echemi logo
Product
  • Product
  • Supplier
  • Inquiry
    Home > Chemicals Industry > New Chemical Materials > Domestic and international status, preparation methods and application prospects of research on superhydrophobic weathering surfaces

    Domestic and international status, preparation methods and application prospects of research on superhydrophobic weathering surfaces

    • Last Update: 2022-04-01
    • Source: Internet
    • Author: User
    Search more information of high quality chemicals, good prices and reliable suppliers, visit www.echemi.com
    Abstract: The radome directly covers the surface of the antenna and is an important part of protecting the antenna feed system of the radar.
    The protective performance of the radome directly affects the reliability of the whole radar.
    The hydrophobicity and aging resistance of the surface of the radome are particularly important
    .
    The principle of hydrophobic surface and the influence of rainwater deposition on antenna transmission loss are briefly described, which proves the importance of superhydrophobicity on the surface of the radome; the principle and importance of the high weather resistance of the radome surface are briefly described, and the superhydrophobic weather resistance is discussed.
    The domestic and international status, preparation methods and application prospects of surface research
    .
    Keywords: radar; radome; super-hydrophobic surface; transmission loss; high weather resistance Chinese Library Classification Number: TN82 Document Identification Code: A Article Number: 1001-3474 (2016) 04-0239-04 The radome directly covers the antenna The surface is an important part to protect the antenna feeder system of the radar.
    The protective performance of the radome directly affects the reliability of the entire radar.
    Among them, the hydrophobicity and aging resistance of the radome surface are particularly important
    .
    Numerous studies have shown that rain has a great influence on the transmission performance of radar antennas.
    Water has a high dielectric constant and loss tangent to microwave and millimeter waves.
    When rain causes water on the surface of the radar antenna or radome, even thin water Films can greatly increase rainwater transmission loss and rainwater noise temperature.
    To reduce this effect, it is necessary to improve the hydrophobicity and airtightness of the radome surface [1]
    .
    The radome is mainly made of polymer composite materials.
    After a long period of sun exposure and rain erosion, the polymer resin in the radome will age and crack, causing defects such as discoloration, chalking and blistering on the surface.
    For this effect, it is necessary to improve the aging resistance of the surface of the radome
    .
    1 Research on the hydrophobicity of the radome surface 1.
    1 The basic principle of surface hydrophobicity Surface wettability is one of the important characteristics of a solid surface, which is mainly determined by its chemical composition and microstructure
    .
    As early as more than 60 years ago, scholars began to study the wettability of solid surfaces.
    Since Wenzel and Cassie published a series of articles on surface wettability, a large number of theoretical and experimental research results have been continuously introduced.
    Significant progress has been made in the controllability of wetness
    .
    The wettability of a solid surface can be measured by the contact angle of the water droplets attached to it.
    It is one of the most important characteristics to measure the hydrophobicity of a superhydrophobic surface
    .
    For a smooth and flat ideal solid surface, the shape of the water droplet on the surface is determined by the surface tension of the contact line of the solid, liquid and gas.
    The contact angle of the water droplet can be expressed by the classic Young's equation: where: θ is the contact angle when the three phases of gas, solid and liquid are in equilibrium; γ SV is the surface tension between the solid and gas interface; γ SL is the surface tension between the solid and liquid interface; γ LV is the surface tension between the liquid and gas interface
    .
    The contact angle is the result of the balance of surface tension between the solid, liquid, and gas interfaces
    .
    A large surface contact angle indicates that the surface is wettable, and a small contact angle indicates wettability
    .
    Generally, those with contact angles less than 90° are called hydrophilic surfaces, those with contact angles greater than 90° are called hydrophobic surfaces, and those with contact angles greater than 150° are called superhydrophobic surfaces, as shown in Figure 1
    .
    The characteristics of superhydrophobic surface are the main content of surface wettability research, and its application research has been greatly developed in recent years
    .
    Young's equation is a special case on a smooth surface that is supposed to exist.
    When the surface is not smooth but has some roughness, the wettability of the surface will change accordingly
    .
    In recent years, theoretical research on the relationship between surface microstructure and wettability has also been intensified, providing theoretical guidance for the preparation of the best superhydrophobic surface structure.
    The differences in different microstructures such as dense, porous, and micro-nano superhydrophobic surfaces, The water film exhibits different wetting, sliding and rolling behaviors on its surface
    .
    The main factors affecting the wettability of solid surfaces are: surface free energy, surface roughness and surface micro-nano structure
    .
    Studies have shown that the contact angle increases with the decrease of surface free energy and increases with the increase of surface roughness, and the surface micro-nano structure has an important influence on wettability
    .
    Among them, low surface free energy materials are the basic conditions for preparing super-hydrophobic surfaces, and surface roughness and surface micro-nano structure are decisive factors.

