Local dynamics in LiCl-CsCl-D₂O water-in-salt solutions according to NMR relaxation

The main purpose of this study was to investigate the local structure and dynamics in 'water-in-salt' solutions, namely the ternary concentrated LiCl-CsCl-D₂O electrolytes. Water based electrolyte solutions are components of natural waters, they are very widespread and possess many practical abilities. NMR was applied as the main technique to study the local structure of the solutions as well as ion and solvent dynamics. The characteristic reorientation times (τ_c) were calculated from spin-lattice relaxation times for²H,⁷Li, and¹³³Cs nuclei. The diffusion coefficients (D) for¹H,⁷Li, and¹³³Cs nuclei were also obtained. We have confirmed that most of the molecules and ions are combined into dynamic clusters, 'cybotactic groups', with lifetimes long enough for them to diffuse as a whole unit. Thus, the results provide direct experimental confirmation of the existence of 'cybotactic groups' predicted earlier for concentrated electrolyte solutions. The precise self-diffusion coefficients show the state of ions in the system and can be used as a reference for modelling of such systems.