Euphorbia-mimetic wax-based superhydrophobic surface treatment

Abstract

A coating composition for the production of superhydrophobic surfaces, comprising i) one or more hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, ii) one or more fatty alcohols, and iii) one or more hydrophobic (co)polymers comprising linear side-chains, wherein the composition contains less than 1% by weight of fluorine determined by combustion ion chromatography.

Description

[0001] BASF Coatings GmbH

[0002] GlasuritstraBe 1 , 48165 Munster

[0003] Germany

[0004] BASF SE

[0005] Carl-Bosch-StraBe 38, 67056 Ludwigshafen am Rhein Germany

[0006] Euphorbia-Mimetic Wax-Based Superhydrophobic Surface Treatment

[0007] FIELD OF THE INVENTION

[0008] The present invention relates to a coating composition for the production of superhydrophobic surfaces comprising i) one or more hydrophobic compounds with a melting point above 25 °C, ii) one or more fatty alcohols and iii) one or more hydrophobic (co)polymers comprising linear side-chains, wherein the composition contains less than 1 % by weight of fluorine and is essentially free of per- and / or polyfluorinated alkyl substances (PFAS). The present invention also relates to the use of said coating composition for post treatment of a substrate surface or parts of a substrate surface.

[0009] Furthermore, the present invention pertains to a composite material with a superhydrophobic surface comprising a substrate and a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface. The present invention also pertains to a process of producing a composite material with a superhydrophobic surface.

[0010] BACKGROUND OF THE INVENTION

[0011] The superhydrophobicity of surfaces is known from nature and leads to highly water repellent materials with beneficial features such as drag reduction, easy-to-clean, self-cleaning, dirt-repellent, anti-stain, anti-stick, anti-fogging, anti-icing, air-retaining, anti-adhesive, bioinert and / or non-fouling (non-biocidal anti-fouling) properties. These properties are highly relevant for applications in industrial products such as aircrafts, trains, ships or other means of (public) transportation, optical materials, (architectural) facades, disposable systems for handling aqueous media such as bioreactors or food-packaging, as well as surfaces for enhanced water condensation e.g. in parts of steam-driven electric plants or for oil / water- separation purposes etc.

[0012] This is why composite materials with a superhydrophobic surface as well as manufacturing processes thereof have caught considerable attention since at least 20 years. Many research efforts have been directed to design materials by mimicry of nature wherein plants such as the famous lotus leaf (Nelumbo nucifera) or certain water ferns (e. g., Salvinia molesta) serve as examples for highly interesting materials with above mentioned properties. Fundamentally, nature teaches that for achieving superhydrophobic properties, a surface should be structured with characteristic features having dimensions from about 10 nm to about 100 pm, preferably on at least two size scales within this range (named “hierarchical structuring” below), and the molecules at the outermost surface should be as hydro- phobic as possible.

[0013] Since decades, superhydrophobic surfaces are proposed for numerous applications. Many publications describe compositions and processes for making such surfaces. However, none of these options have found widespread application yet. Until today superhydrophobic surfaces are used only in some niche applications. This has several reasons as outlined in detail below.

[0014] It remains challenging to design and manufacture synthetic surface structures with beneficial features as stated above on an industrial scale. Most of the synthetic materials and respective manufacturing processes thereof still suffer from performance issues, as they are not scalable, quite often require highly specialised, highly expensive equipment and machinery, rely on complicated, multi-step processes which are hardly scalable, lead to irreproducible results and / or give inhomogeneous quality. It is also an issue that synthetic superhydrophobic composite materials up to today are in most cases not durable in environmental conditions such as exposure to UV radiation, moisture and other weathering conditions, are not free of Substances of Very High Concern (SVHC) such as fluorinated compounds, especially per- and / or polyfluorinated alkyl substances (PFAS) and do not allow for practical handling, thus not fulfilling the requirements for commercialisation.

[0015] It has also turned out to be challenging to provide a versatile coating composition for the creation of superhydrophobicity which can be applied to a wide variety of different substrates, e.g. to substrates differing in surface morphology, material composition, chemical structure and the like. Many state of the art coating compositions still suffer from substrate compatibility issues and can only be applied to very specific substrates.

[0016] Moreover, it remains particularly challenging to reliably create superhydrophobic properties on substrates with flat surfaces, even more so when this is to be achieved by simple processes such as single-step processes and / or coating processes only, i. e., without expensive processes such as precision machining or lithography to create sophisticated surface structures. Even if some initial superhydrophobicity can be created on flat substrate surfaces, the durability of such superhydrophobic surfaces is very low in most cases. Performance is thus significantly reduced or even completely lost upon exposure of the materials to the environment already after short periods of time and can in many cases not be restored. Accordingly, there is a rising demand for materials featuring a facile and easily triggered self-restoration of damaged superhydrophobic surface layers.

[0017] It has been tried to solve the above-mentioned challenges and problems by mimicry of nature, in particular by orientation on features of superhydrophobic surfaces of plants such as Euphorbia plants which rely on fatty alcohols as preferred building blocks to form nanoplatelet morphologies for achieving superhydrophobicity. It is further known that certain polymers, e.g. poly alkyl acrylates, are capable to co-crystallize with fatty alcohols and hydrocarbon species (waxes) and thereby heavily alter the pristine wax crystal morphology.

[0018] Accordingly, WO 2018 / 193094 A1 discloses a superhydrophobic two-component coating composition and a method for producing a superhydrophobic coating, said coating comprising at least one polymer and at least one crystallizable material. However, when applying said principle to a coating composition, i.e., providing a two component coating composition featuring only fatty alcohols and polymers as main components, it has been found that the durability and handling of the resulting composite material is an issue in most use cases. In particular the durability and self-restoration ability of the very thin nanorough surface layer is unsatisfactory when the material is exposed to chemicals, heat, irradiation, mechanical stress, etc. Moreover, the application process of said two-component coating composition to substrate surfaces requires disadvantageously high synthetic efforts, in particular requires heating to high temperatures, expensive and harmful chemicals and complex reaction sequences in order to obtain a nanorough coating. Similarly the restoration ability of the coating layer is not satisfactory and hardly feasible as the damaged material surface needs to be heated to high temperatures above the melting points of the compounds involved. Correspondingly, the two component coating system as disclosed in WO 2018 / 193094 A1 and resulting composite materials therefrom still suffer from performance issues and are not able to address the above-mentioned problems in a mannerthat suffices for most application cases and a large industrial process.

[0019] Accordingly, there is a demand in industry for a coating composition for the production of superhydrophobic surfaces, a corresponding composite material with a superhydrophobic surface and a production process thereof which are improved regarding the above-mentioned challenges and problems.

[0020] SUMMARY OF THE INVENTION

[0021] It was a primary object of the present invention to provide such an improved coating composition for the production of superhydrophobic surfaces, a corresponding composite material with a superhydrophobic surface and a production process thereof. The improved coating composition for the production of superhydrophobic surfaces should preferably be applicable to a wide variety of different substrates, in particular be applicable to substrates with a flat surface topology. Moreover, it should be able to reliably create superhydrophobic properties on substrates, in particular on substrates with a flat surface topology, which are durable even under harsh environmental conditions such as prolonged UV radiation. The improved coating composition for the production of superhydrophobic surfaces and the corresponding composite material with a superhydrophobic surface should be substantially free of Substances of Very High Concern (SVHC) such as fluorinated compounds, especially per- and / or polyfluorinated alkyl substances (PFAS), durable and be composed of easily accessible materials. Furthermore, the improved coating composition for the production of superhydrophobic surfaces, the corresponding composite material with a superhydrophobic surface and the production process thereof should be designed in a manner that allows for upscaling, facile handling, in particular application without the need of highly specialised, highly expensive equipment and machinery, simple production processes without the need of high temperatures and should also lead to reproducible results and / or ho- mogeneous quality of the products. The superhydrophobic surface of the improved composite material should furthermore be easily self-restorable after being damaged without the need of high temperature processes.

[0022] The invention is defined in the claims as attached.

[0023] The present invention concerns in its categories a coating composition for the production of superhydrophobic surfaces, the use of said coating composition for post treatment of a substrate surface or parts of a substrate surface, a composite material with a superhydrophobic surface and a process of producing a composite material with a superhydrophobic surface. Embodiments, aspects or features disclosed for or in connection with one of these categories in each case analogously apply for the other categories of the invention.

[0024] If not stated otherwise, preferred embodiments, aspects or features of the present invention can be combined with other embodiments, aspects or features, especially with other preferred embodiments, aspects or features, irrespectively of the categories to which the embodiments, aspects or features relate. The combination of preferred embodiments, aspects or features with other preferred embodiments, aspects or features in each case again results in preferred embodiments, aspects or features.

[0025] Herein and throughout the present text, the term “superhydrophobic surface” designates a surface exhibiting static water contact angles of at least 140° and droplet roll-off angles of no more than 20° as measured by an optical goniometer using droplets with a volume of 10 pL which is in accordance with definitions found in prior art.

[0026] The superhydrophobic surface preferably exhibits static water contact angles of at least 150° and droplet roll-off angles of no more than 15°, more preferably no more than 10°, as measured by an optical goniometer using droplets with a volume of 10 pL.

[0027] Herein and throughout the present text, the term “hydrophobic” in relation to any defined compound or component such as (co)polymers designates a compound or component that, when dissolved / dispersed in a suitable solvent, cast onto a flat substrate non-soluble in said solvent, and dried, gives rise to a film that exhibits static water contact angles of at least 80°.

[0028] Preferably, the hydrophobic compound or component when dissolved / dispersed in a suitable solvent, cast onto a flat substrate non-soluble in said solvent, and dried, gives rise to an essentially flat film that exhibits static water contact angles of at least 90°.

[0029] Herein and throughout the whole text the term “composite material with a superhydrophobic surface” includes composite materials with two or more different surfaces wherein at least one of those surfaces - but not necessarily all surfaces - features a part that is superhydrophobic. E.g., a composite material in the three-dimensional form of a cube has six different sides (surfaces). According to the present invention at least one of those six sides comprises a superhydrophobic surface, but not necessarily the whole side must be superhydrophobic.

[0030] Herein and throughout the present text, the term “(co)polymers” designates, in accordance with common understanding of the term, a material comprising (co)polymer molecules, i. e., molecules “of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass” (IUPAC Goldbook, “macromolecule (polymer molecule)”: https: / / goldbook.iupac.org / terms / view / M03667, retrieved 2027-06-27). Commonly as well as herein and throughout the present text, these units of repetition are called repeating units or (co)monomers. Also in accordance with the general understanding in the field, (co)monomers used as starting material to form polymers are chemically changed upon polymerisation. E.g., an acrylate monomer as starting material originally comprises a double bond which reacts in propagation in order to form the polymer molecule. The skilled person will understand and account for the different chemical structures of (co)monomers as starting material or within the polymer molecule respectively. Herein and throughout the present text, the number of repetitions of said units is not particularly limited, i. e., the term polymers as used herein also includes oligomers, i. e., molecules consisting of a few repeating units (monomers).

[0031] Herein and throughout the whole text the term “fluorine content” designates all kind of free or bound fluorine within the composite material or coating composition, is thus not limited to elemental fluorine but also includes fluorine atoms or ions as present in fluorinated compounds in the form of molecules or salts. The fluorine content can be determined according to state of the art procedures known to the skilled person, in particular can be determined by combustion of the sample with subsequent detection by ion chromatography to detect fluorine, in short: combustion ion chromatography.

[0032] Herein and throughout the whole text the term “wax platelet” (also referred to as nanoplatelet etc.) designates a three-dimensional structure in the form of a platelet, i.e., a flattened body which expands more in two spatial directions than in a third spatial direction. The size of a wax platelet typically lies in nanoscale dimensions and can reach up to several micrometers in one or two spatial directions. The platelets may be planar, bent and / or twisted. Individual platelets can be spatially isolated, overlapping and / or clustering. Said platelets are mainly formed by wax, wherein wax is to be understood as a diverse class of organic compounds that are lipophilic / hydrophobic, malleable solids near ambient temperatures. Typical organic compounds are alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, which are either present as pure compounds or in a mixture of different compounds. Waxes typically have melting points above about 25-40 °C and melting of wax results in low viscosity liquids. Waxes are insoluble in water but soluble in nonpolar organic solvents such as hexane, benzene, toluene, and chloroform.

