Non-additivities of the particle sizes hidden in model pair potentials and their effects on physical adsorptions

TL;DR

This paper investigates how non-additivities in particle sizes affect colloidal particle adsorption on surfaces, revealing a reversal phenomenon explained by non-additivity of pair potentials, and introduces a new analysis method for these effects.

Contribution

It uncovers the role of non-additivities in particle sizes causing adsorption reversal and proposes a novel method to analyze non-additivity in pair potentials.

Findings

Small particles can be more easily adsorbed, contrary to traditional theories.

The reversal phenomenon is caused by non-additivities in particle sizes.

A new method to analyze non-additivity in pair potentials is developed.

Abstract

It is important to understand mechanism of colloidal particles assembly near a substrate for developments of batteries, heterogeneous catalysts, paints, and cosmetics. Knowledge of the mechanism is also important for crystallizations of the colloidal particles and proteins. In this study, we calculated the physical adsorption of colloidal particles on a flat wall by using the integral equation theory, wherein small and large colloidal particles were employed. In the calculation system, electric double layer potentials were used as the pair potentials. In some cases, it was found from the calculation results that the small particles are more easily adsorbed. The result is unusual from the viewpoint of the Asakura-Oosawa theory: we call it "reversal phenomenon". Then, we investigated mechanism of the reversal phenomenon. As a result, it was found that the inversion phenomenon originates from the non-additivities of the particle sizes. In addition, we invented the method to analyze the non-additivity in the pair potentials. The method will be useful for checks of various simulation results and developments of force fields for simulations of the colloidal particles and proteins.