is adjusted to rotate at 200 rpm. Nanoparticle and polysiloxane are mixed at 200 rpm for 1 hour. At the end of 1 hour, poly siloxane completely surrounds the nanoparticles, thus making the nanoparticles superhydrophobic. Here, nanoparticles of different compositions can be used. That is, the important thing here is the size of the particle used. This is because polysiloxanes bind to particles both physically and chemically. Instead of vinyl- terminated polysiloxane, it can also be made using paraffin wax, beeswax, methyl- terminated polysiloxane and any polymer that has low surface energy and can be shaped with force. The important thing is that the polymer has a low surface energy.

Within the scope of the invention, a method has been developed for obtaining superhydrophobic coatings by mechanochemically modifying micro and nanosized particles without using any solvent and by using polysiloxane and its derivatives with low surface energy. The basis of this method is the use of a mechanochemical production approach. In this approach, micro- and nano-sized inorganic particles are mechanochemically modified with hydrophobic molecules. To demonstrate the mechanochemical approach, a planetary ball mill was used in the method of the present invention. In addition, it is envisaged that other production methods providing mechanochemical effects can also be applied to the approach in the present invention. In the ball milling method, friction and collisions play an important role. Mechanical alloying (MA) is a powder production method that starts with elemental powder mixtures and enables the production of homogeneous materials. It is based on the principle that the size of elemental powders placed in grinding chambers is reduced by ball-chamber collisions. The method is a solid state method that includes repeated cold welding and crushing of powders in high-energy ball mills. Especially during the production of particle reinforced composites, the homogeneous distribution of the hard reinforcing elements in the matrix is an important problem. The mechanical alloying method, which produces composites by powder abrasion between moving balls, is a successful method in this respect. By repeating the cold welding and crushing processes in the microstructure, a homogeneous mixture of brittle and ductile materials is achieved. In this method, nanoparticles to be reduced in size or mixtures prepared to produce nanocomposite powder are placed in the chamber, balls made of the same material as the chamber are added therein and the powders are ground with a certain rotation speed. One of the biggest advantages of this method is that it allows the desired powders or materials to be mixed such that they are cold welded with each other without using any solvent. In the planetary ball mill method, parameters such as rotation speed, number of balls and ball size significantly affect the size and quality of the powder. The above-mentioned parameters are taken into account since they also affect the production rate.

In the planetary ball milling method, it is easier for particles with different hardnesses to mix with each other in a cold weld. In other words, for any two materials to mix with each other, it is important for powder production that one of the materials is soft and the other is hard. Considering this situation in the method of the present invention, polysiloxane and polymer types were used as soft materials and inorganic particles were used as hard materials. It is the size of the particle that affects the performance of the coating, not the type of particle used. The production of superhydrophobic coating cannot be achieved without soft material. When determining the polysiloxane and polymer derivatives to be used in the method of the present invention, preferences are made by considering their surface energies. It is not possible to produce superhydrophobic coatings when polymers with high surface energy, i.e. low contact angle, are used. On the contrary, superhydrophilic particles would be produced. In this method of the present invention, polymer selection was made by considering the publications and sources in the literature.

The major advantages achieved by the present invention are as follows:

1. The production of superhydrophobic surfaces with high repellency will be realized without the use of solvents. The important advantages of not using solvents are listed below.

• Health problems that may occur as a result of the risk of inhalation of solvents in the production facility will be prevented.

• Material and immaterial losses that may occur as a result of flammability of solvents and fire risk in the production facility will be prevented.

• The need for additional safety measures in production facilities due to solvents will be eliminated.

• There will be no need to dispose of solvents generated during production. • By eliminating solvent-related risks during the application of superhydrophobic coatings by the end user, superhydrophobic coatings will be able to be used safely by a wider group of people.

2. The production of superhydrophobic surfaces with high repellency will be realized without the use of silanes. The important advantages of not using silanes are listed below.

• The sensitivity of silanes to moisture and the difficulties this creates in production will be eliminated.

• Difficulties in supplying silanes will be eliminated.

• Problems arising from the restriction of usage area will be prevented.

3. The method of the present invention allows the production of superhydrophobic surfaces by using different inorganic particles and different hydrophobic materials. This is based on the elimination of the dependence on surface chemistry with the advantage of the mechanochemical approach used. As a result, the following advantages will be obtained.

• Superhydrophobic surfaces can be produced with inexpensive and readily available raw materials.

• It has become possible to use waste materials in the production of superhydrophobic coatings.

