Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 99113

99113 - Examining the Hydration Behavior of Aqueous Calcium Chloride (Cacl2) Solution 

The structure of water molecules can be different due to the presence of solute, thereby the macroscopic properties of the solution, such as the specific heat, freezing temperature, and so on. For example, the aqueous calcium chloride solution at the concentration of 50.7 wt. (weight) % CaCl₂ has a freezing temperature of 29 ℃ and latent heat of ~170 kJ/kg, which is a popular inorganic PCM (phase change material) for many applications. These properties are important and associated with the hydration behavior of the solute caused by the interactions between ions-ions, and ions-water. However, few studies have a comprehensive investigation of aqueous calcium chloride solution from a dilute concentration (1% by weight) to a concentrated concentration above the solubility (44.7% by weight). In this work, equilibrium molecular dynamic simulations were performed to study the ion hydration of Ca²⁺ and Cl^- across a wide range of concentrations (from 1 wt.% to 60 wt.% CaCl₂) in the solution based on the GROMACS 2020. The simulation box of 6 × 6 × 6 nm³ has concentration-specific numbers of randomly distributed Ca²⁺, Cl^- ions, and water molecules, where the water molecules were modeled by the three-site simple point charge (SPC) water model, and the GROMOS53a6 force field was used for the Ca²⁺ and Cl^- ions. The system was first equilibrated at 298.15 K and 1 atmospheric pressure. Then, a series of canonical (NVT) simulations were performed also at 298.15 K for 10 nanoseconds with the timestep of 0.002 picoseconds and the leap-frog integrator. The radial distribution functions and first coordination numbers of calcium-water, chloride-water, and calcium-chloride were calculated and agreed with the previous simulation and experimental results at concentrations below the bulk solubility. The water molecules around the Ca²⁺ and Cl^- ions as well as the Cl^- ions in the vicinity of Ca²⁺ ions were visualized by RasMol. The hydration limit of aqueous calcium chloride solution was identified at the 10 wt.% CaCl₂ solution as the coordination numbers were no longer constant above it. In order to have a more comprehensive understanding of the aqueous CaCl₂ solution, the concentration was raised to 60 wt.% CaCl₂. When the concentration reached the bulk solubility of 44.7 wt.% CaCl₂, other than the previous results, a noticeable decrease in the chloride-water coordination number was observed, implying the formation of the ion-pairs started. The results also proved that the set of parameters of Ca²⁺ and Cl^- is good to predict the properties of aqueous calcium chloride solution in regard to the solubility.

Presenting Author: Lida Yan Lehigh University

Presenting Author Biography: Lida Yan is a Ph.D. student in the Department of Mechanical Engineering and Mechanics at Lehigh University supervised by Dr. Ganesh Balasubramanian and Dr. Carlos E. Romero. He received his Bachelor&#39;s Degree in Thermal Energy and Power Engineering from Tianjin University of Commerce, China. <br/>He was involved in several kinds of research including mercury emission control, thermal energy storage, molecular dynamic simulation, etc.

Authors:

Lida Yan Lehigh University
Ganesh Balasubramanian Lehigh University