A nanocomposite coating

Abstract

A method of producing a graphene-dimethyl siloxane polymer (PDMS) nanocomposite coating for an aircraft comprises the steps of reducing graphene oxide to graphene, mixing the graphene with dimethyl siloxane to produce a graphene-dimethyl siloxane polymer nanocomposite, removing gas from the nanocomposite, and providing the nanocomposite for chemical vapour deposition onto the aircraft. The CVD process is preferably carried out at temperatures below the decomposition point of PDMS to maintain the integrity of the graphene and polymer matrix. The graphene-dimethyl siloxane polymer nanocomposite coating may be applied to a wing, a solar panel or a Fresnel lens of the aircraft. The coating may be suitable for use in de-icing of the aircraft, may enhance lightning resistance or may be configured to transmit photons for enhanced energy generation of the solar panels.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from United Kingdom patent application number 2311162.8 filed on 20 July 2023, which is incorporated by reference herein. FIELD This disclosure relates to nanocomposite coatings, particularly to graphene-dimethylsiloxane polymer nanocomposite coatings for aircrafts, and a method of producing graphene-dimethylsiloxane polymer nanocomposite coatings for aircrafts. BACKGROUND The constant growth of air traffic, the demand for performance optimization and the need for minimizing both operating and maintenance costs have encouraged the aircraft industry to move towards more electric solutions. As a result of this trend, the amount of electric power required on board an aircraft has significantly increased through the years, causing major changes in electric power system architectures. Solar energy is a promising energy source, and applying solar energy for use on board an aircraft is a very promising utilization of renewable energy. Since the invention of solar-powered aircraft, the methods to extract and store energy for it have become important research points all around the world. Currently, the main methods to do so are photovoltaic cells, rechargeable batteries, and components of maximum power point tracking (MPPT). Solar-powered aircraft may be equipped with power components such as photovoltaic cells and rechargeable batteries and solar panels may be located on the wings of the aircraft. One of the main challenges with the use of renewable energy as a power source is energy losses during absorption on the surface of the aircraft wings. Due to the unpredictable nature of solar energy and the operational requirements of solar-powered aircraft, it is necessary to design a sophisticated energy and mission management system to achieve a continuous flight over more than one day. Conventional aircraft powering using the traditional solar panels are comparably expensive, and hence the shift is now towards concentrated photovoltaics. Solar energy concentration technology using Fresnel lenses is an effective way to make full use of sunlight. Concentrated photovoltaics is a major application and the highest solar-to-electric conversion efficiency based on imaging Fresnel lens and non-imaging Fresnel lens are reported as over 30% and 31.5A A±A 1.7%, respectively. However, efforts to minimise losses and maximise solar absorption are still sought. In addition to this challenge, aircraft experience challenges with regards to surface deformities during collision with clouds and friction as well as the likelihood of being struck by lightning. Nanomaterials have application in the aerospace industry. Many nanomaterials that are produced today can be used in composites and bring about benefits over traditional materials, such as making the composite more lightweight and increasing a composite’s tensile strength, durability and resistance to impact. Graphene is known for its electrical, mechanical, and thermal properties. It has good electrical conductivity and can efficiently dissipate heat. Therefore, graphene-based polymer material was developed as an advanced material for numerous applications. However, an issue in the fabrication of composite materials is the uniform dispersion of graphene as a filler in the polymer matrix since the level of distribution of the graphene in polymer matrix plays an effective role in controlling the properties of the composites. Furthermore, the poor distribution of the filler material in the polymer matrix induces defects and cracks in the composite. The preceding discussion of the background is intended only to facilitate an understanding of the present disclosure. