Structure and Dynamics of Potassium Chloride in Aqueous Solution

Abstract

The structure and dynamics of potassium chloride in aqueous solution over a wide range of concentrations-and in particular beyond saturation-are studied using molecular dynamics simulations to help shed light on recent experimental studies of nonphotochemical laser-induced nucleation (NPLIN). In NPLIN experiments, the duration, t, of the laser pulse (with wavelength 1064 nm) is found to influence the occurrence of crystal nucleation in supersaturated KCl(aq): if t is less than about 5 ps, no crystal nucleation is observed; if t is greater than about 100 ps, crystal nucleation is observed, and with a known dependence on laser power. Assuming that the laser acts on spontaneously formed solute clusters, these observations suggest that there are transient structures in supersaturated solutions with relaxation times on the scale of 5-100 ps. Ion-cluster formation and ion-cluster lifetimes are calculated according to various criteria, and it is found that, in the supersaturated regime, there are indeed structures with relaxation times of up to 100 ps. In addition, the ion dynamics in this regime is found to show signs of collective behavior, as evidenced by stretched exponential decay of the self-intermediate scattering function. Although these results do not explain the phenomenon of NPLIN, they do provide insights into possible relevant dynamical factors in supersaturated aqueous solutions of potassium chloride.

Laser-induced nucleation of carbon dioxide bubbles

“…When exposed to a train of fs pulses at 1 kHz repetition rate, occasional bubbles were observed, which may indicate occurrence of rare photochemical events requiring multiple pulses. We have previously noted that fs pulses do not induce nucleation in NPLIN of KCl samples, 18 supporting the hypothesis that the mechanism of LIN of CO 2 and NPLIN of crystals has a common origin.…”

Surface Energies and Structure of Salt–Brine Interfaces

“…Lorentz− Berthelot mixing rules were used throughout and are consistent with previous simulations using the same force field. 41 All of the simulations were performed using the LAMMPS MD code developed at Sandia National Laboratories. 42 The Joung−Cheatham force field was found to be the most accurate for the chemical potential of NaCl in water, as well as the solubility limit (4.8 M from free-energy calculations, 5.1 M for coexistence simulations).…”

“…The potential parameters are included in Table . Lorentz–Berthelot mixing rules were used throughout and are consistent with previous simulations using the same force field . All of the simulations were performed using the LAMMPS MD code developed at Sandia National Laboratories …”

Temperature and Pressure Dependence of Salt–Brine Dihedral Angles in the Subsurface

“…The potential parameters are included in Table S1. Lorentz–Berthelot mixing rules were used throughout and are consistent with previous simulations using the same force field . All the simulations were performed using the LAMMPS MD code developed at Sandia National Laboratories …”

“…Lorentz−Berthelot mixing rules were used throughout and are consistent with previous simulations using the same force field. 34 All the simulations were performed using the LAMMPS MD code developed at Sandia National Laboratories. 35 A bulk NaCl system containing 5832 atoms was created with a sodium chloride crystal structure (a = b = c = 51.5 A ̊, α = β = γ = 90°).…”