where E is energy in kcal/mol, λ (the Greek letter lambda) is wavelength in meters, c is 3.00 x 108 m/s (the speed of light), and h is 9.537 x 10-14 kcal•s•mol-1, a number known as Planck’s constant.

W.G.Z. designed the overall research scheme, analyzed the obtained data and revised the manuscript. Y.T.Z. prepared the coating samples, tested the near-infrared spectroscopy and wroted the manuscript. J.L.Z. tested the water contact angle and mechanical properties. Q.F.Z. designed the experimental scheme and characterized the micro-structure.

Latthe, S. S. et al. Self–cleaning superhydrophobic coatings: Potential industrial applications. Prog. Org. Coat. 128, 52–58 (2019).

Ir reflectivitytest

With an instrument called an infrared spectrophotometer, we can 'see' this vibrational transition. In the spectrophotometer, infrared light with frequencies ranging from about 1013 to 1014 Hz is passed though our sample of cyclohexane. Most frequencies pass right through the sample and are recorded by a detector on the other side.

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Creating a composite image with extended depth of field (DOF) involves the intricate process of combining multiple image slices, each with different in-focus ...

Some bonds absorb infrared light more strongly than others, and some bonds do not absorb at all. In order for a vibrational mode to absorb infrared light, it must result in a periodic change in the dipole moment of the molecule. Such vibrations are said to be infrared active. In general, the greater the polarity of the bond, the stronger its IR absorption. The carbonyl bond is very polar, and absorbs very strongly. The carbon-carbon triple bond in most alkynes, in contrast, is much less polar, and thus a stretching vibration does not result in a large change in the overall dipole moment of the molecule. Alkyne groups absorb rather weakly compared to carbonyls.

Organic chemists find it more convenient to deal with wavenumbers rather than wavelengths when discussing infrared spectra.

The microstructure, near-infrared reflectance spectrum, WCA, adhesion strength, flexibility, and impact strength of the coating were studied in this paper. The micro-structure was characterized by scanning electron microscopy (JSM-6510LV, Japan Electronics Corporation, Tokyo, Japan). The near-infrared reflectance spectrum was measured by a UV–VIS-NIR spectrophotometer (UV-3600, Shimadzu Corporation of Japan, Tokyo, Japan). The WCA was measured by a CA measuring instrument (JC2000D7, Shanghai Zhongchen Co., Ltd, Shanghai, China). The adhesion strength of the coating was evaluated by a QFZII adhesion tester (GB 1720-79). The flexibility of the coating was evaluated by a QTY-10A cylindrical bending tester (GB/T 1731-93). The impact strength of the coating was tested by a QCJ impact strength tester (GB/T 1732-93).

The power of infrared spectroscopy arises from the observation that different functional groups have different characteristic absorption frequencies. The carbonyl bond in a ketone, as we saw with our 2-hexanone example, typically absorbs in the range of 5.11 - 5.18 x 1013 Hz, depending on the molecule. The carbon-carbon triple bond of an alkyne, on the other hand, absorbs in the range 6.30 - 6.80 x 1013 Hz. The technique is therefore very useful as a means of identifying which functional groups are present in a molecule of interest. If we pass infrared light through an unknown sample and find that it absorbs in the carbonyl frequency range but not in the alkyne range, we can infer that the molecule contains a carbonyl group but not an alkyne.

Zhang, W., Zhuang, Y. & Zhang, Q. Preparation and properties of multi-color coatings with ultra-low near-infrared reflectivity. Infrared Phys. Technol. 136, 105122 (2024).

Figure 6 displays the WCAs of the coatings with varying total filler additions. It shows that the WCA of the coating increases significantly with the increase in the total filler content. When the total fill content is 10 wt%, the WCA is only 98.5°, indicating a poor hydrophobic effect. This is because the surface of the coating is mainly a resin matrix and relatively thick, preventing the hydrophobic nano-SiO2 from spreading on the surface of the coating, resulting in a low hydrophobicity of the coating. With the increase of the total filler content, the roughness of the coating surface also increases, and the micro-nano rough structural units with mastoid structure characteristics increase significantly, resulting in lower surface energy and larger WCA. When the total filler content is 50 wt%, the coating has a WCA of 152.5°, indicating super-hydrophobic properties.

By adjusting the total filler addition amount, the reflectivity of the coating at 1.06 μm can be modulated between 4.2 and 13.6%, while the WCA can vary from 98.5° to 152.5° based on the graphene to nano-SiO2 mass ratio of 6:4.

Using PDMS-modified APU as a binder and graphene as a near-infrared absorber, a super-hydrophobic ultra-low near-infrared reflectivity PDMS-modified APU/ graphene composite coating with WCA greater than 150° and near-infrared reflectivity of 1.06 μm less than 10% was obtained through coating formulation design and modification technology. The following results are obtained by studying the composition and comprehensive properties of the coating:

The inverted peaks observed in the spectra correspond to molecular stretching and bending vibrations that only occur at certain quantized frequencies. When infrared radiation matching these frequencies falls on the molecule, the molecule absorbs energy and becomes excited. Eventually the molecule returns to its original (ground) state, and the energy which was absorbed is released as heat.

Some kinds of vibrations are infrared inactive. The stretching vibrations of completely symmetrical double and triple bonds, for example, do not result in a change in dipole moment, and therefore do not result in any absorption of light (but other bonds and vibrational modes in these molecules do absorb IR light).

Ir reflectivityformula

Han, P., Huang, X. & Zhang, Q. Laser stealth absorbent of samarium oxysulfide prepared by flux method. Rare Metals 30, 616–620 (2011).

Because electromagnetic radiation travels at a constant speed, each wavelength corresponds to a given frequency, which is the number of times per second that a crest passes a given point. Longer waves have lower frequencies, and shorter waves have higher frequencies. Frequency is commonly reported in hertz (Hz), meaning ‘cycles per second’, or ‘waves per second’. The standard unit for frequency is s-1.

American Polarizers manufactures polarized and non-polarized optical products that are used for scientific and medical instrumentation.

