Capillary Imbibition of Gadolinium Halides into WS2 Nanotubes: a Molecular Dynamics View
The structure of the molten salts GdX3, where X denotes Cl, Br, or I, and the kinetics of their penetration into WS2 nanotubes were investigated using molecular dynamics simulations. The GdCl3 and GdBr3 melts are found to comprise an amorphous framework structure with substantial intermediate-range ordering, as manifested by pair distribution, and angle-resolved pair-pair distribution functions associated with cationic correlations. In contrast, the GdI3 melt is a liquid with short-range cationic ordering. These structural peculiarities cause dramatically different mobility of Gd cations among pure GdX3 melts and explain the relative difference in the capillary activity of WS2 nanotubes regarding the melts, as observed in preliminary experiments. Extended MD simulations of GdCl3 dissolved in molten KCl predict the total degradation of the GdCl3 framework structure below 40 mol %, although no essential uptake of Gd cations by the WS2 nanotube is observed, due to more progressive diffusion of K cations. Our theory suggests that, among the considered halides, only the GdI3 compound is suitable for Gd encapsulation into WS2 nanotubes employing the capillary technique.