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY In accordance with an aspect of the disclosure there is provided a method of producing a graphene-dimethylsiloxane polymer nanocomposite coating for an aircraft comprising: reducing graphene oxide to graphene; mixing the graphene with dimethyl siloxilane to produce a graphene-dimethylsiloxane polymer nanocomposite; removing gas from the graphene-dimethylsiloxane polymer nanocomposite; and providing the graphene-dimethylsiloxane polymer nanocomposite for chemical vapour deposition onto the aircraft. The method may further include a step of drying the graphene-dimethylsiloxane polymer nanocomposite. The graphene may be substantially uniformly distributed in the coating. The method may further include a step of depositing the graphene-dimethylsiloxane polymer nanocomposite onto the aircraft by chemical vapour deposition, wherein the coating may be deposited in a substantially uniform layer on one or more surfaces of one or more wings of the aircraft. The coating may be deposited in a substantially uniform layer on solar panels integrated into or attached onto a surface of the aircraft. The coating may be deposited in a substantially uniform layer on a Fresnel lens located on a surface of a wing of the aircraft. The coating may be configured to transmit photons for enhanced energy generation of the solar panels. The coating may be configured to be flexible. The coating may be configured to enhance durability of the aircraft. The coating may be configured to enhance lightning resistance of the aircraft. The coating may be conductive and, or alternatively, the coating may be hydrophobic. The aircraft may be an unmanned aerial vehicle. The aircraft may be a nano air vehicle. The aircraft may be at least partially solar powered. In accordance with a further aspect of the disclosure there is provided a graphene-dimethylsiloxane polymer nanocomposite coating produced and deposited by the method provided. In accordance with a further aspect of the disclosure there is provided an aircraft having deposited on a surface thereof a graphene-dimethylsiloxane polymer nanocomposite coating produced by the method provided. Embodiments of the technology will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1a is a graph showing Fourier transform infrared spectroscopy results of graphene and graphene / dimethylsiloxane nanocomposites, respectively; Figure 1b is a graph showing a Raman spectra with two distinct Raman scattering peaks of graphene and graphene / dimethylsiloxane nanocomposites, respectively; Figure 2a is a graph showing the mechanical properties of the graphene / dimethylsiloxane composites; and Figure 2b is a graph showing permittivity and loss tangent of graphene / dimethylsiloxane composites at 1 kHz. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS In the present disclosure there is provided a method of producing a graphene-dimethylsiloxane polymer nanocomposite coating for an aircraft. There is further provided a graphene-dimethylsiloxane polymer nanocomposite coating for an aircraft produced by the method disclosed. The method of production includes a method of synthesizing the nanocomposite and a method of depositing the nanocomposite onto a surface of the aircraft. The method of synthesis comprises reducing graphene oxide to graphene. This reduction is achieved by use of a reducing agent, such as, but not limited to, ascorbic acid. The method also includes steps of: mixing graphene with dimethyl siloxilane to produce a graphene-dimethylsiloxilane polymer nanocomposite, and removing gas from the graphene-dimethylsiloxilane polymer nanocomposite, by degassing. The method of synthesis may also include a drying step, whereby the graphene-dimethylsiloxilane polymer nanocomposite is dried to form a film. The method of depositing the graphene-dimethylsiloxilane polymer nanocomposite onto a surface of the aircraft comprises chemical vapour deposition. The graphene in the graphene-dimethylsiloxilane polymer nanocomposite may be substantially uniformly distributed in the coating. The coating may be deposited in a substantially uniform layer on one or more surfaces of the aircraft. In particular, the coating may be deposited onto one or more surfaces of one or more wings of the aircraft. The aircraft may include solar panels integrated into or attached onto a surface of the aircraft. For example, the aircraft may include fuselage integrated photovoltaics. In such a case, the coating may be deposited as a coating on the solar panels. The coating may substantially cover the solar panels. Furthermore, or alternatively, the aircraft may include one or more Fresnel lens on one or more wing of the aircraft. In such cases, the coating may be deposited as a coating on the Fresnel lens. The coating may be flexible. The flexibility of the coating may be as a result of inherent characteristics of the nanocomposite, how the coating is produced, or as a result of how the coating is deposited onto the aircraft. The coating may also or alternatively be durable such that the coating enhances the durability of the aircraft. The durability of the coating may be as a result of inherent characteristics of the nanocomposite, how the coating is produced, or as a result of how the coating is deposited onto the