Optimization of dielectric interfaces using nano structured surfaces

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In this research application, joints, bushing, and terminations with electrical potential separation (e.g. cable sleeves and terminations in medium to extra-high voltage technology) are to be improved concerning their electrical strength. Changes in the electrical behaviour of electrical insulation arrangements, which occur at interfaces based on different material properties, are known. In addition to the intended influence on this behaviour, surface roughness and assembly inaccuracies can cause cavities to form which, above a certain size, allows partial discharges, leading to damage in the insulating material and the interface. For this reason, these cavities should be designed to be as small as possible below the critical size of 10 µm. State of the art is gas permeable materials or other auxiliary materials such as pastes to close these potential cavities. The surface hardness as well as a suitable contact pressure are selected accordingly. Furthermore, preliminary investigations show that a specific surface structuring, e.g., by a triangular structure (100 µm), increases the interface length. The extension of this resulted in an expected increase in electrical strength.Objective: In the present project proposal, the targeted use of wrinkle structuring (wrinkling) using plasma modification is intended to generate required structural sizes (resulting in cavities below 10 µm) on the surface of longitudinal interface materials. This will be lead to an increase in the electrical interface strength and a reduce in the use of additional materials as well as a decrease in the component size.For this purpose, an elastic substrate is stretched and at the same time, a thin, solid film is applied or generated. The subsequent relaxation leads to a stress compromise between the thin, solid film and the elastic substrate. This causes local deformations of the film at the surface, resulting in a periodically sinusoidal wrinkle structure. In the case of uniaxial deformation, the wrinkles form perpendicular to the direction of elongation. The characteristic parameters are the wavelength and the structure height of the wrinkles, which can be precisely adjusted by the different plasma process parameters. Other structuring methods like lithography or laser structuring, which also allow structures in the desired size range, are too slow or too expensive or cannot be scaled to large areas or 3D geometries. Structuring by embossing or printing does not allow the desired size range. Wrinkle structuring, on the other hand, can be flexibly controlled via the manufacturing parameters and can be implemented in a large area and resource-efficiently. Also, the present project proposal aims to structure silicones, which is why in-situ plasma modification combined with controlled deformation of substrates for wrinkle formation is most promising.