Bioinspired Stimuli‐Responsive and Antifreeze‐Secreting Anti‐Icing Coatings

The detrimental impacts of icing on transportation and power industries are well‐known. Inspired by natural systems that secrete a functional liquid in response to stimuli, this work introduces an anti‐icing coating that responds to surface icing by releasing antifreeze liquid. It consists of an outer porous superhydrophobic epidermis and a wick‐like underlying dermis that is infused with antifreeze liquid. The functionality of the new coating is validated through condensation frosting, simulated freezing fog, and freezing rain experiments. In the tested conditions, the introduced anti‐icing skin delays onset of frost, rime, and glaze accumulation at least ten times longer than anti‐icing superhydrophobic and lubricant impregnated surfaces. Furthermore, the coating delays onset of glaze formation ten times longer than surfaces flooded with a thin film of antifreeze. In each of the icing scenarios, the fundamental mechanisms responsible for antifreeze release and their relation to required antifreeze replenishment rates are described.     

Reinigung von Vakuumbauteilen für UHV‐ und UCV‐Anwendungen

Cleaning of vacuum components for UHV and UCV applications Ultra‐clean vacuum components and assemblies are fundamental to some cutting edge high‐tech sectors like semiconductor industry, particle accelerators, and surface analytics. Exceptionally critical for these applications are particles that stick at the vacuum facing surfaces as well as desorption of water and hydrocarbons from the surfaces into the system, because this may interfere with the sensitive ultra‐high vacuum (UHV) and ultra‐clean vacuum (UCV) processes. In this contribution, some established cleaning methods and surface treatments are discussed with respect to their effect on reducing particle contamination and outgassing of water and organic compounds from stainless steel surfaces. It is clarified that the resulting cleanliness severely depends on the detailed steps during the surface treatment and subsequent cleaning. As a consequence, the discussed methods should be chosen and adapted with great care according to the specific demands of the final application area.     

Non‐linear exact geometry 12‐node solid‐shell element with three translational degrees of freedom per node

This paper presents the finite rotation exact geometry (EG) 12‐node solid‐shell element with 36 displacement degrees of freedom. The term ‘EG’ reflects the fact that coefficients of the first and second fundamental forms of the reference surface and Christoffel symbols are taken exactly at each element node. The finite element formulation developed is based on the 9‐parameter shell model by employing a new concept of sampling surfaces (S‐surfaces) inside the shell body. We introduce three S‐surfaces, namely, bottom, middle and top, and choose nine displacements of these surfaces as fundamental shell unknowns. Such choice allows one to represent the finite rotation higher order EG solid‐shell element formulation in a very compact form and to derive the strain–displacement relationships, which are objective, that is, invariant under arbitrarily large rigid‐body shell motions in convected curvilinear coordinates. The tangent stiffness matrix is evaluated by using 3D analytical integration and the explicit presentation of this matrix is given. The latter is unusual for the non‐linear EG shell element formulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Realization of High Performance AR‐coatings with Dust‐ and Water‐Repellent Properties

Hydrophobic coatings enable the manufacture of easy‐to‐clean surfaces having dust‐ and water‐repellent properties. In this work, a hydrophobic coating is deposited as a top layer on an antireflective (AR) multilayer system to produce low reflectance optical surfaces at a normal incident angle in the visible spectrum with dust‐ and water‐repellent properties for applications in precision optics. It is shown that the hydrophobic coating can be considered, from an optical point of view, as two adjacent thin layers having specific thicknesses and densities. In fact, the hydrophobic layer is one monolayer comprising molecular chains with anchoring groups responsible for the chemical bond with the substrate material and functional groups responsible for the water‐ and oil‐repellent properties. Their optical constants are determined and included in the final coating design. High performance AR coatings having an average reflectance of 0.14% at 7° incident angle in the 400‐680nm spectral range together with a pleasing purplered reflex color are produced. Coated lenses exhibit an excellent abrasion resistance, environmental stability, resistance to cleaning agents, homogeneity and water repellence with contact angles against water higher than 110°.     

Anti‐Eis‐Oberflächenbeschichtungen

Anti‐icing coating — optimization by means of plasma technology Ice on surfaces can significantly limit the function of devices and has to be removed by processes with high energy consumption. E. g., the formation of ice on rotor blades of wind turbines is not desired, on the wings of aircrafts it is even dangerous. With the aid of plasma technology, the Fraunhofer IGB has developed an anti‐icing coating for polymeric surfaces. Water‐repellent micro‐ and nanostructured coatings are applied to polymer foils made of impact‐resistant and shockproof polyurethane. Optimization of various process parameters has made it possible to produce ultra‐thin coatings, which reduces the ice's adhesion by over 90 percent. The new nanostructured foils open a wide range of applications.     