aircraft. Aircrafts are often exposed to lightning strikes, and impact from lightning strikes. The coating may improve the aircraft’s resistance to damage resulting from being struck by lightning. The nanocomposite coating may also or alternatively include properties such as high conductivity, light weight, desirable tribological properties, and hydrophobicity. These properties may make the nanocomposite a suitable material for de-icing, flame inhibition, water uptake and corrosion protection of the surface onto which it is deposited. The electrical conductivity of the nanocomposite coating may be, for example, about 1.46 x 106 S / m, the thermal conductivity thereof may be about 4.84 x 103 W / mK, and the density thereof may be about 2.267 g / cm3. These properties may ensure that the aircraft onto which the coating is deposited is protected from damage from lightning strikes. The graphene-dimethylsiloxane polymer nanocomposite may be flexible. The nanocomposite may be configured to be applied in a thin layer to the surface of an aircraft. The polymer-graphene nanocomposite may be configured to withstand high pressures to be suitable for use on aircraft surfaces. The graphene-dimethylsiloxane polymer nanocomposite may be used in many areas of the aerospace industry including the area of unmanned aerial vehicles (UAVs). UAVs may take many forms, from large aircraft to much smaller drones which are referred to as nano air vehicles (NAVs). Nano Air Vehicles (NAV) are a class of unmanned aerial vehicles (UAVs) or drones that are characterized by their small size, typically in the range of a few centimetres to a few decimetres (tens of centimetres). NAVs have especially been realised in recent years because of advances in nanofabrication methods. The graphene-dimethylsiloxane polymer nanocomposite may be used as a coating to be applied on UAVs wings. The graphene-dimethylsiloxane polymer nanocomposite coating may improve impact and lightning resistance of the wings of UAVs and any other aircraft it may be applied to. Using a nanocomposite coating may aid in reducing the weight of a UAV or aircraft, which in turn may reduce the amount of power required to power the UAV or aircraft. The coating may be configured to transmit photons for enhanced energy generation. As the nanocomposites may be applied to the surface of, for example, a Fresnel lens and fuselage integrated concentrated photovoltaics, the coating over these or any solar panels may allow for increased photon transmission and potentially improved energy generation on the aircraft’s concentrated photovoltaic system. The polymer-graphene nanocomposite may be configured to have self-healing properties. Self-healing polymers and nanocomposites are responsive materials. The nanocomposite may therefore have the capability to reversibly heal damage. For aerospace applications, thermosets and thermoplastic polymers may be reinforced with nanocarbon nanoparticles for self-healing of structural damage. During synthesis of the graphene-dimethylsiloxane polymer nanocomposite, the graphene may be distributed uniformly in a polymer matrix. The percentage volume of graphene within the coating may vary depending on the application of the coating. If the electrical properties of the coating needs to be improved, a higher percentage volume of graphene is generally required. For applications in the field of Micro-electromechanical Systems (MEMS) and sensors, flexible coatings with a lower percentage volume of graphene are usually needed as MEMS and sensors generally require higher repeatability and reversible electromechanical response for higher performance and efficiency. Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice. This lattice structure is important for graphene's properties, such as high strength, electrical conductivity, and thermal conductivity. Graphene has certain properties that make it particularly suited for use in aviation applications. For example, graphene is generally non-reflective which may increase light transmission to minimise energy losses. Graphene’s high conductivity, good tribological properties, hydrophobicity, and high surface area makes it a suitable material for de-icing, flame inhibition, water uptake inhibition, and corrosion protection. Dimethylsiloxane (PDMS) is a silicon-based polymer that acts as the matrix or host material in the nanocomposite. PDMS is flexible, biocompatible, and commonly used in various applications. In an example embodiment of the method of synthesizing the nanocomposite, a reducing agent is used to convert graphene oxide to graphene. In particular, ascorbic acid is used as a reducing agent. This reducing agent may be defined as being a “green” reducing agent, which is used to reduce carbon dioxide emissions which cause global warming. Ascorbic acid may be considered a 'green' reducing agent due to its low environmental impact and potential to reduce carbon dioxide emissions associated with the