[0033] In accordance with the primary object of the invention as stated above, the present invention relates to a coating composition forthe production of superhydrophobic surfaces, comprising i) one or more hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, ii) one or more fatty alcohols, iii) one or more hydrophobic (co)polymers, wherein the one or at least one of the more than one hydrophobic (co)polymers comprises linear side-chains, wherein the composition contains less than 1 % by weight of fluorine determined by combustion ion chromatography.

[0034] Hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes are also designated as “hydrophobic compounds”, “hydrophobic and crystallizable compounds”, “hydrophobic compounds with a melting point above 25 °C”, “component i)” or “wax component” throughout the present text.

[0035] The inventors of the present invention have found that a three component coating composition also referred to as ternary blend, comprising above defined components i), ii) and iii) is particularly suitable for the production of superhydrophobic surfaces. When said coating composition is applied to a substrate surface, in particular when it is applied according to a process of the current invention, it advantageously creates long lasting and durable superhydrophobicity on a substrate surface or parts of a substrate surface.

[0036] The coating composition according to the present invention is able to at least partially cover the surface of a wide variety of different substrates and to form self-assembled micro-aggregates thereon, wherein the self-assembled micro-aggregates feature a hierarchical, at least two-tier roughness and wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0037] The coating composition according to the present invention is particularly suitable for the creation of a superhydrophobic surface structure on flat substrates and can be reliably applied to a large variety of substrates differing in surface morphology, material composition, chemical structure and the like.

[0038] Also beneficially the coating composition according to the present invention has a fluorine content determined by combustion ion chromatography of less than 1 % by weight, preferably less than 0.1 % by weight, more preferably less than 0.01 % by weight. In contrast to many state-of-the-art coating compositions, the coating composition according to the present invention thus does not rely on the presence of PFAS and / or other fluorinated compounds which is beneficial since many fluorinated compounds, particularly PFAS, are considered as Substances of Very High Concern (SVHC).

[0039] Without wishing to be bound by any theory, the beneficial effects of the coating composition according to the present invention are most likely caused by synergistic interaction of the three main components as defined above and as further specified within the present text.

[0040] Accordingly, the role of component iii) within the coating composition, i.e., the role of the one or more hydrophobic (co)polymers, is to form an anchor-like structure on the substrate surface, wherein that structure is in the form of micron-sized, self-assembled micro-aggregates featuring a polymer scaffold as aggregate base. The polymer scaffold as aggregate base forms a first level roughness on the substrate surface in the microscale regime and stabilizes the overall two-tier roughness of the final superhydrophobic surface structure. This reinforcement can be further improved by covalent crosslinking of the polymer-chains within the polymer scaffold both to each other and potentially also to a C-H-Bond containing surface using C-H-insertion crosslinking moieties based on benzophenone or alike. Since the one or more hydrophobic (co)polymers within the coating composition comprise linear side-chains, which are capable of inducing (co-)crystallization and / or ordered self-assembly of components i) and ii), the polymeric component iii) also has the function to serve as a kind of “seed” in the formation of the final at least two-tier roughness, wherein said two- tier roughness features the microscale polymer scaffold as aggregate base (first level structure) and nanoscale wax platelets as aggregate surface (second level surface structure). It has been found that the one or more hydrophobic (co)polymers as defined herein is / are capable of inducing (co)crystallization and / or ordered self-assembly of components i) and ii). They can thus also be designated as being capable of inducing (co)crystallization and / or ordered self-assembly of components i) and ii). In particular component iii) is able to induce, accelerate, modify and / or template the formation of wax platelets on the aggregate surface. Said wax platelets are, in these ternary systems, mainly formed by the one or more hydro- phobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes according to component i), of the coating compositions, also referred to as wax component herein. It goes without saying, that component i) does not include any fatty alcohols which are solely counted within component ii). Accordingly, component i) can be designated as being free of any fatty alcohols and includes only those compounds apart from fatty alcohols as explicitly defined herein. The wax platelets are thus formed by self-ordered and / or crystallized domains of the hydrophobic compounds (wax components), which accordingly can also be designated as “crystallizable”. The one or more fatty alcohols according to component ii) of the coating composition serve as amphiphilic phase mediators in the formation of the ordered wax platelet structure which is most likely explained by the structural effects imposed by the hydroxyl-head-to-hydroxyl-head-self-assembly of fatty alcohol molecules in the ternary blends. It is most likely the case that the fatty alcohol molecules form a bridging lipid doublelayer lamella structure between the less ordered polymer-sidechain crystal lattice and the more ordered wax-lattice (platelet environment) which leads to an in-plane co-crystalliza- tion of the hydrophobic (and crystallizable) compounds (wax components) into platelet- or sheet-like (nano)structures.

[0041] The inventors have thus identified a coating composition as defined above and with preferred embodiments as defined below, wherein said coating composition allows for a superhydrophobic coating showing good adhesion to the substrate below and good cohesion within the coating itself to achieve mechanical durability. Furthermore the coating composition can be applied to a wide variety of substrates, in particular to challenging substrates with a flat surface morphology.

[0042] Preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one hydrophobic (co)polymers comprises linear hydrocarbon side-chains.

[0043] More preferably the one or at least one of the more than one hydrophobic (co)polymers comprises linear hydrocarbon side-chains with a number of carbon atoms in the range of from 12 to 48, preferably 12 to 36, more preferably 12 to 28, even more preferably 16 to 24, most preferably 18 to 22. Even more preferably the linear hydrocarbon side-chains are linear alkyl groups with a number of carbon atoms in the range of from 12 to 48, preferably 12 to 36, more preferably 12 to 28, even more preferably 16 to 24, most preferably 18 to 22.

[0044] The above defined preferred embodiment of linear side-chains in the polymer component iii) of the coating composition allows for a particularly effective growth / formation of the second level (nano)platelet structure on the surface of the self-assembled hierarchical microaggregates. It has been found that linear hydrocarbon side-chains are especially capable of inducing (co-)crystallization and / or ordered self-assembly of components i) and ii), even more so when the linear hydrocarbon side-chains feature a number of carbon atoms in the ranges as defined above and / or when the linear hydrocarbon side-chains are linear alkyl groups, in particular linear alkyl groups with a number of carbon atoms in the ranges as defined above.

[0045] Also preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one hydrophobic (co)polymers is a (co)polymer comprising one or more (meth)acrylate monomers and / or one or more (meth)acrylamide monomers.

[0046] It has been found that (meth)acrylate monomers and / or one or more (meth)acrylamide monomers are particularly suitable building blocks for the formation of hydrophobic (copolymers of component iii). These preferred monomers are easily accessible, versatile, able to create stable (copolymers and are also beneficial in terms of substrate bonding thus stabilizing the overall microscale polymer scaffold as aggregate base (first level structure) and enabling strong adhesive binding to the substrate surface which enhances the durability of the superhydrophobic surface crated on the resulting composite material.

[0047] More preferably at least one of the one or more (meth)acrylate monomers and / or (meth)acrylamide monomers comprises linear side-chains, preferably linear hydrocarbon side-chains, more preferably linear alkyl group side-chains, with a number of carbon atoms in the range of from 12 to 48, preferably 12 to 36, more preferably 12 to 28, even more preferably 16 to 24, most preferably 18 to 22.

[0048] Also more preferably at least one of the one or more (meth)acrylate monomers and / or (meth)acrylamide monomers comprises a crosslinking moiety, wherein the crosslinking moiety preferably comprises a functional group selected from the group consisting of

[0049] - C,H-insertion crosslinking (CHic) active groups, preferably substituted benzophenones, anthraquinones, thioxanthones, sulfonyl azides, aromatic azides, diazomethylenes with ester, sulfonyl and / or aromatic substituents,

[0050] - azides,

[0051] - vinylic unsaturated groups,

[0052] - epoxy groups,

[0053] - isocyanate groups,

[0054] - carboxylic acid anhydride groups, and

[0055] - organic carbonates.

[0056] In a particularly preferred embodiment of the present invention at least one of the one or more (meth)acrylate monomers and / or (meth)acrylamide monomers comprises linear sidechains, in particular comprises preferred linear side-chains as defined above, and at least one other of the one or more (meth)acrylate monomers and / or (meth)acrylamide monomers comprises a crosslinking moiety as defined above, in particular comprises a preferred crosslinking moiety as defined above.

[0057] In another preferred aspect of the present invention at least one of the one or more (meth)acrylate monomers and / or (meth)acrylamide monomers comprises linear sidechains, in particular comprises preferred linear side-chains as defined above, and the same (meth)acrylate monomer and / or (meth)acrylamide monomer also comprises a crosslinking moiety as defined above, in particular comprises a preferred crosslinking moiety as defined above.

[0058] It was a particular challenge that the coating composition needs to be selected and / or tailored to exhibit strong interaction forces. Hydrophobic materials typically feature weak in- termolecular interaction forces, e. g., alkanes essentially feature only Van-der-Waals forces. This is why most state-of-the-art coating systems up to today rely on the utilization of strongly hydrophilic materials such as epoxy resins to achieve mechanical durability. Accordingly, while hydrophobicity is desired, this is in conflict with the requirement for strong interactions. To circumvent this, covalent chemical bonds needed to be introduced. To achieve this, the (co)polymers according to component iii) of the coating composition are preferably crosslinkable, i. e., able to form crosslinks with themselves and should preferably also chemically attach to the substrate and / or the other components present in the coating composition. It has been found that above mentioned functional groups are particularly suitable for the formation of crosslinks between polymers and / or between polymers and the substrate.

[0059] When applying the coating composition according to the invention the (co)polymers of component iii) thus preferably form a network of crosslinked (co)polymers on the substrate surface.

[0060] Herein and throughout the present text, the term “crosslinked (co)polymers” designates (co)polymers wherein a bond, several bonds, or a short sequence of bonds links one polymer molecule to another. These links may take the form of covalent bonds or ionic bonds, preferably the links are covalent bonds. Links are generally formed by reactions involving sites or groups on existing polymer molecules, e. g., via C,H-insertion cross-linking (CHic), or by interactions between existing polymer molecules. Preferably many of these links are formed, and collectively, they connect most individual polymer molecules, thus forming an (insoluble) network of crosslinked polymer molecules.

[0061] Also preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one fatty alcohols is a linear alkanol or a linear alkenol, preferably is an alkanol, preferably with a number of carbon atoms in the range of from 16 to 36, more preferably with a number of carbon atoms in the range of from 18 to 30 even more preferably with a number of carbon atoms in the range of from 18 to 26, most preferably with a number of carbon atoms in the range of from 18 to 24.

[0062] Even more preferably the one or at least one of the more than one fatty alcohols is selected from the following group:

[0063] - Stearyl alcohol (1 -octadecanol, CiaHssO),

[0064] - Arachidyl alcohol (1-eicosanol, C20H42O),

[0065] - Behenyl alcohol (1-docosanol, C22H46O),

[0066] - Lignoceryl alcohol (1-tetracosanol, C24H50O), and

[0067] - Ceryl alcohol (1-hexacosanol, C26H54O).

[0068] It has been found that the formation of wax platelets as aggregate surface works in particular well when the fatty alcohol according to component ii) of the coating compositions is selected from the preferred embodiments as stated above. Linearity and / or chain length are thus important features of the fatty alcohol component which is also preferably present in the saturated form.

[0069] Preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is selected from the group consisting of linear alkyl esters, linear alkenyl esters, linear alkanes, linear alkenes and linear alkynes, preferably selected from the group consisting of linear alkanes, linear alkenes and linear alkynes, more preferably the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is an alkane.

