Macroion adsorption: The crucial role of excluded volume and coions

TL;DR

This paper presents a theoretical study on macroion adsorption onto charged surfaces, highlighting the importance of finite macroion size and coion effects, which lead to unexpected surface charge amplification phenomena.

Contribution

It introduces a model that accounts for macroion excluded volume and coion influence, revealing new insights into adsorption mechanisms not captured by previous theories.

Findings

Coions can accumulate near the surface, affecting adsorption.

Finite macroion size leads to unusual adsorption behaviors.

Surface charge amplification occurs due to coion effects.

Abstract

The adsorption of charged colloids (macroions) onto an oppositely charged planar substrate is investigated theoretically. Taking properly into account the finite size of the macroions, unusual behaviors are reported. It is found that the role of the coions (the little salt-ions carrying the same sign of charge as that of the substrate) is crucial to understand the mechanisms involved in the process of macroion adsorption. In particular, the coions can accumulate near the substrate's surface and lead to a counter-intuitive {\it surface charge amplification}.