Nine, M. J., Tung, T. T., Alotaibi, F., Tran, D. N. H. & Losic, D. Facile adhesion-tuning of superhydrophobic surfaces between “lotus” and “petal” effect and their influence on icing and deicing properties. ACS Appl. Mater. Interfaces 9, 8393–8402 (2017).

Our 5.15 x 1013 Hz carbonyl stretching frequency, however, is absorbed by the 2-hexanone sample, and so the detector records that the intensity of this frequency, after having passed through the sample, is something less than 100% of its initial intensity.

Ir reflectivityvs emissivity

Ba, M., Zhang, Z. & Qi, Y. The dispersion tolerance of micro/nano particle in polydimethylsiloxane and its influence on the properties of fouling release coatings based on polydimethylsiloxane. Coatings 7, 7070107 (2017).

The value of ΔE - the energy difference between the low energy (ground) and high energy (excited) vibrational states - is equal to 4.91 kcal/mol, the same as the energy associated with the absorbed light frequency. The molecule does not remain in its excited vibrational state for very long, but quickly releases energy to the surrounding environment in form of heat, and returns to the ground state.

Figure 8 shows SEM images of the coatings prepared under the following conditions: curing temperature of 120 °C, mass ratio of APU to PDMS of 4:6, mass ratio of graphene to nano-SiO2 of 6:4, total filler addition of 40 wt%, and KH560 addition of resin mass of 0 wt%, 4 wt%, and 8 wt% According to the morphology of the coating surface, the addition of KH560 has little effect on the micro-structure of the coating. The resin in the coating is evenly mixed with graphene and nano-SiO2 under different KH560 dosages, the resin layer thickness is suitable, and the graphene is evenly dispersed in the coating. Uniform and slightly agglomerated nano-SiO2 particles can be seen on the surface of the coating, their arrangement is regular, and the structure is tight, leading to a clear micro-nano rough structure.

Zhang, K., Yang, X., Zhu, N., Wang, Z. C. & Yan, H. Environmentally benign paints for superhydrophobic coatings. Colloid Polym. Sci. 295, 709–714 (2017).

With further use of KH560 modified coating, the WCA and 1.06 μm near-infrared reflectivity showed limited changes, but the impact strength of the coating increased significantly from 15 to 50 kg × cm.

Figure 13 shows the WCAs of the coatings with varying mAPU:mPDMS ratios of 1:9, 3:7, 4:6, and 5:5. As shown in the figure, the smaller the mass ratio of APU to PDMS, the larger the WCA of the coating. When the mAPU:mPDMS ratio is 1:9, the coating exhibits a WCA of 158° and excellent super-hydrophobic properties. This occurs because PDMS, the main adhesive in the coating, consists mainly of a large number of non-polar silicon-oxygen-silicon bonds, which results in a very low surface energy. Consequently, the coating also has a very low surface energy, thereby optimizing its hydrophobic properties. As the mass ratio of APU to PDMS gradually increases, the absolute content of PDMS decreases, which reduces the organic content that can reduce the surface energy of the coating. Additionally, the APU utilized acrylic-modified polyurethane, which contains numerous robust polar groups such as hydroxyl and ether bonds that can establish hydrogen bonds with water molecules, enhancing the coating’s wettability. As the mass ratio of APU to PDMS increases, so does the content of APU in the coating, and the wetting effect of the coating on water improves, reducing the WCA of the coating.

Table 1 displays the adhesion strength, flexibility, and impact strength of the coatings at various mGr:mnano-SiO2 ratios. The adhesion strength, flexibility, and impact strength of the coating are affected by varying mass ratios of graphene and nano-SiO2. Overall, the mechanical characteristics of the coating improved as the mGr:mnano-SiO2 ratio increased. When mGr:mnano-SiO2 = 4:6, the coating demonstrated poor adhesion strength, flexibility, and impact resistance. The reason for this phenomenon is that when the nano-SiO2 content is high in the coating, the resin matrix cannot completely cover the filler particles, resulting in ineffective formation of the coating. Furthermore, the coating contains a significant amount of micro-pores, leading to the presence of a weaker boundary layer within the coating, ultimately resulting in poor mechanical properties28,29. As mGr:mnano-SiO2 increases, the special planar network structure, the coordination relationship between carbon atoms, and the special chemical bonding properties of graphene enhance the chemical bonding energy between the resin matrix and the filler. Consequently, greater force is required to damage the coating structure. As a result, the coating’s mechanical properties are gradually enhanced30,31. Considering the near-infrared absorption properties, hydrophobic properties, and mechanical properties of the coating, the optimum mass ratio of graphene to nano-SiO2 in the coating is determined to be 6:4.

The angle plates come in heights up to 670mm/26". They can be used with most Isel Automation slides, gantries and aluminum extrusions to fixture and mount.

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Table 2 shows the adhesion strength, flexibility, and impact strength of the coatings under different proportions of total fillers. It shows that the adhesion strength is reduced from grade 1 with a total filler volume of 10 wt% to grade 2 with a total filler volume of 50 wt%, and the flexibility is reduced from 3 mm with a total filler volume of 10 wt% to 8 mm with a total filler volume of 50 wt%. The impact strength decreased from 40 kg × cm with a total packing volume of 10 wt% to 5 kg × cm with a total packing volume of 50 wt%. This phenomenon is primarily due to the fact that the polyurethane resin contains strong reactive polar groups, such as isocyanate groups, which can form a good interface bond with the filler. When the total filler is only 10 wt%, the content of polyurethane resin is higher, and it has a strong binding force on the filler, resulting in the coating having excellent mechanical properties under these conditions. However, because the resin used in the coating contains PDMS with low surface energy, its binding to the filler is weak, resulting in suboptimal flexibility and impact strength of the coating when the total filler content is low. As the proportion of total filler increases, the content of resin decreases, as does the wrapping strength of resin on the filler and the corresponding binding force. Considering the near-infrared absorption, hydrophobic, and mechanical properties of the coating, the proportion of total fillers in the coating is determined to be 40 wt%.

