Hans-Jürgen Butt (Mainz)
Hans-Jürgen Butt is an exceptional scientist. For more than three decades he publishes highly influential papers and shapes the forefront of colloid and interface science. He started his career in high energy physics, but quickly turned to biophysics and soft matter. As a young postdoc he made a significant step in the usage of atomic force microscopes by developing what is now known as the colloidal probe technique, published in 1991 . The development opened a huge field of research. With his thermal noise meth- od, published in 1995 , Hans-Jürgen Butt solved the important problem of cantilever calibration which was essential for establishing quantitative AFM force measurements. This calibration is nowadays implemented in almost all AFMs. In further developing the colloidal probe AFM, Hans-Jürgen Butt was also the first scientist to measure rolling friction of colloidal particles with this technique, published in 1999 . The unique force resolution of AFM-based methods opened the way to determine the fundamental input parameters for a quantitative understanding of powder flow and similar processes. The interest of Hans-Jürgen Butt continuously broadened. In 2002 he published a paper on the measurement of the hydrodynamic boundary condition on solid surfaces . Using again colloidal probe AFM he was able to measure the slip length of aqueous electrolyte solutions to be below 10 nm.
In recent years Hans-Jürgen Butt continued to work on wetting-related problems. Among the many influential papers, he published in these years, I want to highlight the work on the understanding of the motion on contact lines on superhydrophobic surfaces, published in 2013 . Around this time Hans-Jürgen Butt intensely committed himself to wetting-related phenomena. This commitment resulted in two ERC Advanced Grants for Hans-Jürgen Butt: 2014 “Supro”, dealing with understanding and utilizing superhydrophobic surfaces and 2020 “DynaMo – Dynamic charging at moving contact lines”, dealing with charge separation at moving contact lines.
Besides all these personal scientific achievement, Hans-Jürgen Butt was and continues to be an excellent mentor and his institute is a fertile ground for the next generation of European Colloid and Interface Scientists. He wrote several text books and also serves the scientific community in various positions. He was the president of the German Colloid Society (2007 – 2011), served as the Treasurer of the ECIS (2010 – 2016) and is the president of the IACIS (since 2018).
 H.-J. Butt, Biophys. J., 60, 1438 – 1444 (1991)
 H.-J. Butt, M. Jaschke, Nanotechnology, 6, 1 – 7 (1995)
 L. O. Heim, J. Blum, M. Preuss, H.-J. Butt, Phys. Rev. Lett., 83, 3328 – 3331 (1999)
 E. Bonaccurso, M. Kappl, H.-J. Butt, Phys. Rev. Lett., 88, 76103 (2002)
 P. Papadopoulos, L. Mammen, X. Deng, D. Vollmer, H. J. Butt, Proc. Natl. Acad. Sci. USA, 110, 3254 – 2358 (2013)