• Particles with a wide range of different particle chemistries (TiO2, SiO2, MgO, FeO, ZnO, Au, Ag, Pt) can be modified by this method. In this respect, the invention enables the production of multifunctional superhydrophobic coatings.

• Superhydrophobic surfaces can be produced with new generation nanomaterials (graphene, MXene and similar two-dimensional nanomaterials, carbon nanotubes and similar one-dimensional nanomaterials). • The production of superhydrophobic powders with different materials will allow the production of multifunctional surfaces. The combination of the properties of the material (e.g. plasmonic, magnetic, photocatalytic, photoabsorbance, electrical conductivity, antibacterial, antiviral, etc.) and superhydrophobicity property will create new application areas.

4. Superhydrophobic coating was obtained without the need for any thermal treatment. The disadvantages of on-site application of thermal heating are overcome.

5. The superhydrophobic surfaces produced by the invention exhibit superior mechanical strength and non-wetting properties in water.

6. Superhydrophobic surfaces produced with the invention show stability under water for a long time and maintain their superhydrophobic properties.

EXPERIMENTAL STUDIES

In order to experimentally explain the importance of the soft material in the method of the present invention, all parameters used in the method of the present invention were kept constant and only low surface energy carnauba wax was used instead of the soft material. Carnauba wax is known as a brittle and hard material. The experimental study is described in detail in Example 1.

Example 1: 2 grams of silica nanoparticles and 1 gram of carnauba wax were placed in a chamber containing 20 balls and mixed at 200 rpm for 1 hour. To measure the contact angle of the obtained powder sample, the powder sample was adhered to a tape and the contact angle was measured with a contact angle device by using 4-5 pL water drops. The dripped water is absorbed by the powder. Thus it is understood that carnauba wax does not mix with hydrophilic silica nanoparticles, that is, it does not physically or chemically bind to silica nanoparticles. This example illustrates the importance of low surface energy material with soft properties for superhydrophobic coating with Experiment 1.

In order to demonstrate the importance of the ball mill method used in the method of the present invention, it has been worked at lower rotational speeds and experimental proof has been presented. It is very difficult to produce superhydrophobic coating mixing manually, i.e. by hand, without using the ball milling method. Furthermore, it is expected that if superhydrophobic coatings are produced manually, very small quantities can be produced, and this will impose a limitation for industrial applications. To explain this experimentally, we tried to demonstrate this by working at lower rotational speeds. In the explanation with Example 2, the experimental study is explained in more detail.

Example 2: 2 grams of silica nanoparticles and 1 gram of vinyl-terminated polysil oxane were placed in a chamber containing 20 balls and mixed at 100 rpm for 30 minutes. To measure the contact angle of the obtained powder sample, the powder sample was adhered to the tape and the contact angle was measured with a contact angle device by using 4-5 pL water drops. The contact angle of the produced coating was measured as 130 degrees. As can be seen, the powder produced at low rotational speed (rpm) did not exhibit superhydrophobic properties.

Production speed is important in industrial applications. Production speed is also important in terms of energy consumption. Therefore, experimental studies have been carried out to increase the production speed in the method of the present invention. In the method of the present invention, it is possible to produce hydrophobic powders with hydrophobic properties in very short periods of time at high rotational speeds. In the explanation with Example 3, the experimental study is explained in more detail.

Example 3: In this section, the effect of the rotational speed of the chamber on the superhydrophobic coating and its effect on the production rate is investigated. 2 grams of silica nanoparticles and 1 gram of vinyl-terminated polysiloxane were placed in a chamber containing 20 balls and mixed at 100 rpm for 15 minutes. The same process was also performed at 200 rpm and 400 rpm. Here, the duration was kept constant at 15 minutes. At the end of 15 minutes, in order to measure the contact angle of the powders produced by using 100 rpm, 200 rpm and 400 rpm, these powders were adhered to the tape and the contact angle was measured with a contact angle device by using 4-5 pL water drops. The contact angle of the powder produced at 100 rpm is 0 degree. That is, it absorbs water quickly. The contact angle of the powder produced with 200 rpm is 167 degrees and the roll off angle is 4 degrees. The contact angle of the powder produced with 400 rpm was measured as 172 degrees and the roll off angle as 1.5 degrees. As can be seen, it is possible to produce the powder required for the superhydrophobic coating provided by the method of the present invention within a period as short as 15 minutes.

As mentioned above, in the method of the present invention, the particle type does not affect the contact angle of the coating, i.e. its superhydrophobic property. In the method of the present invention, the same results can be obtained by using different types of particles to explain this experimentally. In the explanation with Example 4, the experimental study is explained in more detail.