Synchrotron‐Based Micro‐CT and Refraction‐Enhanced Micro‐CT for Non‐Destructive Materials Characterisation

X‐ray computed tomography is an important tool for non‐destructively evaluating the 3‐D microstructure of modern materials. To resolve material structures in the micrometer range and below, high brilliance synchrotron radiation has to be used. The Federal Institute for Materials Research and Testing (BAM) has built up an imaging setup for micro‐tomography and ‐radiography (BAMline) at the Berliner storage ring for synchrotron radiation (BESSY). In computed tomography, the contrast at interfaces within heterogeneous materials can be strongly amplified by effects related to X‐ray refraction. Such effects are especially useful for materials of low absorption or mixed phases showing similar X‐ray absorption properties that produce low contrast. The technique is based on ultra‐small‐angle scattering by microstructural elements causing phase‐related effects, such as refraction and total reflection. The extraordinary contrast of inner surfaces is far beyond absorption effects. Crack orientation and fibre/matrix debonding in plastics, polymers, ceramics and metal‐matrix‐composites after cyclic loading and hydro‐thermal aging can be visualized. In most cases, the investigated inner surface and interface structures correlate to mechanical properties. The technique is an alternative to other attempts on raising the spatial resolution of CT machines.     

Self‐Sensitized Carbon Nitride Microspheres for Long‐Lasting Visible‐Light‐Driven Hydrogen Generation

A new type of metal‐free photocatalyst is reported having a microsphere core of oxygen‐containing carbon nitride and self‐sensitized surfaces by covalently linked polymeric triazine dyes. These self‐sensitized carbon nitride microspheres exhibit high visible‐light activities in photocatalytic H₂ generation with excellent stability for more than 100 h reaction. Comparing to the traditional g‐C₃N₄ with activities terminated at 450 nm, the polymeric triazine dyes on the carbon nitride microsphere surface allow for effective wide‐range visible‐light harvesting and extend the H₂ generation activities up to 600 nm. It is believed that this new type of highly stable self‐sensitized metal‐free structure opens a new direction of future development of low‐cost photocatalysts for efficient and long‐term solar fuels production.     

Multiplexed Molecular Imaging of Fresh Tissue Surfaces Enabled by Convection‐Enhanced Topical Staining with SERS‐Coded Nanoparticles

There is a need for intraoperative imaging technologies to guide breast‐conserving surgeries and to reduce the high rates of re‐excision for patients in which residual tumor is found at the surgical margins during postoperative pathology analyses. Feasibility studies have shown that utilizing topically applied surface‐enhanced Raman scattering (SERS) nanoparticles (NPs), in conjunction with the ratiometric imaging of targeted versus untargeted NPs, enables the rapid visualization of multiple cell‐surface biomarkers of cancer that are overexpressed at the surfaces of freshly excised breast tissues. In order to reliably and rapidly perform multiplexed Raman‐encoded molecular imaging of large numbers of biomarkers (with five or more NP flavors), an enhanced staining method has been developed in which tissue surfaces are cyclically dipped into an NP‐staining solution and subjected to high‐frequency mechanical vibration. This dipping and mechanical vibration (DMV) method promotes the convection of the SERS NPs at fresh tissue surfaces, which accelerates their binding to their respective biomarker targets. By utilizing a custom‐developed device for automated DMV staining, this study demonstrates the ability to simultaneously image four cell‐surface biomarkers of cancer at the surfaces of fresh human breast tissues with a mixture of five flavors of SERS NPs (four targeted and one untargeted control) topically applied for 5 min and imaged at a spatial resolution of 0.5 mm and a raster‐scanned imaging rate of >5 cm² min^?1.     

