The primary goal of this research project is the identification of the smallest structural unit providing the electro-chemo-mechanical coupling in nanoporous materials and polymer-coated nanoporous hybrids.
The experimental approach starts with nanoporous gold (as synthesised by project B2) out of which we cut micrometre-sized columns via focused ion beam milling (FIB). These samples are brought into an electrochemical environment which allows us to control the electric potential and, therefore, the charge at the metal surfaces and/or that inside the polymer coating on these surfaces. The charging of the surface and/or the coating results in changes of dimension and mechanical properties of the whole nanoporous structure. Both will be measured in-situ, i.e. while the sample is still placed in an electrochemical cell, with the help of a specifically modified nanoindentation device.
The main scientific question is to find out how the strongly anisotropic functional behaviour of a single ligament transfers into the isotropic behaviour of the whole nanoporous network.
The ratio between the sample size (regulated by FIB cutting) and the structure size (controlled by fabrication) determines whether the sample behaves more like an averaged isotropic structure or a single anisotropic ligament. Consequently, we plan experiments with consecutive reduction of the sample size (at constant structure size) which could go down to even single massive gold nanometre-sized columns representing single ligaments in order to find the size of the functional structure unit and identify the underlying processes.
|Dr. rer. nat. Jürgen Markmann,
1. C.A. Volkert & E.T. Lilleodden: Size effects in the deformation of submicron Au columns. Philos. Mag 86, 5567-5579, 2006
2. B.-N.D. Ngô et al.: On the origin of the anomalous compliance of dealloying-derived nanoporous gold. Scripta Materialia 130, 74-77, 2017 - with B2
3. N. Mameka et al.: Nanoporous gold - Testing Macroscale samples to probe small-scale mechanical behavior. Mater. Res. Lett. 4, 27-36, 2015 - with B2 and B4
... and more on the list of publications.