Modeling Zeta Potential for Nanoparticles in Solution: Water Flexibility Matters.

Area of Science:

• Physical Chemistry
• Computational Materials Science
• Surface Science

Background:

• Electrokinetic phenomena are crucial for understanding fluid behavior at charged interfaces.
• Accurate modeling of aqueous solutions near surfaces like titanium dioxide (TiO2) is essential for various applications.
• The influence of water model choice on electrokinetic properties remains an active area of research.

Purpose of the Study:

• To investigate the electrokinetic properties of NaCl solutions near a negatively charged TiO2 surface using different water models.
• To assess the impact of solvent flexibility and system geometry on electro-osmotic mobility and flow direction.
• To evaluate the accuracy of zeta potential determination based on molecular dynamics simulations.

Main Methods:

• Employed nonequilibrium molecular dynamics (NEMD) simulations.
• Studied five mainstream TIPxP water models (TIP3P-FB, TIP3Pm, TIP4P-FB, TIP4P-Ew, TIP4P/2005).
• Calculated electro-osmotic (EO) mobility and determined zeta potential (ZP) using the Helmholtz-Smoluchowski formula.

Main Results:

• Lack of water flexibility decelerates forward EO flow and can induce flow reversal at moderate to high NaCl concentrations.
• Different TIPxP water models exhibit varying degrees of impact on EO mobility and flow.
• Simulated ZP values show improved agreement with experimental data when flexible water models are used.

Conclusions:

• Solvent flexibility is a critical factor for accurately predicting electrokinetic phenomena near TiO2 surfaces.
• Flexible water models provide more reliable zeta potential determination compared to rigid models.
• Findings underscore the importance of selecting appropriate water models for simulating interfacial phenomena in aqueous electrolyte solutions.