Prof. Dr. Jörg Weissmüller
Lady Davis Visiting Professor, Faculty of Materials Science and Engineering, Technion, Haifa, Israel, TUHH Institute of Materials Physics and Technology, Germany.
One of the current visions of material science is achieving enhanced or entirely novel material’s properties by exploiting the size- and interface-effects that are entailed by nanoscale structuring. Few materials provide as beautiful a test bed for such approaches as dealloying-made nanoporous metals. Dealloying provides engineered macroscopic bodies that are structured, at the nanoscale, as uniformly interconnected metal networks. Their formation relies on spontaneous nanoscale pattern formation during alloy corrosion, touching on intriguing issues in nonequilibrium thermodynamics. Equally fascinating is the quest for understanding the mechanical behavior: the network microstructure is closely similar to that of spinodally decomposed alloys, and strength as well as stiffness depend decisively on the topology of the interpenetrating phases pore and solid. At the atomic scale, the mechanical behavior is affected by surface excess elasticity and by the impact of capillary forces on the strength of small bodies. Its high structural definition and reproducibility makes nanoporous gold an ideal model system for exploring these effects and for unraveling the impact of capillarity for small-scale plasticity. In fact, recent experiments provide first experimental insights into issues such as the proposed (based on numerical studies) surface-induced tension−compression asymmetry of strength at the nanoscale. Experiment also has unraveled the relative contributions of surface stress and surface tension on strength. Such studies exploit another fascinating research opportunity: the state of the pore surfaces in nanoporous metal can be modulated under control of electric or chemical potentials. Such modulation not only serves to reveal surface effects on the mechanics, but it also provides a tool for obtaining novel functional behavior. As one highlight, hybrid materials made from nanoporous gold and water as the constituent phases display piezoelectricity, a phenomenon that is conventionally thought to be restricted to insulators such as ceramics.