DE102017211592B4 - Methods for producing omniphobic surfaces, an omniphobic surface coating, uses of the omniphobic surface coating and use in a heat exchanger - Google Patents

Abstract

Process for coating components with an omniphobic surface coating, containing at least one metal-organic framework compound and an impregnating agent, with the steps, - electrochemical deposition of the metal-organic framework compound on the component by means of electrolysis, from an electrolyte solution containing at least one metal ion, at least one linker compound and a solvent ,- Application of an impregnating agent to the metal-organic framework, the metal ioni) being dissolved as a metal ion salt in the electrolyte solution and/orii) generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the electrode and the electrolyte solution and/or is provided in the electrolyte solution, and wherein the component is a) simultaneously an electrode or b) is introduced into an electric field between at least two electrodes, wherein the linker connection is an organ Che, at least monodentate compound, and wherein the impregnating agent has a low surface tension of <30 mN / m.

Description

The invention relates to a method for producing an omniphobic surface coating on components, the surface coating as such and its use in heat exchangers.

A vapor condenses on a solid surface, for example a wall, as a liquid if the temperature of the surface is below a saturation temperature of the vapor. This process is called condensation.

Condensation in heat exchangers is widely used in the efficient use of waste heat from industrial plants, e.g. B. vaporous water condenses on the surface of a heat exchanger and can be used to heat air or domestic water, for example.

The condensation of the water vapor on the surface of the heat exchanger can take place with the formation of a closed, coherent film (film condensation), which forms on the surface. However, it can also take the form of droplet condensation, in which the surface is wetted by droplets that are spatially separated from one another.

The formation of a liquid film is often disruptive and undesirable. Droplet condensation, on the other hand, is much more advantageous, since it is characterized by significantly higher heat transfer coefficients than film condensation.

It has therefore long been the subject of research and development activities.

The majority of previous studies on droplet condensation were carried out using the water vapor/water system.

There are different approaches to realize the droplet condensation of water vapor.

This can be achieved, for example, by hydrophobic functionalization of the heat exchanger surface. The chemical and physical properties of the surface are changed in such a way that it has the lowest possible wettability to water and thus a large water contact angle. Such surfaces have a medium or low surface energy.

In the chemical functionalization of surfaces for dropwise condensation, non-polar molecules are bound to the surface by means of coating processes (see e.g. KOCH, G. [ua]: Study on plasma enhanced CVD coated material to promote dropwise condensation of steam. In: International Journal of Heat and Mass Transfer 1998, Vol 41, No 13, pp 1899-1906 ISSN 0017-9310 (P), 1879-2189 (E), DOI:10.1016/S0017-9310(97)00356-6, KOCH, Gerd KRAFT Kjeld LEIPERTZ Alfred Parameter study on the performance of dropwise condensation Revue Generale de Thermique 1998 Vol 37 No 7 pp 539-548 ISSN 0035-3159 (P); 0035-3159 (E) DOI: 10.1016/S0035-3159(98)80032-9 KOCH G ZHANG DC LEIPERTZ A Condensation of steam on the surface of hard coated copper discs In Heat and Mass Transfer 1997 Vol 32 No 3 pp 149-156 ISSN 0947-7411 (P) 1432-1181 (E) DOI: 10.1007/s002310050105 MP BONNAR, Mark P [ua] : Plasma polymer films for dropwise condensation of steam. I n: chemical vapor deposition. 1997, Vol. 3, No. 4, pp. 201-207. ISSN 0948-1907 (P);1521-3862 (E). DOI: 10.1002/cvde. 19970030408; BONNAR, Mark P. [et al.]: Hydrophobic coatings from plasma polymerized vinyltrimethylsilane. In: Chemical Vapor Deposition. 1999, Vol. 5, No. 3, pp. 117-125.ISSN 0948-1907 (P); 1521-3862 (E). DOI: 10.1002/(SICI)1521-3862(199906)5:3<117::AID-CVDE117>3.0.CO;2-4; ENRIGHT, Ryan [et al.]: Dropwise condensation on micro- and nanostructured surfaces. In: Nanoscale and Microscale Thermophysical Engineering. 2014, Vol. 18, No. 3, pp. 223-250. ISSN 1556-7265 (P); 1556-7273 (E). DOI:10.1080/15567265.2013.862889).

Furthermore, the droplet condensation can be implemented by implanting atoms in the surface layer of the materials (see BANI KANANEH, A. [ua]: Experimental study of dropwise condensation on plasma-ion implanted stainless steel tubes. In: International Journal of Heat and Mass Transfer 2006 49, No. 25-26, p. AP; LEIPERTZ, A.: Dropwise condensation heat transfer on ion implanted aluminum surfaces. In: International Journal of Heat and MassTransfer. 2008, Vol. 51, No. 5-6, pp. 1061-1070. ISSN 0017-9310 (P );1879-2189(E).DOI:10.1016/j.ijheatmasstransfer.2006.05.047).

In addition to the chemical properties of the condensation surface, the wetting and condensation behavior is also influenced by the surface morphology (cf. 8th ).

A combination of water-repellent surface material and targeted structuring in the micro- and nanometer range made it possible to create superhydrophobic surfaces with very high water contact angles (θ > 150°) (cf. 8b) , see also WIER, Kevin A.; McCARTHY, Thomas J.: Condensation on ultrahydrophobic surfaces and its effect on droplet mobility: Ultrahydrophobic surfaces are not always water repellant. In: Langmuir. 2006, Vol. 22, No. 6, pp. 2433-2436. ISSN 0743-7463 (P);1520-5827 (E). DOI: 10.1021/la0525877; BOREYKO, Jonathan B.; CHEN, Chuan-Hua: Self-propelled dropwise condensate on superhydrophobic surfaces. In: PHYSICAL REVIEW LETTERS. 2009, Vol. 103, No.18, pp. 184501-1 - 184501-4. ISSN 0031-9007 (P); 1079-7114 (E). DOI:10.1103/PhysRevLett.103.184501 and MILJKOVIC, Nenad; ENRIGHT, Ryan; WANG, Evelyn N.: Effect of droplet morphology on growth dynamics and heat transfer during condensation on superhydrophobic nanostructured surfaces. In: ACS Nano. 2012, Vol. 6, No. 2, pp. 1776-1785. ISSN1936-0851 (P); 1936-086X (E). DOI: 10.1021/nn205052a).

If additionally, as in 8c ) shows that the adhesion of the condensate drops to the surface is avoided, such surfaces enable a further increase in heat transfer during the condensation of water vapor compared to smooth hydrophobic surfaces (MILJKOVIC, Nenad; ENRIGHT, Ryan; WANG, Evelyn N.: Modeling and optimization of superhydrophobic condensation In: Journal of Heat Transfer 2013, Vol. 1.4024597).

For the description of the heat transfer during droplet condensation of organic and non-aqueous material systems, detailed investigations are still lacking. This means that the use of the droplet condensation mechanism to increase the efficiency of apparatus and processes in these material systems has so far been difficult to implement in practice.

Potential areas of application for the droplet condensation of organic and non-aqueous systems are, for example, processes for solvent recovery, but also closed cycle processes in heat pumps, chillers and organic Rankine Cycle systems. Especially with the material systems used here, the use of droplet condensation compared to film condensation is even more interesting and technically relevant than with steam/water.

However, the common feature of the condensing refrigerants and solvents is a significantly lower surface tension than water, which makes it even more difficult to realize droplet condensation.

However, the increased heat transfer caused by droplet condensation makes this mechanism extremely interesting from an economic point of view for a large number of technical processes. Mentioned here are, for example, condensers in ORC systems for generating electricity from waste heat or the stationary and mobile use of heat pumps and chillers.

An increased heat transfer during the condensation of the refrigerant advantageously means that smaller heat transfer surfaces can be used with the same effect.

For example, with water cooling and the refrigerant isobutane used, by tripling the heat transfer on the refrigerant side by means of droplet condensation, savings of 20% to 30% of the heat transfer surface can be achieved compared to film condensation. This enables the construction of very compact and weight-saving devices and a lower use of materials. As a result, the manufacturing costs for the devices can also be reduced if the coating technologies are integrated in line with market requirements.

Droplet condensation is also an economically attractive alternative to production processes for the recovery of organic solvents from polluted exhaust air, especially in the printing industry, in the coating and painting of wood, metal and plastic surfaces, in the manufacture of pharmaceuticals and lacquers, paints and adhesives conventional methods.

So far, for example, adsorption processes or thermal or catalytic oxidation have been used for the above-mentioned processes. In contrast to thermal or catalytic oxidation, for example, droplet condensation allows the recovered solvents to be used as a material.

The common feature of the relevant fluids from the group of refrigerants and solvents is that they have a significantly lower surface tension γ _LV than water. This is usually < 50 mN/m, often even < 30 mN/m.

This usually leads to significantly lower contact angles compared to water. In the case of numerous, particularly hydrophobic surfaces, this even leads to complete wetting with the organic or anhydrous fluids. The realization of the droplet condensation is therefore considerably more difficult with these fluids.

The approaches described above for the implementation of droplet condensation of water vapor are therefore only conditionally applicable to the relevant fluids from the group of refrigerants and solvents suitable. Instead of hydrophobic surfaces, droplet condensation of cold and solvents requires omniphobic surfaces that have low wettability to a large number of polar and non-polar liquids. It is known from the literature that smooth omniphobic surfaces with very low surface energy γ _SV can be produced by coating with fully fluorinated systems (RYKACZEWSKI, Konrad [ua]: Dropwise condensation of low surface tension fluidson omniphobic surfaces. In: Scientific Reports. 2014, Vol. 4, Article number: 4158, pages 1-8 ISSN 2045-2322 (E) DOI: 10.1038/srep04158, MAYER, TM [ua]: Chemical vapor deposition of fluoroalkylsilane monolayer films for adhesion control in microelectromechanical systems In: Journal of Vacuum Science and Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena 2000 Vol 18 No 5 pp 2433-2440 ISSN 0734-211X(P) 2166-2754 (E ) DOI: 10.1116/1.1288200; TSIBOUKLIS, John; NEVELL, Thomas G.: Ultra-low surface energy polymers: The molecular design requirements. In: Advanced Materials. 2003, Vol. 15, No. 7-8, p.647 -650 ISSN 0935-9648 (P) 1521-4095 (E) DOI: 10.1002/adma.200301638 CHHATRE, Shreerang S [inter alia]: Fluoroalkylated silicon-containing surfaces - estimation of solid-surface energy. In: ACS Applied Materials & Interfaces. 2010, Vol.2, No. 12, pp. 3544-3554. ISSN 1944-8244 (P); 1944-8252 (E). DOI:10.1021/am100729j).

However, due to their low mechanical stability, such coatings are not suitable for numerous technical applications (GROTEN, Jonas; RÜHE, Jürgen: Surfaces with combined microscale and nanoscalestructures: A route to mechanically stable superhydrophobic surfaces?. In: Langmuir.2013, Vol. 29, No. 11, pp. 3765-3772 ISSN 0743-7463 (P);1520-5827 (E) DOI:10.1021/la304641q).