Plasma‐Induced Hetero‐Nanostructures on a Polymer with Selective Metal Co‐Deposition

Plasma‐induced pattern formation is explored on polyethylene terephthalate (PET) using an oxygen plasma glow discharge. The nanostructures on PET are formed through preferential etching directed by the co‐deposition of metallic elements, such as Cr or Fe, sputtered from a stainless‐steel cathode. The local islands formed by metal co‐deposition have significantly slower etching rates than those of the pristine regions on PET, generating anisotropic nanostructures in pillar‐ or hair‐like form during plasma etching. By covering the cathode with the appropriate material, the desired metallic or polymeric elements can be co‐deposited onto the target surfaces. When the cathode is covered by a relatively soft material composed of only carbon and hydrogen, such as polystyrene, nanostructures typically induced by preferential etching are not observed on the PET surface, and the surfaces are uniformly etched. A variety of metals, such as Ag, Cu, Pt, or Si, can be successfully co‐deposited onto the PET surfaces by simply using a cathode covered in the desired metal; high‐aspect‐ratio nanostructures coated with the co‐deposited metal are subsequently formed. Therefore this simple single‐step method for forming hetero‐nanostructures—that is, nanoscale hair‐like polymer structures decorated with metals—can be used to produce nanostructures for various applications, such as catalysts, sensors, or energy devices.     

Uniform Spread of High‐Speed Drops on Superhydrophobic Surface by Live‐Oligomeric Surfactant Jamming

Inkjet printing of water‐based inks on superhydrophobic surfaces is important in high‐resolution bioarray detection, chemical analysis, and high‐performance electronic circuits and devices. Obtaining uniform spreading of a drop on a superhydrophobic surface is still a challenge. Uniform round drop spreading and high‐resolution inkjet printing patterns are demonstrated on superhydrophobic surfaces without splash or rebound after high‐speed impacting by introducing live‐oligomeric surfactant adhesion. During impact, the live‐oligomeric surfactant molecules aggregate into dynamic, wormlike micelle networks, which jam at the solid–liquid interface by entangling with the surface micro/nanostructures to pin the contact line and jam at the spreading periphery to keep the uniform spreading lamellar shape. This efficient uniform spreading of high‐speed impact drops opens a promising avenue to control drop impact dynamics and achieve high‐resolution printing.     

Droplet Transport on a Nano‐ and Microstructured Surface with a Wettability Gradient in Low‐Temperature or High‐Humidity Environments

Directional driving of a droplet can be achieved on a gradient‐exhibiting, nanostructured microhump (GNMH) surface at low temperature and high humidity. The GNMH surface is fabricated using a commercial carbon fiber plate with an array of microscale hump structures; nanotechniques are used to form varying nanostructures on the microhump array, producing the micro‐ and nanostructured surface. The different nanostructures result in a wettability gradient along the surface, enabling droplet transport with the help of vibration—even at low temperature or high humidity. In contrast, simply nanostructured surfaces or microstructured surfaces that also have a wettable gradient do not enable droplet transport at low temperature or high humidty. In a range of subzero temperatures or in a range of high‐humidity conditions, the GNMH surface retains its superhydrophobicity and ability for directional droplet transport along its wettability gradient. These results may assist in the design of surfaces required for cold environments, such as microreactors, chemical analytic devices, and sensors.     

Temperature‐Enhanced Solvent Vapor Annealing of a C3 Symmetric Hexa‐peri‐Hexabenzocoronene: Controlling the Self‐Assembly from Nano‐ to Macroscale

Temperature‐enhanced solvent vapor annealing (TESVA) is used to self‐assemble functionalized polycyclic aromatic hydrocarbon molecules into ordered macroscopic layers and crystals on solid surfaces. A novel C₃ symmetric hexa‐peri‐hexabenzocoronene functionalized with alternating hydrophilic and hydrophobic side chains is used as a model system since its multivalent character can be expected to offer unique self‐assembly properties and behavior in different solvents. TESVA promotes the molecule's long‐range mobility, as proven by their diffusion on a Si/SiO_x surface on a scale of hundreds of micrometers. This leads to self‐assembly into large, ordered crystals featuring an edge‐on columnar type of arrangement, which differs from the morphologies obtained using conventional solution‐processing methods such as spin‐coating or drop‐casting. The temperature modulation in the TESVA makes it possible to achieve an additional control over the role of hydrodynamic forces in the self‐assembly at surfaces, leading to a macroscopic self‐healing within the adsorbed film notably improved as compared to conventional solvent vapor annealing. This surface re‐organization can be monitored in real time by optical and atomic force microscopy.     