Example 4: In this section, the effect of particle type and size on the method of the present invention is examined. For this process, 4 different particles were used. These are as follows: 1) Silica (SiO2) (11 nm in size), 2) Titanium dioxide (TiO2) (21 nm in size), 3) Magnesium (Mg) (0.06-0.3 mm in size), 4) Silicon carbide (SiC) (0.03 mm in size). To explain the experiment in terms of silica nanoparticles, 2 grams of silica nanoparticles (SiO2) with a size of 11 nm and 1 gram of vinyl- terminated polysiloxane were placed in a chamber containing 20 balls and mixed at 200 rpm for 60 minutes. Here, the same process was performed for magnesium, titanium dioxide and silicon carbide, by keeping the rotational speed, time and ratio of vinyl-terminated polysiloxane constant. To measure the contact angle of the obtained powder samples, the powder sample was adhered to the tape and the contact angle was measured with a contact angle device by using 4-5 pL water drops. The contact angle of the powder produced by using silica nanoparticles and titanium dioxide was measured as 172 degrees and the roll of angle as ~ 1.5. The contact angle of the powder produced by using magnesium was measured as 154 degrees and the roll off angle as 18 degrees. Finally, the contact angle of the powder produced by using silicon carbide was measured as 153 degrees and the roll off angle as 24 degrees. Considering the results presented here, it is observed that the size of the particle affects the contact angle and the roll off angle. As the size of the particle used increases, i.e. when micron-sized particles are used, the contact angle decreases significantly while the roll off angle increases considerably. But this type of problem is not encountered when nano-sized particles are used. With this experimental study, it was revealed that the type of particle has no effect on the method of present invention, but the particle size has an effect thereon.

Polysiloxane materials are known as low surface energy materials and are frequently used to produce both hydrophobic and superhydrophobic coatings. The main known siloxanes are as follows: vinyl-terminated poly siloxane and methyl- terminated polysiloxane. When vinyl-terminated polysiloxane is heat treated, it changes from viscous to solid form due to cross-linking. Vinyl-terminated polysiloxanes are usually used as 2 kits. Kit 1 is vinyl-terminated polysiloxane and Kit 2 is the cross-linking (curing) agent. When vinyl-terminated polysiloxane and the agent are mixed, it is cured for 24 hours under ambient conditions or for 30 minutes at 80 °C. After the curing process, no heat treatment can be applied. It cannot be shaped by a second heat treatment due to cross-links. In contrast to vinyl- terminated polysiloxane, methyl-terminated polysiloxane does not contain crosslinkers. In other words, no change occurs in the form of methyl-terminated polysiloxane when any heat treatment is applied. It continues to exist in a viscous form even if heat treatment is applied. The vinyl-terminated polysiloxane used in the method of the present invention is a high purity and expensive material. Methyl- terminated polysiloxane, paraffin wax and ecoflex, which are less expensive and readily available materials, can also be used instead of vinyl-terminated polysiloxane to produce the superhydrophobic coating presented in the method of the present invention. In the explanation with Example 5, the experimental study is explained in more detail.

Example 5: In this section, the effect of different materials on the contact angle of the superhydrophobic coating produced by the method of the present invention is investigated. For this process, 4 different substances were used. These are as follows: 1) Vinyl-terminated polysiloxane, 2) Methyl-terminated polysiloxane, 3) Paraffin wax, 4) Ecoflex. To explain the experiment in terms of vinyl-terminated polysiloxane, 2 grams of silica nanoparticles (SiO2) with a size of 11 nm and 1 gram of vinyl-terminated polysiloxane were placed in a chamber containing 20 balls and mixed at 200 rpm for 60 minutes. Here, the same process was performed for methyl-terminated polysiloxane, paraffin wax and ecoflex by keeping the rotational speed, time and silica content constant. To measure the contact angle of the obtained powder samples, the powder sample was adhered to the tape and the contact angle was measured with a contact angle device by using 4-5 pL water drops. The contact angle of the powder produced by using vinyl-terminated polysiloxane, methyl- terminated polysiloxane and ecoflex was measured as 170-172 degrees and the roll off angle as ~1.5. The contact angle of the powder produced with paraffin wax was measured as 157 degrees and the roll off angle as -15. Considering the results obtained herein, it is shown that other polymers can also be used instead of vinyl- terminated polysiloxane.