As already described above, the wetting and condensation behavior is also influenced by the surface morphology. It is known that by a combination of suitable surface morphology and impregnation of the surface with a suitable low surface energy lubricant, omniphobic surfaces can be created. Current investigations show that a hierarchical structuring of the surface (structuring in the micrometer range with additional roughness in the nanometer range) is a possibility to minimize the adhesion of condensate droplets on the surface and at the same time to increase the resistance of the impregnation.

In the publication by S. Anand et al. (ANAND, Sushant [ua]: Enhanced condensation on lubricant-impregnated nanotextured surfaces. In: ACS Nano. 2012, Vol. 6, No. 11, pp. 10122-10129. ISSN1936-0851 (P); 1936-086X (E ).DOI: 10.1021/nn303867y), nanostructures are produced on the surface of a sample by means of photolithography and subsequent etching, for example, and then treated with an impregnating agent in order to achieve improved droplet condensation of water.

Disadvantages are the previously known multi-stage processes for producing hierarchical micro- and nanostructures, which include, for example, photolithographic processes or the use of carbon nanotubes, are extremely cost-intensive and less suitable for industrial processes, especially for the coating of complex components.

Components must be coated before the final assembly and may no longer be welded, otherwise the applied coating will be damaged. Likewise, an immersion bath would be unsuitable for applying the layers for large and complex components, since the size of the immersion bath limits the size of the component and an inhomogeneous coating is to be expected with complex components. This in turn would be a reason for increased corrosion.

An alternative way of structuring surfaces is to use metal-organic frameworks (MOFs).

A favorable property of the MOFs are structurally based pores at the molecular level and an associated very high porosity and surface area. MOFs are also characterized by high stability or insolubility in almost all solvents and temperature resistance of up to 350 °C. So far, applications in the field of catalysis, gas storage and purification as well as analytics are known for MOFs (CZAJA, Alexander U.; TRUKHAN, Natalia; MÜLLER, Ulrich: Industrial applications of metal-organic frameworks. In: Chemical Society reviews. 2009, 38, No. 5, pp. 1284-1293.ISSN 0306-0012(P);1460-4744(E).DOI:10.1039/B804680H).

Various methods are known for the production of MOF coatings, which include both classic layer growth techniques such as spin coating processes, dip coating or spraying and stepwise reactive coatings (see, inter alia, ARIGA, Katsuhiko [ua]: Layer-by-layer nanoarchitectonics: Invention, innovation, and evolution. In: Chemistry Letters (CL) 2014, Vol 43, No 1, pp 36-68 ISSN 0366-7022(P), 1348-0715 (E), DOI: 10.1246/cl.130987, ZACHER, Denise [ua]: Thin films of metal-organic frameworks In: Chemical Society reviews 2009, Vol. 38, No. 5, pp. 1418-1429. ISSN 0306-0012 (P); 1460-4744 (E). DOI: 10.1039/B805038B; HE, C. et al., "Exceptional hydrophobicity of a large-pore metal-organic zeolite", J. Am. Chem. Soc. 2015, Vol. 137, No. 22, pp. 7217-7223,; ZHAO, Junjie [ua]: Conformal and highly adsorptive metal-organic framework thin films via layer-by-layer growth on ALD-coated fiber mats. In: Journal of Materials Chemistry A: Materials for Energy and Sustainability. 2015, Vol. 3, No. 4, pp. 1458-1464. ISSN 2050-7488 (P); 2050-7496 (E). DOI: 10.1039/C4TA05501B; LIU, Sainan [inter alia]: Hydrophobic-ZIF-71 filled PEBA mixed matrix membranes for recovery of biobutanol via pervaporation. In: Journal of Membrane Science. 2013, Vol. 446, pp. 181-188. ISSN 0376-7388 (P); 1873-3123 (E). DOI:10.1016/j.memsci.2013.06.025).

Furthermore, MOF layers can also be grown using cost-effective, industrially scalable electrochemical methods, with MOF synthesis and coating being implemented directly in one step. Crystallite sizes and distances and the associated layer thickness and surface morphology can be controlled.

DE 103 55 087 A1 from 2003 describes a method for the electrochemical production of crystalline MOFs in powder form from a reaction medium containing bidentate compounds and metal ions, which are provided by oxidation of an anode containing the corresponding metal.

Further publications followed, for example by Ameloot et al. (AMELOOT, Rob [ua]: Patterned growth of metal-organic framework coatings by electrochemical synthesis. In: Chemistry of Materials. 2009, Vol. 21, No. 13, pp. 2580-2582. ISSN 0897-4756 (P); 1520-5002 (E).DOI: 10.1021/cm900069f).

SCHÜTH, Ferdi: Porous materials at a glance. In: Chemie Ingenieur Technik, 2010, 82, 6, 769 - 777, ISSN 1522. DOI: 10.1002/cite.201000063 - gives an overview of porous materials, which can be classified in particular by their pore size. Among other things, MOFs are described which have a significantly larger pore size than zeolites and show pore sizes in the mesopore range. MOFs with a hierarchical pore structure, which have both macro and meso and nanopores, are not disclosed.

HARTMANN, Martin [among others]: Adsoptive Separation of Isobutene and Isobutane on Cu ₃ (BTC) ₂ . In: Langmuir 2008, 24, 16 8643 - 8642. ISSN 0743-7463. - describes the production of copper-based MOFs, including by means of an electrochemical reaction. The linker molecule is placed in the electrolyte and the MOF connection is produced by electrolysis using copper electrodes.

The electrochemical deposition of MOFs on metals has also been discussed in review articles (see e.g. AL-KUTUBI, Hanan [ua]: Electrosynthesis of metal-organic frameworks: opportunities. In: ChemElectroChem. 2015, Vol. 2, No. 4, p. 462-474 ISSN 2196-0216 (E) DOI: 10.1002/celc.201402429 or LI, Wei-Jin [ua]: Metal-organic framework thin films: Electrochemical fabrication techniques and corresponding applications & perspectives In: Journal of A: Materials for Energy and Sustainability 2016 Vol 4 No 32 pp 12356-12369 ISSN 2050-7488 (P) 2050-7496 (E) DOI: 10.1039/C6TA02118B). Campagnol et al. published for the first time investigations into the mechanism of anodic deposition of metal-organic frameworks. (CAMPAGNOL, Nicolö [et al.]: On the electrochemical deposition of metal-organic frameworks. In: Journal of Materials Chemistry A: Materials for Energy and Sustainability. 2016, Vol. 4, No. 10, pp. 3914-3925. ISSN 2050 -7488(P);2050-7496(E).DOI:10.1039/C5TA10782B).

With the expansion to bipolar electroplating, the coating of complex components of any geometric shape is also possible (see e.g. YADNUM, Sudarat [ua]: Site-selective synthesis of Janus-type metal-organic framework composites. In: Angewandte Chemie. 2014, Vol. 126, No. 15, pp. 4082-4086. ISSN 0044-8249 (P); 1521-3757 (E). DOI: 10.1002/anie.201400581).

On surfaces that only work with an additional structure in the micro- and nanometer range, an increased heat transfer is not to be expected immediately during the condensation of fluids with very low surface tension, in contrast to the condensation of water vapour. Instead, in these cases, the formation of drops in the gaps floods the surface structure and forms a closed condensate film (film condensation, see RYKACZEWSKI, Konrad [ua]: Dropwise condensation of low surface tension fluids on omniphobic surfaces. In: Scientific Reports. 2014, 4, Article number: 4158, pp. 1-8. ISSN 2045-2322 (E). DOI: 10.1038/srep04158).

The formation of a condensate film can be prevented by additionally impregnating the micro- and nanostructured surfaces with an oil or lubricant.

To produce the nanostructured surfaces use z. B. Rykaczewski et al. Silicon substrates coated with aluminum nanoparticles. After applying one Lubricants based on fluoropolymers, improved heat transfer through droplet condensation was observed for solvents with surface tensions of 15 to 28 mN/m (see also RYKACZEWSKI, Konrad [ua]: Dropwise condensation of low surface tension fluidson omniphobic surfaces. In: Scientific Reports. 2014 4, Article number: 4158, pp. 1-8 ISSN 2045-2322 (E) DOI: 10.1038/srep04158 ANAND, Sushant [ua]: Enhanced condensation on lubricant-impregnated nanotextured surfaces In: ACS Nano 2012, Vol 6, No 11, pp 10122-10129 ISSN1936-0851 (P) 1936-086X (E) DOI: 10.1021/nn303867y XIAO, Rong [ua]: Immersion condensation on oil-infused heterogeneous surfaces for enhanced heat transfer. In: Scientific Reports. 2013, Vol. 3, Article number: 1988, pp. 1-6. ISSN 2045-2322 (E). DOI: 10.1038/srep01988).

US 2013/0 220 813 A1 describes a method for producing impregnated micro-/nanostructured surfaces to improve the droplet condensation of water or solvents with low surface tension. Depending on the desired function, micro- or nanostructured silicon substrates are covered with oil-based or water-based or ionic liquids or perfluoroalkylated silanes, resulting in superhydrophobic surfaces that allow the condensate to form droplets without the impregnating agent being washed out or replaced by the condensate.

By structuring a base material with low surface energy in combination with impregnation, surfaces with omniphobic properties can also be produced, which are also characterized by very low adhesion of drops to the surface. T.-S. Wong et al. describe in their publication the coating of photolithographically generated nanostructured surfaces with impregnating agents in order to make them omniphobic. "Lubricant-Infused Surfaces" (LIS) and "Slippery Lubricant Infused Porous Surfaces" (SLIPS) are reported, which show improved droplet condensation. (WONG, Tak-Sing [ua]: Bioinspired self-repairing slippery surfaces with pressurestable omniphobicity. In: Nature. 2011, Vol. 477, No. 7365, pp. 443-447. ISSN 0028-0836 (P); 1476- 4687 (E) DOI: 10.1038/nature10447; see also SMITH, J. David [ua]: Droplet mobility on lubricant-impregnated surfaces. In: Soft Matter. 2013, Vol. 9, No. 6, pp. 1772-1780 ISSN 1744-683X (P) 1744-6848 (E) DOI:10.1039/C2SM27032C and PARK, Kyoo-Chul [ua]: Condensation on slippery asymmetric bumps In: Nature 2016, Vol. 7592, pp. 78-82 ISSN 0028-0836 (P);1476-4687 (E).DOI:10.1038/nature16956).

WO 2012/100 099 A2 discloses the representation of omniphobic surfaces, so-called "slippery liquid-infused porous surfaces" (SLIPS), in which a lubricant is applied to a rough surface of a substrate, penetrating it and also covering it at the same time. A liquid outer layer forms on the surface, which is immobilized by the substrate and forms a repellent surface, for example.

