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Die Elektrifizierung von Fahrzeugen stellt die OEMs und deren Zulieferer vor komplexe Herausforderungen. Dabei müssen auch Materialien, die in anderen Industrien bereits als Stand der Technik bekannt sind, für den neuen Anwendungsfall adaptiert werden. Ein Beispiel hierfür sind Wärmeleitpasten als Gapfiller, die nun für wärmeleitende Verbindungen zur Batteriekühlung in Serien-Elektrofahrzeugen verwendet werden sollen. Hierbei spielen Eigenschaften, wie die Dichte, die Viskosität sowie die damit einhergehende Verarbeitbarkeit, neben den Kosten eine entscheidende Rolle.

In this study, electron beam (EB) curable acrylates are investigated for their use as planarization layers. Planarization layers can be used in multilayer thin film encapsulations for all kinds of flexible electronics, such as organic light emitting diodes (OLED), organic photovoltaics (OPV) and printed switching circuits, antennas, and sensors. Planarization layers cover particles and defects of the substrate and thus a plain smooth surface is created for optimized growing conditions of thin films, optimizing encapsulation properties. The thin film encapsulation prevents organic electronics from degradation due to invasive oxygen and water vapor. Several commercially available monomers and oligomers with different molar mass and number of reactive double bonds are investigated. The acrylates are deposited on polyethylene terephthalate (PET) web and glass substrates and cured by EB. The surfaces are analyzed using white light interferometry (WLI) and scanning electron microscopy (SEM). Density measurements and nanoindentation are also carried out to get information about the volume shrinkage and the elastic modulus. The correlation between chemical properties, degree of crosslinking, volume shrinkage and surface roughness are investigated. This work demonstrates that electron beam curing of acrylates is a promising method to generate smooth surfaces. It presents an increasing degree of crosslinking and volume shrinkage with decreasing molecular weight between crosslinks. Also, for comparable molecular weight between crosslinks, the volume shrinkage is higher for acrylates forming thermoplastics than for elastomers or duromers.

Structural parts made of fiber reinforced plastics do not play a predominant role in automobile mass production due to the costs associated with storage condition, low level of automation, long processing times and safety and health regulations. The idea was to develop a holistic approach which can solve the problems with understanding the whole process chain from molecule to the finished product and integration in common technical infrastructure. A promising strategy was to create a matrix resin which combines easy processing of thermoplastics with superior mechanical properties of thermosets. The new matrix can pre-applied on all type of fibers. The resulting tack-free prepreg has a long shelf life at room temperature in consequence of phase separation of matrix raw materials which can be eliminated by raising the temperature. The resulting material has high reactivity and can be cured to a thermoset within a few minutes. Individual specification of the material like glass temperature, cure rate and toughness can be adjusted.

Wood foam and metal sponges are exotic materials with interesting properties that deviate from those of conventional materials. By merging both materials, the Fraunhofer Institutes WKI, IFAM and IWU generate a novel, lightweight composite that is sustainable both in its production and in its use.

The onycophoran Epiperipatus hilkae secrets a sticky slime that solidifies almost immediately upon contact with air and under high humidy environmental condition forming a glassy like material. The general adhesive biochemical composition, the releasing and hardening mechanism have been partially described. In this study, the structural characterization of the extracellular microstructures and nanostructures forming the solid adhesive of the secretion from Epiperipatus hilkae velvet worm is presented. The adhesive secretion is formed by macro-threads, which, in their solid state, are composed of globular particles approximately 700 nm in diameter that are distributed homogeneously throughout the matrix surface, and nanoparticles approximately 70 nm in diameter that self-assemble forming fiber-like structures. Nanoparticles with non roundish forms are also observed. These 70 nm particles could be associated to proteins that form high density coverage films with low roughness; suggesting the formation of two dimensional ordered films. A crystalline and an amorphous phase composes the solidified secretion. The glassy or viscoelastic properties depend on the time in contact with air before being adhered to a solid surface and/or the mechanical stimulus; suggesting a key role of the drying on the hardening process.

