Estimation of Nanoparticle's Surface Electrostatic Potential in Solution Using Acid-Base Molecular Probes II: Insight...

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Computational Chemistry

Background:

• Acid-base indicators are widely used to determine surface electrostatic potential (Ψ) in colloidal systems like micellar solutions.
• The method relies on measuring the indicator's apparent acidity constant in the system and a reference solution.
• A key challenge is the significant dissimilarity in Ψ values obtained using different indicators for the same system.

Purpose of the Study:

• To investigate the factors causing dissimilarity in surface electrostatic potential (Ψ) measurements using acid-base indicators.
• To quantitatively assess the impact of probe hydration, localization, and surfactant choice on Ψ values.
• To identify the most accurate indicators for determining Ψ in colloidal systems.

Main Methods:

• Utilized in silico molecular dynamics (MD) simulations to predict Ψ values.
• Examined the influence of five different probes and two nonionic surfactants.
• Analyzed probe hydration in the Stern layer and probe localization within micelles.

Main Results:

• Probe hydration in the Stern layer accounts for approximately half of the observed dissimilarity in Ψ values.
• Probe localization is important but difficult to quantify due to the irregular Stern layer structure.
• Identified the most accurate indicators among the tested probes for Ψ determination.

Conclusions:

• Molecular dynamics simulations can quantitatively assess factors affecting indicator-based Ψ measurements.
• Probe hydration is a critical factor influencing the accuracy of surface electrostatic potential determination.
• Combining experimental Ψ measurements with MD simulations can optimize probe and surfactant selection for nanoparticle characterization.