The material of the substrate is preferably porous and can be a polymer, metal, precious stone, glass, carbon or a ceramic. The rough surface can have a hierarchical structure with micro- and nanoscale structures.

the end U.S. 9,121,307 B2 a method for the production of SLIPS is also known. Metal, glass or polymer substrates are used, the surface of which is made rough or porous by adding fibers or particles or by electrochemical deposition of polymers. The successive deposition of nano or microparticles on the substrates also leads to sufficiently structured surfaces. The surface structured in this way is additionally chemically functionalized, for example with a perfluorocarbon oil, and then covered with a hydrophobic lubricant, consisting of liquids which have a high affinity for the underlying surface, in order to immobilize the lubricant. Depending on the type of impregnation agent, the surfaces produced in this way have a high phobicity against various types of gases and liquids.

In addition to smooth, omniphobic surfaces with fully fluorinated coatings, the impregnation of nanostructured surfaces with fluorine-containing impregnating agents also represents an attractive approach for efficient droplet condensation of fluids with a surface tension of < 20 mN/m.

Disadvantageously, these coating processes could only be used on regular substrates. Complex components, such as the surface of a heat exchanger, cannot be functionalized in this way.

the end U.S. 2,919,115 A impregnated porous condenser surfaces are known which enable efficient droplet condensation. For this purpose, metal substrates are first subjected to a wet-chemical etching and pickling process in order to make the surface porous. Subsequent incubation of the component in a hydrophobic impregnating agent, such as oleic acid, leads to a hydrophobic coating that adheres well to the substrate due to the porosity of the surface. At the same time, the pores form a kind of reserve voir for the impregnating agent, so that it can be transported again and again to the surface of the substrate via capillary forces in order to replace any impregnating agent that may have been removed with the water vapour. This ensures constant hydrophobicity of the surface. The disadvantage of the etching and pickling process is that it uses chromic sulfuric acid, a chemical that is extremely problematic in terms of process technology.

In MOFs, the metal ions can be linked multidimensionally via organic linker molecules. These linker molecules can in turn have several coordinating functional groups (S. BAUER, Sebastian; STOCK, Norbert: MOFs - Metallo-organic framework structures. Functional porous materials. In: Chemie ineuer Zeit. 2008, Vol. 42, H. 1, p. 12- 19. ISSN 0009-2851 (P);1521-3781 (E).DOI: 10.1002/ciuz.200800434). MOFs usually have moderate surface energies due to the coordination bonding and the organic molecules in the structure. By modifying the linkers, such as. B. Introduction of ring substituents in aromatic systems, it is possible to adapt the physicochemical properties of the MOFs for individual applications (MAJI, Tapas Kumar; KITAGAWA, Susumu: Chemistry of porous coordination polymers. In: Pure and Applied Chemistry. 2007, Vol. 79, No. 12, pp. 2155-2177. ISSN0033-4545 (P); 1365-3075 (E). DOI: 10.1351/pac200779122155).

With regard to hydrophobic surface coatings, only MOF powders or MOF coatings on glass with hydrophobic or superhydrophobic properties are known from the literature. To describe e.g. B. Meng et al. the production of superhydrophobic and thus superoleophilic surfaces by impregnating glass surfaces onto which MOF powder particles have been dip-coated with stearic acid and a perfluoroalkylsilane (MENG, Wen [ua]: Porous coordination polymer coatings fabricated from Cu ₃ (BTC) ₂ 3 H ₂ O with excellent superhydrophobic and superoleophilic properties. In: New Journal of Chemistry. 2016, Vol. 40, No. 12, pp. 10554-10559. ISSN 0398-9836(P); 1369-9261 (E). DOI: 10.1039 /C6NJ02717B).

Further publications are dedicated to the hydrophobicization of MOF powders, such as CHEN, Teng-Hao [et al.]: Superhydrophobic perfluorinated metal-organic frameworks. In: Chemical Communications: ChemComm. 2013, Vol. 49, No. 61, pp. 6846-6848.ISSN 0009-241X (P); 1364-548X (E). DOI: 10.1039/C3CC41564C or NGUYEN, Joseph G.; COHEN, Seth M.: Moisture-resistant and superhydrophobic metal-organic frameworks obtained via postsynthetic modification. In: Journal of the American Chemical Society. 2010, Vol. 132, No. 13, pp. 4560-4561. ISSN 0002-7863(P); 1520-5126(E). DOI: 10.1021/ja100900c.

The (super-)hydrophobic properties of the MOF powders are achieved by pre- or post-synthetic functionalization of the linker molecules or by impregnation. In the case of coatings, the hydrophobicity is additionally favored by size differences of the assembled MOF particles in the micrometer range. However, previous (super)hydrophobic MOF coatings are not repellent to liquids with a low surface tension (e.g. common refrigerants and solvents), and complete wetting actually occurs. During condensation, the surfaces would be “flooded” by the condensate due to nucleation within the porous surface structures and film condensation would occur.

On the other hand, droplet condensation of fluids with low surface tension is possible on lubricant-impregnated surfaces (LIS). So far, however, these have only been achieved by complex, e.g. B. photolithographic nanostructuring processes. The known LIS also work with a hydrophobic functionalization of the base material. The disadvantage of the coatings applied in this way is that they have low mechanical stability. The lubricants are partially removed or washed out from the photolithographically structured surface by the condensing liquids. Coating processes for complex components are also not possible with these processes.

The object of the invention is to provide a simple method for producing stable, omniphobic surface coatings which, among other things, enable efficient droplet condensation of organic and/or anhydrous fluids with a low surface tension.

• - Elektrochemische Abscheidung der metallorganischen Gerüstverbindung auf dem Bauteil mittels Elektrolyse, aus einer Elektrolytlösung, enthaltend mindestens ein Metallion, mindestens eine Linkerverbindung und ein Lösungsmittel,
• - Aufbringen eines Imprägniermittels auf die metallorganische Gerüstverbindung wobei das Metallion
  1. i) als Metallionensalz in der Elektrolytlösung gelöst ist und/oder
  2. ii) durch elektrolytische Oxidation oder Reduktion eines in Bauteil und/oder Elektrode enthaltenen Metallionenvorläufers an der Grenzfläche zwischen Bauteil und Elektrolytlösung generiert wird und/oder in der Elektrolytlösung bereitgestellt wird und wobei das Bauteil
     1. a) gleichzeitig Elektrode ist oder
     2. b) in ein elektrisches Feld zwischen mindestens zwei Elektroden eingebracht wird,

wobei die Linkerverbindung eine organische, mindestens einzähnige Verbindung ist,
wobei das Imprägniermittel eine geringe Oberflächenspannung von <30 mN/m aufweist.The object is achieved by a method for coating components with an omniphobic surface coating containing at least one metal-organic framework compound and an impregnating agent, with the steps

• - Electrochemical deposition of the metal-organic framework on the component by means of electrolysis, from an electrolyte solution containing at least one metal ion, at least one linker compound and a solvent,
• - Applying an impregnating agent to the metal-organic framework, wherein the metal ion
  1. i) is dissolved as a metal ion salt in the electrolyte solution and/or
  2. ii) is generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the component and the electrolytic solution and/or is provided in the electrolytic solution and the component
     1. a) is also an electrode or
     2. b) is introduced into an electric field between at least two electrodes,

wherein the linker compound is an organic, at least monodentate compound,
whereby the impregnating agent has a low surface tension of <30 mN/m.

According to the invention, the omniphobic surface coating is produced on the component by electrochemical deposition of a layer of at least one metal-organic (framework) compound and subsequent application of an impregnating agent.

According to the invention, the first step is the electrochemical deposition of the metal-organic (framework) compound on the surface of the component.

At least one component of the MOF coating (linker compound and/or metal ion) must be formed at the interface between the component and the electrolyte solution in order to initiate the coating process.

In one embodiment, the electrochemical deposition takes place potentiostatically, galvanostatically and/or with current and/or with voltage pulses. Potentiostatic and galvanostatic process control are preferred for homogeneous coatings. Pulsed processing is preferably used for structured coatings where distances of several micrometers are generated between coated areas.

For this purpose, the component is either immersed in an electrolyte solution and/or filled with an electrolyte solution.

According to the invention, the electrolyte solution contains at least one linker compound and a solvent.

Metal-organic frameworks are formed from metal ions and organic molecules (linker compounds), which act as connecting elements between the metal ions forming nodes. The linker compounds enter into coordinate bonds with the metal ion and one-, two- and three-dimensional networks can be formed.

According to the invention, the linker compound is an at least monodentate organic compound or a mixture of several of these compounds.

The term “at least monodentate” organic compound refers to an organic compound that contains at least one functional group that is capable of forming at least one coordinate bond with a given metal ion.

For the purposes of the invention, complex compounds are also referred to as metal-organic frameworks in which the organic linker molecules contain only one functional group capable of forming a coordinate bond with a metal ion, or which coordinate with only one functional group on the metal ion. A framework can still be formed because two linker molecules can be connected to one another, for example by hydrogen bonds. These 2 monodentate linkers then form a coordination unit, which as a result functions like a bidentate linker compound.

In one embodiment, the organic, at least monodentate compound contains at least one functional group selected from carboxylate groups, sulfonate groups, phosphonate groups, imidazolate groups, pyridine groups, phenanthroline groups, triazolate groups and/or tetrazolate groups.

In one embodiment, the linking compound is an imidazolate.

