Keynote Speaker
Dr. Ruediger Berger
Examples of Infrared Nano-Spectroscopy and Imaging in Soft Matter: Polymers in Porous Materials, Thin Film Coatings in Battery Materials and Solar Cells
Semi-crystalline polymers are solids that should only flow above their melting temperature. Contrary to this widespread opinion, we show that a semi-crystalline polymer can flow at temperatures below the melting point in nanoscopic cylindrical pores [1]. Polyethylene oxides (PEO) imbibes in pores with 400 nm diameter, made in anodized aluminium oxide. The PEO imbibition length is in the range of 400 to 800 nm. The imbibed PEO has a meniscus at the growth front which raises the question is the PEO in such a confinement liquid like or crystalline? We measure three noticeable absorption peaks at 1149, 1100, and 1061 cm−1 with nano-infrared imaging and spectroscopy, which are characteristic for semi-crystalline PEO [1].
Interfaces in batteries are crucial for their performance. Depending on the stability window of the electrolyte, degradation occurs at the interfaces between the electroyte and the electrodes. Therefore protective coatings are deposited to avoid detrimental side reactions at the cathode. These coatings should be as thin as possible and pinhole-free to avoid charge transfer and capacity losses. We use infrared nano-spectroscopy and imaging to verify the composition and distribution of the polyvinylpyrrolidone (PVP)/ sulfonated poly(phenylene sulfone)s in Li+ (sPPs-Li) complex coatings on LiNi0.9Mn0.05Co0.05O2 (NCM) particles. We find characteristic peaks for the PVP/ sPPs-Li coating even for 1-2 nm thin coatings. Infrared imaging reveals that the PVP/sPPs-Li coating is evenly distributed and no pinholes are present on NCM particles [2].
Nanoscale topographic features in bulk heterojunction materials are often associated to a specific component on the device. However, the nanoscale features are not the pure phase of the respective components. Detailed information can only be gained by correlation of surface and bulk-sensitive measurements with nanometer resolution. Here, infrared nano-spectroscopy is an ideal tool for understanding the composition and distribution of phases. As a model system, we study the subsurface and surface micromorphology of PTB7:PC71BM blends. The combination of different infrared modes reveals that the lens-shaped PC71BM domains are covered by a PTB7-rich skin layer. The valleys around the lens-shaped PC71BM domains are PTB7-rich. The size of the PC71BM domains is determined by the type and concentration of additives [3].
References
[1] C.-H. Tu, M. Steinhart, R. Berger, M. Kappl, H.-J. Butt, G. Floudas, Sci. Adv. 9, eadg8865 (2023)
[2] B.-X. Shi, F. Weber, R. Berger, Felix H. Richter, J. Mater. Chem. A, 13, 2600-2614 (2025)
[3] C. Sprau, J. Kattenbusch, Y. Li, E. Müller, D. Gerthsen, R. Berger, J. J. Michels, A. Colsmann, Solar Rapid Research Letters 5, 2100238 (2021).