Mass effects for thermodiffusion in dilute aqueous solutions

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Thermodiffusion describes concentration gradients in mixtures due to temperature gradients.
• The Soret coefficient quantifies this effect, but its molecular-level understanding is limited.
• Previous studies suggest molecular mass differences significantly impact the Soret coefficient.

Purpose of the Study:

• To investigate the mass dependence of the Soret coefficient in dilute aqueous solutions using molecular dynamics simulations.
• To explore how relative and absolute molecular masses affect thermodiffusion.
• To determine if mass effects can alter the thermophilic/thermophobic nature of solutions.

Main Methods:

• Molecular dynamics simulations were employed in a thermophoretic setting.
• Dilute aqueous solutions with varying solute and solvent masses were simulated.
• The Soret coefficient was calculated to analyze mass-dependent behavior.

Main Results:

• The mass dependence of the Soret coefficient aligns with prior experimental and simulation findings.
• The Soret coefficient is sensitive to the relative mass difference between solute and solvent, not their absolute masses.
• Adjusting solute and solvent masses can reverse the direction of solute accumulation, switching between thermophobic and thermophilic states.

Conclusions:

• Molecular mass is a critical factor in thermodiffusion, with relative mass differences being key.
• The mass effect can override other contributions, allowing control over solution behavior.
• Moments of inertia have a minor influence compared to total molecular mass on the Soret coefficient.