In one embodiment, the linker compound is selected from
1,4-Benzenedicarboxylates (BDC)
Tetramethyl-1,4-benzenedicarboxylates (TBDC)
2-amino-1,4-benzenedicarboxylates (NH ₂ -BDC)
1,3,5-Benzene Tricarboxylates (BTC)
2,6-Naphthalenedicarboxylates (NDC)
Biphenyl-3,4',5-tricarboxylates (BPT)
2'-Fluoro-biphenyl-3,4'-5-tricarboxylates Benzene-2,5-dihydroxy-1,4-dicarboxylates (dhbcd)
2,5-dimethoxy-1,4-benzenedicarboxylates (DMBDC)
Benzene Hexacarboxylates (BHC)
Furan-2,5-dicarboxylates (fdc)
Pyridine-2,6-dicarboxylates (pda, dpa)
4-Hydroxyquinoline-2-carboxylates (hqc)
2,2'-biquinoline-4,4'-dicarboxylates (bqdc)
3-Hydroxypyrazine-2-carboxylates (hpzc)
2,3-pyrazinedicarboxylates (pza)
Imidazole-4,5-dicarboxylates (IDC)
4,5-imidazoledicarboxylates (imidc)
2-propyl-1H-imidazole-4,5-dicarboxylates (Hpimda)
4-(1H-Tetrazol-5-yl)-biphenyl-3-carboxylates (tbca)
Thiophene-2,5-dicarboxylates (TDC, TDA)
9,9-dimethylfluorene-2,7-dicarboxylates (MFDA)
Polychlorotriphenylmethyltricarboxylate radicals (PTMTC)
1,5-Naphthalenedisulfonates (1,5-NDS)
2,6-Naphthalenedisulfonates (2,6-NDS)
Anthraquinone-2,6-disulfonates (AQDS)
4,4'-oxybenzoates (OBA)
3,5-disulfobenzoates (dsb)
4,4',4"-S-triazine-2,4,6-triyl-tribenzoates (TATB)
1,3,5-benzenetribenzoates (BTB)
4,4'-biphenyldicarboxylic acids (BPDC)
Cis-1,3,5-cyclohexanetricarboxylic acids (CTC)
Pyrazinedicarboxylic Acids (H ₂ pzdc)
1,1'-Phenanthroline-2,9-dicarboxylic acids (H ₂ phenDCA)
2,5-pyridinedicarboxylic acids (H ₂ pydc)
4,5-imidazoledicarboxylic acids (H ₃ ImDC)
4,4'-bipyridine-2,2',6,6'-tetracarboxylic acids (H ₄ BPTCA)
4,4'-(Hexafluoroisopropylidene)bis(benzoic acids) (H ₂ hfipbb)
4,4-[(2,5-Dimethoxy-1,4-phenylene)-di-2,1-ethenediyl]bisbenzoic acids (H ₂ pvdc)
(carboxymethyl)iminodi(methylphosphonic acids) (H ₂ cmp)
2-aminoterephthalic acids (H ₂ ATPT)
Etidronic acids (H ₅ hedp)
2-(carboxylic acid)-6-(2-benzimidazolyl)pyridines (Hcbmp)
Phosphonoacetic Acids (H ₃ PPA)
Tris-(4-carboxyphenyl)phosphine oxides (H ₃ TPO)
Tris-(benzimidazol-2-ylmethyl)amines (ntb)
1,4-phenylenediacetates (pda)
1,1',1"-(2,4,6)-trimethylbenzene-1,3,5-triyl)tris(methylene)tripyridinium-4-oleates (TTP)
1,1'-Phenanthrolines (phen)
1,3-Benzeneditrazol-5-ylene (m-BDTH)
5-(Pyridin-4-yl)isophthalates (PIA)
5-tert-butyl isophthalates (tip)
methyl isophthalates (mip)
Imidazolates (Im)
1,2,3-Triazolates (Tz)
4,4'-bipyridines (bipy)
1,2,3-triazolato[4,5-b]pyridines (tzpy)
Tricarboxylato-triphenylamines (tca)
adipates (ad)
2-Fluoro-4-(1H-tetrazol-5-yl)benzoates (FTZB)
4,4',4"-(Benzenetricarbonyltris(azanediyl))tribenzoates (BTATB)
1,1',1"-(Benzene-1,3,5-triyl)tripiperidine-4-carboxylates (BTPCA)
1,10-bis(4-carboxybenzyl)-4,40-bipyridines (BPYBC)
Glutarates (glu)
Succinates (succ)
isonicotinates (Ina)
fumarates (fma)

In one embodiment, the linker compound is formed from at least one linker precursor compound during electrolysis.

Within the meaning of the invention, a linker precursor compound is a compound from which the corresponding linker compound is generated in situ by an electrochemical reaction and/or chemical reaction as a result of an electrochemical reaction. This can be done, for example, by electrolytic or electrolytically induced substitution, addition, reduction, cleavage, ring closure reaction, ring opening reaction, deprotonation, proton transfer and/or radical reaction.

In one embodiment, the linker precursor compound is selected from the free acids or anhydrides of the linker compound. The linker precursor compounds for the linker compounds imidazolates, triazolates and tetrazolates are their corresponding imidazoles, triazoles or tetrazoles, respectively.

In one embodiment, the total concentration of the linker compound and/or linker precursor compound in the electrolyte solution is 0.001 mol/l to 2.500 mol/l, preferably 0.01 mol/l to 1.5 mol/l, particularly preferably 0.01 mol/l to 0 .5 mol/l.

In one embodiment, the chemical reaction for forming the linker compound from the linker precursor compound is triggered by the electrochemical conversion of at least one component of the electrolyte solution during the electrolysis.

Components of the electrolyte solution are, for example, metal ion salts, conductive salts, solvents and/or structure-directing additives.

For example, the cathodic reduction of a nitrate salt in the electrolyte solution, in which hydroxide ions are formed, can change the pH to such an extent that z. B. acid groups are deprotonated and, for example, the linker carboxylates are formed from the free carboxylic acids.

In one embodiment, acid or imidazole groups are deprotonated by changing the pH, for example by water decomposition during electrolysis.

According to the invention, the electrolytic solution contains at least one solvent. According to the invention, the term solvent includes pure solvents, which comprise only one solvent component, as well as solvent mixtures that is, mixtures of at least two solvent components.

In principle, all solvents and/or all solvent mixtures in which the starting materials used in the process can be dissolved under the selected reaction conditions, such as pressure and temperature, are conceivable as solvents.

In one embodiment, the solvent is selected from water; Alcohols, carboxylic acids, nitriles, ketones, halogenated alkanes, acid amides, amines, sulfoxides, pyridine, N-formylamides, N-acylamides, aliphatic ethers and/or cyclic ethers and/or mixtures thereof.

In one embodiment, solvent molecules also function as linker precursors.

In one embodiment, the electrolyte solution additionally contains a conductive salt and/or structure-directing additive.

Conductive salts or conductive additives are compounds that increase the conductivity of the electrolyte solution in order to influence the homogeneity of the electrochemically deposited coating. Increasing the conductivity of the electrolyte solution lowers the ohmic resistance during deposition, which means that the electric field is more homogeneous. This leads to a more uniform (spatial) distribution of the dissolution current and thus to a deposited coating that is structured more uniformly, especially with regard to the layer thickness.

For the purposes of the invention, a conductive salt is also understood to mean a mixture of several conductive salts.

In one embodiment, the conductive salt is selected from organic and/or inorganic salts.

In one embodiment, the organic salt is selected from organic sulfates, sulfonates, borates, phosphates, phosphonates, carboxylates and/or ammonium salts. In one embodiment, the ammonium salts are selected from ammonium surfactant salts.

According to the invention, ammonium surfactants are salts containing quaternary ammonium ions NR ₄ ⁺ , where R is selected from H and/or alkyl, where all R can be the same or different and where at least one R radical contains at least 2 carbon atoms.

In one embodiment, the ammonium salts are selected from ammonium surfactant methyl sulfates, preferably methyltributylammonium methyl sulfate, ammonium hydroxides, preferably tetrabutylammonium hydroxide, ammonium surfactant tetrafluoroborates, preferably tetrabutylammonium tetrafluoroborate, and ammonium surfactant hexafluorophosphates, preferably tetrabutylammonium hexafluorophosphate.

In one embodiment, the carboxylates are selected from acetates and/or oxalates.

In one embodiment, the inorganic salt is selected from nitrates, nitrites, sulfates, sulfites, disulfites, sulfides, carbonates, hydrogen carbonates, phosphates, hydrogen phosphates, dihydrogen phosphates, pyrophosphates, chromates, cyano salts, hydroxides, chlorides, perchlorates, chlorates, bromides, bromates, tetrafluoroborates , iodides, iodates and/or fluorides, preferably from nitrates and/or sulfates.

In one embodiment, the concentration of the conductive salt in the electrolyte solution is 0.01 mol/l to 2.00 mol/l, preferably 0.05 mol/l to 0.5 mol/l.

In one embodiment, the electrolyte solution additionally contains a structure-directing additive.

Structure-directing additives are compounds that deliberately cause or direct structuring of a compound in a specific spatial manner for a limited time or permanently. Limited in time means that the directing molecule is not built into the structure and this z. B. by washing with a solvent after the reaction leaves again but the structure formed is retained. Indefinitely means that the directing molecule either becomes part of the new structure or remains in the structure as an independent molecule, e.g. B. in a pore, in a porous material.

For the purposes of the invention, a structure-directing additive is also understood to mean a mixture of a plurality of structure-directing additives.

In one embodiment, the structure-directing additives are selected from anionic, cationic and/or neutral surfactants.

In one embodiment, the structure-directing additives are selected from imidazoles, pyridines, acetates, oxalates, citrates, lauryl sulfates, organic ammonium salts, preferably from imidazoles and ammonium salts.

According to the invention, the electrolyte solution contains at least one metal ion.

For the purposes of the invention, this is the metal ion required for the synthesis of the metal-organic framework or a mixture of several different metal ions.

In one embodiment, the at least one metal ion for synthesizing the metal-organic framework is selected from Cu ⁺ , Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , Co ²⁺ , Co ³⁺ , Al ³⁺ , Mg ²⁺ , Ti ⁴⁺ , Ti ³⁺ , Zr ⁴⁺ , Mn ³⁺ , Mn ⁴⁺ , Cr ³⁺ , V ²⁺ , V ³⁺ , V ⁴⁺ , Mo ³⁺ , W ³⁺ , Ni ²⁺ , Ni ⁺ , Ag ⁺ , Au ⁺ , Sn ²⁺ , Sn ⁴⁺ , Si ²⁺ , Si ⁴⁺ , Pb ²⁺ , Pb ⁴⁺ and/or Zn ²⁺ , preferably Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , Al ³⁺ and /or Zn ²⁺ .

1. i) als Metallionensalz in der Elektrolytlösung gelöst und/oder
2. ii) durch elektrolytische Oxidation oder Reduktion eines in Bauteil und/oder Elektrode enthaltenen Metallionenvorläufers an der Grenzfläche zwischen Bauteil und Elektrolytlösung generiert und/oder in der Elektrolytlösung bereitgestellt.

According to the invention, the at least one metal ion is either

1. i) dissolved as a metal ion salt in the electrolyte solution and/or
2. ii) generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the component and the electrolyte solution and/or provided in the electrolyte solution.

Metal ion precursor, or also metal ion precursor compound, refers to the compound in which the metal ion necessary for the synthesis of the metal-organic framework compound, in particular chemically bonded, is present. The metal ion precursor thus contains the metal ion necessary for the synthesis of the metal-organic framework in—particularly chemically—bound form, which metal ion does not yet have the oxidation state necessary for the synthesis of the MOFs. By oxidizing or reducing this metal ion precursor or metal ion precursor compound upon electrolysis, the metal ion is provided in the electrolytic solution.

According to the invention, the metal ion precursor is contained in the component and/or electrode.

For example, if one wants to produce a MOF coating with Mn ²⁺ as the metal ion, the component and/or the electrode can contain manganese as the metal or manganese oxide (e.g. MnO ₂ or Mn ₃ O ₄ ) as the metal ion precursor.

Metallic manganese is then (anodically) oxidized to produce Mn ²⁺ in the electrolytic solution; Manganese oxides such as MnO ₂ or Mn ₃ O ₄ would be (cathodically) reduced (Mn ⁴⁺ to Mn ²⁺ or Mn ³⁺ to Mn ²⁺ ).

According to the invention, the at least one metal ion in variant i) is dissolved in the electrolyte solution as a metal ion salt. The metal ion then already has the oxidation state necessary for the synthesis of the MOFs.

It then applies that the linker compound is generated electrolytically or electrochemically induced from a linker precursor compound at the interface between component and electrode.