[0070] Also preferred is a coating composition according to the present invention, wherein the number of carbon atoms of the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is in the range of from 16 to 36, more preferably is in the range of from 22 to 30, most preferably is in the range of from 26 to 30.

[0071] It has been found that the formation of wax platelets as aggregate surface works in particular well when the hydrophobic (and crystallizable) compounds of component i), i.e. compounds apart from fatty alcohols and with a melting point above 25 °C, are selected from the preferred embodiments as stated above. Lamellae formation, nano-platelet growth and stability, co-crystallization compatibility with polymer component iii) and / or fatty alcohol component ii) are enhanced if the hydrophobic (and crystallizable) compounds with a melting point above 25 °C are present in a chemical form as defined above and / or with the respective number of carbon atoms as defined above.

[0072] Even more preferably the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is selected from the following group:

[0073] - n-octacosane (n-C2sH58) ,

[0074] - n-nonacosane (n-C29Heo), and

[0075] - n-docosane (n-C22H46) .

[0076] The hydrophobic compounds (apart from fatty alcohols) with a melting point above 25 °C according to component i) of the coating composition may be present in the form of a mixture of different compounds. In one particular preferred embodiment the hydrophobic compounds with a melting point above 25 °C according to component i) of the coating composition is paraffin wax (or petroleum wax) which consists of a mixture of hydrocarbon molecules, in particular hydrocarbon molecules containing between 20 and 40 carbon atoms.

[0077] Preferred is a coating composition according to the present invention, wherein the hydro- phobic compounds with a melting point above 25 °C have a maximum deviation in the number of carbon atoms of 4 or less, preferably 3 or less, more preferably 2 or less.

[0078] Also preferred is a coating composition according to the present invention, wherein the fatty alcohols have a maximum deviation in the number of carbon atoms of 4 or less, preferably 3 or less, more preferably 2 or less.

[0079] Above defined preferred embodiments, wherein either the hydrophobic compounds with a melting point above 25 °C or the fatty alcohols or both components of the coating composition have a narrow range in terms of chain length, i.e., are as monodisperse as possible, are beneficial in terms of lamellae formation, nano-platelet growth and stability, co-crystal- lization compatibility with the polymer component and further aspects of second level (nano)roughness formation. In particular platelet formation is favoured when the chain lengths within component i) and / or ii) are “matching”.

[0080] Preferred is a coating composition according to the present invention, wherein the coating composition comprises an organic solvent, wherein preferably the organic solvent comprises one or more solvents selected from the group consisting of substituted and nonsubstituted linear, branched, and cyclic alkanes, alkenes, alkynes, chlorinated alkanes, alcohols, substituted and non-substituted aromatic and heteroaromatic compounds; more preferably the organic solvent is selected from the group consisting of toluene, substituted toluenes like xylene and mesitylene, solvent naphta, cyclohexane, chloroform (CHCh), dichloromethane (CH2CI2), and mixtures thereof, even more preferably the organic solvent is selected from the group consisting of toluene, chloroform (CHCh), dichloromethane (CH2CI2), and mixtures thereof.

[0081] The presence of a solvent within the coating composition allows for a good miscibility of the main components. It further allows for a good applicability of the coating composition on a substrate surface. The amount and the nature of the solvent is preferably selected in order to allow for a facile handling of the coating composition in terms of, e. g., viscosity and shelf life, and can be adapted according to the needs, in particular needs and confinements arising from the coating process in which the coating composition is to be applied.

[0082] Preferred is a coating composition according to the present invention, wherein the weight ratio of the total amount of hydrophobic (co)polymers to the total amount of fatty alcohols is in a range of from 1 :0.1 to 1 :10, preferably is in a range of from 1 :0.2 to 1 :5, more preferably is in a range from 1 :0.25 to 1 :3.

[0083] Own experiments have shown that above defined preferred weight ratios of the total amount of polymeric component iii) to the total amount of fatty alcohol component ii) are particularly beneficial in terms of a reliable and dense (nano)platelet growth (second level surface structure) with ternary coating composition systems. The weight ratio of component i) on the other hand is very flexible and not limited by any numbers as the one or more hydrophobic compounds with a melting point above 25 °C of component i) mainly serve as feedstock for (nano)platelet formation.

[0084] In accordance with the primary object of the invention as stated above, the present invention relates to the use of a coating composition according to the invention for post treatment of a substrate surface or parts of a substrate surface.

[0085] Preferably, the coating composition according to the invention is used to form a superhydrophobic substrate surface, in particular used to produce a composite material with a superhydrophobic surface as defined herein above and herein after.

[0086] Even more preferably, the coating composition according to the invention is used in a process according to the present invention.

[0087] Particularly preferably the coating composition according to the invention is used for post treatment of a substrate selected from the group consisting of

[0088] - materials in aerospace applications, in particular materials in or on board of airplanes,

[0089] - materials in marine applications, in particular materials in or on board of ships or boats,

[0090] - materials in transportation applications, in particular materials in or on board of cars, lorries, or trains,

[0091] - containers and parts of containers,

[0092] - buildings and parts of buildings, in particular architectural coatings,

[0093] - electronic devices and parts of electronic devices, and

[0094] - packaging materials, in particular packaging materials for food, packaging materials for chemicals and agrochemicals, packaging materials for electronic devices, and the like.

[0095] Generally, in order to benefit from C-H-insertion crosslinking in terms of micro-aggregate to substrate surface binding and / or adhesion as described above, post treatments of organic substrates containing saturated C-H-Bonds with the coating composition according to the invention is preferred.

[0096] In accordance with the primary object of the invention as stated above, the present invention relates to a composite material with a superhydrophobic surface comprising a) a substrate, and b) a surface structure obtained by applying a coating composition according to the present invention to a surface or parts of a surface of the substrate and at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface, wherein the surface structure, preferably the whole composite material, contains less than 1 % by weight of fluorine determined by combustion ion chromatography.

[0097] The substrate of the composite material preferably is a synthetic material, more preferably is a synthetic material selected from the group consisting of glass, metals, silicon, polymer materials including elastomeric and thermoplastic polymers, compound materials such as fiber-reinforced materials, naturally derived polymer compounds such as cellulose-based materials, resins, coatings and paints such as automotive, marine, aerospace, industrial, coil, architectural, decorative coatings and paints, concrete, paper, wood, and textiles, as well as mixtures, compounds, films, webs and laminates thereof.

[0098] Also preferred is a composite material with a superhydrophobic surface, wherein at least parts of the surface of the substrate, preferably all parts of the surface of the substrate which are covered with the surface structure, are free of elevations and / or depressions with spatial dimensions vertical to the substrate surface of above 100 pm, preferably above 50 pm, more preferably above 25 pm. In other words: the surface of the substrate which is covered with the surface structure preferably is essentially free of any larger elevations and / or depressions, thus considered flat or at least almost flat.

[0099] In another preferred aspect of the present invention a composite material with a superhydrophobic surface is preferred, wherein at least parts of the surface of the substrate, preferably all parts of the surface of the substrate which are covered with the surface structure, are free of elevations and / or depressions with spatial dimensions vertical to the substrate surface of above 10 pm, preferably above 5 pm, more preferably above 1 pm. In other words: the surface of the substrate which is covered with the surface structure preferably is essentially free of any substantial elevations and / or depressions and can thus be considered as a very flat surface. This is inter alia the case in a polished silicon wafer substrate which is a particularly suitable and preferred substrate according to the present invention.

[0100] Correspondingly, the surface structure according to the present invention is compatible with a wide variety of different substrates, and is in particular suitable for covering a synthetic material and / or a flat or almost flat substrate. The present invention thus enables the creation of superhydrophobicity on very challenging types of substrates which gives rise to plentiful areas of use in many different products.

[0101] The present invention however is not limited to flat substrate surfaces and can also be applied to a “rough” substrate surface featuring elevations and / or depressions. In particular riblet structures and also paper, cardboard and the like are suitable substrates featuring surface topologies which are explicitly covered by the present invention.

[0102] The present invention thus also pertains to a composite material with a superhydrophobic surface, wherein the surface of a substrate is at least partially covered by a surface structure (also called surface layer). Said surface structure comprises self-assembled microaggregates with a distinct hierarchical form and structure. The micro-aggregates feature at least a two-tier roughness as they comprise i) a polymer scaffold as aggregate base in microscale dimensions, i.e., the first tier or level of the aggregate structure, and ii) wax platelets as aggregate surface in nanoscale dimensions, i.e., the second tier or level of the aggregate structure. The geometric form of the surface structure enables particularly stable Cassie-Baxter (solid / air-composite) wetting states with water (as described for the lotus leaf in literature) and generates superhydrophobicity of the surface of the composite material. The synergistic interaction of the aggregate base in microscale dimensions and the aggregate surface in nanoscale dimensions leads to beneficial properties of the composite material in terms of stability and durability, substrate compatibility and furthermore results in a peculiar strong superhydrophobic effect. The self-assembled micro-aggregates of the surface structure are preferably essentially formed by hydrophobic compounds / materials which further enhances the superhydrophobic effect.

[0103] Individual self-assembled micro-aggregates may be of any shape, height and size. The overall distribution of individual self-assembled micro-aggregates on the surface of the substrate may vary depending on the production method, the coating composition and / or the substrate used for producing the composite material. The present invention is not limited to a specific coverage rate of the substrate surface nor by any other distinct feature such as the height of the surface layer as long as the overall structure falls within the definitions defined herein. Individual self-assembled micro-aggregates may be spatially separated, in some cases may also overlap or form clusters.

[0104] Preferred is a composite material according to the invention, wherein at least 50%, preferably at least 70%, more preferably at least 80%, most preferably at least 90% of the substrate surface is covered with self-assembled micro-aggregates. Since the geometric nature of the micro-aggregates does not allow for a gapless coverage of the substrate surface - mostly separated micro-aggregates are not the same as a closed layer - the term “covered” as used herein allows for the presence of free space between the self-assembled micro-aggregates. A substrate surface is thus considered to be covered with self-assembled micro-aggregates when the ratio of the substrate surface area featuring self-assembled micro-aggregates to the ratio of the substrate surface area not featuring self-assembled micro-aggregates, i.e. the free space between the self-assembled micro-aggregates, is at least 1 to 20, preferably is at least 1 to 10, more preferably is at least 1 to 7, even more preferably is at least 1 to 5 and most preferably is at least 1 to 3.

[0105] The term “comprises wax platelets as aggregate surface” does not mean that the whole surface of the self-assembled micro-aggregates needs to be completely covered by wax platelets. It suffices that a significant part of the aggregate surface is covered by wax platelets, preferably at least 50% of the aggregate surface, more preferably at least 80% of the aggregate surface, even more preferably at least 90% of the aggregate surface is covered by wax platelets.

[0106] The surface topology of the composite material can be best investigated via electron microscopy such as transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscope (SEM) or other known methods.

[0107] Preferred is a composite material with a superhydrophobic surface, wherein the average size of one self-assembled micro-aggregate is in a range of from 10 pm2to 500 pm2, preferably is in a range of from 20 pm2to 250 pm2.

[0108] It has been found that said preferred dimensions of one self-assembled micro-aggregate are particularly suitable in order to create a reliable and durable superhydrophobic surface layer.

[0109] Also preferred is a composite material with a superhydrophobic surface, wherein the polymer scaffold is covalently bound to the substrate surface.

[0110] Said preferred embodiment of the present invention creates an even stronger adhesive interaction of the self-assembled micro-aggregates with the substrate surface which leads to a higher stability and durability of the superhydrophobic surface layer. Covalent bonds are preferably created by crosslinks formed between the (co)polymer chains of the polymer scaffold with the substrate surface.

[0111] In a particular preferred embodiment said crosslinks are formed via C,H-insertion crosslinking (CHic reaction), wherein one or more active (co-)monomers of the (co)polymers serve as crosslinking moieties which may be activated upon photochemical and / or thermal activation and are thus able to insert into C-H bonds of the substrate surface.