Infrared wavelength

Chai, X. et al. Silver-modified chromium(III) oxide as multi-band compatible stealth materials for visual/infrared stealth and radar wave transmission. Compos. Sci. Technol. 216, 109038 (2021).

Ge, Z., Ren, H., Fu, S. & Chen, S. Synergistic effects of zwitterionic segments and a silane coupling agent on zwitterionic shape memory polyurethanes. RSC Adv. 7, 42320–42328 (2017).

Lin, Y., Liao, Y., Chen, Z. & Connell, J. W. Holey graphene: A unique structural derivative of graphene. Mater. Res. Lett. 5, 209–234 (2017).

You will obtain infrared spectra for a number of the compounds you will synthesize in the laboratory component of this course.

If our ketone sample is irradiated with infrared light, the carbonyl bond will specifically absorb light with this same frequency, which by equations 4.1 and 4.2 corresponds to a wavelength of 5.83 x 10-6 m and an energy of 4.91 kcal/mol. When the carbonyl bond absorbs this energy, it jumps up to an excited vibrational state.

Radiometer definition: an instrument for demonstrating the transformation of radiant energy into mechanical work, consisting of an exhausted glass vessel ...

The SEM images of the coatings prepared by mGr:mnano-SiO2 at 4:6, 6:4, and 8:2 are shown in Fig. 2 when mAPU:mPDMS is 4:6 and the total filler amount is 30 wt%. The surface micro-structure of the coating varies significantly depending on the mass ratios of graphene to nano-SiO2. When the mass ratio of graphene to nano-SiO2 increases, the surface particle characteristics formed by nano-SiO2 agglomeration significantly weaken, the lamellar structure characteristics of multilayer graphene enhance, and the coating surface becomes more compact. When mGr:mnano-SiO2 is 4:6, the flake graphene is evenly divided into the resin and nano-SiO2, and a large amount of nano-SiO2 is distributed on the surface of the coating, leading to a rough surface texture with a surface roughness of 2–6 μm. When mGr:mnano-SiO2 is 6:4, its dispersion in the resin matrix is more uniform due to the large specific surface area of graphene and its good compatibility with APU-modified PDMS25,26. This reduces the surface roughness of the coating and increases its regularity. When mGr:mnano-SiO2 is 8:2, the graphene content is more, the nano-SiO2 content is less, and the graphene is fully dispersed in the resin, the coating surface structure is dense, and the rough structure is almost eliminated.

Just like ocean waves, electromagnetic waves travel in a defined direction. While the speed of ocean waves can vary, however, the speed of electromagnetic waves – commonly referred to as the speed of light – is essentially a constant, approximately 300 million meters per second. This is true whether we are talking about gamma radiation or visible light. Obviously, there is a big difference between these two types of waves – we are surrounded by the latter for more than half of our time on earth, whereas we hopefully never become exposed to the former to any significant degree. The different properties of the various types of electromagnetic radiation are due to differences in their wavelengths, and the corresponding differences in their energies: shorter wavelengths correspond to higher energy.

Zhang, W., Zhuang, Y., Zhang, J. et al. Preparation and performance control of ultra-low near-infrared reflectivity coatings with super-hydrophobic and outstanding mechanical properties. Sci Rep 14, 20059 (2024). https://doi.org/10.1038/s41598-024-71164-1

The reflectivity of the coating at 1.06 μm can be varied from 6.4 to 8.4% and the WCA from 138.5° to 149.5° by modifying the mass ratio of graphene to nano-SiO2.

Zhang, J., Zhang, W., Guan, Q., Li, X. & Lv, D. Preparation and properties of epoxy resin and polyurethane blend resin-based low-infrared-emissivity coatings. Coatings 12, 12111708 (2022).

Bai, S., Guan, X., Li, H. & Ou, J. Effect of the specific surface area of nano-silica particle on the properties of cement paste. Powder Technol. 392, 680–689 (2021).

Visible light has a wavelength range of about 400-700 nm. What is the corresponding frequency range? What is the corresponding energy range, in kcal/mol of photons?

Under the optimal formulation and modified conditions, the coating simultaneously meets the design requirements of 1.06 μm ultra-low near-infrared reflectivity (9.3%), super-hydrophobicity (WCA 152°), and outstanding mechanical properties (adhesion strength grade 2, flexibility 3 mm, impact strength 50 kg × cm). The coating has enormous potential for use in high-performance laser stealth materials.

Covalent bonds in organic molecules are not rigid sticks – rather, they behave more like springs. At room temperature, organic molecules are always in motion, as their bonds stretch, bend, and twist. These complex vibrations can be broken down mathematically into individual vibrational modes, a few of which are illustrated below.

The vibrations of a 2-hexanone molecule are not, of course, limited to the simple stretching of the carbonyl bond. The various carbon-carbon bonds also stretch and bend, as do the carbon-hydrogen bonds, and all of these vibrational modes also absorb different frequencies of infrared light.

Figure 5 shows SEM images of the coatings prepared under the curing temperature of 120 °C, APU to PDMS mass ratio of 4:6, graphene to nano-SiO2 mass ratio of 6:4, and total filler amount of 10 wt%, 30 wt%, 40 wt%, and 50 wt%. It shows that the roughness of the coating surface increases with total filler content. At the total filler amount of 50 wt%, the surface roughness of the coating can reach 3–8 μm. In addition, the surface porosity of the coating increases while its density decreases. When the filler content in the coating is 10 wt%, the composite fillers composed of graphene and nano-SiO2 are scattered throughout the coating and cannot cover the entire coating, there are more resins between the functional fillers, and the surface is very smooth. As the composite filler content increased to 30 wt%, the density of graphene and nano-SiO2 distributed in the coating increased significantly, but the coating still had a large and thick resin matrix. When the total filler content reaches 40 wt%, a significant number of micro-nano rough structural units composed of nano-SiO2 and resin matrix develop on the coating surface. These rough structural units enhance the coating’s wetting resistance, leading to improved hydrophobic performance. In addition, as the amount of composite fillers in the coating increases, the content of graphene also increases and becomes more evenly dispersed in the resin and nano-SiO2. This increased dispersion improves the coating’s ability to absorb incident near-infrared light, resulting in relatively low reflectivity at 1.06 μm, thereby meeting the requirements of laser stealth. When the coating contains an excessive amount of composite fillers (Fig. 5d, h), the nano-SiO2 particles push out each other, increasing the surface roughness of the coating and causing a large number of pores to appear, significantly weakening the mechanical properties of the coating.