The linker compound is then generated in the electrolyte solution by electrochemical reaction and/or chemical reaction as a result of an electrochemical reaction in situ from the corresponding linker precursor compound(s) at the interface between the component and the electrolyte solution.

The at least one metal ion can be an electrolyte component present in the form of a corresponding metal ion salt, ie it can be present dissolved in the electrolyte solution. Then the metal ion already has the oxidation state necessary for the synthesis of the MOFs.

In one embodiment, a metal salt containing a metal ion in the oxidation state necessary for the synthesis of the MOFs is dissolved directly in the electrolyte solution.

In one embodiment, the concentration of the metal ion salt or a mixture of several metal ion salts in the electrolyte solution is 0.005 mol/l to 1 mol/l, preferably 0.05 mol/l to 0.1 mol/l.

In one embodiment, at least one metal ion salt and at least one linker precursor compound are initially introduced into the electrolyte solution for coating the component.

In one embodiment, the metal ion is generated in the electrolyte solution by metal ion precursors contained in at least one of the electrodes that are not the component being electrolytically induced converted to the metal ion and provided in the electrolyte solution. The metal ion is then also present in the electrolyte solution in the oxidation state necessary for the synthesis of the MOFs.

The linker compound is then also generated in the electrolyte solution by an electrochemical reaction and/or chemical reaction as a result of an electrochemical reaction in situ from the corresponding linker precursor compound(s) at the interface between the component and the electrolyte solution.

At least one component of the MOF coating (metal ion or linker compound) must therefore be formed at the interface between the component and the electrolyte solution in order to protect the coating to ensure processing. This formation of the component is initiated electrolytically or electrochemically.

This means that either the MOF metal ion is formed electrolytically at the interface between the component and the electrolyte solution from a metal ion precursor and/or the linker compound is formed at the interface by electrolysis from a linker precursor compound.

The formation of the MOF therefore takes place as a result of an electrochemical reaction on the component or a chemical reaction as a result of an electrochemical reaction on the component. The electrochemical reaction is triggered and controlled by applying an electric field to the component (component switched as an electrode) or by placing the component in an electric field (component not switched as an electrode).

In one embodiment, metal ions and linker compounds present in the electrolyte solution already form MOF crystal building blocks (ie, smaller particles) in the solution, some of which are integrated into the growing coating at the interface. However, a metal ion precursor and/or a linker precursor compound must still be available to the system.

According to the invention, according to variant ii), the at least one metal ion is generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the component and the electrolyte solution.

According to the invention, the component is either a) simultaneously an electrode or b) is placed in an electric field between two electrodes.

In variant a), the component is also an electrode. This means that at least one of the electrodes required for the electrolysis is then represented by the component.

In one embodiment, the component is at the same time an electrode containing metal ion precursors and the metal ion originates directly from the surface of the component to be coated.

In one embodiment, the component contains a material containing at least one metal ion precursor, selected from pure metal and/or metal alloys, for example brass, bronze, German silver, steel, Inconel, Hastelloy, Monel, titanium alloy, duralumin, etc. and/or metal compounds, for example metal oxides and/or hydroxides.

In one embodiment, the metal is preferably selected from Cu, Fe, Al and/or Zn.

In one embodiment, the metal oxides and/or hydroxides are preferably selected from Cu ₂ O, CuO, Fe ₂ O ₃ , Fe ₃ O ₄ , Al ₂ O ₃ , Al(OH) ₃ and/or ZnO.

In one embodiment, the component comprises an electrically conductive carrier material and a coating containing a metal ion precursor, this coating being selected from metals and/or metal alloys and/or metal oxides and/or metal hydroxides.

In one embodiment, the coating containing metal ion precursors is a coating containing metal, wherein the metal is selected from Cu, Fe, Co, Al, Mg, Ti, Zr, Mn, Cr, V, Mo, W, Ni, Ag, Au, Sn , Si, Pb and/or Zn, preferably Cu, Fe, Al and/or Zn.

In one embodiment, the coating containing metal ion precursors is a coating containing metal oxides and/or hydroxides, selected e.g. from Al ₂ O ₃ , (Al(OH) ₃ , Cu ₂ O, CuO, Cu(OH) ₂ , Fe ₃ O ₄ , Fe ₂ O ₃ , FeO(OH) Co ₃ O ₄ , CoOOH, Co( OH) ₃ , CoO, Ti ₂ O ₃ , Ti(OH) ₂ , Ti(OH) ₃ , Ti(OH) ₄ , TiO ₂ , MnO(OH), MnO(OH) ₂ , Mn ₃ O ₄ , Mn ₂ O ₃ , MnO ₂ , Cr ₂ O ₃ , Cr(OH) ₃ , Cr(OH) ₄ , CrO ₂ , CrO ₃ , VO ₂ , V ₂ O ₃ , V ₂ O ₄ , V ₂ O ₅ , MoO ₂ , MoO ₃ , Ni ₃ O ₄ , Ni ₂ O ₃ , NiO, (NiOH) ₂ , AgOH, Ag ₂ O, Ag ₂ O ₃ , SiO ₂ , Pb(OH) ₂ , Pb(OH) ₄ , Pb ₃ O ₄ , PbO ₂ and/or ZnO, Zn(OH) ₂ , and mixtures thereof or other mixed compounds with other ions such as SO ₄ ^2- , SO ₃ ^2- , etc. (e.g. verdigris), preferably Al ₂ O ₃ , Cu ₂ O, CuO, Fe ₂ O ₃ , Fe ₃ O ₄ and/or ZnO.

In one embodiment, the coating containing metal ions is a coating containing a metal alloy. In one embodiment, the metal alloy is selected from brass, bronze, German silver, steel, Inconel, Hastelloy, Monel, titanium alloy and/or duralumin.

In one embodiment, the carrier material is selected from electrically conductive polymers, carbons, such as. As graphite, carbon fibers, carbon nanotubes or other carbon allotropes.

In one embodiment, the carrier material is provided with a coating containing a metal ion precursor.

According to the invention, the metal ion can be formed electrolytically by oxidation or reduction of a metal ion precursor contained in the component at the interface between the component and the electrolyte solution are generated, the component being connected as an electrode.

In one embodiment, the component is connected as a metal ion-generating electrode during the electrochemical deposition.

In one embodiment, the component is switched as an anode during the electrochemical deposition. The metal ion precursor or metal ion precursor compound contained in the component is then anodically oxidized and the metal ion passes into the electrolyte solution. The reaction with the linker compound also present in the electrolyte solution results in the formation and electrochemical deposition of the metal-organic framework on the component.

In the case of electrochemical deposition, in which the component acts as a metal ion-generating anode, the component contains metal ion precursors with a lower oxidation state than the metal ion of the resulting metal-organic framework.

In the case of electrochemical deposition, in which the component acts as an anode, the component is connected as an anode. By applying a voltage, metal ion precursors contained in the surface or top layer of the component to be coated are anodically oxidized and the metal ion on the component is thus supplied to the electrolyte solution. There, the metal ion reacts with the linker compound contained in the electrolyte solution to form the metal-organic framework compound, which is deposited on the component.

In one embodiment, the voltage during the electrochemical deposition in variant a) is 0.2 to 40 V or −10 to 10 V compared to a mercury sulfate reference electrode, preferably −2.5 to 1 V compared to a mercury/mercury sulfate reference electrode.

The MOFs are deposited until the layer thickness of the MOF is from 0.1 to 1000 μm, preferably from 1 to 100 μm, particularly preferably from 2 to 20 μm, in particular from 3 to 10 μm.

The layer thickness is determined by means of scanning electron and light microscopy.

The duration of the electrolysis is 30 s to 5 h, preferably 5 min to 60 min, particularly preferably 10 to 30 min.

In one embodiment, the component is switched as a cathode during the electrochemical deposition.

In the case of electrochemical deposition, in which the component acts as a metal ion-generating cathode, the component contains metal ion precursors with a higher oxidation state than the metal ion of the resulting metal-organic framework.

In the case of electrochemical deposition, in which the component acts as a metal ion-generating cathode, the component is switched as a cathode. By applying a voltage, the metal ion precursor contained in the surface or top layer of the component to be coated is reduced cathodically and the metal ion on the component is thus supplied to the electrolyte. There, the metal ion reacts with the linker compound contained in the electrolyte solution to form the metal-organic framework compound, which is deposited on the component.

It is also possible that the metal ion precursor compound is not present as a component metal or component coating, for example, but as a metal ion salt dissolved in the electrolyte solution. The metal ion then does not yet have the oxidation state necessary for the synthesis of the MOFs, which is why the metal ion salt is first reacted electrochemically and the metal ion necessary for the MOF synthesis is formed.

As an example z. B. permanganate salts such as KMnO ₄ in question, which are then electrochemically reduced to Mn ²⁺ ions on the component.

As already described above, in one embodiment the linker compound is generated from a linker precursor compound contained in the electrolyte solution.

In one embodiment, the linker compound is formed from at least one linker precursor compound during electrolysis. This can be done by an electrochemical reaction and/or a chemical reaction as a result of an electrochemical reaction.

In one embodiment, the electrochemical reaction of the electrolyte initiates the chemical reaction to form the linker compound from the linker precursor compound. For example, the cathodic reduction of a nitrate salt in the electrolyte solution, in which hydroxide ions are formed, can change the pH to such an extent that z. B. acid groups are deprotonated and, for example, the linker carboxylates are formed from the free carboxylic acids.

In one embodiment, acid or imidazole groups are deprotonated by changing the pH, for example by water decomposition during electrolysis.

In one embodiment, the device functions as a linker compound generating electrode.

In one embodiment, the device functions as a linker compound generating cathode.

In that case, the component consists of any electrically conductive material and the metal ions originate from the electrode containing metal ion precursors connected as an anode and/or from the metal ion salt dissolved in the electrolyte solution.

In one embodiment, however, the component also contains, as the cathode generating the linker compound, a metal ion precursor with a higher oxidation state than the metal ion of the metal-organic framework compound to be formed.

During electrochemical deposition, in which the component acts as a cathode that generates a linker compound, the linker precursor compound contained in the electrolyte solution is converted electrochemically or chemically as a result of an electrochemical reaction to form the corresponding linker compound on the component. This occurs, for example, by cleavage of the precursor compound or by deprotonation as a result of a pH change by reduction that consumes hydrogen protons. The pH value can also be changed by reducing solvent or conductive salt components, for example water and/or nitrate ions, by generating hydroxide ions.

By applying a voltage, the linker connection is fed to the electrolyte solution on the component. There, the linker compound reacts with the metal ion contained in the solution to form the metal-organic framework compound, which is deposited on the component.

In one embodiment, the component acts as an anode that generates a linker connection. Then the component consists of any electrically conductive material or the component contains metal ion precursors with a lower oxidation state than the metal ion of the metal-organic framework compound.