production process. Other suitable reducing agents may also be used, such as, but not limited to sodium borohydride, hydrazine monohydrate, hydrohalic acid, magnesium silicate glass wafers, and thiourea dioxide. These reducing agents offer various advantages in terms of reduction efficiency, environmental impact, and scalability. The method further includes a step of mixing the graphene with dimethyl siloxane. For example, a magnetic stirrer may be used to mix the graphene and dimethyl siloxane together, to form a graphene / dimethyl siloxane film. A further step of the method involves degassing of the graphene / dimethyl siloxane mixture by using a vacuum pump to remove gas from the mixture. A further step includes drying the graphene / dimethyl siloxane mixture. Drying the graphene / dimethyl siloxane mixture may for example include drying the mixture at a temperature of between 30 and 70°C. In some cases, the mixture is dried at a temperature of between 40 and 60°C. In some cases, the mixture is dried at a temperature of between 45 and 55°C. In some examples, the mixture is dried at a temperature of about 50°C. Drying the graphene / dimethyl siloxane mixture may include drying the mixture for a duration of between 18 and 30 hours. In some cases, the mixture is dried for a duration of between 21 and 27 hours. In some cases, the mixture is dried for a duration of between 23 and 25 hours. In some examples, the mixture is dried for a duration of about 24 hours. Thus, in some examples, this drying step involves drying the film at 50°C for 24 hours to produce a graphene / dimethyl siloxane film. The optimal drying conditions may vary based on factors such as the thickness of the film, the concentration of graphene in the mixture, and the desired mechanical properties of the final nanocomposite. A chemical vapour deposition method is then used to deposit the graphene / dimethyl siloxane film onto the desired surface of the aircraft. For example, the film may be deposited by this method onto the surface of a solar panel integrated into one or more wing of the aircraft. During the synthesis method of the graphene-dimethylsiloxane polymer nanocomposite the doping concentration of graphene may be increased. Further, during the process of synthesizing a graphene-dimethylsiloxane (PDMS) nanocomposite, the original lattice structure of the graphene is maintained, including during and after chemical vapour deposition. In other words, the lattice constant of graphene is preserved during the synthesis process and the subsequent deposition. As such, the original lattice structure of the graphene is maintained, including during and after chemical vapour deposition. This preservation of graphene's lattice structure is achieved through several steps and considerations. These include one or more of: a controlled reduction process, controlled mixing process, controlled temperature processing, optimized Chemical Vapor Deposition (CVD) parameters, specific substrate selection, and in-situ characterization. The step of controlled reduction process may for example involve the use of mild reducing agents like ascorbic acid helps preserve the graphene lattice structure during the reduction of graphene oxide to graphene. This controlled or 'green' reduction method minimizes structural defects that could arise from more aggressive reduction techniques. The mixing process may be controlled by ensuring that when mixing graphene with dimethylsiloxane, low shear mixing techniques are employed, such as using a magnetic stirrer at controlled speeds. This controlled mixing helps prevent mechanical damage to the graphene sheets and maintains their lattice integrity. Controlled-Temperature Processing may for example entail conducting the drying and curing processes at suitable temperatures (e.g. as described above) to avoid thermal stress that could disrupt the graphene lattice structure. Therefore, the temperature processing is controlled. Parameters of Chemical Vapor Deposition (CVD) may be controlled by ensuring careful control of temperature, pressure, and gas flow rates ensures that the graphene lattice remains intact during the CVD process. The process is typically carried out at temperatures below the decomposition point of PDMS to maintain the integrity of both the graphene and the polymer matrix. Substrates with thermal expansion coefficients close to that of graphene help minimize stress on the graphene lattice during temperature changes in the deposition process and are therefore selected for CVD. A further consideration is in-situ characterization. This is achieved by using techniques such as Raman spectroscopy to monitor the graphene structure in real-time during synthesis and deposition, allowing for immediate adjustments to maintain lattice integrity. By carefully controlling these parameters, a sp2 hybridized carbon structure of graphene is preserved throughout the synthesis and deposition process, ensuring