Nan Gao, Florian Geyer, Dominik W. Pilat, Sanghyuk Wooh, Doris Vollmer, Hans-Jürgen Butt, Rüdiger Berger,
Nature Physics 14, 191 - 196 (2018)

How drops start sliding over solid surfaces

It has been known for more than 200 years that the maximum static friction force between two solid surfaces is usually greater than the kinetic friction force. In contrast to solid-solid friction, there is a lack of understanding of liquid-solid friction, i.e. the forces that impede the lateral motion of a drop of liquid on a solid surface. Here, we report that the lateral adhesion force between a liquid drop and a solid can be divided into a static and a kinetic regime. This striking analogy with solid-solid friction is a generic phenomenon that holds for liquids of different polarities and surface tensions on smooth, rough and structured surfaces.

Jongkuk Ko, Jiyun Song, Hyunsik Yoon, Taeyong Kim, Changhee Lee, Rüdiger Berger and Kookheon Char,
Advanced Materials Interfaces 2016

Controlled Mutual Diffusion between Fullerene and Conjugated Polymer Nanopillars

We describe a new approach to control the nanomorphology of organic solar cells. In particular, the nanomorphology was studied in nanostructural and electrical properties of the pillar samples using scanning probe microscopy. Conductive scanning force microscopy in quantitative imaging mode, applied to the pillar-based samples for the first time, allows us to establish a clear relationship between nanomorphology, nanoelectrical property, and macroscale device performance. Higher local currents are displayed with a yellow color in the above image.