During electrochemical deposition, in which the component acts as an anode that generates a linker compound, the linker precursor compound contained in the electrolyte solution is converted electrochemically or chemically as a result of an electrochemical reaction to form the corresponding linker compound on the component. This is done, for example, by oxidation of the linker precursor compound, e.g. B. an aldehyde functionality to the corresponding carboxylic acid functionality. Cleavage of the linker precursor compound may also occur, such as acidic deprotection of protected carboxylic acid groups.

However, the conversion of the linker precursor compound into the linker compound can also be effected by a pH change by means of an electrolytic oxidation that consumes hydroxide ions or by oxidation of solvents such as water or conductive salt components that generate hydrogen ions.

During electrolysis, the linker compound is added to the electrolyte solution on the component. There, the linker compound reacts with the metal ion contained in the electrolyte solution to form the metal-organic framework compound, which is deposited on the component. The metal ion can be a component of the electrolyte in the form of a metal salt and/or the metal ions originate from the electrode containing metal ion precursors connected as a cathode and/or the metal ion is also attached to the component containing a metal ion precursor with a lower oxidation state than the metal ion of the metal-organic framework by anodic reaction added to the electrolyte solution.

The electrodes can also be different from the component. This corresponds to variant b) in the process according to the invention.

According to the invention, in variant b), the component is introduced into an electric field between two electrodes.

The metal-organic framework is then electrochemically deposited indirectly anodically or indirectly cathodically on the component using bipolar electroplating technology.

In this case, the component is introduced into an electric field generated in the electrolyte solution by at least two electrodes, by means of which the component is polarized, as a result of which electrochemical deposition takes place on the component.

The component is then not connected at the same time as an electrode or as an electrode.

In this procedure, also referred to as bipolar electroplating, the component is placed in an electric field between at least one positively polarized and at least one negatively polarized electrode.

In one embodiment, the coating space of the component, ie the area surrounding the component containing the electrolyte solution, is separated from the electrode spaces by membranes so that the conversion of electrolyte components, such as the linker precursor compound tion at the electrodes is minimized or prevented.

According to the invention, in variant ii), the metal ion is generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the component and the electrolyte solution and/or is provided in the electrolyte solution

In one embodiment, the metal ion required for the synthesis of the metal-organic framework is released from the component due to the polarization caused by the electric field between the at least two electrodes, with the metal ion being released from the component by electrochemical oxidation or reduction and passing into the electrolyte solution. There it reacts with the linker compound contained in the solution and is deposited on the component as a metal-organic framework compound. One then speaks of indirect anodic or indirect cathodic deposition.

In one embodiment, the component contains metal ion precursors selected from pure metal and/or metal alloys and/or metal oxides and/or hydroxides, as are also described above for a component as a metal ion-supplying electrode.

In one embodiment, the component comprises an electrically conductive carrier material and a coating containing metal ions, this coating being selected from metals and/or metal alloys and/or metal oxides and/or hydroxides, as already described above for a component as an electrode supplying metal ions .

In one embodiment, the carrier material of the component is selected from electrically conductive polymers, carbons, carbon fibers and materials as already described above for variant a) for a component which is coated with metal ion precursor materials of a higher or lower oxidation state.

In one embodiment, the component, in particular its surface, comprises an electrically conductive material, for example metals, metal oxides, semiconductor materials, ITO or FTO glass, conductive polymers. The linker precursor compound is then converted electrolytically or electrochemically to form the linker compound at the interface between the component and the electrolyte solution.

The electric field between the electrodes must be correspondingly strong for the indirect forms of deposition.

In one embodiment, the voltage during the electrochemical deposition in variant b) is 1 to 100 volts, preferably 5 to 20 V.

The metal-organic framework compounds are deposited as a uniformly thick layer on the component. After deposition, the coated component is rinsed with water or a solvent and dried if necessary.

In one embodiment, the metal ions required for the synthesis of the MOF coating are provided from one of the electrodes (corresponds to variant b—the component is not an electrode) by oxidation or reduction in the electrolyte solution (variant ii).

• - das Metallion als Metallionensalz in der Elektrolytlösung gelöst und/oder wird nach Variante ii)
• - durch elektrolytische Oxidation oder Reduktion eines in Bauteil und/oder Elektrode enthaltenen Metallionenvorläufers an der Grenzfläche zwischen Bauteil und Elektrolytlösung generiert und/oder in der Elektrolytlösung bereitgestellt,

wobei das Bauteil a) gleichzeitig Elektrode ist oder b) nicht gleichzeitig Elektrode ist, sondern in ein elektrisches Feld zwischen zwei Elektroden eingebracht wird.According to the invention, according to variant i)

• - The metal ion is dissolved as a metal ion salt in the electrolyte solution and/or is, according to variant ii)
• - generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the component and the electrolyte solution and/or provided in the electrolyte solution,

the component a) being an electrode at the same time, or b) not being an electrode at the same time, but being placed in an electric field between two electrodes.

• Das mindestens eine Metallion ist als Metallionensalz, vorzugsweise in der zur Synthese der MOF notwendigen Oxidationsstufe, in der Elektrolytlösung gelöst, eine der zur Elektrolyse eingesetzten Elektroden ist gleichzeitig Bauteil und die Linkerverbindung wird an der Grenzfläche von Bauteil und Elektrolytlösung generiert.

The following cases are therefore possible:

• The at least one metal ion is dissolved in the electrolyte solution as a metal ion salt, preferably in the oxidation state required for the synthesis of the MOF. One of the electrodes used for electrolysis is also a component and the linker connection is generated at the interface between the component and the electrolyte solution.

The at least one metal ion is generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component at the interface between the component and the electrolyte solution, with at least one of the electrodes used for the electrolysis being a component at the same time.

The at least one metal ion is provided by electrolytic oxidation or reduction of a metal ion precursor contained in an electrode in the electrolyte solution and the linker connection is generated electrolytically at the interface between the component and the electrolyte solution, with at least one of the electrodes used for electrolysis being a component at the same time.

For the combination of i) and / or ii) with variant b), this means: The component is in a electric field is introduced between at least two electrodes and the at least one metal ion is dissolved in the electrolyte solution as a metal ion salt in the oxidation state necessary for the synthesis of the MOF and/or is provided in the electrolyte solution by electrolytic oxidation or reduction of a metal ion precursor contained in an electrode and/ or is generated and provided by electrolytic oxidation or reduction of the component containing a corresponding metal ion precursor at the interface between the component and the electrolyte solution, the component not being an electrode at the same time.

In one embodiment, the layer of metal-organic framework compounds contains micropores and/or macropores and/or mesopores, some with different pore types, e.g. B. slit pores. The term micropores refers to pores with a diameter of up to 2 nm. The term mesopores refers to pores with a diameter of 2 nm to 50 nm. The term macropores refers to pores with a diameter > 50 nm.

The specific surface area (BET) of the metal-organic framework compounds produced according to the invention is above standard DIN ISO 9277 2014-01-00. Determination of the specific surface area of solids by gas adsorption - BET method (ISO 9277:2010). pp. 1-30. The specific surface area of the MOF coating produced according to the invention is 5 m ² /g to 2500 m ² /g.

However, scanning electron microscopy is a more suitable method (e.g. compared to physisorption measurements) for investigating the MOF coatings produced according to the invention in order to examine the porosity/structure and the shape of the porosity. So it is relevant how the pores on the crystallite surface are designed. The determination of the BET surface area by physisorption measurements, on the other hand, can be misleading, since a high BET surface area in m ² /g could also be due to pores in the "interior of the crystallite", while the crystallite surface is relatively smooth.

Scanning electron microscopic investigations show a particularly structured crystallite growth within the MOF coating due to the electrochemical deposition. For example, evenly arranged MOF crystallites with an octahedral geometry can be found in the coating, which cause a microscale surface morphology ( 1 ) and, on closer inspection of the surface of a single crystallite, also show nanoscale structures. Likewise, compositions of nanocrystallites can have a nanoscale and microscale superstructure ( 4 ) form. Thus, MOF morphologies with gaps in the nanoscale range from 10 to 100 nm are observed (see 2 and 5 ). These intermediate spaces advantageously have continuity.

In addition, the crystallites have a structure-related microporosity, so that a triple hierarchical structuring of the surface is advantageously found.

In one embodiment, the MOF layers produced according to the invention have a triple hierarchical structure. In terms of the invention, this means that the surface is structured both in the micrometer and in the nanometer range and the surface also has micropores.

This hierarchically constructed structure of the surface and the coating base material can advantageously be produced in just one process step, while previously known, mostly photolithographic processes require several complex process steps.

The observed micro- and/or nanostructures with an additional nanoroughness and porosity caused by the micropores are advantageously suitable for ensuring improved adhesion of the impregnating agent subsequently applied.

Advantageously, the MOF coatings produced according to the invention already have larger water contact angles than, for example, MOF coatings that were realized by coating with hydrothermally produced MOF.

A further advantage of the MOFs produced according to the invention is the high stability of the crystalline framework compounds, which is ensured by the coordinate bonds of linkers and metal ions.

Due to the very high porosity of the surface, omniphobic, low-volatile oils can be infiltrated, which are absorbed and held by the morphologically adapted MOF coatings like a sponge.

In one embodiment, the component is dried after coating with the MOF at a pressure of 1000 mbar to 10 ^-10 mbar and a temperature in the range -40°C to 180°C.

According to the invention, after the electrochemical deposition of the organometallic Framework connection the application of an impregnation agent with a low surface tension of < 30 mN/m on the MOF coating.

An additional impregnation of the MOF coating advantageously leads to omniphobic properties of the surface of the component.

Omniphobic means that the surface is repellent to a wide range of polar and non-polar fluids. Polar and non-polar fluids with low surface tensions of >10 mN/m to 50 mN/m, preferably up to 30 mN/m, also have an increased contact angle on these surfaces, so that droplet condensation is possible. The same applies to fluids with a higher surface tension.

To enable droplet formation of fluids with low surface tension, an impregnating agent with a low surface tension of < 30 mN/m is applied to the MOF coating.

In one embodiment, the impregnating agent has a lower surface tension than the fluid or mixture of fluids to be condensed.

Advantageously, prior treatment with perfluorosilanes, as is known from the prior art for photolithographically produced microstructures, is no longer necessary in order to ensure the desired wetting properties and sufficient adhesion of the impregnating agent on the MOF coating.

In one embodiment, the impregnating agent has a low surface tension of <30 mN/m, preferably <20 mN/m.

In one embodiment, the impregnating agent is selected from oils, fats and/or perfluor-based thickeners.

In one embodiment, the impregnating agent is selected from perfluorinated polymers and/or perfluoroalkyl ethers and/or partially fluorinated and/or polyfluorinated polymers or alkyl ethers.

In one embodiment, the impregnating agent is applied by dipping and/or spraying and/or spin coating and/or spin coating processes.

In one embodiment, the omniphobic surface coating produced according to the invention has a contact angle of 115° when wetted with water and/or 60° when wetted with acetone and/or 95° when wetted with diiodomethane.