The LibreTexts libraries are Powered by NICE CXone Expert and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Legal. Accessibility Statement For more information contact us at info@libretexts.org.

polarize · ​[intransitive, transitive] to separate or make people separate into two groups with completely opposite opinions. Public opinion has polarized on ...

Alexander, S., Eastoe, J., Lord, A. M., Guittard, F. & Barron, A. R. Branched hydrocarbon low surface energy materials for superhydrophobic nanoparticle derived surfaces. ACS Appl. Mater. Interfaces 8, 660–666 (2015).

Rasitha, T. P., Krishna, N. G., Anandkumar, B., Vanithakumari, S. C. & Philip, J. A comprehensive review on anticorrosive/antifouling superhydrophobic coatings: Fabrication, assessment, applications, challenges and future perspectives. Adv. Colloid Interface 324, 103090 (2024).

Notice in the figure above that visible light takes up just a narrow band of the full spectrum. White light from the sun or a light bulb is a mixture of all of the visible wavelengths. You see the visible region of the electromagnetic spectrum divided into its different wavelengths every time you see a rainbow: violet light has the shortest wavelength, and red light has the longest.

12.6: Infrared Spectroscopy is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

Figure 14 shows the near-infrared reflectance spectra of the coatings with varying mAPU:mPDMS ratios. The coating has minimal effect on the reflectivity of 1.06 μm near-infrared light at various APU to PDMS mass ratios. The result shows that the adhesive has little effect on the laser stealth effect of the coating, and that graphene, as a near-infrared absorber, is the core factor that determines the ultra-low near-infrared reflectivity of the coating. Firstly, the stoichiometric numbers of graphene and nano-SiO2 decreased with the increase of the mass ratio of APU to PDMS in the coating formulation, but the value change was only 0.04%, indicating that the change in graphene content had little effect on the composition of the whole formulation. Secondly, the change of mAPU:mPDMS has very little effect on the micro-structure of the coating. Although the graphene content in the coating decreases slightly with the increase of mAPU:mPDMS, its near-infrared reflectivity at 1.06 μm remains approximately 10%, maintaining outstanding laser stealth performance.

The above materials have made remarkable progress in single super-hydrophobic performance and the functional characteristics of various stealth materials. Han et al. prepared samarium oxysulfide using the flux method, which has a low reflectivity at 1064 nm19. Chai et al.20 prepared a multi-band compatible stealth material by modifying Cr2O3 with silver and colored pigments with low emissivity materials. In the early stage of their research, a multi-spectrum compatible coating with an infrared emissivity of 0.506 and 1.06 μm near-infrared reflectivity of 41.6% was prepared using the glass rod scraping method21. In addition, this research group has also developed earth yellow and medium green ultra-low near-infrared reflectivity coatings22. The effective stealth capabilities of the material rely not just on the functional properties of the filler, but also on the presence of polar bonds between the resin matrix and the filler. These bonds create a robust interface bond and enhance the material’s micro-structure, facilitating the enhancement of its functional properties23,24. Improving the micro-interface structure and surface energy of materials is the primary focus and challenge of this project. Overcoming this issue is of great significance for achieving good super-hydrophobic and mechanical properties of stealth materials.

Su, H. et al. Lotus leaf-like Ni-decorated SiC with combined superhydrophobicity and enhanced microwave absorption performance. Colloid Surface A 650, 129602 (2022).

After polishing the tinplate substrate with 360-mesh sandpaper, wipe the surface of the substrate with anhydrous ethanol, and put it aside for half an hour. The modified resin was obtained by the blending modification method. APU and PDMS with a mass ratio of 4:6 were first weighed in a clean disposable plastic cup and thoroughly stirred with a glass rod to obtain the blended APU with PDMS. Then, the total filler was set to 30 wt%, with varying mass ratios (4:6, 5:5, 6:4, 7:3, and 8:2) of graphene to nano-SiO2 composite filler mixed with the above-modified resin, and an appropriate amount of diluent was added to adjust viscosity. The mixture was then subjected to an ultrasonic wave of 50 W for 5 min to ensure that the resin matrix and the functional filler were thoroughly mixed, resulting in the fine dispersion of the paint. No obvious particles could be seen in the paint, and the paint had good fluidity. A certain amount of APU curing agent and PDMS curing agent was added according to the fixed ratio, and the paint product was obtained after evenly mixing. Subsequently, the paint was uniformly applied to the tinplate surface using the glass rod scraping coating method. The coating was allowed to dry at room temperature for 6 h before baking in an oven at 120 °C for 3 h to produce the coating sample for testing. The appropriate mass ratio of graphene and nano-SiO2 was determined based on the near-infrared reflectivity, WCA, and mechanical properties of the coating. Using the same coating preparation method, based on the best mass ratio of graphene to nano-SiO2, the effects of total filler additions (10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt%), KH560 content (0 wt%, 2 wt%, 4 wt%, 6 wt%, and 8 wt%), the mass ratio of APU to PDMS (1:9, 2:8, 3:7, 4:6, and 5:5), and DOP content (0 wt%, 1 wt%, 3 wt%, 5 wt%, and 7 wt%) on the properties of the coating were studied. Finally, a super-hydrophobic ultra-low near-infrared reflectivity coating with good flexibility, excellent adhesion strength, and impact strength was obtained. The coating preparation process is shown in Fig. 1.