[0112] Preferred is a composite material with a superhydrophobic surface, wherein the superhydrophobic surface is self-healing, preferably self-healing upon heating the surface of the composite material to a temperature in the range of 1 °C to 20 °C, preferably 5 °C to 10 °C, below the melting point of the wax platelets.

[0113] It has been found that the composite material with a superhydrophobic surface according to the invention has the ability to “self-heal”. This is most likely made possible by the hierarchical, at least two-tier roughness, of the self-assembled micro-aggregates which form the surface structure and in particular made possible by the presence of wax platelets which mainly consist of component i) of the coating composition, i.e. mainly consist of hydrophobic (and crystallizable) compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, and their ability to (re)form by ordered self-assembly and / or (co-)crystallization. The term “self-healing” means that the superhydrophobic properties of the original surface platelet structure of a composite material can be at least partially, in most cases almost completely, restored after damage. In particular the wax platelets as aggregate surface are prone to damage and / or altering processes upon mechanical or chemical exposure. This can lead to an unwanted reduction of the superhydrophobic performance of the composite material. However, said damage can be substantially reversed by regrowth of the wax platelets as aggregate surface. This regrowth is induced or accelerated in a self-healing process, in particular upon annealing processes, so-called heat-induced self-healing. It has been found that heating the surface of the composite material to a temperature in the range of 1 °C to 20 °C, preferably 5 °C to 10 °C, below the melting point of the wax platelets is particularly suitable for an accelerated regrowth of the wax platelets.

[0114] The self-healing process of the composite material can be investigated and evidenced via electron microscopy such as transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscope (SEM) or other known methods.

[0115] Preferred is a composite material with a superhydrophobic surface according to the present invention, wherein the surface structure of the composite material is obtained by applying a coating composition according to the present invention to a surface or parts of a surface of a substrate in a process according to the present invention.

[0116] Accordingly, the coating composition as defined herein is able to create a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface which leads to a composite material with a superhydrophobic surface and which addresses the primary object of the invention as stated above.

[0117] The surface structure of the composite material according to the present invention is thus formed by the main components of the coating composition (preferably a coating composition as defined herein above as being preferred), i.e. the self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness are essentially made of: i) one or more hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, ii) one or more fatty alcohols, iii) one or more hydrophobic (co)polymers, wherein the one or at least one of the more than one hydrophobic (co)polymers comprises linear side-chains.

[0118] The polymer scaffold as aggregate base is preferably essentially made of the polymer component iii) of the coating composition (preferably a polymer component iii) as defined herein above as being preferred).

[0119] The wax platelets as aggregate surface are preferably essentially made of components i) and ii) of the coating composition (preferably by components i) and ii) as defined herein above as being preferred).

[0120] Preferred is a composite material with a superhydrophobic surface according to the present invention, wherein the surface structure, preferably the whole composite material, contains less than 0.1 % by weight of fluorine, preferably less than 0.01 % by weight of fluorine, determined by combustion ion chromatography.

[0121] Preferred is a composite material with a superhydrophobic surface according to the present invention, wherein

[0122] - the composite material is a drag-reducing material, in particular a riblet material, preferably the composite material is a component of aircrafts, trains, ships or other means of transportation, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, or pipes, and / or

[0123] - the composite material is an anti-icing and / or easy-to-clean and / or self-cleaning and / or anti-fogging material and / or anti / non-fouling material, preferably an optical material or a riblet material, preferably the composite material is a component of indoor lightings, outdoor lightings, optical devices, lidar sensors, radar sensors, laser-based systems, heads-up displays, aug- mented / virtual reality devices, aircrafts, trains, ships or other means of transportation, solar power plants including photovoltaic and photothermic solar power plants, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, or pipes, and / or

[0124] - the composite material is an air-retaining material, preferably also an anti / non-fouling material, preferably the composite material is a component of pipes, offshore structures, surfboards, ship hulls, ship propellers, hydrofoils, underwater turbines, pumps, hydroelectric power plants, tidal power plants, aquariums, swimming pools, water containers or water tanks including ships' ballast water tanks, and / or

[0125] - the composite material is a porous material, preferably the composite material is a membrane, a woven or non-woven fabric, and / or paper.

[0126] The composite material according to the present invention is preferably characterized by preferred embodiments as stated herein below:

[0127] Preferred is a composite material with a superhydrophobic surface according to the present invention, wherein the average number of wax platelets on the surface of the self-assembled micro-aggregates is in a range of from 5 to 500 per 100 pm2, preferably is in a range of from 10 to 300 per 100 pm2, more preferably is in a range of from 20 to 200 per 100 pm2, determined by scanning electron microscopy.

[0128] Also preferred is a composite material with a superhydrophobic surface according to present invention, wherein at least 50%, preferably at least 80% of the wax platelets of the surface structure have a three-dimensional shape, determined by scanning electron microscopy, characterized in that

[0129] - the extension of a wax platelet in at least two spatial directions is in the range of from 0.5 pm to 10 pm, and / or

[0130] - the height of a wax platelet is at least three times smaller than its width and / or length, and / or

[0131] - the aspect ratio of width to length of a wax platelet (w:l) is in a range of from 5:1 to 1 :5, preferably 10:1 to 1 :10. and / or

[0132] - the height of a wax platelet is in a range of from 0.05 pm to 0.5 pm, and / or

[0133] - the width and / or length of a wax platelet is in a range of from 0.5 pm to 5 pm, and / or

[0134] - the length of the smallest cross-section through the wax platelet is at least 10 times smaller, preferably at least 20 times smaller, more preferably at least 30 times smaller, than the maximum spatial extension of the wax platelet in the plane being perpendicular to the smallest cross-section through the wax platelet.

[0135] Said above-defined preferred embodiments of the composite material according to the present invention pertaining to the average number of wax platelets and the geometrical features of the wax platelets have been found to be particularly suitable for the creation of a long lasting and stable superhydrophobic surface structure / layer.

[0136] In accordance with the primary object of the invention as stated above, the present invention relates to a process of producing a composite material with a superhydrophobic surface, preferably a composite material with a superhydrophobic surface according to the present invention, at least comprising the following steps: a) preparing or providing a coating composition according to the invention, b) wetting a surface or parts of a surface of a substrate with the prepared or provided coating composition, so that the surface or parts of the surface of the substrate are covered by the coating composition, c) drying the wetted substrate, so that a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface is obtained.

[0137] The overall process and the individual process steps according to the present invention are very simple and do not require for complex machinery, thus allowing for practical handling in a wide variety of applications and with different kinds of material. The process according to the present invention also has a much lower energy consumption than processes known in the art which usually require hours of heating in order to obtain a superhydrophobic surface structure, see inter alia the process described for the two-component coating composition in WO 2018 / 193094 A1 .

[0138] The process according to the invention as described above allows for the facile production of stable and preferably self-healing hydrophobic coating layers. The coating layer synergistically adds the superhydrophobic function to the composite material surface, in particular to flat substrates. The resulting composite material with a superhydrophobic surface is hierarchically structured as it features self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0139] Preferred is a process according to the present invention, comprising the additional step of d) at least partially crosslinking the one or more hydrophobic (co)polymers with themselves and / or with potential organic substrates, wherein preferably the step of at least partially crosslinking is initiated by radiation and / or heat, more preferably by radiation, even more preferably by UV radiation, most preferably by UV radiation from sunlight.

[0140] Said step of at least partially crosslinking may also be identical to the step of drying.

[0141] Moreover and favourably, the step of crosslinking the one or more hydrophobic (copolymers facilitates and enhances durability of the hydrophobic surface layer. The resulting (nano)layers in the form of crosslinked self-assembled micro-aggregates can be used on various substrates for various applications, e. g., for Salvinia effect, anti-icing / easy-to-clean riblets or optics, and are generally useful for adding I enhancing superhydrophobicity on top of a former flat substrate surface.

[0142] Also preferred is a process according to the present invention, wherein the step of wetting a surface or parts of a surface of a substrate with the prepared or provided coating composition is carried out by any object coating method such as spin coating, dip coating, or spray coating, or by any roll-to-roll coating methods such as Mayer rod coating, slot-die coating, curtain coating or gravure coating, and combinations thereof, preferably by spin coating and / or dip coating and / or spray coating.

[0143] Further preferred is a process according to the present invention, wherein the coating composition according to the present invention is prepared by completely dissolving the main components i), ii) and iii) of the coating composition in a solvent, preferably at a temperature in a range from 30 °C to 60 °C, also preferably under stirring.

[0144] Also preferred is a process according to the present invention, further comprising one or more of the following additional steps:

[0145] - shaking, stirring, and / or otherwise mixing the prepared or provided and optionally stored coating composition before the step of wetting,

[0146] - removing dust and / or other contaminations from the surface of the substrate, preferably by washing with water and / or at least one solvent before the step of wetting, more preferably by rinsing with and / or by immersion in water and / or at least one solvent, preferably a solvent selected from isopropanol, acetone and ethanol.

[0147] EXAMPLES

[0148] The following examples according to the present invention are meant to further explain and illustrate the present invention without limiting its scope.

[0149] 1 . Exemplary coating compositions for the production of superhydrophobic surfaces:

[0150] 1.1 Materials:

[0151] The following materials have been used as preferred embodiments of components in the coating composition. We note that any other materials fulfilling the definitions as set forth in the claims are also suitable. i) hydrophobic (and crystallizable) compounds with a melting point above 25 °C:

[0152] - n-docosane (n-C22H46) (99%, purchased from Sigma-Aldrich)

[0153] - n-octacosane (n-C2sH58) (99%, purchased from Sigma-Aldrich)

[0154] - n-nonacosane (n-C29Heo) (analytical standard, purchased from Sigma-Aldrich) ii) fatty alcohols:

[0155] - 1 -octadecanol (n-CisHs -OH) (pharmaceutical standard, purchased from Sigma-Aldrich)

[0156] - 1 -docosanol (n-C22H45-OH) (> 97%, purchased from Sigma-Aldrich)

[0157] - 1-hexacosanol (n-C26H53-OH) (> 97%, purchased from Sigma-Aldrich) iii) hydrophobic (co)polymers comprising linear side-chains (and being capable of inducing (co-)crystallization and / or ordered self-assembly of components i) and ii)):

[0158] - poly(behenyl acrylate-co-2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate) (for synthesis, see below; the monomer behenyl acrylate was provided by BASF SE)

[0159] - poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone)) (for synthesis, see below; the monomer behenyl acrylate was provided by BASF SE) iv) solvents:

[0160] - toluene (synthesis grade, purchased from Carl Roth)

[0161] - dichloromethane (CH2CI2) (synthesis grade, purchased from Carl Roth)

[0162] - chloroform (CHCh) (synthesis grade, purchased from Carl Roth) v) alternative amphiphilic compounds not according to the present invention: - n-octadecylamine (n-CisH37-NH2) (> 99%, purchased from Sigma-Aldrich)

[0163] - behenic acid (n-C2iH43-COOH) (analytical standard, purchased from Sigma-Aldrich).

[0164] Synthesis of poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone)):

[0165] Poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone)) (p(BehAc-co-MABP)) with a molar fraction of MABP = 5% based on the total amount of substance, prepared by free- radical polymerisation using azobisisobutyronitrile (AIBN), having an average molecular weight Mw in the range of 25 to 150 kDa depending on the reaction conditions of the free- radical polymerisation and with the following general formula (I):

[0166] In one example, p(BehAc-co-MABP) was prepared by free-radical polymersiation as follows: Behenyl acrylate (50 g, available from BASF labelled “Behenyl Acrylate 22 F (BEA 22 F)”) was dissolved in chloroform (50 mL) and flushed over neutral alumina to remove any inhibitor (this step is, however, considered optional). Afterwards, chloroform was removed at reduced pressure, followed by drying in high vacuum over night. The solid was combined with 4-methacryloyloxy benzophenone (MABP; synthesised according to literature; 1 .75 g) and redissolved in toluene (100 mL) at 60 °C in a three-neck flask. The solution was purged with nitrogen for 20 min before closing the flask to retain a nitrogen atmosphere. The solution was retained at about 58 °C. AIBN (0.43 g) was dissolved in toluene (5 mL), added to the reaction mixture and the mixture was stirred for 48 h. According to reaction control by thin-layer chromatography (cyclohexane / ethyl acetate 20:1 ; staining with KMnC ), this corresponded to full monomer conversion. The reaction mixture was then slowly added to warm acetone (45 °C; 2 L). The precipitate was filtered off and dried in high vacuum over night. Characterisation by DSC and NMR confirmed that the opaque, crystalline solid obtained was p(BehAc-co-MABP) with a molar fraction of MABP of about 5%.