Fluids with low surface tensions of >10 to <30 mN/m advantageously have a contact angle of at least 35 degrees, preferably at least 50 degrees, on the components coated according to the invention, which is suitable for droplet condensation.

Advantageously, the omniphobic surfaces produced according to the invention are mechanically more stable than previously known smooth, perfluorinated omniphobic surfaces.

A further advantage of the combination of the inventive coating of the surface of the component with metal-organic framework compounds and their impregnation lies in the improved adhesion of the impregnating agent to the hierarchically structured MOF layer due to favorable intermolecular interactions between the impregnating agent and MOF. The washing out of the impregnating agent by the condensate, which is often observed in the prior art, can be reduced as a result.

The individual physicochemical properties of the respective MOF compound can advantageously be influenced by the selection of the linker compound. It is even possible to adjust the extent to which the contact angle of the condensing fluids is increased by the lubricant, which is presumably due to improved interaction of the linker molecules with the lubricant.

The combination of imidazolate-based MOFs and perfluoroalkyl ether-based impregnating agents has proven to be particularly advantageous. The surface energy of the MOFs with an imidazolate linker is still significantly lower than that of the carboxylate MOFs, which can lead to particularly good adhesion of the impregnating agent to the MOF coating.

Components with a complex structure or components on an industrial scale can also advantageously be provided with an omniphobic surface coating using the method according to the invention.

A further advantage of the method according to the invention lies in the short time it takes to produce an omniphobic surface coating on components.

The invention also relates to an omniphobic surface coating containing a metal-organic framework and an impregnating agent, the metal-organic framework being micro and/or meso and/or macro contains pores and/or channels, the metal-organic framework having a pore volume of 0.002 cm ³ /g to 3.500 cm ³ /g, preferably 0.010 cm ³ /g to 0.080 cm ³ /g, the metal-organic framework having a specific surface area of 5 m ² /g to 2500 m ² /g, preferably 50 m ² /g to 1500 m ² /g, the layer thickness of the surface coating being 0.1 μm to 1000 μm, preferably 2 μm to 100 μm, particularly preferably 2 to 10 μm is, wherein the impregnating agent has a surface tension of <30 mN/m, preferably <20 mN/m.

The invention also relates to the use of an omniphobic surface coating according to the invention on components for droplet condensation of fluids with a surface tension of <75 mN/m, preferably <50 mN/m, particularly preferably <30 mN/m.

In one embodiment, the fluids are selected from organic solvents and/or refrigerants and/or mixtures of these.

In one embodiment, the fluids are selected from alcohols, ketones, aromatic and/or aliphatic hydrocarbons, halogenated hydrocarbons, and/or inorganic fluids.

The invention also relates to the use of an omniphobic surface coating according to the invention in heat exchangers.

In one embodiment, the heat exchangers are selected from recuperative heat exchangers, for example tube bundle heat exchangers, plate heat exchangers and spiral heat exchangers.

The heat-transferring surfaces of the heat exchanger are coated on one or both sides.

The subject matter of the invention is also a heat exchanger, comprising an omniphobic surface coating, produced by a method according to the invention.

In one embodiment, the heat exchanger is selected from tube bundle heat exchangers, plate heat exchangers and/or spiral heat exchangers.

For the realization of the invention, it is also expedient to combine the above-described configurations, embodiments and features of the claims with one another in an expedient manner. The following exemplary embodiments are intended to explain the invention in more detail, but without restricting it thereto:

• 1 eine Rasterelektronenmikroskopische Aufnahme der Kupfer-Trimesat-MOF-Beschichtung auf einem Kupferbauteil gemäß Beispiel 1, welche die Mikrostrukturierung der Beschichtung aus der Draufsicht zeigt;
• 2 eine Rasterelektronenmikroskopische Aufnahme der Kupfer-Trimesat-MOF-Beschichtung auf einem Kupferbauteil gemäß Beispiel 1, welche die Submikrostrukturierung der Beschichtung aus der Draufsicht zeigt;
• 3 ein mit Cobalt-K_α-Strahlung (λ = 1,790307 Ä) gemessenes Röntgendiffraktogramm der Kupfer-Trimesat-MOF-Beschichtung auf einem Kupferbauteil gemäß Ausführungsbeispiel 1, wobei der 2θ-Wert in Grad auf der Abszissenachse und die Signalintensität als Zählimpuls linear auf der Ordinatenachse aufgetragen ist. Darunter ist ein zur Auswertung verwendetes berechnetes Referenzdiffraktogramm abgebildet;
• 4 eine Rasterelektronenmikroskopische Aufnahme der Mangan-Dihydrogentrimesat-MOF-Beschichtung auf einem Edelstahlbauteil gemäß Ausführungsbeispiel 2. Zu sehen ist die Mikrostrukturierung der Beschichtung aus der Draufsicht;
• 5 eine Rasterelektronenmikroskopische Aufnahme der Mangan-Dihydrogentrimesat-MOF-Beschichtung auf einem Edelstahlbauteil gemäß Beispiel 2. Zu sehen ist die Submikrostrukturierung der Beschichtung aus der Draufsicht;
• 6 das mit Cobalt-K_α-Strahlung (λ = 1,790307 Å) gemessene Röntgendiffraktogramm der Mangan-Dihydrogentrimesat-MOF-Beschichtung auf einem Edelstahlbauteil gemäß Beispiel 2, wobei der 20-Wert in Grad auf der Abszissenachse und die Signalintensität als Zählimpuls linear auf der Ordinatenachse aufgetragen ist. Darunter abgebildet ist ein zur Auswertung verwendetes Referenzpulverdiffraktogramm der MOF-Verbindung.
• 7 eine schematische Darstellung der elektrochemischen Abscheidungszellen gemäß der Beispiele 1 und 2 mit Arbeitselektrode (AE), Gegenelektrode (GE), Referenzelektrode (RE), Salzbrücke (SB) und Elektrolyt (schraffiert dargestellt).
• 8 Benetzungszustände eines Wassertropfens auf a) glatten und b), c) strukturierten, hydrophoben Oberflächen.

The illustrations each show:

• 1 a scanning electron micrograph of the copper trimesate MOF coating on a copper component according to example 1, which shows the microstructuring of the coating from the top view;
• 2 a scanning electron micrograph of the copper trimesate MOF coating on a copper component according to example 1, which shows the submicrostructure of the coating from the top view;
• 3 an X-ray diffractogram of the copper trimesate MOF coating on a copper component measured with cobalt K _α radiation (λ=1.790307 λ) according to exemplary embodiment 1, with the 2θ value in degrees on the abscissa axis and the signal intensity as a linear count is plotted on the ordinate axis. A calculated reference diffractogram used for the evaluation is shown below;
• 4 a scanning electron micrograph of the manganese dihydrogen trimesate MOF coating on a stainless steel component according to exemplary embodiment 2. The microstructuring of the coating can be seen from the top view;
• 5 a scanning electron micrograph of the manganese dihydrogen trimesate MOF coating on a stainless steel component according to example 2. The submicrostructure of the coating can be seen from the top view;
• 6 the X-ray diffractogram of the manganese dihydrogen trimesate MOF coating on a stainless steel component according to Example 2, measured with cobalt K _α radiation (λ=1.790307 Å), the 20 value in degrees on the abscissa axis and the signal intensity as a linear count is plotted on the ordinate axis. A reference powder diffractogram of the MOF compound used for the evaluation is shown below.
• 7 a schematic representation of the electrochemical deposition cells according to Examples 1 and 2 with working electrode (AE), counter electrode (GE), reference electrode (RE), salt bridge (SB) and electrolyte (shown hatched).
• 8th Wetting states of a water droplet on a) smooth and b), c) structured hydrophobic surfaces.

exemplary embodiments

Example 1: Impregnated copper trimesat MOF coating on a copper component

The surface of the ultra-pure copper component was first cleaned with a lint-free tissue soaked in ethanol, then rinsed with deionized water and dried in a stream of air.
In an electrochemical deposition cell ( 7 ), consisting of a teflon body in the form of a hollow cylinder, which is open at the top and has a circular recess in the bottom, a sealing ring and a teflon plate screwed to the bottom, the flat component measuring 1.5 cm x 1.5 cm made of ultra-pure copper as the working electrode (anode) and the surface area introduced into the electrolyte solution is coated.
A platinum counter-electrode (cathode, area 2 cm×2 cm) at a distance of about 1 cm from the working electrode and a mercury/mercury sulfate reference electrode were introduced via a salt bridge into the upper opening of the electrochemical deposition cell.

An area fraction of the working electrode of 0.78 cm ² was immersed in the electrolyte solution consisting of 10 mL of a 3:1 (v/v) mixture of 100% ethanol and deionized water containing 0.05 mol/L trimesic acid and 0.06 mol/l tributylmethylammonium methyl sulfate, introduced at a temperature of 50 °C. A potential of 0.5 V versus the mercury/mercuric sulfate reference electrode was applied for 10 min with a Heka PG310 potentiostat. One minute after the end of the polarization, the electrolyte was removed, the component sample was removed and rinsed twice each with 15 ml ethanol and 15 ml deionized water and initially dried in air.

The average layer thickness of the microstructured copper Trimsat MOF coating produced in this way was determined to be 12.5 μm on average on the basis of cross-sectional photographs taken with the FEG Gemini Leo 1530 scanning electron microscope (Zeiss). The X-ray diffractogram of the copper trimesate MOF coating produced in this way on a flat copper component is in 3 (top) showing the characteristic signal pattern of a copper trimesate MOF. A calculated diffractogram of the compound HKUST-1, whose structure is stored in the Cambridge Structural Database under CCDC number 112954, serves as a reference ( 3 , below). The measurement was performed in reflection mode with a Philips 1050 diffractometer with a cobalt K _α radiation source (λ = 1.790307 Å).

After drying for three hours, the electrodeposited MOF was impregnated with Krytox GPL 105 (DuPont) lubricant.

Before impregnation, the surface was first dried for three hours under vacuum conditions at 3×10 ^-3 mbar and room temperature (25° C.).

• 114° ± 1° für Wasser,
• 95° ± 1° für Diiodmethan und
• 61° ± 1° für Aceton.

The impregnation then took place at ambient pressure in a protective gas atmosphere (argon) in a glove box. The impregnation was carried out by dripping the lubricant until the surface was completely covered. The surface was left in this state for 10 minutes. In order to remove superfluous lubricant, the surface was then blown with dry nitrogen for approx. 20 seconds. On the impregnated surface, contact angle measurements according to standard DIN 55660-2 2011-12-00 were carried out on the contact angle measuring device DSA100 (KRÜSS). Coating materials - Wettability - Part 2: Determination of the surface free energy of solid surfaces by measurement of the contact angle. p. 1-18). The following contact angles were measured:

• 114° ± 1° for water,
• 95° ± 1° for diiodomethane and
• 61° ± 1° for acetone.