For the use as RFID antennas conductive adhesives were developed and investigated which are UV curable and could be applied with printing methods like offset printing or flexography. Further investigated aspects of the materials have been the range of the distance between emitter and receiver. The resulting formulations which are based on acrylates filled with silver pigments for the conductivity allow to cure layers with a thickness of up to 50 μm with a maximal volume resistance of 1.6 x 10 -5 Ω/cm.

Cellulose as natural and non-toxic material is very interesting for biological applications. Its poor solubility in organic solvents can be improved by introduction of long alkyl chains. Phosphate-substituted cellulose derivatives form ultra-thin layers on several metal surfaces [1, 2]. The layers were applied on the surfaces via dip coating from dilute solutions and characterised by contact angle measurements. Initial corrosion tests were performed. These polymers were applied as adhesion promoters for steel-, titanium- and hydroxy apatite surfaces. Medical implants were pre-treated by UV irradiation, coated with the cellulose derivatives and activated by hot water treatment. The adhesion of the implants surpassed that of conventionally used PMMA systems.

In recent works the self-assembly process has been investigated to replace the present chromating procedure on reactive metals like aluminium and the improve the lacquer adhesion and corrosion inhibition. These self-assembling layers were formed of small bifunctional organic molecules with phosphate or phosphonic acid groups attached to the metal substrate. The idea of this work was to apply these results and techniques to cellulose derivatives on implant metals. The formation of ultra-thin layers of phosphorylated cellulose derivatives has been reported previously. These ultrathin layers were built on metal substrates like aluminium, titanium or steel for adhesion promotion and corrosion inhibition. Hydroxypropyl-2-phosphatepropyl cellulose was synthesised for adhesion on hydrophilic metallic surface. Hydroxypropyl-2-cinnamoylpropylester cellulose was prepared in order to crosslink the adsorbed layers. The layers were formed on metal surfaces via dip coating from dilute solutions and characterised by means of contact angle measurements, SEM investigations and FT-IR spectroscopy. Initial corrosion tests were performed.

New hairy-rod like cellulose polymer layers were developed as a model system for corrosion protection and adhesion promotion in medical technology. Using the Langmuir-Blodgett technique a mixture of a cinnemate containing and a phosphate containing cellulose were transferred on titanium and steel surfaces. The cinnemate can be crosslinked by ultraviolet light (UV). Differences in the formation of multilayers were found and analyzed by atomic force microscopy, scanning auger microscopy and ellipsometric measurements. Phosphate cellulose forms homogenous layers at all substrate surfaces. With increasing layer thickness a mixture with low phosphate content becomes homogenous, too. Only mixtures with high content of phosphate keep imperfections with increasing layer thickness. For the pure component cinnemate cellulose the imperfections arise only in the case of titanium surfaces.

Vibrational circular dichroism (VCD) spectra of anisotropic thin solid samples are often superimposed with large contributions of linear birefringence and linear dichroism. In this study a theoretical approach is given on how to extract the true VCD spectrum out of such superimposed spectra. To verify this approach, the VCD spectra of achiral polymer films were examined. The polymers are supposed to give a zero line as VCD spectrum after eliminating the linear contributions. Applying our approach, in which four VCD spectra in different but selected sample orientations are recorded, and calculating their average, leads to the expected result, i.e., a zero line for achiral polymers. The advantage of this method for the elimination of artifacts from solid-state VCD spectra is that no further measurements are required (e.g., linear dichroism measurements or the determination of the orientation with the maximum anisotropy).

Common available conductive adhesives are filled with about 70-90 weight percent of silver particles. There is the technical need to lower the filler content for decreasing the viscosity and the pressure to finally decrease the costs for the highly expensive silver. Our approach to decrease the silver content with at the same time similar conductivity was to use nano-sized silver particles with different modified surfaces to obtain self-organized distribution of the silver particles in the liquid adhesive film followed by conventional curing techniques like temperature or UV curing. Through the self-organization, a bridging of the particles should be achieved which gives a similar conductivity as in highly filled commercial adhesives which follows percolation theory. The influence of the surface modification on the strength of the interaction between differently modified silver particles and the distribution in the liquid adhesive was simulated with Dissipative Particle Dynamics (DPD). Surface modification was verified with surface enhanced Raman spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS). The distribution of the silver particles in the cured adhesive film was investigated with scanning electron microscopy (SEM).