In this method of the present invention, experimental study was carried out to investigate the effect of the viscosity of the methyl-terminated polysiloxane used in example 5 on superhydrophobic powder. In fact, here we are examining the effect of the length of the polymer chain. As the viscosity increases, the length of the polymer chain also increases.

Example 6: In this section, the effect of methyl-terminated polysiloxane with different viscosities on the contact angle of the superhydrophobic coating produced by the method of the present invention is investigated. Methyl-terminated polysil oxane with 4 different viscosities of 10 cSt, 100 cSt, 1000 cSt and 10000 cSt was used. To explain the experiment in terms of methyl-terminated poly siloxane with a viscosity of 10 cSt, 2 grams of silica nanoparticles (SiO2) with a size of 11 nm and 1 gram of methyl-terminated polysiloxane were placed in a chamber containing 20 balls and mixed at 200 rpm for 60 minutes. The same process was also performed for methyl-terminated polysiloxane with viscosities of 100 cSt, 1000 cSt and 10000 cSt and powder samples were obtained. To measure the contact angle of the obtained powder samples, the powder sample was adhered to the tape and the contact angle was measured with a contact angle device by using 4-5 pL water drops. The contact angle of the powder produced by using methyl-terminated polysil oxane with a viscosity of 10 cSt is 110 degrees. In other words, it does not show superhydrophobic properties. The contact angle of the powder produced by using methyl-terminated polysiloxane with a viscosity of 100 cSt is 169 degrees. The contact angle of the powder produced by using methyl-terminated poly siloxane with a viscosity of 1000 cSt and 10000 cSt is 172 degrees. In other words, superhydrophobic coating is not obtained when polysiloxane with very low viscosity is used, while superhydrophobic coating is obtained when polysiloxane with a viscosity of 100 cSt and higher is used.

In the method of the present invention, a washing process was used to demonstrate the chemical grafting of methyl-terminated polysiloxane into the particles. The experimental study is described in detail in example 7.

Example 7: In this section, a superhydrophobic powder prepared with methyl- terminated poly siloxane with a viscosity of 10000 cSt and silica nanoparticles with a size of 11 nm was used. 0.2 gram each of this superhydrophobic powder was taken into the centrifuge tube. Then 10 mL of toluene was added into this tube and then stirring was done by means of a mechanical stirrer at 1500 rpm for 15 minutes. After stirring, centrifugation was performed at 4000 rpm for 15 minutes. After centrifugation, particles settle to the bottom of the tube. After this process, the toluene was decanted from the tube and pure toluene was added again. Then, mixing and centrifugation was performed again. This process was repeated 4 times. At the end of these processes, the particles after centrifugation were kept in an oven at 80 °C for 12 hours and thus drying, i.e. solvent removal, was performed. After 12 hours, chemical characterization of these powder particles was performed by considering both the contact angle and the Raman spectra. Despite washing with toluene, these particles still exhibit a high contact angle (172°) and maintain their superhydrophobic properties. In the Raman spectra, there are still spectra of methyl- terminated polysiloxane after the 4th washing. These processes show that the methyl-terminated polysiloxane is chemically bound to the silica nanoparticle. Toluene is frequently used for dissolving polysiloxanes. Therefore, toluene is preferred in this section. It is believed that if the methyl-terminated polysiloxane was not chemically but physically bound to the silica nanoparticles, the washing process repeated 4 times would remove the nanoparticles and these particles would show hydrophilic properties. Furthermore, in this case, it is believed that the spectra of methyl-terminated polysiloxane would not be observed in the Raman analysis performed after the washing process repeated 4 times.

It is explained in detail in example 8 that the superhydrophobic coating produced in the method of the present invention shows superhydrophobic properties when it remains under water for a long period of time and it is better compared to the surfaces produced with other silanes.

Example 8 : The nanoparticles with a size of 11 nm modified with 3 different low surface energy molecules (1) alkyl silane, 2) fluoro silane and 3) silicone used in the method of the present invention were tested for water stability. Double-sided tape was adhered to the surface of glass slides with a size of 2.5x2.5 cm². Then, 0.2 grams of powders modified with the specified molecules were placed on the surface of these slides and pressed with a weight of 5 kg. After pressing, these surfaces were placed in 40 mL of water and kept in water for 96 hours. The surface of the substrate prepared with alkyl silane-modified silica nanoparticles was completely wetted at the end of 96 hours. The surface of the substrate prepared with fluorasilane-modified silica nanoparticles was also completely wetted at the end of 96 hours. However, the substrate prepared with silicone-modified silica nanoparticles used in the method of the present invention is completely dry when it is taken out of the water. That is, it still maintains its high repellency. This also demonstrates the advantage of superhydrophobic silica nanoparticles prepared with silicone. In other words, it can maintain its superhydrophobic property also under water. It is especially prominent in the protection of surfaces that are constantly in water. However, the substrates prepared with alkyl silane and fluorasilane lose their superhydrophobicity properties after being kept under water for a certain period of time and their surfaces become wet. Due to this property provided by the method of the present invention, it can be used in marine vessels and can protect the surfaces by preventing the growth of micro-organisms on the surface of marine vessels.

