Understanding the Relation between Pulse Duration and Topography Evolution of Polyether Ether Ketones Textures by Ultrashort Infrared Laser Interference Patterning

Advanced polymeric materials, such as polyether ether ketones (PEEK), have been placed as direct substitutes for metals and ceramics in diverse applications, such as the machinery industry and biomedical engineering. Moreover, surface treatments allow the emergence of brand-new properties or the improvement of preexisting ones, such as friction, lubrication, wettability, cellular infiltration, or osseointegration. A paramount approach to achieving topographical modifications is by using laser micro/nanoprocessing techniques such as direct laser interference patterning (DLIP). Herein, PEEK foils are structured with DLIP method using ultrashort pulses. The influence of the pulse duration between 266 fs and 15 ps and the pulse-to-pulse overlap on the resulting surface topography and chemistry is assessed. As a result, well-defined line-like textures with a period of 5.8 μm and aspect ratios up to 0.88 are achieved. Furthermore, it is possible to explore and understand the behavior of surface phenomena such as swelling, increase/decrease of laser–material interaction onset, and laser-induced periodic surface structures formation. A comprehensive topographical and chemical characterization study demonstrates that these distinctive topographical features occur because of multiphoton absorption, incubation effects, and heat accumulation. These phenomena allow structuring polymeric substrates that are low-absorbing and challenging to pattern with conventional nanosecond infrared (IR) laser sources

New solar selective coating based on carbon nanotubes

Carbon nanotubes (CNTs) can be applied to assemble a new type of solar selective coating system for solar thermal applications. In this work the predominant absorption processes occurring by interaction with π-plasmon and Van Hove singularities (VHS) were investigated by UV-VIS-NIR spectroscopy and ellipsometry. Not only optical properties for as deposited SWCNT thin films itself, but also the potential for systematic tailoring will be presented. Besides low cost technologies required, the adjustability of optical properties, as well as their thermal stability render CNT based solar selective coatings as promising alternative to commercially available coating systems

Thermal operating window for PEDOT:PSS films and its related thermoelectric properties

The intrinsically conducting polymer PEDOT:PSS is widely used and has found high recognition due to its excellent electrical conductivity. Its potential applications cover many fields, e.g. thermoelectric energy conversion. Therefore we compared the thermoelectric properties of pristine and DMSO treated PEDOT:PSS films at potential operating temperatures. Here we observed the electrical degradation of the film up to complete failure. Further, the thermal aging of PEDOT:PSS still lacks of understanding. It is pointed out that PEDOT:PSS films show a complex degradation mechanism which includes a morphological and a chemical part. In the range of room temperature and ∼160 °C PEDOT:PSS films follow the known exponential degradation which imposes morphological degradation, while at higher temperatures this law is not suitable to match the experimental data. Thus we extended the known exponential equation by an additional exponential degradation term which shows good agreement with the experimental data. The optical absorption spectrum indicates a loss in bipolaron and polaron charge carriers, which reflects the degradation behavior. It can be seen that changes in the optical absorption spectrum after isothermal annealing for more than 50 h occur at temperatures around 120 °C, which marks the transition from morphological to chemical degradation

Improving component cleanliness during laser remote ablation processes with high-power lasers by optimized emission blower and suction strategies

Laser remote processing with high-performance laser sources enables materials such as metals or fiber composites to be cut, welded or ablated flexibly and quickly. All these manufacturing processes produce process and material specific particulate as well as gaseous emissions. This must be recorded quantitatively and qualitatively in order to implement appropriate protective measures with regard to occupational health and safety as well as to minimize the crosscontamination of the component to be treated. Ideally, an additional cleaning step should be avoided by optimizing the arrangement of the process suction and blower. Particle distributions as well as gas phase analyses during the remote ablation process were recorded during ablation tests on metals or carbon-based composites. The structure quality and the contamination of the sample surface after laser material processing as well as after the additional cleaning process were determined. Subsequently, the samples were thermally joined to evaluate the influences

Parameters Influencing the Photocatalytic Activity of Suspension-Sprayed TiO2 Coatings

Publisher Copyright: © 2014, ASM International.Photocatalytic properties of titania have been studied very intensively for a variety of applications, including air and water purification. In order to clarify the influence of the phase composition and other parameters, thermal spraying with suspensions was applied to produce photocatalytically active titania coatings starting from two commercially available anatase and rutile submicron powders. Aqueous suspensions containing 40% solids by weight were sprayed with an HVOF process using ethylene as the fuel gas. The spray parameters were chosen in order to produce mechanically stable coatings and to preserve a high content of the initial crystalline phases of the powders. The coating microstructures, phase compositions, and surface properties were characterized. The photocatalytic performance was evaluated by degradation of the pink dye Rhodamine B (RB) using two techniques: degradation of an aqueous solution of RB and discoloration of impregnated RB. All the coatings exhibited photocatalytic activity to varying degrees, depending on the phase composition as well as other factors, namely, the coating microstructure, surface morphology, surface hydroxylation, light absorption, and interaction with the pollutant.The authors would like to thank B. Wolf and S. Schultz (Fraunhofer IWS) for help with the metallographic preparation and the spectroscopy measurements and Dr. M. Yamada (Toyahashi University of Technology, Toyahashi, Japan) for kind delivery of the ceramic substrates. Part of this work was performed under DVS research project 02.064 ‘‘Funktionalisierung von Keramikoberflächen dur-ch thermisch gespritzte Schichten’’ (‘‘Functionalization of ceramic surfaces by thermal spraying’’), AiF No. 17.371 BR, funded via AiF by the Federal Ministry of Economics and Technology within the framework of the program for promotion of ‘‘Industrial Joint Research (IGF).’’ The authors gratefully acknowledge this financial support.Peer reviewe