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Table 5 shows the adhesion strength, flexibility, and impact strength of the coatings with different DOP additions. It can be seen that the addition of DOP significantly improved the flexibility of the coating, from the original 4 mm without DOP to 2 mm (optimal flexibility) when the DOP addition is 5 wt%. The addition of KH560 has maintained the impact strength of the coating at its best, DOP has not influenced the adhesion strength of the coating, which remains at grade 2. The primary factor is that the DOP molecular structure consists of polar ester groups and non-polar carbon chains, facilitating their insertion into the resin molecular chains. This action reduces the inter-molecular force of the resin, the degree of cross-linking between the resin chains after curing, and the brittleness of the coating, thereby greatly enhancing the flexibility of the coating. Based on the above consideration, it is determined that the DOP addition amount is 1 wt%. The optimal DOP addition results in a coating with 9.3% near-infrared reflectivity, 152° WCA, grade 2 adhesion strength, 3 mm flexibility, and 50 kg × cm impact strength. The coating meets the design requirements of ultra-low near-infrared reflectivity, super-hydrophobicity, and outstanding mechanical properties.

Meng, S. et al. Preparation and properties of high abrasion resistant superhydrophobic coating on the PCB. Colloid Surface A 689, 133674 (2024).

In this study, the glass rod scraping coating method was used to prepare composite coatings with APU as an adhesive, PDMS as a blend modifier, graphene as a near-infrared absorber, and nano-SiO2 as a modified filler for rough surface structure. Graphene was introduced into the coating to achieve ultra-low near-infrared reflectance, nano-SiO2 to achieve super-hydrophobic performance, and interface modifiers such as KH560 and DOP to optimize the coating’s overall performance. The reflectivity at the wavelength of 1.06 μm and the WCA of the coatings were systematically studied. The effects of the amount of graphene, nano-SiO2, APU, PDMS, KH560, and DOP on the micro-structure, mechanical properties, WCA, and 1.06 μm near-infrared reflectivity of the coatings are discussed in detail. The prepared super-hydrophobic and ultra-low near-infrared reflectivity coatings have a wide range of potential applications in various laser stealth equipment.

Permeh, S., Lau, K. & Duncan, M. Degradation of coatings for steel in environments susceptible to corrosion associated with fouling. Struct. Infrastruct. E. 16, 1186–1200 (2019).

Zhou, Y. et al. Robust superhydrophobic surface based on multiple hybrid coatings for application in corrosion protection. ACS Appl. Mater. Interfaces 11, 6512–6526 (2019).

Figure 7 shows the near-infrared reflectance spectra of the coatings with varying total filler additions. The reflectivity of the coating at 1.06 μm decreases from 7.7% with a total filler addition of 10 wt% to 4.2% with a total filler addition of 20 wt% and then increases to 13.6% with a total filler addition of 50 wt%. The reason for this phenomenon is that graphene has excellent near-infrared absorption properties21,22. Even with a total filler proportion of only 10 wt%, a small amount of uniformly dispersed graphene in the coating can still efficiently absorb near-infrared light. This reduces the coating’s reflectivity at 1.06 μm to as low as 7.7%. When the proportion of total filler increased to 20 wt%, the absolute content of graphene in the coating also increased and remained evenly dispersed. This enhanced the coating’s absorption of near-infrared light and reduced reflectivity to as low as 4.2% at 1.06 μm. However, as the total filler content increased, the reflectivity of the coating to near-infrared light increased. The primary factor is that as the total filler amount in the coating continues to rise, so does the absolute content of nano-SiO2, which not only has no absorption effect on near-infrared light, but also has a certain reflection effect. In addition, when the proportion of total filler is too large, it will not only increase the gap on the surface of the coating, but also easily cause a large number of nano-SiO2 to gather on the surface of the coating and weaken the absorption of the coating to near-infrared light. When the total filler content is too high, the near-infrared light absorption of the coating is reduced due to the combined action of the above factors.

Figure 16 shows the WCAs of the coatings with DOP additions of 0 wt%, 1 wt%, and 3 wt%. It can be seen that DOP has a certain wetting effect on the coating, as the WCA of the coating decreases from 155° when DOP is not added to the coating to 149° when 3 wt% is added. The reason for this change could be that the addition of DOP introduces some polar ester groups, which increases the surface energy of the coating and thus reduces the WCA. However, even with a 1 wt% DOP addition, the coating maintains a good super-hydrophobic property, with a WCA 152°.

Anitha, C., Azim, S. S. & Mayavan, S. Salvinia inspired fluroine free superhydrophobic coatings. Appl. Surf. Sci. 449, 250–260 (2018).

Ir reflectivitypdf

When talking about electromagnetic waves, we can refer either to wavelength or to frequency - the two values are interconverted using the simple expression:

Let's take 2-hexanone as an example. Picture the carbonyl bond of the ketone group as a spring. This spring is constantly bouncing back and forth, stretching and compressing, pushing the carbon and oxygen atoms further apart and then pulling them together. This is the stretching mode of the carbonyl bond. In the space of one second, the spring 'bounces' back and forth 5.15 x 1013 times - in other words, the ground-state frequency of carbonyl stretching for a the ketone group is about 5.15 x 1013 Hz.

Figure 3 shows the WCAs of the coatings with varying mGr:mnano-SiO2 of 4:6, 6:4, and 8:2. It can be seen that as the mass ratio of graphene to nano-SiO2 increases the micro-nano rough structure and the WCA decreases. When mGr:mnano-SiO2 is 4:6, the WCA reaches 149.5°, owing to the extensive distribution of nano-SiO2 on the coating surface. There are more mastoid-shaped micro-nano rough structural units constructed by resin matrix and nano-SiO2 on the surface. A large number of mastoid-shaped micro-nano rough structures will increase the contact between the liquid phase and gas phase, thereby increasing the WCA between solid and liquid27. When mGr:mnano-SiO2 is 6:4, the roughness of the coating surface is reduced, and the high specific surface area of graphene increases the surface energy of the coating, thus reducing the WCA.

Shi, S. H. et al. Lightweight Zn-Philic 3D-Cu scaffold for customizable zinc ion batteries. Adv. Funct. Mater. 34, 2312664 (2024).