that the final nanocomposite retains the desirable properties of graphene, such as high electrical conductivity and mechanical strength. This is important to maintain the desirable properties of graphene and ensure its effectiveness in reinforcing the PDMS matrix. Additionally, the graphene is embedded within the structure of the dimethylsiloxane (PDMS) matrix. By maintaining the lattice structure of graphene during the synthesis and deposition method, the resulting nanocomposite may exhibit improved mechanical strength, electrical conductivity, and other enhanced properties attributed to graphene. This nanocomposite may find applications in various fields, such as flexible electronics, sensors, and aircraft coatings, where the combination of graphene's unique properties and PDMS's flexibility and biocompatibility offers desirable properties. The synthesised graphene / dimethylsolixane nanocomposites may have improved flexibility which may assist in resistance against surface defects. Further, it may be used as a coating for light transmission to limit energy losses during aircraft operation, for example the coating may be applied to Fresnel lenses for aircrafts. Figures 1a and 1b and Figures 2a and 2b show results of structural characterisation tests performed on the graphene-dimethylsiloxane polymer nanocomposite to evaluate its material properties in relation to its intended application. Figure 1a is a graph showing Fourier transform infrared (FTIR) spectroscopy results of graphene and graphene / dimethylsiloxane nanocomposites. The FTIR was used to detect the present functional groups in the graphene / polymer nanocomposites. For graphene, the absorption peak at 3100-3500 cm-1 corresponds to the -OH stretching vibration, which is the absorption peak formed by the -OH on the graphene sheet. The absorption peak near 1730 cm ' is due to the stretching vibration absorption of C=O in the carboxyl group. The absorption peak near 1630 cm1 is caused by the C=C stretching vibration. The absorption peak near 1400 cm-1 is ascribed to the in-plane bending vibration of the C-H group. The absorption peak near 1100 cm-1 corresponds to the stretching vibration of the C-O-C group. They indicate that graphene contains the oxygencontaining groups. Figure 1 b shows two distinct Raman scattering peaks for GO (graphene oxide). One is the D peak at 1350 cm1 and the other is the G peak at 1593 cm1. The D peak is generated by the vibration of sp3 hybridized carbon atoms, reflecting the defects of the internal structure of graphene. And the G peak is produced by the sp2 hybrid carbon ring and atomic stretching vibration, representing the symmetry and order degree in the graphene molecular structure. In the Raman analysis, the intensity ratio of the D peak to the G peak (ID / IG) is often used to indicate the disorder degree of the graphite sheet. The ID / IG of GO obtained by the experiment was 0.67. Neither graphene nor graphite had a D peak, indicating that the obtained oxygen-containing group on the GO resulted in the appearance of a D peak of the defect peak. Figure 2a shows the mechanical properties of the graphene / dimethylsiloxane composites tested by a universal tensile tester. The mechanical properties of the composites may increase by increasing the graphene content when the added amount of graphene is low. This is because graphene plays a reinforcing role for dimethylsiloxane because it is a small-layer structure and has a quantum effect that may improve the mechanical performance of dimethylsiloxane. From the results shown in Figure 2a, the tensile properties of graphene / dimethylsiloxane composites reach the highest value when the graphene content is 2 wt%, the tensile strength is 1 MPa, and the elongation at break is 280%. However, the mechanical properties of the composites appear to be decreased when the content of graphene is increased to a certain ratio because the viscosity of the mixture becomes too large which may cause structural defects in dimethylsiloxane. Despite this, it may still have improved mechanical properties compared to pure dimethylsiloxane. The graphene-dimethylsiloxane polymer nanocomposite coating may be used in a wide variety of applications and has particular use in the field of aviation. In particular, the graphene-dimethylsiloxane polymer nanocomposite coating may be used as a surface coating for the wings of aircraft or the surfaces of Fresnel lenses. The coating may be applied to these surfaces under specific conditions to allow for the coating to be a suitable thickness and to suitably adhere to the surface. Also, the coating may be applied in such a way that the entire surface is properly covered. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. The language used in the specification has been principally selected for readability and 5 instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims. 10 Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 15