    .
    1.
    2 The hydrophobicity of the radome surface and the microwave transmission loss The hydrophobicity of the radome surface is very important, because the transmission loss of an antenna mainly depends on the thickness of the water film on its surface, and the increase in loss is proportional to the thickness of the water film
    .
    If the surface of the radome is not hydrophobic, the thickness of the water film will increase quickly and vary in thickness, and the dielectric constant and loss tangent tan δ of the water are both very large, which will have a great impact on the antenna signal transmission, even causing radar The antenna cannot work; but if the surface of the radome is hydrophobic, according to Cary's surface water film thickness theory analysis, the hydrophobic surface will quickly reach a constant water film thickness regardless of the amount of rainfall.
    This is because the water on the hydrophobic surface becomes spherical and easy It is fluid, not easy to condense and appears to be drier
    .
    The test results also show that with the increase of rainfall, the hydrophobic surface can play a more effective drying effect, so that the surface of the radome is always maintained at a constant water film thickness, which is thin and uniform
    .
    In order to intuitively understand the importance of the hydrophobicity of the radome surface, Figure 2 compares the relationship between a common radome surface and a hydrophobic radome surface under different rainfall, frequency, transmission loss, and noise temperature [2]
    .
    Figure 2 The relationship between rainfall, frequency, transmission loss, and noise temperature.
    It can be seen from the figure that as the frequency increases, the impact of rain is greater; and the greater the rainfall, the super-hydrophobic surface improves the system transmission loss and noise temperature It is also becoming more and more significant
    .
    The hydrophobicity of the radome surface is an important performance that affects the reliability of radar telecommunications in rainy weather
    .
    1.
    3 Weather resistance of the hydrophobic surface The wettability of the hydrophobic surface is not static.
    If the surface hydrophobic material is exposed to atmospheric pollution, mechanical abrasion, or due to ultraviolet radiation, atmospheric environmental corrosion, etc.
    , it is very easy to degrade, and the surface contact angle gradually decreases.
    , Eventually becoming a non-hydrophobic surface, and the transmission loss on the surface of the radome will also increase rapidly
    .
    Hydrophobic materials on solid surfaces are mostly made of polymer materials.
    Strong ultraviolet radiation and rain erosion have the greatest impact on the aging of the materials.
    In harsh environments, the aging speed of the hydrophobic surface is very fast, and it often degenerates into a non-hydrophobic surface in two to three years
    .
    Figure 3 shows that the surface of the radome of a product has been exposed to outdoor exposure for two years, and the surface material has deteriorated to become a non-hydrophobic surface.