Figure 12 shows SEM images of the coatings prepared under the following conditions: mGr:mnano-SiO2 of 6:4, total filler addition of 40 wt%, KH560 addition of 4 wt%, and mass ratios of APU to PDMS of 1:9, 3:7, 4:6, and 5:5. As can be seen in Fig. 10a, a large mass ratio difference between APU and PDMS results in uneven local coating thickness, disordered and irregular distribution of nano-SiO2, and a coating surface with large voids and high roughness. As mAPU:mPDMS increases (Fig. 12b, c, d), the nano-SiO2 in the coating becomes denser and more evenly distributed, and the graphene is also evenly dispersed, which makes the coating surface more regular and compact.

Notice that the scale at the bottom of the infrared spectrum for 2-hexanone shown is calibrated in wavenumbers (cm−1). A wavenumber is the reciprocal of a wavelength (1/λ); thus, a wavenumber of 1600 cm−1 corresponds to a wavelength of

Super-hydrophobic functional materials with a WCA greater than 150° have excellent waterproof, anti-fouling, anti-corrosion, and self-cleaning properties, and have a wide range of applications5,6,7,8. The resistance of solids to wetting is primarily determined by the interplay between the surface roughness structure and the presence of low surface energy materials9,10,11. Research has demonstrated that creating micro-nano rough structures on the surface of low-surface energy materials can enhance air contact and promote the formation of additional gas–liquid interfaces. This leads to a notable increase in the contact angle between the liquid and solid surfaces12,13. However, materials with high roughness and low surface energy often have poor binding with the substrate, making it difficult to meet the mechanical properties requirements of super-hydrophobic materials in practical applications. To resolve this issue, numerous efforts have been made to transform hydrophilic materials into super-hydrophobic materials. Meng et al. used air injection to combine the uncured PDMS adhesive with SiO2 to prepare a hydrophobic coating that can be successfully applied on the circuit board14. Zhang et al. synthesized an aqueous super-hydrophobic coating with a concentration of 42% in a mixed solvent of ethanol and water using an appropriate amount of nano-SiO2 and PVP protective polymer as the main raw materials15. C. Anitha added metal silicate, nano-SiO2, nano-TiO2, and aluminum stearate into silicone resin to prepare a super-hydrophobic coating with outstanding performance using the spraying method16. In addition, due to its unique micro-structure, graphene has distinctive photoelectromagnetic properties, which have important applications in the field of water zinc-ion batteries and electromagnetic interference shielding17,18.

Shi, S. H. et al. 3D-printed carbon-based conformal electromagnetic interference shielding module for integrated electronics. Nano-Micro Lett. 16, 85 (2024).

Figure 9 shows the WCAs of the coatings prepared with the addition of KH560 at 0 wt%, 4 wt%, and 8 wt% of the resin mass. It shows that the WCA can be increased from 149° without adding KH560 to 153° when adding 4 wt%, resulting in a coating with super-hydrophobic properties. As the amount of KH560 added to the coating increases, the influence of the coating’s WCA is minimal. The reason is that the silico-oxygen bond in KH560 can chemically react with the hydroxyl group on the surface of the inorganic material, forming a hydrophobic Si–O–Si group. This reaction lowers the surface energy of the coating, further enhancing its hydrophobic properties32. The specific action mechanism and process are shown in Fig. 10.

Zhuang, Y., Zhang, W. & Zhang, Q. Preparation and characterization of high-performance composite coatings compatible with near-infrared low reflectivity and low infrared emissivity. Coatings 13, 13122033 (2023).

The energy of molecular vibration is quantized rather than continuous, meaning that a molecule can only stretch and bend at certain 'allowed' frequencies. If a molecule is exposed to electromagnetic radiation that matches the frequency of one of its vibrational modes, it will in most cases absorb energy from the radiation and jump to a higher vibrational energy state - what this means is that the amplitude of the vibration will increase, but the vibrational frequency will remain the same. The difference in energy between the two vibrational states is equal to the energy associated with the wavelength of radiation that was absorbed. It turns out that it is the infrared region of the electromagnetic spectrum which contains frequencies corresponding to the vibrational frequencies of organic bonds.

Rauner, N. et al. A coating that combines lotus-effect and contact-active antimicrobial properties on silicone. Adv. Funct. Mater. 28, 1801248 (2018).

Optics: : [op-tiks] - noun ... A branch of physics that studies electromagnetic radiation (for example, light and infrared radiation), its interactions with ...

Figure 4 displays the near-infrared reflectance spectra of the coatings at various mass ratios of graphene to nano-SiO2. The near-infrared reflectivity of coatings with the same total filler addition amount is lower than 10% in the tested near-infrared range. Moreover, the reflectivity of the coating gradually decreases with the increase of mGr:mnano-SiO2. The near-infrared reflectance at 1.06 μm decreases from 8.4% at mGr:mnano-SiO2 = 4:6 to 6.4% at mGr:mnano-SiO2 = 8:2. The reduction of nano-SiO2 content causes the coating surface to become more regular. In addition, the graphene microstructure is composed of a large number of benzene ring structures, and it has an extremely long and complex conjugated system. Therefore, it strongly absorbs near-infrared light, and its incorporation into the coating can achieve ultra-low near-infrared reflectivity. Additionally, as the graphene content increases, it becomes fully dispersed in the resin matrix, resulting in better coverage of the nano-SiO2 particles. This enables the coating to efficiently absorb near-infrared light and reduce near-infrared reflectivity.