Claims

1. A method of producing a graphene-dimethylsiloxane polymer nanocomposite coating for an aircraft comprising:reducing graphene oxide to graphene;mixing the graphene with dimethyl siloxilane to produce a graphene-dimethylsiloxane polymer nanocomposite;removing gas from the graphene-dimethylsiloxane polymer nanocomposite; and providing the graphene-dimethylsiloxane polymer nanocomposite for chemical vapour deposition onto the aircraft.

2. The method as claimed in claim 1, including drying of the graphene-dimethylsiloxane polymer nanocomposite.

3. The method as claimed in either one of claims 1 or 2, wherein the graphene is substantially uniformly distributed in the coating.

4. The method as claimed in any one of the preceding claims, including depositing the graphene-dimethylsiloxane polymer nanocomposite onto the aircraft by chemical vapour deposition wherein the coating is deposited in a substantially uniform layer on one or more surfaces of one or more wings of the aircraft.

5. The method as claimed in any one of claims 1 to 3, wherein the coating is deposited in a substantially uniform layer on solar panels integrated into or attached onto a surface of the aircraft.

6. The method as claimed in any one of claims 1 to 3, wherein the coating is deposited in a substantially uniform layer on a Fresnel lens located on a surface of a wing of the aircraft.

7. The method as claimed in any one of the preceding claims, wherein the coating is configured to transmit photons for enhanced energy generation of the solar panels.

8. The method as claimed in any one of the preceding claims, wherein the coating is configured to be flexible.

9. The method as claimed in any one of the preceding claims, wherein the coating is configured to enhance durability of the aircraft.

10. The method as claimed any one of the preceding claims, wherein the coating is configured to enhance lightning resistance of the aircraft.

11. The method as claimed in any one of the preceding claims, wherein the coating is conductive.

12. The method as claimed in any one of the preceding claims, wherein the coating is hydrophobic.

13. The method as claimed in any one of the preceding claims, wherein the aircraft is an unmanned aerial vehicle.

14. The method as claimed in any one of the preceding claims, wherein the aircraft is a nano air vehicle.

15. The method as claimed in any one of the preceding claims, wherein the aircraft is at least partially solar powered.

16. A graphene-dimethylsiloxane polymer nanocomposite coating produced and deposited by the method of any one of claims 1 to 15.

17. An aircraft having deposited on a surface thereof a graphene-dimethylsiloxane polymer nanocomposite coating produced by the method of any one of claims 1 to 12.Application No: GB2410273.3Examiner:Dr Karen PayneClaims searched: 1-17Date of search: 10 January 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-3 US 2014 / 0011969 Al (UNIV LOUISVILLE RES FOUND) See paragraphs 9-11. X 1 -3 2018 IEEE 18th International Conference on Nanotechnology (IEEE-NANO), Vol. 2018-July, 2018, Cabibihan et al., "Graphene-filled PDMS composite for tactile sensing of surgical graspers, pp. 1-4. See page 2. X 1-3 CN 116261317 A (SHENZHEN DARBOND INTERFACE MAT CO LTD) See WP1 Abstract Accession No. 2023-65430W. X 16, 17 US 10183754 Bl (AGARWAL et al.) See columns 1 &2. X 16, 17 Polymers, Vol. 11, 2019, Ha et al., "Development of multi-functional graphene polymer composites having electromagnetic interference shielding and de-icing properties", pp. 2101: 1-9. See pages 1-3.Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From C23C 0016 / 00 01 / 01 / 2006 B64D 0015 / 12 01 / 01 / 2006 Hl OF 0077 / 30 01 / 01 / 2025

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