Template‐Free,Surfactant‐Mediated Orientation of Self‐Assembled Supercrystals of Metal–Organic Framework Particles

Mesoscale self‐assembly of particles into supercrystals is important for the design of functional materials such as photonic and plasmonic crystals. However, while much progress has been made in self‐assembling supercrystals adopting diverse lattices and using different types of particles, controlling their growth orientation on surfaces has received limited success. Most of the latter orientation control has been achieved via templating methods in which lithographic processes are used to form a patterned surface that acts as a template for particle assembly. Herein, a template‐free method to self‐assemble (111)‐, (100)‐, and (110)‐oriented face‐centered cubic supercrystals of the metal–organic framework ZIF‐8 particles by adjusting the amount of surfactant (cetyltrimethylammonium bromide) used is described. It is shown that these supercrystals behave as photonic crystals whose properties depend on their growth orientation. This control on the orientation of the supercrystals dictates the orientation of the composing porous particles that might ultimately facilitate pore orientation on surfaces for designing membranes and sensors.     

A Shape‐Adaptive Thin‐Film‐Based Approach for 50% High‐Efficiency Energy Generation Through Micro‐Grating Sliding Electrification

Effectively harvesting ambient mechanical energy is the key for realizing self‐powered and autonomous electronics, which addresses limitations of batteries and thus has tremendous applications in sensor networks, wireless devices, and wearable/implantable electronics, etc. Here, a thin‐film‐based micro‐grating triboelectric nanogenerator (MG‐TENG) is developed for high‐efficiency power generation through conversion of mechanical energy. The shape‐adaptive MG‐TENG relies on sliding electrification between complementary micro‐sized arrays of linear grating, which offers a unique and straightforward solution in harnessing energy from relative sliding motion between surfaces. Operating at a sliding velocity of 10 m/s, a MG‐TENG of 60 cm² in overall area, 0.2 cm³ in volume and 0.6 g in weight can deliver an average output power of 3 W (power density of 50 mW cm^?2 and 15 W cm^?3) at an overall conversion efficiency of ～50%, making it a sufficient power supply to regular electronics, such as light bulbs. The scalable and cost‐effective MG‐TENG is practically applicable in not only harvesting various mechanical motions but also possibly power generation at a large scale.     

Diffusion–Freezing‐Induced Microphase Separation for Constructing Large‐Area Multiscale Structures on Hydrogel Surfaces

Hydrogels with multiscale structured surface have attracted significant attention for their valuable applications in diverse areas. However, current strategies for the design and fabrication of structured hydrogel surfaces, which suffer from complicated manufacturing processes and specific material modeling, are not efficient to produce structured hydrogel surfaces in large area, and therefore restrict their practical applications. To address this problem, a general and reliable method is reported, which relies on the interplay between polymer chain diffusion and the subsequent freezing‐induced gelation and microphase separation processes. The basic idea is systematically analyzed and further exploited to manufacture gel surfaces with gradient structures and patterns through the introduction of temperature gradient and shape control of the contact area. Moreover, the formed micro/nanostructured surfaces are exemplified to work as capillary systems and thus can uplift the liquid spontaneously indicating the potential application for anti‐dehydration. It is believed that the proposed facile and large‐area fabrication method can inspire the design of materials with various functionalized surfaces.     

Bioinspired Mechanically Robust Metal‐Based Water Repellent Surface Enabled by Scalable Construction of a Flexible Coral‐Reef‐Like Architecture

Mechanical robustness is a central concern for moving artificial superhydrophobic surfaces to application practices. It is believed that bulk hydrophilic materials cannot be use to construct micro/nanoarchitectures for superhydrophobicity since abrasion‐induced exposure of hydrophilic surfaces leads to remarkable degradation of water repellency. To address this challenge, the robust mechanical durability of a superhydrophobic surface with metal (hydrophilic) textures, through scalable construction of a flexible coral‐reef‐like hierarchical architecture on various substrates including metals, glasses, and ceramics, is demonstrated. Discontinuous coral‐reef‐like Cu architecture is built by solid‐state spraying commercial electrolytic Cu particles (15–65 µm) at supersonic particle velocities. Subsequent flame oxidation is applied to introduce a porous hard surface oxide layer. Owing to the unique combination of the flexible coral‐reef‐like architecture and self‐similar manner of the fluorinated hard oxide surface layer, the coating surface retains its water repellency with an extremely low roll‐off angle (<2°) after cyclic sand‐paper abrasion, mechanical bending, sand‐grit erosion, knife‐scratching, and heavy loading of simulated acid rain droplets. Strong adhesion to glass, ceramics, and metals up to 34 MPa can be achieved without using adhesive. The results show that the present superhydrophobic coating can have wide outdoor applications for self‐cleaning and corrosion protection of metal parts.     