To summarize the results of the experimental studies, in our method of the present invention, polysiloxane and silica nanoparticles were made superhydrophobic by taking them into the chamber at a certain ratio by using the ball milling method. In the ball milling method, polysiloxane and silica are homogeneously compact and show superhydrophobic properties. The same results can be obtained by using any kind of nanoparticles instead of silica. It was shown that the polysiloxane and its derivatives used are chemically bonded to the nanoparticles. The surface developed by the method of the present invention shows stable superhydrophobic properties under water.

Characterization of the Method of the Present Invention:

In stability tests, characterization was performed using powders obtained with vinyl-terminated polysiloxane and silica nanoparticles with a size of 11 nm.

Chemical stability: To examine the chemical resistance of the powder coated on the tape, it was kept in solutions of pHl and pH14 for 24 hours. After 24 hours, no significant change in the contact angle of the coating was observed.

Abrasion test with weight:

In order to examine the abrasion resistance of the powder, which we have coated on the tape with a surface area of 1cm², under a weight, it was adhered under a weight of 550 grams and moved on a 1000 grit silicon carbide abrasive surface and the abrasion resistance of the superhydrophobic coating was examined. The coated tape was moved 300 cm on the abrasive surface and the contact angle was measured. The initial contact angle is 172 degrees while the contact angle after 300 cm of abrasion is 169 degrees. In other words, no significant change was observed in the contact angle of the coating. When characterizing the abrasion resistance of the coating under weight, the sample was taken after every 10 cm and the contact angle was measured and the abrasion process was performed. This process was repeated 30 times.

Stability against UV light:

To determine the resistance of the powder coated on the tape against ultraviolet light, we exposed it to ultraviolet light for 120 hours. No change in the contact angle of the coating was observed. That is, the coating has a very high resistance to ultraviolet light.

Impact test with water:

In the water impact test, an impact was created on the surface by spraying water on the surface from a distance of 2.5 cm by using a spray gun with a nozzle diameter of 0.35 mm and its resistance to water was determined. At the end of the 200-round process, the contact angle of the superhydrophobic coating was measured as 162 degrees.

Claims

CLAIMS A method for the mechanochemical preparation of superhydrophobic powders, which is developed to make hydrophilic nanoparticles hydrophobic, and comprises the following process steps:

- adding the polymer with low surface energy and nanoparticles into the chamber,

- placing the balls into this chamber and performing the mixing process,

- obtaining the superhydrophobic nanoparticles, which are the final product. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein inorganic particles having a particle size of 250 microns or less are used as nanoparticles. A method for the mechanochemical preparation of superhydrophobic powders according to claim 2, wherein the nanoparticles selected from a group comprising silica, titanium dioxide, zinc oxide, aluminum oxide, silicon carbide, magnesium oxide, boron carbide, copper oxide, boron nitride, calcium oxide, iron oxide, silver, and mixtures thereof are used. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein the low surface energy polymer selected from the group comprising vinyl-terminated polysiloxane, paraffin wax, beeswax, methyl-terminated polysiloxane and mixtures thereof is used. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein 2 parts by weight of silica nanoparticles and at least 1 part by weight of poly siloxane are added to the chamber made of tungsten carbide.

6. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein a plurality of balls made of tungsten carbide are placed in a chamber made of tungsten carbide.

7. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein, in the process step of placing balls made of tungsten carbide in the chamber and mixing, the mixing is performed by rotating the chamber at 200 rpm for 1 hour.

8. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein the methyl-terminated poly siloxane having a viscosity of at least 100 cSt is grafted into the nanoparticles.

9. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein the size of the nanoparticle used is at most 250 pm, considering the optimized ratios.

10. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein the grinding time of the chamber is at least 30 minutes at a rotational speed of 200 rpm.

11. A method for the mechanochemical preparation of superhydrophobic powders according to claim 1, wherein the grinding time of the chamber is at least 60 minutes at a rotational speed of 100 rpm.