    .
    Figure 3 The aging surface of the hydrophobic surface of the radome after two years of outdoor exposure.
    For the radome itself, its base material is made of polymer composite material.
    The base material is also in the harsh environment of high temperature, high humidity and strong radiation.
    Affected by the aging of the environment, the radome without protective measures will soon be powdered and cracked.
    After the matrix resin absorbs water, its wave-transmitting and mechanical properties will gradually decrease
    .
    Therefore, the surface protection performance of the radome must attach great importance to its weather resistance while considering its hydrophobicity
    .
    2 Hydrophobic and weather-resistant surface of the radome The hydrophobicity of the surface of the radome is an important factor affecting the electrical performance of the radar, so the hydrophobicity of the surface of the radome should be considered when designing
    .
    After fully understanding the development status of hydrophobicity on the surface of radome at home and abroad, in recent years we have carried out research on related topics such as "super-hydrophobic weather-resistant coating on composite material surface".
    After a lot of experimental research and engineering applications, the radome has been developed.
    The surface hydrophobic and weather-resistant composite coating technology has been successfully applied to a radome
    .
    Its main key technologies are the development of hydrophobic weather-resistant coatings for radomes and the construction technology of radome hydrophobic coatings
    .
    2.
    1 Hydrophobic weather-resistant coating for radome It can be known from the principle of hydrophobic solid surface that the hydrophobic surface is mainly prepared by reducing the free energy of the material and modifying the micro-nano structure.
    For polymer materials such as radome, the hydrophobic surface is prepared.
    The main solution is to coat a hydrophobic coating with low surface free energy and obtain a rough micro-nano surface structure
    .
    Therefore, the performance of the hydrophobic coating is the main factor that determines the hydrophobicity of the radome surface.
    The preparation of the hydrophobic coating should first choose a resin with low surface free energy, and silicone resin and organic fluorine resin have the lowest surface free energy among known substances
    .
    2.
    1.
    1 Silicone resin Silicone resin generally refers to a polysiloxane with a highly branched structure.
    Its molecular chain has good flexibility and is easily transformed into a structure with lower free energy.
    Therefore, it is compatible with other polymers.
    Relatively lower than its surface free energy, only slightly higher than that of organic fluorine resin
    .
    However, silicone resin coatings generally have disadvantages such as poor adhesion, and can usually be modified with epoxy resin, acrylic resin, and polyurethane resin, which have the advantages of different resins and are more suitable for practical engineering applications.

