(591a) Transport Properties of Aqueous Solutions in Porous Silica

Nanoconfined water and aqueous solutions exhibit many geologically and technologically important properties which are still not completely understood, such as the mechanism of SiO₂ dissolution or the dynamic transitions of confined aqueous solutions at low temperatures [1].

We present a study of the strucural and transport properties of pure water and aqueous LiCl solutions confined in nanoporous silicates (MCM-41 and SBA-15). The complex dynamics of the system involves fast motions inside pores, slow diffusion of water in bulk silica, as well as surface dissociation of water and SiO₂ dissolution. We evaluate the dynamics of these processes with respect to the pore size, ion concentration, and temperature. Results obtained from simulation studies are compared with available quasi-elastic neutron scattering (QENS) experiments.

Since most of the studied processes are characterized by very long diffusion relaxation times or rare reactive events, typically in the order of nano- to microseconds, they pose a challenge for usual atomistic simulations. To overcome these complications, we use a combination of the reaction ensemble Monte Carlo technique (RxMC) [2] and long GPU accelerated molecular dynamics simulations. The force fields used include common non-reactive models (e.g. SPC/E) for speed, as well as reactive potential models (ReaxFF [3]) for the details of reactive steps.

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3) A. C. T. van Duin, S. Dasgupta, F. Lorant, and W. A. Goddard III, J. Phys. Chem. A 2001, 105, 9396-9409.