Water Organization and Dynamics on K-Feldspar (WODYF)

Feldspar minerals are abundant in most igneous rocks and constitute about 50 vol.-% of Earths crust. Hence, it is not surprising that feldspar minerals play a central role in many geological processes. For instance, weathering of feldspars and other silicate minerals is an important step in the so-called geological carbonate-silicate cycle, which controls atmospheric carbon dioxide levels on the timescale of tens of thousands to millions of years. Moreover, feldspar mineral dust particles can get into the atmosphere, where they facilitate the formation of ice in clouds. Contrary to everyday experience, clean water droplets in clouds can stay liquid down to temperatures as low as -40 C. If these supercooled water droplets, then, encounter feldspar mineral particles, the contacting feldspar surface can act as an ice nucleus causing the water droplets to freeze. Since liquid water has very different chemical and physical properties from ice, this process is crucial for precise modelling of clouds and, thus, for our understanding of weather and climate. However, despite of extensive previous research, it remains unclear why feldspar particles are efficient ice nuclei. Especially, our understanding of the molecular structure and processes at the interfaces of feldspar minerals with water and ice are still lacking. With this project, we aim to uncover the structure and dynamics of water molecules at the feldspar-water and feldspar-ice interface. Moreover, since feldspar particles in the atmosphere are commonly in contact with not only pure water but aqueous solutions, we aim to understand the impact of environmental conditions such as pH and salt concentration on the interfacial structure. To this end, Tobias Dickbreder (University of Vienna) will employ interface-sensitive vibrational spectroscopy to investigate how the organization and bonding relationships of water molecules at the feldspar-water interface change depending on the conditions and upon freezing. The interpretation of experimental data will be conducted in close collaboration with the groups of theoreticians Bernhard Reischl (University of Helsinki), Christoph Dellago (University of Vienna) and Marialore Sulpizi (Ruhr Universität Bochum). By the combination of experiment and theory, we aim to establish a detailed molecular understanding of the feldspar-water interface.