    .
    2.
    1.
    2 Organic fluorine resin Organic fluorine resin refers to a polymer material containing fluorine atoms in the polymer molecular chain
    .
    Due to the large electronegativity and small diameter of fluorine atoms, it will promote the aggregation effect of carbon atoms on the surface, making the organic fluororesin have very low surface free energy and surface tension
    .
    In addition, the bond energy of the C-F bond is as high as 4602 kJ/mol, which is the highest among the known chemical bonds, so its molecular structure is very stable and not easy to aging and breaking
    .
    Compared with other resins, organic fluorine resins have incomparable advantages in terms of surface hydrophobicity, friction resistance and weather resistance.
    However, they also have disadvantages such as difficulty in film formation, high curing temperature and low adhesion.
    The cost is high
    .
    Usually, the organic fluorine resin is also modified by other resins to be suitable for the actual application of the product
    .
    In recent years, people's research on organic fluororesin has been intensified, and some special materials with new functions have also been coming out
    .
    2.
    1.
    3 Preparation of hydrophobic coatings Silicone resins and organic fluororesins are materials with excellent hydrophobic properties, but a single resin cannot be used to prepare a coating with good comprehensive performance.
    It must be made of two or more resins through physical or chemical The method is modified.
    The performance comparison of several commonly used resins currently applied to the surface of the radome is shown in Table 1 [3, 4]
    .
    Table 1 Comparison of performance of commonly used resins for radome coatings.
    Resin modification is divided into physical and chemical methods.
    The physical method is to mix and stir the two resins directly, but there are disadvantages such as poor dispersion and poor film-forming properties; chemical methods have molecules Link branches and resin copolymerization, etc.
    , coatings have the excellent properties of both resins, and are currently commonly used modification methods
    .
    Resin-modified coatings have been applied to a certain degree in industrialization.
    Coating on the surface of the radome can greatly increase the contact angle of the originally hydrophilic solid surface and have a certain degree of surface hydrophobicity
    .
    In order to further improve the hydrophobicity of the coating, a small amount of nano ultrafine fillers can be added to the modified resin coating, so that the prepared coating has a nano micro-nano structure, and the surface contact angle can be increased to about 130-150° to achieve super-hydrophobicity.
    Effect
    .
    Table 2 shows the experimental results of the influence of the amount of nanofiller added on the contact angle of the coating
    .
    Table 2 Comparison of the performance of commonly used resins for radome coatings.
    From Table 2, it can be seen that the contact angle of the coating increases significantly after the nano-filler is added to the modified resin coating.
    As the amount of nano-filler increases, the contact angle of the coating Increase first and then decrease.
    When the mass fraction of nano-filler is 0.
    4%, the contact angle reaches the maximum
    .
    As the amount of nano-filler continues to increase, the contact angle of the coating decreases.
    This is because the addition of excessive nanoparticles is prone to agglomeration, which reduces the proportion of nano-sized particles and causes the contact angle of the coating to drop
    .
    The selection and modification of the hydrophobic coating on the surface of the radome must also consider the weather resistance, wave permeability and adhesion of the coating.
    At present, common coatings include fluorine-modified polyurethane, fluorine-modified epoxy resin, and silicone-modified polyurethane.
    , And then by adding quantitative nano ultrafine fillers, the hydrophobic properties of the coating can be further improved
    .
    2.
    2 Construction technology of the hydrophobic coating of the radome The supporting construction technology of the hydrophobic weather-resistant coating of the radome is the key technology to ensure that the coating can be applied in engineering, and at the same time to further improve the hydrophobicity, weather resistance and adhesion of the coating.
    Subject experiments and pilot tests have formed the "hydrophobic composite coating technology for radome"
    .
    2.
    2.
    1 Substrate treatment Add a layer of waterproof lubricating film when forming the outer skin of the radome composite material, so that the surface of the radome itself has a certain degree of hydrophobicity and can reduce the water absorption rate of the radome
    .
    In order to enhance the adhesion of the primer, it is necessary to completely remove the release agent on the surface of the radome, and then mechanically polish it to a certain degree of roughness
    .
    2.
    2.
    2 If the primer hydrophobic paint is directly coated on the substrate, its adhesion is difficult to meet the requirements, and it needs to be coated with a primer in the middle.
    Commonly used primers include epoxy resin, acrylic resin and some other resin modifications.
    In order to improve the adhesion and compatibility of the coating, multiple primers can be applied, and the thickness and roughness of each primer are different
    .
    After testing, the binding force of the composite primer with the substrate and the hydrophobic topcoat can meet the requirements of use
    .
    2.
    2.
    3 Hydrophobic topcoat The hydrophobic topcoat should be silicone modified resin coating or fluororesin modified coating
    .
    In order to further improve the surface hydrophobicity, coatings with different roughness can be prepared by controlling the spraying process of the topcoat
    .
    Experiments have shown that controlling different coating viscosity, spraying distance and angle, the hydrophobic properties of the coatings obtained are very different
    .
    Under normal spraying conditions, the surface of the prepared coating is flat and smooth; by changing the spraying process parameters, a slightly rough surface and a certain micro-projection structure can be prepared, and the hydrophobic effect is significantly improved, so as to achieve a super-hydrophobic coating surface The surface contact angle is more than 150°3.
    Compared with foreign countries, the hydrophobicity of the radome surface has been studied for a long time.
    The United States, Japan and the United Kingdom first applied high-hydrophobic coatings to the radome to obtain hydrophobic and aging resistant coatings.
    On the surface, it greatly improves the reliability of telecommunications in rainy days [5]
    .
    At present, foreign technology in the production and construction of high-hydrophobic coatings such as fluorine-containing resins has been quite mature; domestic research on super-hydrophobic coating technology for radomes is rare, and there is no public report
    .
    Figure 4 is the surface of the hydrophobic radome of an American company, Figure 5 is the surface of the super-hydrophobic radome prepared by us, and Figure 6 is the water droplets on the surface of the conventional polyurethane coating
    .
    After measurement, the radome we made has reached a super-hydrophobic surface with a surface contact angle of over 150°, which is close to or reaching the level of similar foreign products
    .
    At present, research on improving the construction process performance, coating adhesion, weather resistance and anti-static properties of the coating is the focus of further work
    .
    4 Conclusion In order to ensure the telecommunications reliability of the radar in all-weather operation, improving the hydrophobicity of the radome surface is an important means to reduce rainwater transmission loss
    .
    Coating a high-hydrophobic and weather-resistant composite protective coating on the surface of the radome can achieve super-hydrophobicity and anti-aging effects, and can prevent accumulation of water and snow and ice.
    The reliability is greatly improved, and it has a good application prospect
    .
    The research and development of super-hydrophobic and weather-resistant coatings on the surface of the radome is an urgent need for products, and it is also the direction of future development
    .
    This article is an English version of an article which is originally in the Chinese language on echemi.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to service@echemi.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

    Contact Us

    The source of this page with content of products and services is from Internet, which doesn't represent ECHEMI's opinion. If you have any queries, please write to service@echemi.com. It will be replied within 5 days.

    Moreover, if you find any instances of plagiarism from the page, please send email to service@echemi.com with relevant evidence.