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When you plug in your toaster, you expect metallic contacts to form and carry electricity. You can safely ignore the many microscopic contacts that form and break when you unplug it. We cannot ignore them when designing stretchable conductors, sensors, or batteries containing conductive particles in insulating matrices. I will show how we used FIB-SEM tomography to reconstruct the networks formed by conductive filler particles in conductive polymer composites (CPCs). The results show that the macroscopic conductivity of these materials is strongly influenced by local contact resistances. These contacts can be tuned: we made CPCs with carbon platelets as conductive components for soft-robotics applications and found that aligning them considerably changes the local contact geometry, bulk conductivity, and piezoresistive response—the change in electrical resistance under strain. In other cases, metallic contacts are needed but should remain breakable. I will show how we created small sintering necks between silver particles to produce redispersible conductors and facilitate recycling. When metal particles approach molecular dimensions, even “contact” becomes difficult to define. I will show how organic shells keep gold nanoparticles and nanowires a few nanometres apart. Using small-angle X-ray scattering, we quantify this spacing and show how it depends on the local molecular arrangement. Making contact is easy at this scale: remove the organics, and the particles fuse. But how can that contact be broken again? I will end with the curious case of ultrathin metal nanowires and their Rayleigh-Plateau instability. Conductive polymer composites contain electrically connected metal particles. We reconstruct them in 3D using FIB-SEM tomography and analyze them as networks. Their contacts dominate the macroscopic conductivity - and can be tuned. Short CV: Tobias Kraus is a physicochemist, chemical engineer, and materials scientist trained at TU Munich, MIT, and the University of Neuchâtel. He obtained his PhD at ETH Zurich and the IBM Research Laboratory. Today, Tobias works with his team at the INM – Leibniz-Institute for New Materials in Saarbrücken, Germany, and holds the chair for colloid and interface chemistry at Saarland University. In his research, Tobias studies and curtails the interactions between particles, polymers, and small molecules. This leads to predictable, hierarchical assemblies for structured interfaces and functional materials. His group investigates hybrid materials for flexible and transparent electronics, reversible interfaces for soft and recyclable electronic devices, optical sensors, and their formation during 2D and 3D printing.

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