[0167] According to the manufacturer, parts of the behenyl acrylate used (BASF, “Behenyl Acrylate 22 F (BEA 22 F)”) are from biogenic material such as plant-based material, preferably from vegetable oil such as canola oil. This can be shown by C-14 analysis. Preferably, the part from biogenic material is the behenyl chain. Accordingly, both the behenyl acrylate itself and the p(BehAc-co-MABP) comprise a share of material from renewable sources. When all the behenyl chains in pure behenyl acrylate are from renewable sources, this corresponds to a share of atoms of at least about 81 % by mass. The share in the p(BehAc- co-MABP) can be calculated on this basis.

[0168] Synthesis of poly(behenyl acrylate-co-2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate) (p(BehAc-co-(4-NitroPEDAz))):

[0169] The synthesis was conducted strictly analogous to the synthesis of poly(behenyl acrylate- co-(4-methacryloyloxy benzophenone)) described above. Modified details were the careful exclusion of daylight during all steps to prevent premature crosslinking by the daylightsensitive crosslinker, as well as a modified amount of 2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate to satisfy the desired 5 mol% according to the differing molecular weight of the co-monomer (1 .92 g).

[0170] Poly(behenyl acrylate-co-2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate) (p(BehAc-co-(4-Nitro-PEDAz))) with a molar fraction of 4-NitroPEDAz = 5% based on the total amount of substance, prepared by free-radical polymerisation using azobisisobu- tyronitrile (AIBN), with the following general formula (II):

[0171] (II)

[0172] In one example, p(BehAc-co-(4-NitroPEDAz)) was prepared by free-radical polymersiation as follows: Behenyl acrylate (50 g, available from BASF labelled “Behenyl Acrylate 22 F (BEA 22 F)”) was dissolved in chloroform (50 mL) and flushed over neutral alumina to remove any inhibitor (this step is, however, considered optional). Afterwards, chloroform was removed at reduced pressure, followed by drying in high vacuum over night. The solid was combined with 2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate (4-NitroPEDAz; synthesised according to literature; 1.92 g) and redissolved in toluene (100 mL) at 60 °C in a three-neck flask. As soon as 4-NitroPEDAz was employed in the procedure, the reaction mixture and isolated solid(s) were handled under exclusion of daylight using aluminum foil and / or brown-glass equipment due to the photosensitivity towards daylight of 4-Ni- troPEDAz. The solution was purged with nitrogen for 20 min before closing the flask to retain a nitrogen atmosphere. The solution was retained at about 58 °C. AIBN (0.43 g) was dissolved in toluene (5 mL), added to the reaction mixture and the mixture was stirred for 48 h. According to reaction control by thin-layer chromatography (cyclohexane / ethyl acetate 20:1 ; staining with KMnC ), this corresponded to full monomer conversion. The reaction mixture was then slowly added to warm acetone (45 °C; 2 L). The precipitate was filtered off and dried in high vacuum over night. Characterisation by DSC and NMR confirmed that the opaque, citrus-yellow crystalline solid obtained was p(BehAc-co-(4-NitroPEDAz)) with a molar fraction of 4-NitroPEDAz of about 5%.

[0173] 1 .2 Preparation of coating compositions according to the invention:

[0174] CC-1 : Coating composition CC-1 was prepared by dissolving 12.5 g / L of the copolymer poly(behenyl acrylate-co-2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate), 25 g / L of n-octacosane (n-C2sH58) as wax component, and 12.5 g / L of 1 -docosanol (n-C22H45-OH) as fatty alcohol in toluene.

[0175] CC-2: Coating composition CC-2 was prepared by dissolving 25 g / L of the copolymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), 50 g / L n-octacosane (n- C28H58) as wax component, and 25 g / L 1 -docosanol (n-C22H45-OH) as fatty alcohol in chloroform.

[0176] CC-3: Coating composition CC-3 was prepared by dissolving 17 g / L of the copolymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), 33 g / L n-octacosane (n- C28H58) as wax component, and 50 g / L 1 -docosanol (nC22H45-OH) as fatty alcohol in chloroform.

[0177] All coating compositions according to the invention contained less than 0.01 % by weight of fluorine determined by combustion ion chromatography and were essentially free of per- and / or polyfluorinated alkyl substances (PFAS).

[0178] The fluorine content was determined by combustion ion chromatography as follows: The sample is thermohydrolysed at about 1000 °C in an oxygen-water vapor stream. The evolved hydrogen fluoride is absorbed into an aqueous solution, and detected as fluoride ions by ion chromatography. Detection is achieved by monitoring conductivity, wherein conductivity of the eluent is reduced by suitable suppressor equipment.

[0179] 2. Exemplary processes according to the present invention of producing a composite material with a superhydrophobic surface:

[0180] AM-1 - spray coating process using coating composition CC-2:

[0181] The substrates to be treated were glued with double-sided tape to the backside of a fume hood at room temperature. The substrates were wiped with isopropanol and left to dry passively until visibly dry, or used as received in case of fibrous substrates (commercial copypaper). For one cycle of spraying, a coating composition CC-2 as defined above was sprayed using a commercial pneumatic spray gun (commercial name Krautzberger Mignon 4) with an air pressure of 4 bar through a nozzle with 0.5 mm diameter, passing over all parts of the substrate that were to be coated, and then left to dry in the fume hood at room temperature for 60 seconds. Optionally, the spraying cycle was repeated (as indicated in the examples).

[0182] AM-2 - dip coating process using coating composition CC-2:

[0183] For the dip coating process, the respective substrates were cleansed of impurities and dust using Isopropanol and then left to dry passively until visibly dry. The substrates were then immersed into coating composition CC-2 at a controlled speed, and promptly retrieved at the same speed. For a coating composition CC-2 according to the invention, a retrieval speed greater than 1 m / min was identified to deposit a sufficient amount of material, Immersion speed and time spent between immersion and retrieval are less influential and were not varied. The resulting wetted materials were left hanging in constant fume hood air flow until their front side appeared dry.

[0184] In some cases curing of the coating layer via UV irradiation from a Stratagene Stratalinker 2400, A = 254 nm, with a dose of 1-2 J / cm2was performed after drying.

[0185] AM-3 - spray coating process using coating composition CC-1

[0186] The substrates to be treated were placed on appropriate holders inside a fume hood at room temperature. The substrates were wiped with isopropanol and left to dry passively until visibly dry. The room was illuminated by red light only. For one cycle of spraying, a coating composition CC-1 as defined above was sprayed using a commercial pneumatic spray gun (commercial name SATA HVLP) with an air pressure of 2 bar through a nozzle with 0.8 mm diameter, passing over all parts of the substrate that were to be coated, and then left to dry in the fume hood at room temperature. Optionally, the spraying cycle was repeated (as indicated in the examples).

[0187] 3. Exemplary composite materials with a superhydrophobic surface:

[0188] 3.1 Substrates:

[0189] The following substrates have been used as preferred embodiments. We note that any other materials fulfilling the definitions as set forth in the claims are also suitable.

[0190] Flat and synthetic substrates:

[0191] - PET film: A commercially available PET film, double-sided urethane coated for enhanced adhesion to inks and coatings, especially to UV-curing inks, with a layer thickness of 125 pm, provided by SKC, South Korea

[0192] - polished silicon wafer: Single-side polished (1 10-plane), diameter 125 mm, thickness 625+ 25 pm, purchased from Si-Mat -Silicon Materials e.K., D-86916 Kaufering

[0193] - HDPE plate: Commercially available plates with thicknesses of either 1 or 2 mm, UV- stabilized (probably using soot, black in colour), provided by S-Polytec GmbH (Kranenburg, Germany)

[0194] - paper sheet: Commercially available copy paper (“Evercopy premium”, grammage 80g / m2, fully recycled and bleached), provided by PAPETERIES DE CLAIREFONTAINE, France

[0195] - aluminium

[0196] - glass: MS10UW2 - Microscope Slides, 1 mm Thick, purchased from Thorlabs, Inc.

[0197] - crosslinked poly(dimethyl acryl amide-co-(4-methacryloyloxy benzophenone))-thin film on polished silicon wafer: polished silicon wafer as specified above, copolymer was self-synthesized

[0198] - crosslinked poly(1 H,1 H,2H,2H-perfluorodecyl acrylate-co-(4-methacryloyloxy benzophe- none))-thin film on polished silicon wafer: polished silicon wafer as specified above, copolymer was self-synthesized following a well-known standard procedure (free-radical polymerisation) similar to the procedure described for P(BehAc-co-MABP) above

[0199] The latter two substrates were prepared as follows:

[0200] A polished Silicon wafer was rinsed subsequently with toluene, acetone and isopropanol and then dried thoroughly using a nitrogen stream. The wafers were then spin-coated for 30 seconds at 1500 rpm with 60 pL of a (Triethoxy)-benzophenone-silane solution (10% in toluene) and the obtained substrates were cured at 120°C for 20 minutes to silanize the wafer’s surface with benzophenone units for later covalent surface-attachment of polymer networks.

[0201] After another rinsing- and drying-step as described above, The wafers were spin-coated for 30 seconds at 3000 rpm with 100 pL of a polymer solution of either 30 g / L poly(dimethyl acryl amide-co-(4-methacryloyloxy benzophenone)) in ethanol or 30 g / L poly(1 H,1 H,2H,2H-perfluorodecyl acrylate-co-(4-methacryloyloxy benzophenone)) in

[0202] NOVEC 7200. The obtained polymer thin films on benzophenone-modified Si were then subjected to 254 nm UV radiation at a dosage of 1 J / cm2using a Stratalinker 2400 (Strat- agene, USA), resulting in covalent attachment of the polymers to the wafer and curing of the applied polymer network to prevent re-dissolution and detachment during coating with the compositions according to the invention.

[0203] Riblet substrate:

[0204] The riblet substrate featuring microscale elevations (not flat) was prepared via a method as described in WO 2021058658 A1 , claim 1 , by performing, in this order, the steps 1 , 2-ii, 3-ii, 4, 5-ii from another commercial, radiation-curable coating composition C2a which comprises at least one urethane acrylate, at least one photoinitiator, and also commercial additives, corresponding to a preferred coating composition C2a as described in WO 2021058658 A1 .

[0205] 3.2 Composite materials according to the invention:

[0206] CM-1 : Composite material CM-1 , depicted in Fig. 1 , has been prepared by applying coating composition CC-1 (as described above) to a commercially available PET film as substrate in a spray coating process AM-3 (as described above).

[0207] CM-2: Composite material CM-2, depicted in Fig. 2, has been prepared by applying coating composition CC-1 (as described above) to the riblet substrate (as described in detail above) in a spray coating process AM-3 (as described above).

[0208] CM-3: Composite material CM-3, depicted in Fig. 3A, has been prepared by applying coating composition CC-2 (as described above) to a polished silicon wafer as substrate in a spray coating process AM-1 (as described above).

[0209] CM-4: Composite material CM-4, has been prepared by applying coating composition CC-2 (as described above) to the riblet substrate (as described in detail above) in a spray coating process AM-1 (as described above).

[0210] CM-5: Composite material CM-5, depicted in Fig. 3B, has been prepared by applying coating composition CC-2 (as described above) to an HDPE plate as substrate in a spray coating process AM-1 (as described above).

