Study on the Correlation between the Microstructure and Physical Properties of ZnCl₂ Aqueous Solution

Area of Science:

• Physical Chemistry
• Solution Chemistry
• Materials Science

Background:

• Understanding the relationship between microstructure and macroscopic properties is crucial for solution chemistry.
• Aqueous zinc chloride solutions exhibit complex behaviors with varying concentrations.

Purpose of the Study:

• To investigate the correlation between the microstructure and physical properties of aqueous zinc chloride solutions.
• To elucidate the microscopic mechanisms behind the observed macroscopic property changes.

Main Methods:

• Macroscopic physical property measurements (conductivity, viscosity).
• Microstructure analysis using Raman spectroscopy.
• Computational modeling including molecular dynamics (MD) simulations and density functional theory (DFT).

Main Results:

• Conductivity increases then decreases with ZnCl2 concentration; viscosity consistently rises.
• Raman spectroscopy reveals changes in hydrogen bond types (DDAA to DA).
• MD simulations show formation of Zn2+-Cl- contact ion pairs and decreased ion diffusion.
• DFT calculations correlate Raman shifts with Zn2+ hydration cluster changes from [Zn(H2O)6]2+ to [ZnCl2(H2O)4].

Conclusions:

• The decrease in conductivity is attributed to the formation of Zn2+-Cl- contact ion pairs.
• Increased viscosity is linked to the interactions between ions (or ion pairs) and water molecules, forming hydrated species.