DOI: 10.1002/adem.201500364 Adaptive Silicon Oxycarbide Coatings With Controlled Hydrophilic or Hydrophobic Properties** By Boris Reznik,* ,1 Jordan Denev and Henning Bockhorn The study presents a method for producing of adaptive silicon oxycarbide (Si–O–C) coatings from pyrolyzed polymethylsilsesquioxane as well as a dedicated technique for molecular design of the polymer precursor. The coating texture is spontaneously formed as a result of crack propagation during shrinkage of the solidified polymer. The coatings contain periodic grooves and in situ formed scrolled filaments. The synthesized coatings undergo a transition between hydrophobic and hydrophilic states. The scrolled fibers exhibit thermal adaptive behavior. The coatings are obtained on different substrates from the polymer precursor fractions exhibiting different molecular weights. 1. Introduction Metallic and ceramic materials are typically considered as “dead matter.” However, at elevated temperatures (approx. 650–1 100  C) tailored surfaces have the potential to react to effects from the environment in a very specific way and, thus, may provide special functionalities to a technical component. Therefore, the development of “living” or adaptive materials, which can exhibit a reversible shape change due to temperature or pressure variations, is an important scientific and technical challenge. Furthermore, the use of materials for reducing energy losses can be realized by decreasing the hydrodynamic surface friction and hence also the drag. [1,2] It is known, that the skin of fast swimming sharks displays a prominent riblet structure on its surface. These riblets turned out to reduce the drag loss significantly. [3] However, due to the difficulties in production of such shaped surfaces the advantages of these structures cannot be fully utilized for high-temperature applications. Therefore, the Priority DFG- Programme 1299 “Adaptive Surfaces for High-Temperature Applications” targets to find technical solutions allowing a controlled fabrication of surfaces with these riblet-like textures. Silicone oxycarbide derived from polysiloxanes is an attractive coating material for high-temperature applications including fuel-injection pumps, heat transfer tubes, ignition plugs, and thermal shields exhibiting anticorrosion behavior. [4–6] The advantages of the polymer precursor route to glasses or ceramics over a traditional ceramic processing route are: i) polymers can generally be converted to metastable ceramics at temperatures less than 1 200  C; ii) polymers can be readily purified; iii) ceramics coatings exhibiting complex shapes can be fabricated; iv) porous ceramics coatings can be used as catalysts, adsorbents as well as supports for heterogeneous metal catalysis; and v) chemical and physical properties of the derived coatings can be tuned by designing preceramic polymers and controlling the polymer pyrolysis. [4] However, up to now, no studies have been carried out focusing on the high-temperature perfor- mance of Si–O–C coatings which exhibit adaptive properties. The following results demonstrate that by means of controlled surface structuring adaptive properties of this material can be achieved. A series of preliminary results of our research group formed the basis of the development of the method for producing Si–O–C coatings exhibiting adaptive (“living”) surface properties. First, in 2011 [5] a spontaneous formation of micrometer-sized scrolled Si–O–C filaments was observed at the surfaces of manually fractured free-standing flake-shaped glassy residues (flakes) obtained after pyrolysis of a poly- methylsilsesquioxane (PMS) powder. Later, [6] it was noticed that after PMS pyrolysis, in a combustion porcelain boat (Figure 1a), a large amount of free-standing flakes are formed (Figure 1b). Furthermore, it was recognized, that the surface of the flake top (Figure 1c) is smooth while the flake bottom surface, which was previously connected to the boat surface, [*] Dr. B. Reznik, Dr. J. Denev, Dr. H. Bockhorn Karlsruhe Institute of Technology (KIT), Engler-Bunte-Insti- tute, Combustion division, 76131 Karlsruhe, Germany E-mail: boris.reznik@kit.edu 1 The present address: Division of Structural Geology and Tectonophysics, KIT, Institute of Applied Geosciences, 76131 Karlsruhe, Germany [**] This work was supported by the German DFG-Priority program 1299: “Adapting surfaces for high temperature applications.” Mr. H. Weickenmeier is thanked for the technical assistance. We thank to M. Ströbele and F. Parhat for the conducting of pyrolysis experiments. We thank also to Dr. C. Eberl for the nanoindentation tests. ADVANCED ENGINEERING MATERIALS 2016, 18, No. 5 © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 703 FULL PAPER