Tuning Molecular Self‐Assembly on Bulk Insulator Surfaces by Anchoring of the Organic Building Blocks

Molecular self‐assembly constitutes a versatile strategy for creating functional structures on surfaces. Tuning the subtle balance between intermolecular and molecule‐surface interactions allows structure formation to be tailored at the single‐molecule level. While metal surfaces usually exhibit interaction strengths in an energy range that favors molecular self‐assembly, dielectric surfaces having low surface energies often lack sufficient interactions with adsorbed molecules. As a consequence, application‐relevant, bulk insulating materials pose significant challenges when considering them as supporting substrates for molecular self‐assembly. Here, the current status of molecular self‐assembly on surfaces of wide‐bandgap dielectric crystals, investigated under ultrahigh vacuum conditions at room temperature, is reviewed. To address the major issues currently limiting the applicability of molecular self‐assembly principles in the case of dielectric surfaces, a systematic discussion of general strategies is provided for anchoring organic molecules to bulk insulating materials.     

Kalte Normaldruck‐Jetplasmen zur lokalen Oberflächenbehandlung

Cold non‐thermal plasma jets for local surface treatment under normal pressure Plasmas at normal pressure are of considerable interest for surface technology because the industrial application requires no vacuum devices. Among other approaches, cold non‐thermal plasma jets represent an emerging technique to generate plasmas at normal pressure with attractive advantages. They allow ambient process temperatures and require only moderate operating voltages (1.5‐2.5 kV). They offer the advantage that the treated surfaces are not placed between the electrodes thus favoring local treatment of non flat, structured 3D surfaces. Moreover, the dimension of the sources is scalable and their integration into automated processes is simple. A capacitively coupled version (27.12 MHz) of a cold plasma jet suitable for surface treatment at atmospheric pressure is presented along with its plasma physical and technical properties and a series of successful applications, including plasma activation of surfaces for increasing printability, adhesion control, surface cleaning, microfluidics, decontamination, its use in plasmamedicine and for deposition of thin SiO₂ films as protective coatings. The device allows the operation with rare gases (e.g. Ar) and reactive gases as N₂, air or admixtures of silicon‐containing compounds.     

Substrate Templating upon Self‐Assembly of Hydrogen‐Bonded Molecular Networks on an Insulating Surface

Molecular self‐assembly on insulating surfaces, despite being highly relvant to many applications, generally suffers from the weak molecule–surface interactions present on dielectric surfaces, especially when benchmarked against metallic substrates. Therefore, to fully exploit the potential of molecular self‐assembly, increasing the influence of the substrate constitutes an essential prerequisite. Upon deposition of terephthalic acid and trimesic acid onto the natural cleavage plane of calcite, extended hydrogen‐bonded networks are formed, which wet the substrate. The observed structural complexity matches the variety realized on metal surfaces. A detailed analysis of the molecular structures observed on calcite reveals a significant influence of the underlying substrate, clearly indicating a substantial templating effect of the surface on the resulting molecular networks. This work demonstrates that choosing suitable molecule/substrate systems allows for tuning the balance between intermolecular and molecule–surface interactions even in the case of typically weakly interacting insulating surfaces. This study, thus, provides a strategy for deliberately exploiting substrate templating to increase the structural variety in molecular self‐assembly on a bulk insulator at room temperature.     

In‐phase and out‐of‐phase thermomechanical fatigue behavior of 4Cr5MoSiV1 hot work die steel cycling from 400 °C to 700 °C

The hysteresis loops, stress and strain behavior, lifetime behavior and fracture characteristic of 4Cr5MoSiV1 hot work die steel at a wide range of mechanical strain amplitudes (from 0.5% to 1.3%) during the in‐phase (IP) and out‐of‐phase (OP) thermomechanical fatigue (TMF) tests cycling from 400 °C to 700 °C under full reverse strain‐controlled condition were investigated. Stress‐mechanical strain hysteresis loops of 4Cr5MoSiV1 steel are asymmetric, and stress reduction appears at high‐temperature half cycles owing to a decrease in strength with increasing temperature. 4Cr5MoSiV1 steel always exhibits continuous cyclic softening for both types of TMF tests, and the cyclic softening rate is larger in OP loading condition. OP TMF life of 4Cr5MoSiV1 steel is approximately 60% of IP TMF life at the same mechanical strain amplitude and maximum temperature. Lifetime determined and predicted in both types of TMF tests is adequately described by the Ostergren model. Fracture surfaces under IP TMF loading display the striation and tear ridge, showing quasi‐cleavage characteristics, and the cracks are less but longer. However, fracture surfaces under OP TMF loading mainly display the striation and dimple characteristics, and the cracks are more and shorter.