Emissivity andreflectivityformula

The development of ultra-low near-infrared reflectivity coatings with outstanding engineering properties remains a challenge in laser stealth materials research. Herein, we reported a laser stealth coating with outstanding mechanical properties, super-hydrophobicity, and an ultra-low near-infrared reflectivity for 1.06 μm wavelength. The effects of the mass ratio of graphene to nano-SiO2, the proportion of total filler, the addition of KH560, the mass ratio of Polydimethylsiloxane (PDMS) to acrylic-modified polyurethane (APU), and the addition of dioctyl phthalate (DOP) on the coating properties were thoroughly discussed. The coating can achieve a low reflectivity of 9.3% at 1.06 μm and a high water contact angle of 152° at a mass ratio of 7:3 for PDMS to APU and 6:4 for graphene to nano-SiO2 with a total filler amount of 40 wt%. KH560 can play a bridging role between the blended resin matrix and nano-SiO2, which can significantly improve the impact strength of the coating. The DOP, which contains a polar ester group and a non-polar carbon chain structure, can be inserted between the molecular chains of the resin to weaken the intermolecular force of the resin, so that the flexibility of the coating can be significantly improved. Adding KH560 at 4 wt% and DOP at 1 wt%, resulted in a coating with ultra-low near-infrared reflectivity of 1.06 μm (9.3%), super-hydrophobic properties, outstanding adhesion strength (grade 2), flexibility (2 mm), and impact strength (50 kg cm). The above super-hydrophobic ultra-low near-infrared reflectivity coating has significant potential for use in the field of laser stealth equipment, and it can serve as a useful reference for optimizing the mechanical properties of super-hydrophobic functional coatings.

The hydrophobic and mechanical properties of the coating can be significantly improved by adjusting the mass ratio of APU to PDMS, but the effect on the near-infrared reflectivity of the coating is limited.

where ν (the Greek letter ‘nu’) is frequency in s-1. Visible red light with a wavelength of 700 nm, for example, has a frequency of 4.29 x 1014 Hz, and an energy of 40.9 kcal per mole of photons.

Figure 15 shows SEM images of the coatings prepared with DOP additions of 0 wt%, 1 wt%, and 3 wt% under the conditions of mAPU:mPDMS of 3:7, mGr:Mnano-SiO2 of 6:4, the total filler addition amount of 40 wt%, and the KH560 addition amount of 4 wt%. It can be seen that the DOP-modified coating has little effect on the surface micro-structure of the coating. Without or with a small amount of DOP, the graphene in the coating is uniformly dispersed, and the nano-SiO2 is widely distributed, neatly arranged and compact. The bonding between the filler and the resin is appropriate, and the resin thickness is consistent. The size and arrangement of rough structural units on the surface of the coating are uniform.

EFFILUX designs and manufactures LED Lighting products for industrial vision and optical measurement systems. EFFILUX offers several ranges of led light..

emissivity +reflectivity= 1

This work was financially supported by the National Natural Science Foundation of China (61705029) and Key Project of Scientific Research Plan of Higher Education in Anhui Province (2022AH051121).

Li, W. et al. The effects of interfacial water and SiO2 surface wettability on the adhesion properties of SiO2 in epoxy nanocomposites. Appl. Surf. Sci. 502, 144151 (2020).

Yang, G., Li, L., Lee, W. B. & Ng, M. C. Structure of graphene and its disorders: A review. Sci. Technol. Adv. Mat. 19, 613–648 (2018).

With the rapid advancement of modern military technology, the requirement of stealth coating on all kinds of equipment is increasing. Because the coating surface is exposed to the complex battlefield environment rich in dust and other pollutants for an extended period of time, the coating’s stealth performance, adhesion strength, flexibility, impact strength, and appearance are damaged. In particular, the gradual loss of stealth effect may result in serious battlefield security issues for weapons and equipment1,2. According to the ‘lotus effect’, the hydrophobicity of the coating can be improved3,4, which can spontaneously clean the surface pollutants to effectively improve the service life of the stealth coating. Therefore, when designing stealth coatings, it is necessary to consider the effective compatibility of the stealth effect and super-hydrophobic properties.

Liu, J., Wang, X., Li, H. & Yang, W. Delamination mechanism maps for coatings/substrates system subjected to adhesive contact loads. Thin Solid Films 626, 159–167 (2017).

Latthe, S. S. et al. Recent developments in air-trapped superhydrophobic and liquid-infused slippery surfaces for anti-icing application. Prog. Org. Coat. 137, 105373 (2019).

There are a number of things that need to be explained in order for you to understand what it is that we are looking at. On the horizontal axis we see IR wavelengths expressed in terms of a unit called wavenumber (cm-1), which tells us how many waves fit into one centimeter. On the vertical axis we see ‘% transmittance’, which tells us how strongly light was absorbed at each frequency (100% transmittance means no absorption occurred at that frequency). The solid line traces the values of % transmittance for every wavelength – the ‘peaks’ (which are actually pointing down) show regions of strong absorption. For some reason, it is typical in IR spectroscopy to report wavenumber values rather than wavelength (in meters) or frequency (in Hz). The ‘upside down’ vertical axis, with absorbance peaks pointing down rather than up, is also a curious convention in IR spectroscopy. We wouldn’t want to make things too easy for you!

Hoshian, S., Jokinen, V., Somerkivi, V., Lokanathan, A. R. & Franssila, S. Robust superhydrophobic silicon without a low surface-energy hydrophobic coating. ACS Appl. Mater. Interfaces 7, 941–949 (2014).

Malekkhouyan, R. et al. The influence of size and healing content on the performance of extrinsic self-healing coatings. J. Appl. Polym. Sci. 138, 49964 (2020).

By introducing DOP into the coating, the flexibility of the coating can be significantly improved while maintaining its ultra-low near-infrared reflectivity and super-hydrophobic properties.

The notion that electromagnetic radiation contains a quantifiable amount of energy can perhaps be better understood if we talk about light as a stream of particles, called photons, rather than as a wave. (Recall the concept known as ‘wave-particle duality’: at the quantum level, wave behavior and particle behavior become indistinguishable, and very small particles have an observable ‘wavelength’). If we describe light as a stream of photons, the energy of a particular wavelength can be expressed as:

Wu, H., Zhu, L. N., Yue, W., Fu, Z. Q. & Kang, J. J. Wear-resistant and hydrophobic characteristics of PTFE/CF composite coatings. Prog. Org. Coat. 128, 90–98 (2019).

Rahman, M. K. et al. High-efficiency electrospray deposition method for nonconductive substrates: Applications of superhydrophobic coatings. ACS Appl. Mater. Interfaces 13, 18227–18236 (2021).