[0211] CM-6: Composite material CM-6, depicted in Fig. 3C, has been prepared by applying coating composition CC-2 (as described above) to a paper sheet as substrate in a spray coating process AM-1 (as described above).

[0212] CM-7: Composite material CM-7 has been prepared by applying coating composition CC3 (as described above) to a HDPE-Plate as substrate in a spray coating process AM-1 (as described above).

[0213] The resulting composite materials according to the invention contained less than 0.01 % by weight of fluorine determined by combustion ion chromatography as described in detail above and were essentially free of per- and / or polyfluorinated alkyl substances (PFAS).

[0214] The resulting composite materials have been analysed via scanning electron microscopy (SEM; JEOL JSM-IT800 HL) in order to investigate and characterize the geometrical structure of the surface. As can be seen from the results of the scanning electron microscopy analysis, see the Figures, all exemplary composite materials according to the present invention are characterized by a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0215] The surfaces of composite materials according to the invention which have been prepared from materials and coating compositions via processes as described above all showed static water contact angles of at least 140° and droplet roll-off angles of no more than 20° as measured by an optical goniometer using droplets with a volume of 10 pL and thus fulfil the requirements to be labelled as superhydrophobic surface.

[0216] 4. Performance tests of composite materials according to the present invention

[0217] 4.1 Heat-induced self-healing:

[0218] The method of damage chosen to investigate self-healing was linear abrasion in accordance to common testing guidelines for superhydrophobic surfaces. The damaged surfaces depicted in Fig. 10 was prepared by wedging a stripe of SiC sandpaper (1000 grit) between composite material CM-7 (as described above) and a 3D-printed stamp with rectangular surface area towards the composite material of 1 ,5x1 ,5 cm2. Said stamp was loaded with

[0219] 100 g of weight (resulting pressure 4.4 kPa) and the sandpaper was pulled over the composite material for a distance of 10 cm with a constant retraction speed of 0.2 m / min.

[0220] After composite material CM-7 was damaged as described above, resulting in the loss of the original surface structure, in particular the loss of the hierarchical at least two-tier roughness of the micro-aggregates and the loss of wax platelets as aggregate surface, the damaged composite material has been subjected to a heat-induced self-healing process by annealing the composite material for 1 hour on a pre-heated laboratory heating plate, followed by storage of the composite material at room temperature (ca. 20 °C) for 1 hour after which scanning electron microscopy (SEM) images were taken. The temperatures used in the annealing process were 27 °C, 40 °C, and 50 °C respectively. As can be seen from the scanning electron microscopy (SEM) images depicted in Fig. 10, the original surface structure was (at least partially) restored upon heating the surface of the composite material. In particular the hierarchical at least two-tier roughness of the micro-aggregates can be restored since wax platelets as aggregate surface are regrown. Said effect is more pronounced I accelerated upon heating at elevated temperatures.

[0221] 4.2 Droplet test for wetting properties:

[0222] For the droplet test, the respective composite materials were placed horizontally on a lab bench. Small water droplets of = 3 mm - 5 mm in diameterwere dispensed onto the surface of the respective composite material from a disposable plastic pipette and photographed. Then, the respective composite materials were manually moved horizontally on the lab bench with an initial acceleration of about 2 to 5 m / s2up to a speed of about 0.3 to 0.6 m / s, and it was assessed whether the droplets remained on the same location of the surface of the respective composite material (i. e., if they moved together with the respective composite material), or if they lagged behind due to inertia (i. e., in the extreme case, they would remain at the same position relative to the lab bench). The observed behaviour was rated as indicated by the following symbols:

[0223] • desired anti-wetting behaviour if droplets largely lagged behind the movement of the composite material, i. e., if droplets largely remained at the same position relative to the lab bench, x undesired wetting behaviour if droplets largely followed the movement of the composite material, i. e., if droplets largely remained at the same location of the surface of the respective composite material,

[0224] O in intermediate cases. Droplet test results for selected composite materials are compiled in Table 1. This table does not include data shown in Table 2 below.

[0225] Table 1. Droplet tests for selected composite materials.

[0226] S _amp .le Com . p "os . ite S „u .bst .rat .e Coa .t.i.ngacom- C „oat ..ing process Dr .o. prlet test r material positiona rrating

[0227] 1-1 CM-1 PET film CC-1 AM-3, 1 cycle *

[0228] 1-2 CM-1 PET film CC-1 AM-3, 3 cycles *

[0229] 1-3 CM-2 Riblet CC-1 AM-3, 1 cycle * substrate

[0230] 1-4 CM-2 Riblet CC-1 AM-3, 3 cycles * substrate

[0231] 1-5 CM-3 Si wafer CC-2 AM-1 *

[0232] 1-6 CM-5 HDPE CC-2 AM-1 * plate

[0233] 1-7 CM-6 Paper CC-2 AM-1 *

[0234] 1-R1 PET film none nonex

[0235] 1-R2 PET film none nonex

[0236] 1-R3 Riblet none nonexsubstrate

[0237] 1-R4 Riblet none nonexsubstrate

[0238] As can be seen from the results of the droplet tests composite materials according to the present invention (CM-1 , CM-2, CM-3, CM5 and CM-6 respectively) which have been prepared from a coating composition according to the present invention (CC-1 or CC-2 respectively) in a process according to the present invention (AM-1 or AM-3 respectively) significantly outperform composite materials not according to the invention (reference samples 1-R1 , 1 -R2, 1-R3 and 1-R-4) in terms of wetting properties. In particular the presence of a surface structure at least partially covering the surface of the substrate and comprising selfassembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface which is obtained from treating the original substrate surface with a coating composition according to the present invention is essential for achieving a high degree of superhydrophobicity. The results also show that the coating composition according to the present invention is very versatile and can be applied to a wide variety of different substrates, in each case leading to a superhydrophobic surface with beneficial wetting properties. Furthermore the superhydrophobic surface is obtainable upon facile and simple processes which do not require for complex machinery or heating procedures, thus allowing for practical and economical handling in a wide variety of applications and with different kinds of material.

[0239] 4.3 Weathering test:

[0240] Samples of composite material CM-4 (riblet substrates, coated using coating composition CC-2 via spray coating process AM-1) were subjected to an accelerated weathering test to determine their resistance against UV light. For this, samples were first mounted on metal platelets painted white with standardised measures for sample handling. Before starting the test, initial wetting properties of new samples were assessed using the droplet test described above. The metal platelets with the samples on top were then mounted into a weathering device (Atlas, Weather-Ometer Ci 400015000, SUGA GX90; light from a xenon high-pressure light source, filtered by borosilicate glass, intensity about 0.51 W / m2± 0.02 W / m2at a wavelength of 340 nm; sample chamber ventilated with ambient air) and exposed to illumination and humidity (continuous illumination; cycles of spraying with deionised water (18 min; relative humidity of the air inside the sample chamber during this time above 95%) followed by drying (102 min; relative humidity of the air inside the sample chamber during this time about 70% ± 5%) under illumination). Samples were tested for a total duration of 1000 h with intermediate and final checks using the droplet test described above after 250 h, 500 h, 750 h, and 1000 h. Once the droplet test of a specific sample revealed undesired performance (rating x), the weathering test of said specific sample was aborted.

[0241] The results of the droplet tests before starting the weathering test (labelled “0 h”) as well as during and after the weathering test are reported in Table 2.

[0242] Table 2. Weathering stability assessed by droplet test.

[0243] Sample Spraying Droplet test rating after weathering test for different times AM-1 O h 250 h 500 h 750 h 1000 h

[0244] 2--I 1 cycle O O O O O

[0245] 2-2 3 cycles • • • • •

[0246] As can be seen from the results of the weathering stability tests composite materials according to the present invention (samples 2-1 , 2-2 and 2-3 respectively) which have been prepared from a coating composition according to the present invention (CC-2) in a process according to the present invention (AM-1) significantly outperform the composite material not according to the invention (reference sample 2-4 which has not been coated with a coating composition according to the present invention) in the droplet test. Furthermore, the surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface which creates the superhydrophobicity and which is obtained from treating the original substrate surface with a coating composition according to the present invention is very durable under weathering conditions (repeated exposure to UV radiation, moisture and drying steps) for a time span of up to 1000 h, and most likely even longer. Said durability of the composite materials under weathering conditions can already be achieved when only one cycle of a coating process according to the present invention is performed on the substrate.

[0247] BRIEF DESCRIPTION OF THE DRAWINGS

[0248] Further advantages, features and details of the invention result from the following description of the preferred embodiments as well as from the drawings. In the following, a summary of the figures is given.

[0249] Fig. 1 shows scanning electron microscopy (SEM) images of a composite material with a superhydrophobic surface according to the present invention which has been prepared from a coating composition according to the present invention on a commercially available PET film.

[0250] Fig. 2 shows scanning electron microscopy (SEM) images of a composite material with a superhydrophobic surface according to the present invention which has been prepared from a coating composition according to the present invention on a riblet substrate.

[0251] Fig. 3 shows video snapshots and scanning electron microscopy (SEM) images of three different composite materials with a superhydrophobic surface according to the present invention which have been prepared from a coating composition according to the present invention on different substrates.

[0252] Fig. 4 shows scanning electron microscopy (SEM) images of composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention wherein the fatty alcohol component has been varied.

[0253] Fig. 5 shows scanning electron microscopy (SEM) images of composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention wherein the wax component has been varied.

[0254] Fig. 6 shows scanning electron microscopy (SEM) images of composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention wherein the weight ratio of the total amount of the polymeric component to the total amount of fatty alcohols has been varied.

[0255] Fig. 7 shows scanning electron microscopy (SEM) images of composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention wherein the solvent has been varied.

[0256] Fig. 8 shows scanning electron microscopy (SEM) images of six different composite materials with a superhydrophobic surface according to the present invention which have been prepared from a coating composition according to the present invention on different substrates.

[0257] Fig. 9 shows a scanning electron microscopy (SEM) image of a composite material with a superhydrophobic surface according to the present invention which has been prepared on a polished silicon wafer from a coating composition according to the present invention and shows scanning electron microscopy (SEM) images of three composite materials not according to the present invention.

[0258] Fig. 10 shows scanning electron microscopy (SEM) images of the heat-induced self-healing of a composite material with a superhydrophobic surface according to the present invention which has been prepared on a HDPE-plate from a coating composition according to the present invention.

[0259] Fig. 11 shows a schematic representation of a composite material with a superhydrophobic surface according to the present invention.

[0260] DETAILED DESCRIPTION OF THE DRAWINGS

[0261] Fig. 1 shows scanning electron microscopy (SEM) images of a composite material with a superhydrophobic surface according to the present invention which has been prepared from coating composition CC-1 according to the present invention on a commercially available PET film as an example of a flat and synthetic substrate free of elevations and / or depressions with spatial dimensions of above 25 pm. The coating composition CC-1 used was a solution of 12.5 g / L of the copolymer poly(behenyl acrylate-co-2-(2-diazo-(4-nitro- phenyl) acetoxy) ethyl methacrylate), 25 g / L of n-octacosane (n-C2sH58) as wax component, the term “wax component” herein is equal to component i) of the coating composition, i.e. is equal to the hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, and 12.5 g / L of 1 -docosanol (n-C22H45-OH) as fatty alcohol in toluene. The coating composition was applied to the substrate in a spray coating process AM-1 according to the present invention. As can be seen from the scanning electron microscopy (SEM) images the resulting composite material features a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface. The average size of one self-assembled micro-aggregate is in a range of from 20 pm2to 250 pm2, wherein some of the self-assembled micro-aggregates are isolated on the substrate surface and other micro-aggregates form overlapping clusters. The high resolution SEM image clearly shows the presence of wax platelets as aggregate surface.

