2018, Purtov, Julia, Verch, Andreas, Rogin, Peter, Hensel, René

Natural functional surfaces often rely on unique nano- and micropatterns. To mimic such surfaces successfully, patterning techniques are required that enable the fabrication of three-dimensional structures at the nanoscale. It has been reported that two-photon polymerization (TPP) is a suitable method for this. However, polymer structures fabricated by TPP often tend to shrink and to collapse during the fabrication process. In particular, delicate structures suffer from their insufficient mechanical stability against capillary forces which mainly arisein the fabrication process during the evaporation of the developer and rinsing liquids. Here, we report a modified development approach, which enables an additional UV-treatment to post cross-link created structures before they are dried. We tested our approach on nanopillar arrays and microscopic pillar structures mimicking the moth-eye and the gecko adhesives, respectively. Our results indicate a significant improvement of the me- chanical stability of the polymer structures, resulting in fewer defects and reduced shrinkage of the structures.

2017, Staudinger, U., Zyla, G., Krause, Beate, Janke, A., Fischer, D., Esen, C., Voit, B., Ostendorf, A.

Femtosecond laser-induced two-photon polymerization (2PP) of carbon nanofiller doped polymers was utilized to produce electrically conductive microstructures, which are expected to be applicable as microelectronic components or micro-electromechanical systems in sensors. The nanocomposites were processed by compounding an inorganic-organic hybrid material with two different types (short and long) of single walled carbon nanotubes (SWCNTs). Different SWCNT contents were dispersed in the polymer by sonication to adjust the electrical conductivity of the nanocomposites. Low surface resistivity values of ~ 4.6 × 105 Ω/sq. could be measured for coated reference films with a thickness of 30 μm having an exceptionally low SWCNT content of 0.01 wt% of the long type of SWCNTs. In contrast, a higher minimum resistivity of 1.5 × 106 Ω/sq. was exhibited for composites with a higher content, 2 wt%, of short SWCNTs. The structural quality of the microstructures processed by 2PP was mainly influenced by the dispersion quality of the SWCNTs. To characterize the electrical conductivity, conductive atomic force microscopy was applied for the first time. In microstructures with 0.05 wt% of the long type of SWCNTs, a contact current could be detected over a wide range of the measured area visualizing the electrical conductive CNT network, which has not been reported before.