Figure 17 shows the near-infrared reflectance spectra of the coatings with varying DOP additions. The addition of DOP has a slightly positive impact on the absorption of the coating at 1.06 μm near-infrared light, but the resulting change in reflectivity is only 1.356%. The unique molecular structure of DOP contains both polar ester groups and non-polar carbon chains, which enables easy insertion into the resin’s molecular chain. This weakens inter-molecular forces within the resin, reduces fine gaps in the coating, and improves filler dispersion. These are conducive to enhancing the absorption of graphene to near-infrared light, so as to achieve the effect of reducing the near-infrared reflectivity of the coating.

Emissivity vsreflectivity

Table 3 shows the adhesion strength, flexibility, and impact strength of the coatings with different KH560 additions. The addition of KH560 did not affect adhesion strength and flexibility of the coating, but it significantly improved impact strength. Even a small amount of KH560 can increase the impact strength of the coating to its optimum level (50 kg × cm). This is attributed to the bridging effect of KH560 as a standard coupling agent. One end of the molecular structure of KH560 can react with groups such as silica bond and hydroxyl group in inorganic fillers to form covalent bonds, and the other end can engage with active groups like amino group, hydroxyl group, and carboxyl group present in the resin binder to establish chemical bonds. These interactions serve to improve the interface bonding strength between materials, and the adhesion strength between resin and substrate, resin and filler. The coating’s impact strength is significantly enhanced in the end33. Considering the near-infrared absorption properties, hydrophobic properties, and mechanical properties of the coating, the optimal addition of KH560 in the coating is determined to be 4 wt%.

Table 4 shows the adhesion strength, flexibility, and impact strength of the coatings having different APU to PDMS mass ratios. It shows that the adhesion strength of the coating increases as the absolute content of PDMS decreases, while the flexibility deteriorates. However, the impact strength of the coating has been maintained in the best state due to the presence of KH560. When the absolute content of PDMS is high, the binding between resin, filler, and substrate is primarily determined by the silicon-oxygen bond in PDMS, which has high bond energy and very low binding force. As the absolute content of PDMS decreases, the absolute content of PU increases gradually, and the content of amino, hydroxyl, and carboxyl groups also increases. These groups readily establish covalent and hydrogen bonds with oxygen atoms or hydroxyl groups on the substrate’s surface, consequently enhancing the adhesion strength of the coating. In addition, as the absolute content of APU increases, so do the strong reactive groups such as the isocyanate group and hydroxyl group, resulting in a significant increase in the cross-linking density. Consequently, the coating’s hardness and brittleness increase, ultimately reducing flexibility. The impact strength of the coating is also always optimal thanks to the presence of KH560. To maintain near-infrared reflectivity at 1.06 μm below 10%, and achieve both super-hydrophobic and good mechanical properties, the optimal mAPU:mPDMS ratio is determined to be 3:7.

Guo, Q. et al. Study on the effects of interfacial interaction on the rheological and thermal performance of silica nanoparticles reinforced epoxy nanocomposites. Compos. Part B-Eng. 116, 388–397 (2017).

Yuan, W. Z. & Zhang, L. Z. Lattice Boltzmann simulation of droplets impacting on superhydrophobic surfaces with randomly distributed rough structures. Langmuir 33, 820–829 (2017).

Multilayer graphene (Gr, purity 95 wt%, thickness 3–8 nm, particle size 5–50 μm, number of layers 5–10, specific surface area 2600–3000 m2/g), Nano-SiO2 (purity 99.99 wt%, diameter 10–30 nm, specific surface area 100–500 m2/g), Acrylic modified polyurethane (APU, liquid, solid content 66.67 wt%), APU curing agent (liquid, solid content 33.24 wt%), polydimethylsiloxane (PDMS, liquid, solid content 99.99 wt%), PDMS curing agent (liquid, solid content 99.99 wt%), KH560 (liquid, purity 99.99 wt%), DOP (dioctyl phthalate, a commonly used plasticizer, liquid, purity 99.99 wt%), the diluent is composed of butyl acetate and acetone by mass ratio of 1:1, tinplate substrate (12 cm × 5 cm × 0.28 mm). All other reagents are analytically pure. APU and supporting curing agent are mixed with a 2:1 mass ratio as coating binder, while PDMS and supporting curing agent are mixed in a 10:1 mass ratio as modified resin.

Figure 11 displays the near-infrared reflectance spectra of the coatings with varying KH560 additions. It can be seen that the modification of KH560 has little effect on the near-infrared reflectivity of the coating at 1.06 μm, with a variation of only 0.6%. The main reason is that when the ratio of fillers, the proportion of total fillers, and the ratio of resin remain constant, the addition of a small amount of KH560 has no significant effect on the micro-structure of the coating, and the graphene that absorbs near-infrared light is still evenly and widely distributed between the nano-SiO2 and the resin. Even if the silicon-oxygen bond of KH560 interacts with PU, PDMS, and some inorganic fillers to increase the binding force between the adhesive and the filler, the resin thickness, the void between the filler and the resin, and the overall micro-structure of the coating change slightly. These minor changes have little effect on the near-infrared absorption capacity of the coating, allowing it to maintain outstanding near-infrared low reflectivity properties.

Electromagnetic radiation, as you may recall from a previous chemistry or physics class, is composed of electrical and magnetic waves which oscillate on perpendicular planes. Visible light is electromagnetic radiation. So are the gamma rays that are emitted by spent nuclear fuel, the x-rays that a doctor uses to visualize your bones, the ultraviolet light that causes a painful sunburn when you forget to apply sun block, the infrared light that the army uses in night-vision goggles, the microwaves that you use to heat up your frozen burritos, and the radio-frequency waves that bring music to anybody who is old-fashioned enough to still listen to FM or AM radio.

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High-energy radiation (such as gamma- and x-rays) is composed of very short waves – as short as 10-16 meter from crest to crest. Longer waves are far less energetic, and thus are less dangerous to living things. Visible light waves are in the range of 400 – 700 nm (nanometers, or 10-9 m), while radio waves can be several hundred meters in length.