[0262] Fig. 2 shows scanning electron microscopy (SEM) images of a composite material with a superhydrophobic surface according to the present invention which has been prepared from coating composition CC-1 according to the present invention on a riblet substrate. The riblet substrate featuring microscale elevations was prepared via a method as described in WO 2021058658 A1 , claim 1 , by performing, in this order, the steps 1 , 2-ii, 3-ii, 4, 5-ii from another commercial, radiation-curable coating composition C2a which comprises at least one urethane acrylate, at least one photoinitiator, and also commercial additives, corresponding to a preferred coating composition C2a as described in WO 2021058658 A1 . The coating composition CC-1 used was a solution of 12.5 g / L of the copolymer poly(behenyl acrylate-co-2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate), 25 g / L of n-octacosane (n-C2sH58) as wax component, and 12.5 g / L of 1 -docosanol (n-C22H45-OH) as fatty alcohol in toluene. The coating composition was applied to the substrate in a spray coating process AM-1 according to the present invention. As can be seen from the scanning electron microscopy (SEM) images the resulting composite material features a surface structure at least partially covering the surface of the substrate and comprising self-assembled microaggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface. The average size of one self-assembled micro-aggregate is in a range of from 20 pm2to 250 pm2, wherein some of the self-assembled micro-aggregates are isolated on the substrate surface and other micro-aggregates form partially overlapping clusters. The high resolution SEM image clearly shows the presence of wax platelets as aggregate surface.

[0263] Fig. 3 shows video snapshots (on the top) and scanning electron microscopy (SEM) images of three different composite materials with a superhydrophobic surface according to the present invention which have been prepared from a coating composition CC-2 according to the present invention on different substrates. All substrates are synthetic substrates. The substrates used were polished silicon wafer in Fig. 3 (A), a HDPE plate in Fig. 3 (B) and a sheet of paper in Fig. 3 (C). The coating composition CC-2 used in all three cases was a solution of 25 g / L polymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), 50 g / L n-octacosane (n-C2sH58) as wax component, and 25 g / L 1 -docosanol (n-C22H45-OH) in chloroform. The coating composition was applied to the different substrates in a spray coating process AM-1 according to the present invention. As can be seen from the scanning electron microscopy (SEM) images all three resulting composite materials feature a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface. Some of the self-assembled micro-aggregates are isolated on the substrate surface and other micro-aggregates form partially overlapping clusters. The high resolution SEM images on the bottom clearly shows the presence of wax platelets as aggregate surface in all three cases. The surface structure of the polished silicon wafer in Fig. 3 (A) features smaller self-assembled micro-aggregates with an estimated average size of one self-assembled micro-aggregate in the range of from 10 to 20 pm2which are predominantly isolated on the substrate surface with free space in between. The surface structure of the HDPE plate in Fig. 3 (B) features medium sized selfassembled micro-aggregates with an estimated average size of one self-assembled microaggregate in the range of from 20 to 50 pm2which are partially isolated on the substrate surface and partially form small clusters leaving some uncovered substrate surface space in between. The surface structure of the paper sheet in Fig. 3 (C) features medium sized self-assembled micro-aggregates with an estimated average size of one self-assembled micro-aggregate in the range of from 20 to 50 pm2which completely cover the substrate surface and predominantly form medium to large sized clusters of micro-aggregates. As can be seen from the video snapshots (on the top), when a suspension of 50% by weight of soil in water is poured on the composite materials, it is immediately repelled from the surface indicating a strong superhydrophobicity of the composite materials according to the present invention. Although all three different substrates result in different surface structures in terms of substrate surface coverage, size and shape of micro-aggregates and the like, the surface coating according to the invention in each case leads to a composite material featuring a pronounced superhydrophobicity. Accordingly, the coating composition according to the present invention is very versatile and can be successfully and reliably applied to a wider variety of different substrates.

[0264] Fig. 4 shows scanning electron microscopy (SEM) images of composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention. In each case the coating compositions were applied to the substrate in a dip coating process AM-2 according to the present invention. The coating composition used was a solution of 10 g / L of polymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), 20 g / L of n-octacosane (n-C2sH58) as wax component and 10 g / L of different fatty alcohols in chloroform. The fatty alcohols used as component ii) of the coating composition were the following n-alcohols: 1 -octadecanol (n-CisH37-OH) in Fig. 4 (A), 1 -docosanol (n-C22H45-OH) in Fig. 4 (B), and 1-hexacosanol (n-C26H53-OH) in Fig. 4 (C) respectively. All of these alcohols are thus linear alkanols (n-alcohols) with a number of carbon atoms in the range of from 18 to 30. As can be seen from the high resolution scanning electron microscopy (SEM) images the resulting composite materials in all three cases feature a surface structure comprising self-assembled micro-aggregates, wherein the self-assembled micro-aggregates comprise wax platelets as aggregate surface. The overall surface structures (not shown in Fig. 4) of the composite materials in each case comprise self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0265] Fig. 5 shows scanning electron microscopy (SEM) images of three different composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention. In each case the coating compositions were applied to the substrate in a dip coating process AM-2 according to the present invention. The coating composition used was a solution of 10 g / L of polymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), 10 g / L of the fatty alcohol 1 -docosanol (n-C22H45-OH) and 20 g / L of different n- alkanes as wax component in chloroform. The n-alkanes used as wax component of the coating composition were the following: n-C22H46 in Fig. 5 (A), n-C2sH58 in Fig. 5 (B), and n-C29Heo in Fig. 5 (C) respectively. The three tested n-alkanes used as wax component, i.e. as the hydrophobic (and crystallizable) compounds with a melting point above 25 °C, are thus linear alkanes with a number of carbon atoms in the range of from 22 to 30. As can be seen from the high resolution scanning electron microscopy (SEM) images the resulting composite materials in all cases feature a surface structure comprising self-assembled micro-aggregates, wherein the self-assembled micro-aggregates comprise wax platelets as aggregate surface. The overall surface structures of the composite materials in each case comprise self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0266] Fig. 6 shows scanning electron microscopy (SEM) images of six different composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention wherein the weight ratio of the total amount of hydrophobic (co)polymers to the total amount of fatty alcohols is in a range of from 1 :0.25 to 1 :3. In each case the coating compositions were applied to the substrate in a dip coating process AM-2 according to the present invention. The coating compositions applied to the substrate contained X parts of the copolymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), 2-X parts of n-octacosane (n-C2sH58) as wax component, and N X parts of 1-docosanol (n-C22H45-OH) as fatty alcohol component, the sum of all parts in each coating composition amounting to a total concentration of 100 g / L; all components dissolved in chloroform. Above mentioned weight ratio of the total amount of hydrophobic (co)polymers to the total amount of fatty alcohols has been modified as follows: 1 :0.25 (N = 0.25) in Fig. 6 (A), 1 :0.5 (N = 0.5) in Fig. 6 (B), 1 :1 (N = 1) in Fig. 6 (C), 1 :1 .5 (N = 1 .5) in Fig. 6 (D), 1 :2 (N = 2) in Fig. 6 (E),

[0267] 1 :3 (N = 3) in Fig. 6 (F). As can be seen from the high resolution scanning electron microscopy (SEM) images the resulting composite materials in all six cases feature a surface structure comprising self-assembled micro-aggregates, wherein the self-assembled microaggregates comprise wax platelets as aggregate surface. The overall surface structures (not shown in Fig. 6) of the composite materials in each case comprise self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the selfassembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0268] Fig. 7 shows scanning electron microscopy (SEM) images of two different composite materials with a superhydrophobic surface according to the present invention which have been prepared on polished silicon wafers from coating compositions according to the present invention wherein the solvent has been varied. In both cases the coating compositions were applied to the substrate in a dip coating process AM-2 according to the present invention. The coating compositions applied to the substrate contained 10 g / L of the copolymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone)), 20 g / L of n-octacosane (n-C2sH58) as wax component, and 10 g / L of 1 -docosanol (n-C22H45-OH) as fatty alcohol. The components of the coating composition were dissolved in dichloromethane (CH2CI2) Fig. 7 (A), and chloroform (CHCh) Fig. 7 (B) respectively. As can be seen from the high resolution scanning electron microscopy (SEM) images the resulting composite materials in both cases feature a surface structure comprising self-assembled micro-aggregates, wherein the self-assembled micro-aggregates comprise wax platelets as aggregate surface. The overall surface structures of the composite materials in each case comprise selfassembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the micro-self-assembled aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface.

[0269] Fig. 8 shows scanning electron microscopy (SEM) images of six different composite materials with a superhydrophobic surface according to the present invention which have been prepared from a coating composition according to the present invention on different substrates. In all cases the coating compositions were applied to the substrate in a dip coating process AM-2 according to the present invention. The coating compositions CC-1 applied to the substrate contained 10 g / L of the copolymer poly(behenyl acrylate-co-(4-methacry- loyloxy benzophenone)), 20 g / L of n-octacosane (n-C2sH58) as wax component, and 10 g / L of 1 -docosanol (n-C22H45-OH) as fatty alcohol, all components dissolved in chloroform (CHCh). The coating composition was applied on the following flat substrates featuring a different surface energy and a different chemical composition: aluminium in Fig. 8 (A), glass in Fig. 8 (B), polished silicon wafer in Fig. 8 (C), a crosslinked poly(dimethyl acryl amide-co-(4-methacryloyloxy benzophenone))-thin film on polished silicon wafer in Fig. 8 (D), HDPE plate in Fig. 8 (E), and a crosslinked poly(1 H,1 H,2H,2H-perfluorodecyl acrylate- co-(4-methacryloyloxy benzophenone))-thin film on polished silicon wafer in Fig. 8 (F). As can be seen from the high resolution scanning electron microscopy (SEM) images the resulting composite materials in all six cases feature a surface structure comprising self-assembled micro-aggregates, wherein the self-assembled micro-aggregates comprise wax platelets as aggregate surface. The overall surface structures of the composite materials in each case comprise self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface. Accordingly, the coating composition according to the present invention is very versatile and can be successfully and reliably applied to a wider variety of different substrates.

[0270] Fig. 9 shows in Fig. 9 (A) a scanning electron microscopy (SEM) image of a composite material with a superhydrophobic surface according to the present invention which has been prepared on a polished silicon wafer from a coating composition according to the invention comprising a fatty alcohol as amphiphilic compound. Fig. 9 (B), Fig. 9 (C) and Fig. 9 (D) show scanning electron microscopy (SEM) images of three composite materials not according to the present invention, wherein coating compositions not according to the invention were used and also applied on a polished silicon wafer. In all cases the coating compositions were applied to the substrate in a dip coating process AM-2 according to the present invention. In detail: All coating compositions applied contained 10 g / L of the copolymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone), and 20 g / L of n-octa- cosane (n-C2sH58) as wax component. All components were dissolved in chloroform (CHCh). The following additional compounds were present in an amount of 10 g / L in the coating compositions: 1 -octadecanol (n-CisH37-OH) as fatty alcohol in Fig. 9 (A), n-do- cosane (n-C22H46) in Fig. 9 (B), n-octadecylamine (n-CisH37-NH2) in Fig. 9 (C), and be- henic acid (n-C2iH43-COOH) in Fig. 9 (D) respectively. Accordingly, only the composite material in Fig. 9 (A) was prepared from a three-component coating composition featuring a fatty alcohol as amphiphilic compound. As can be seen from the high resolution scanning electron microscopy (SEM) image depicted in Fig. 9 (A) the resulting composite material features a surface structure comprising self-assembled micro-aggregates, wherein the selfassembled micro-aggregates comprise wax platelets as aggregate surface. In case of the composite material depicted in Fig. 9 (B) no amphiphilic compound was present in the coating composition, instead an additional n-alkane n-C22H46 was present. Said coating de composition thus resembles a two-component coating composition only comprising a copolymer and wax components and is therefore comparable to state of the art coating compositions as e.g. disclosed in WO 2018 / 193094 A1 . As can be seen from the high resolution scanning electron microscopy (SEM) image depicted in Fig. 9 (B) aggregates are formed on the surface of the substrate. However these aggregates do not feature any hierarchical structure nor do they feature wax platelets as aggregate surface. The presence of an amphiphilic compound in a three-component coating composition as defined in the present invention is thus essential for the formation of a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface. In case of the two composite materials depicted in Fig. 9 (C) and Fig. 9 (D) amphiphilic compounds other than fatty alcohols were used. As can be seen from the high resolution scanning electron microscopy (SEM) images neither the presence of the long chain amine n-CiaH37-NH2 in Fig. 9 (C) nor the presence of the long chain carboxylic acid n-C2iH43- COOH in Fig. 9 (D) resulted in the formation of micro-aggregates with a hierarchical structure featuring wax platelets as aggregate surface. Instead very small and undefined surface depositions were observed in Fig. 9 (C) or a large undefined layer of clusters were observed in Fig. 9 (D). Accordingly, the mere presence of an amphiphilic compound in a three-component coating composition does not suffice to form hierarchical aggregate structures on the surface of a substrate. Instead, it is crucial that the amphiphilic compound is a fatty alcohol as defined herein.

