Dr. Stefan Johann Gstöhl

Portrait Stefan Gstöhl

Post Doc

Paul Scherrer Institut
Forschungsstrasse 111
5232 Villigen PSI

My background is interdisciplinary, as I studied food science at ETH Zürich, where I graduated recently in the Laboratory of Food Process Engineering with a PhD. Foods are complex materials composed of multiple phases, such as foams, emulsions, suspensions, or mixtures thereof. Processing changes their microstructure depending on stress or strain, which can be used to optimize desired properties. Within the scope of my thesis, I studied the flow and extrusion of granular pastes. A working prototype to elucidate flow and structure under controlled rheological conditions was developed for the TOMCAT beamline.

My objective now is a comprehensive material testing platform. We strive for compatibilization of rheological and dynamic mechanical analysis with fast tomography. Such a platform would facilitate mechanical experiments at the beamline. It is potentially a door-opener to wide-ranging material testing protocols in the world of synchrotron x-ray tomography. Bringing such experiments under the hood of a unique platform will allow users to change from one testing protocol to another without the need for highly specialized and purpose-fitted testing setups.

Furthermore, my research on granular materials continues, especially at critically high packing fractions. Such materials rapidly change between fluid and solid state. Besides their industrial relevance and hazardous properties in natural catastrophes, granular materials fascinate me with their simple appearance - at first sight. Yet they astonish with a whole range of ever-changing mechanical properties originating from vastly unknown microscopic events. Thus, they remain a poorly understood topic in material science and physics. The introduction of water, for example, renders dry sand into a shape-retaining material, which is then suitable to construct sandcastles until it liquefies as suspended sand in the surf of the sea. Microstructure elucidation at the TOMCAT beamline under controlled stress or strain opens new pathways for studying steady-state, transient, and dynamic properties of materials.