Internal Research Project I-05

Fast Field Cycling Relaxometry: A valid tool to study molecular dynamics in salt precipitates


In porous media, salt precipitation causes many changes in water flow processes, which are responsible for numerous problems such as salinization in agriculture or damaging of building materials. How this changes the behavior of porous media is mainly determined by processes at interfaces that occur on a very small spatial scale. More precisely, the properties of the salt-solution or sand/salt-solution interface at the molecular level control the water dynamics and ultimately the water transport.
Research project C01 deals with simulation of changes of pore structures and adjustable wetting behavior on the small scale. Recently, a further step has been taken in the field of atomistic simulations, where the motion of water molecules is calculated based on Newton´s equations of motions and atoms are treated as classical particles. The validity of these models is greatly improved by correlation of the results with experimental observations.
This internal project aims on the determination of molecular dynamics at the salt-fluid inter-face in porous media. We will make use of Fast- field cycling relaxometry (FFC) as a non-invasive NMR method and moreover the only technique which permits the measurements of longitudinal relaxation time T1 over a wide range of Lamor frequencies. This makes so-called NMR dispersion curves accessible, from whose evaluation surface correlation times and surface residence times are obtained by adapting suitable models. For instance, the biphasic exchange model published by Korb et al. or the related Brownian random walk model of Levitz are suitable candidates. In detail, we will determine the molecular dynamics in pure salt solutions, pure salt-solu-tion interfaces and porous sand-salt/solution media at the example of sodium chloride and sodium sulfate.

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