[0271] Fig. 10 shows in Fig. 10 (A) a scanning electron microscopy (SEM) image of a composite material with a superhydrophobic surface according to the present invention which has been prepared on a HDPE plate from a coating composition according to the invention before any damage- and healing attempts were made. Fig. 10 (B), Fig. 10 (C) and Fig. 10 (D) show scanning electron microscopy (SEM) images of the heat-induced self-healing of a composite material with a superhydrophobic surface according to the present invention. A composite material has been prepared by applying coating composition CC-3 to a HDPE plate in a spray coating process AM-1 according to the present invention. The coating composition CC-3 according to the present invention applied to the substrate contained 17 g / L of the copolymer poly(behenyl acrylate-co-(4-methacryloyloxy benzophenone)), 33 g / L of n-octacosane (nC2sH58) as wax component, and 50 g / L of 1 -docosanol (n-C22H45-OH) as fatty alcohol, all components being dissolved in CHCh. The surface structure of said composite material has then been damaged by means of linear sandpaper abrasion as described above, resulting in the loss of the original surface structure, in particular the loss of - M - the hierarchical at least two-tier roughness of the micro-aggregates and the loss of wax platelets as aggregate surface. The damaged composite material has then been subjected to a heat-induced self-healing process by tempering the composite material for 1 hour followed by storage of the composite material at room temperature (ca. 20°C) for one more hour after which scanning electron microscopy (SEM) images were taken. The temperatures used in the tempering process were 27 °C in Fig. 10 (B), 40 °C in Fig. 10 (C), and 50 °C in Fig. 10 (D). As can be seen from the scanning electron microscopy (SEM) images Fig. 10 (B), Fig. 10 (C), and Fig. 10 (D) the original surface structure can be restored upon heating the surface of the composite material. In particular the hierarchical at least two-tier roughness of the micro-aggregates can be restored since wax platelets as aggregate surface are regrown. Said effect is more pronounced I accelerated upon heating at elevated temperatures.

[0272] Fig. 11 shows a schematic representation of a composite material 100 with a hierarchically structured superhydrophobic surface according to the present invention. As visualized in Fig. 11 said composite material 100 comprises a substrate 200 and a surface structure 300 at least partially covering the surface of the substrate. The surface structure 300 comprises self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base. The backbone of the polymer 301 which is an example of a hydrophobic (co)polymer comprising linear side-chains capable of inducing (co-)crystallization and / or ordered selfassembly, is preferably connected or bound to the surface of the substrate (not explicitly depicted in Fig. 11). The side chains of the polymer 301 interact with fatty alcohol molecules 302 which form a bridging lipid double-layer lamella structure caused by a hydroxyl- head-to-hydroxyl-head-self-assembly. The fatty alcohol molecules 302 serve as amphiphilic phase mediators in the formation of the ordered I co-crystallized wax platelet structure 303. Said wax platelet structure 303 forms the aggregate surface and is essentially composed of hydrophobic (and crystallizable) compounds with a melting point above 25 °C (wax component). Wax platelets are formed and / or restored in a self-healing process upon addition of new hydrophobic (and crystallizable) compounds with a melting point above 25 °C 304 which are present in the coating composition or on the surface of the composite material.

[0273] List of reference signs:

[0274] 100 composite material

[0275] 200 substrate

[0276] 300 surface structure

[0277] 301 hydrophobic (co)polymer comprising linear side-chains (and thus being capable of inducing (co-)crystallization and / or ordered self-assembly)

[0278] 302 fatty alcohol molecules in a lipid double-layer lamella structure 303 wax platelet structure

[0279] 304 hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes

Claims

CLAIMS1 . A coating composition for the production of superhydrophobic surfaces, comprising i) one or more hydrophobic compounds with a melting point above 25 °C and selected from the group consisting of alkyl esters, alkenyl esters, alkanes, alkenes and alkynes, ii) one or more fatty alcohols, iii) one or more hydrophobic (co)polymers, wherein the one or at least one of the more than one hydrophobic (co)polymers comprises linear side-chains, wherein the composition contains less than 1 % by weight of fluorine determined by combustion ion chromatography.

2. A coating composition according to claim 1 , wherein the one or at least one of the more than one hydrophobic (co)polymers comprises linear hydrocarbon side-chains, more preferably linear hydrocarbon side-chains with a number of carbon atoms in the range of from 12 to 48, preferably 12 to 36, more preferably 12 to 28, even more preferably 16 to 24, most preferably 18 to 22, even more preferably the linear hydrocarbon side-chains are linear alkyl groups with a number of carbon atoms in the range of from 12 to 48, preferably 12 to 36, more preferably 12 to 28, even more preferably 16 to 24, most preferably 18 to 22.

3. A coating composition according to any of the preceding claims, wherein the one or at least one of the more than one hydrophobic (co)polymers is a (co)polymer comprising one or more (meth)acrylate monomers and / or one or more (meth)acrylamide monomers, wherein preferably at least one of the one or more (meth)acrylate monomers and / or (meth)acrylamide monomers comprises- linear side-chains, preferably linear hydrocarbon side-chains, more preferably linear alkyl group side-chains, with a number of carbon atoms in the range of from 12 to 48, preferably12 to 36, more preferably 12 to 28, even more preferably 16 to 24, most preferably 18 to 22, and / or- a crosslinking moiety, wherein the crosslinking moiety preferably comprises a functional group selected from the group consisting of- C,H-insertion crosslinking (CHic) active groups, preferably substituted benzophenones, anthraquinones, thioxanthones, sulfonyl azides, aromatic azides, diazomethylenes with ester, sulfonyl and / or aromatic substituents,- azides,- vinylic unsaturated groups,- epoxy groups,- isocyanate groups,- carboxylic acid anhydride groups, and- organic carbonates.

4. A coating composition according to any of the preceding claims, wherein the one or at least one of the more than one fatty alcohols is a linear alkanol or a linear alkenol, preferably is an alkanol, preferably with a number of carbon atoms in the range of from 16 to 36, more preferably with a number of carbon atoms in the range of from 18 to 30, even more preferably with a number of carbon atoms in the range of from 18 to 26,most preferably with a number of carbon atoms in the range of from 18 to 24.

5. A coating composition according to any of the preceding claims, wherein the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is selected from the group consisting of linear alkyl esters, linear alkenyl esters, linear alkanes, linear alkenes and linear alkynes, preferably selected from the group consisting of linear alkanes, linear alkenes and linear alkynes, more preferably the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is an alkane, wherein preferably the number of carbon atoms of the one or at least one of the more than one hydrophobic compounds with a melting point above 25 °C is in the range of from 16 to 36, more preferably is in the range of from 22 to 30, most preferably is in the range of from 26 to 30.

6. A coating composition according to any of the preceding claims, wherein- the hydrophobic compounds with a melting point above 25 °C have a maximum deviation in the number of carbon atoms of 4 or less, preferably 3 or less, more preferably 2 or less, and / or- the fatty alcohols have a maximum deviation in the number of carbon atoms of 4 or less, preferably 3 or less, more preferably 2 or less.

7. A coating composition according to any of the preceding claims, wherein the coating composition comprises an organic solvent, wherein preferably the organic solvent comprises one or more solvents selected from the group consisting of substituted and non-substituted linear, branched, and cyclic alkanes, alkenes, alkynes, chlorinated alkanes, alcohols, substituted and non-substituted aromatic and heteroaromatic compounds,preferably the organic solvent is selected from the group consisting of toluene, substituted toluenes like xylene and mesitylene, solvent naphta, cyclohexane, chloroform (CHCh), dichloromethane (CH2CI2), and mixtures thereof, more preferably the organic solvent is selected from the group consisting of toluene, chloroform (CHCh), dichloromethane (CH2CI2), and mixtures thereof.

8. A coating composition according to any of the preceding claims, wherein the weight ratio of the total amount of hydrophobic (co)polymers to the total amount of fatty alcohols is in a range of from 1 :0.1 to 1 :10, preferably is in a range of from 1 :0.2 to 1 :5, more preferably is in a range from 1 :0.25 to 1 :3.

9. A coating composition according to any of the preceding claims, wherein the composition contains less than 0.1 % by weight of fluorine, preferably less than 0.01 % by weight of fluorine, determined by combustion ion chromatography.

10. Use of a coating composition according to any of the preceding claims for post treatment of a substrate surface or parts of a substrate surface, wherein preferably the substrate is selected from the group consisting of- materials in aerospace applications, in particular materials in or on board of airplanes,- materials in marine applications, in particular materials in or on board of ships or boats,- materials in transportation applications, in particular materials in or on board of cars, lorries, or trains,- containers and parts of containers,- buildings and parts of buildings, in particular architectural coatings,- electronic devices and parts of electronic devices, and- packaging materials, in particular packaging materials for food, packaging materials for chemicals and agrochemicals, packaging materials for electronic devices, and the like.

11. A composite material with a superhydrophobic surface comprising a) a substrate, and b) a surface structure obtained by applying a coating composition according to any of claims 1 to 9 to a surface or parts of a surface of the substrate and at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface, wherein the surface structure, preferably the whole composite material, contains less than 1 % by weight of fluorine determined by combustion ion chromatography.

12. A composite material with a superhydrophobic surface according to claim 1 1 , wherein- the substrate is a synthetic material, preferably is a synthetic material selected from the group consisting of glass, metals, silicon, polymer materials including elastomeric and thermoplastic polymers, compound materials such as fiber-reinforced materials, naturally derived polymer compounds such as cellulose-based materials, resins, coatings and paints such as automotive, marine, aerospace, industrial, coil, architectural, decorative coatings and paints, concrete, paper, wood, and textiles, as well as mixtures, compounds, films, webs and laminates thereof and / or- at least parts of the surface of the substrate, preferably all parts of the surface of the substrate which are covered with the surface structure, are free of elevations and / or depressions with spatial dimensions vertical to the substrate surface of above 100 pm, preferably above 50 pm, more preferably above 25 pm.

13. A composite material with a superhydrophobic surface according to any of claims 11 or 12, wherein- the average size of one self-assembled micro-aggregate is in a range of from 10 pm2to 500 pm2, preferably is in a range of from 20 pm2to 250 pm2, and / or- the polymer scaffold is covalently bound to the substrate surface.

14. A composite material with a superhydrophobic surface according to any of claims 11 to 13, wherein- the superhydrophobic surface is self-healing, preferably self-healing upon heating the surface of the composite material to a temperature in the range of 1 °C to 20 °C, preferably 5 °C to 10 °C, below the melting point of the wax platelets.

15. A process of producing a composite material with a superhydrophobic surface, preferably a composite material with a superhydrophobic surface according to any of claims 11 to 14, at least comprising the following steps: a) preparing or providing a coating composition according to any of claims 1 to 9, b) wetting a surface or parts of a surface of a substrate with the prepared or provided coating composition, so that the surface or parts of the surface of the substrate are covered by the coating composition, c) drying the wetted substrate, so that a surface structure at least partially covering the surface of the substrate and comprising self-assembled micro-aggregates featuring a hierarchical, at least two-tier roughness, wherein the self-assembled micro-aggregates comprise a polymer scaffold as aggregate base and wax platelets as aggregate surface is obtained.

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