Example 2: Impregnated manganese dihydrogen trimesate MOF coating on a stainless steel component

The surface of the stainless steel component was first cleaned with a lint-free tissue soaked in ethanol, then rinsed with deionized water and dried in a stream of air. In an electrochemical deposition cell ( 7 ), consisting of a teflon body in the form of a hollow cylinder, which is open at the top and has a circular recess in the bottom, a sealing ring and a teflon plate screwed to the bottom, the flat component made of stainless steel measuring 1.5 cm x 1, 5 cm as a working electrode (cathode) and coated the area introduced into the electrolyte solution.

A stainless steel counter electrode (anode, area 1.6 cm x 3 cm), which was aligned vertically at a distance of about 0.5 cm from the working electrode, and a mercury/mercury sulfate reference electrode were introduced into the upper opening of the electrochemical deposition cell via a salt bridge.

A surface area of the working electrode of 0.78 cm ² was the aqueous 0.1 mol/l manganese (II)-sulfate-containing electrolyte solution at room temperature (23-25 °C) and a potential of -2.0 V versus a mercury/mercuric sulfate reference electrode applied for 30 minutes with a Methrom Autolab PGSTAT204 potentiosate. The aqueous manganese(II) sulfate electrolyte solution was then removed from the electrochemical deposition cell and the structure, including the manganese coating electrochemically deposited on the stainless steel component, was rinsed three times with 50 ml of deionized water and once with 50 ml of ethanol and exposed to air at room temperature for 2 min dried.
Immediately thereafter, in order to avoid increased oxidation of the manganese coating in air, 10 ml of an electrolyte solution containing 0.05 mol/l trimesic acid and 0.025 mol/l 2-methylimidazole as a structure-directing additive were added in a 1:1 (v/v) Mixture of 100% ethanol and deionized water, introduced into the electrolytic cell at room temperature.
The component was now connected as a working electrode (anode) in order to dissolve the manganese coating in an electrochemically controlled manner, and a platinum counter-electrode (cathode, area 2 cm
* 2 cm), which was aligned parallel to the working electrode at a distance of about 1 cm.
A potential of -1.25 V versus the mercury/mercuric sulfate reference electrode was applied for 60 min. One minute after the end of the polarization, the electrolyte was removed, the component sample was removed and rinsed twice each with 15 ml ethanol and 15 ml deionized water and initially dried in air.

The average layer thickness of the microstructured manganese dihydrogen trimesate MOF coating produced in this way was determined to be 15.3 μm on the basis of cross-sectional photographs taken with the FEG Gemini Leo 1530 scanning electron microscope (Zeiss).

The X-ray diffractogram of the manganese dihydrogen trimesate MOF coating produced in this way on a flat stainless steel component is in 6 (top) and shows the characteristic signal pattern of a manganese dihydrogen trimesate MOF, with low-intensity, strongly broadened signals, which can be attributed to the nanocrystallinity of the MOF crystallites. The crystallites also form a mesoporous superstructure in the coating composite, which 5 is shown.

Due to the low layer thickness, a correspondingly marked signal can also be observed in the measuring area, which can be assigned to the stainless steel component.
The measurement was performed in reflection mode with a Philips 1050 diffractometer with a cobalt K _α radiation source (λ = 1.790307 Å).
A reference sample was produced for the evaluation, which had suitable crystals for an X-ray single-crystal structure determination and, after comminution, also for X-ray powder diffractometry. After seven days, the crystals were removed from a 1:1 mixture of aqueous 0.1 M manganese(II) sulfate solution and a solution analogous to the MOF coating electrolyte (0.05 mol/l trimesic acid and 0.025 mol/l 2-methylimidazole in a 1:1 (v/v) mixture of 100% ethanol and deionized water).
That for reference in 6 The powder diffraction pattern shown (below) of this sample was performed in transmission mode using a Stoe Stadi P diffractometer with a cobalt K _α1 radiation source (λ = 1.78896 Å). The structure and the identity of the compound [Mn(H ₂ BTC) ₂ (H ₂ O) ₄ ] were determined by X-ray single crystal structure determination. For this purpose, a measurable crystal was selected under the light microscope, glued to a thin glass thread and measured on an Oxford Diffraction Xcalibur single crystal diffractometer with a Sapphire 2 CCD detector at λ = 0.71073 Å. Data reduction was done with CrysalisRed from Oxford Diffraction and the final evaluation steps, structure solution and refinement, with SheIXS and ShelXL implemented in XStep32 from Stoe.

After drying for three hours, the electrodeposited MOF was impregnated with Krytox GPL 105 (DuPont) lubricant.

• 65° ± 3° für Wasser,
• 95° ± 1° für Diiodmethan und
• 65° ± 2° für Aceton.

Before impregnation, the surface was first dried for three hours under vacuum conditions at 3×10 ^-3 mbar and room temperature (25° C.).
The impregnation then took place at ambient pressure in a protective gas atmosphere (argon) in a glove box. The impregnation was carried out by dripping the lubricant until the surface was completely covered. The surface was left in this state for 10 minutes. In order to remove superfluous lubricant, the surface was then blown with dry nitrogen for approx. 20 seconds.
On the impregnated surface, contact angle measurements according to standard DIN 55660-2 2011-12-00 were carried out on the contact angle measuring device DSA100 (KRÜSS). Coating materials - Wettability - Part 2: Determination of the surface free energy of solid surfaces by measuring the contact angle. pp. 1-18. The following contact angles were measured:

• 65° ± 3° for water,
• 95° ± 1° for diiodomethane and
• 65° ± 2° for acetone.

The reduced water contact angle compared to Example 1 is due to the physicochemical properties of the linker molecule structure, which in the manganese dihydrogen trimesate MOF has four firmly bound hydrophilic water molecules per formula unit, on which the structure of the structure containing hydrogen bonds is dependent in this organometallic compound. This illustrates the described possibility of influencing the extent of the contact angle increase of the fluids to be condensed through the impregnating agent or through the choice of the MOF or linker compounds.

Scanning electron microscopy is a very suitable method for examining the MOF coatings produced according to the invention (eg in comparison to physisorption measurements) in order to examine the porosity/structuring and the shape of the porosity. So it is relevant how the pores on the crystallite surface are designed. However, the determination of the BET surface area by physisorption measurements is misleading, since a high BET surface area in m ² /g could be due to pores in the "interior of the crystallite", while the crystallite surface is relatively smooth.

The SEM images show the roughness/structuring on the micrometer scale ( 1 or. 4 ) as well as in the submicrometer scale or nanoscale ( 2 or. 5 ) The superhierarchically structured MOF coating produced according to the invention (copper trimesate MOF coating on a copper component according to Example 1 (see 1 and 2 ) and manganese dihydrogen trimesate MOF coating on a stainless steel component according to embodiment 2 (see 4 and 5 )).

The "black" areas are the gaps/pores in which the lubricant is stored without causing a smooth crystallite surface. The bright areas can be assigned to the crystalline MOF compound. In the 1 , 2 , 4 and 5 shows the morphology/shape of the MOF coatings.

The crystallinity is shown by the reflections in X-ray diffraction ( 3 or. 6 ). The recordings are made before impregnation.

Claims (17)

Process for coating components with an omniphobic surface coating, containing at least one metal-organic framework compound and an impregnating agent, with the steps, - electrochemical deposition of the metal-organic framework on the component by means of electrolysis, from an electrolyte solution containing at least one metal ion, at least one linker compound and a solvent, - Applying an impregnating agent to the metal-organic framework, wherein the metal ion i) is dissolved as a metal ion salt in the electrolyte solution and/or ii) is generated by electrolytic oxidation or reduction of a metal ion precursor contained in the component and/or electrode at the interface between the electrode and the electrolyte solution and/or is provided in the electrolyte solution, and where the component a) is also an electrode or b) placed in an electric field between at least two electrodes will, wherein the linker compound is an organic, at least monodentate compound, and wherein the impregnating agent has a low surface tension of <30 mN/m. procedure after claim 1 , characterized in that the electrochemical deposition takes place potentiostatically, galvanostatically and/or with current and/or with voltage pulses. procedure after claim 1 , characterized in that the organic, at least monodentate compound contains at least one functional group selected from carboxylate groups, sulfonate groups, phosphonate groups, imidazolate groups, pyridine groups, phenanthroline groups, triazolate groups and/or tetrazolate groups. Procedure according to one of Claims 1 until 3 , characterized in that the linker compound is formed during the electrolysis from at least one linker precursor compound. procedure after claim 4 , characterized in that the chemical reaction for forming the linker compound from the corresponding linker precursor compound is triggered by the electrochemical conversion of at least one component of the electrolyte solution during the electrolysis. procedure after claim 4 or 5 , characterized in that the linker precursor compound is selected from the free acids or anhydrides of the linker compounds. Procedure according to one of Claims 1 until 6 , characterized in that the electrolyte solution additionally contains a conducting salt and/or structure-directing additive. Procedure according to one of Claims 1 until 7 , characterized in that the at least one metal ion for the synthesis of the metal-organic framework is selected from Cu ⁺ , Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , Co ²⁺ , Co ³⁺ , Al ³⁺ , Mg ²⁺ , Ti ^{4 +} , Ti ³⁺ , Zr ⁴⁺ , Mn ³⁺ , Mn ⁴⁺ , Cr ³⁺ , V ²⁺ , V ³⁺ , V ⁴⁺ , Mo ³⁺ , W ³⁺ , Ni ²⁺ , Ni ⁺ , Ag ⁺ , Au ⁺ , Sn ²⁺ , Sn ⁴⁺ , Si ²⁺ , Si ⁴⁺ , Pb ²⁺ , Pb ⁴⁺ and/or Zn ²⁺ . Procedure according to one of Claims 1 until 8th , characterized in that the component is a metal ion precursor containing material. Procedure according to one of Claims 1 until 9 , characterized in that the component comprises an electrically conductive carrier material and a coating containing metal ion precursors. Procedure according to one of Claims 1 until 10 , characterized in that the component is switched during the electrochemical deposition as a metal ion-generating electrode. Procedure according to one of Claims 1 until 11 , characterized in that the component functions as a linker connection generating electrode. Procedure according to one of Claims 1 until 12 , characterized in that the impregnating agent is selected from perfluorinated polymers and/or perfluoroalkyl ethers and/or partially fluorinated and/or polyfluorinated polymers or alkyl ethers. Omniphobic surface coating containing a metal-organic framework compound and an impregnating agent, the metal-organic framework compound containing micro- and/or meso- and/or macropores, the metal-organic framework compound having a pore volume of 0.002 cm ³ /g to 3.5 cm ³ /g, wherein the metal-organic framework compound has a specific surface area of 5 m ² /g to 2500 m ² /g, the layer thickness of the surface coating being 100 nm to 1 mm, the impregnating agent having a surface tension of <30 mN/m. using an omniphobic surface coating Claim 14 on components for droplet condensation of fluids with a surface tension of < 75 mN/m. using an omniphobic surface coating Claim 14 in heat exchangers. Heat exchanger comprising an omniphobic surface coating Claim 14 or produced in a process according to any one of Claims 1 until 13 .

Images