Spontaneous symmetry breaking of charge-regulated surfaces

TL;DR

This paper reveals that charge-regulated surfaces can spontaneously develop different charge densities, even opposite signs, leading to attractive forces between identical surfaces, challenging traditional assumptions.

Contribution

It demonstrates the spontaneous symmetry breaking of charge densities on identical surfaces using density functional theory, highlighting new electrostatic interaction mechanisms.

Findings

Surfaces can have different charge densities, including opposite signs.

Attractive forces can occur between identical surfaces due to charge asymmetry.

Symmetry breaking occurs as surfaces approach each other.

Abstract

The interaction between two chemically identical charge-regulated surfaces is studied using the classical density functional theory. In contrast to common expectations and assumptions, under certain realistic conditions we find a spontaneous emergence of disparate charge densities on the two surfaces. The surface charge densities can differ not only in their magnitude, but quite unexpectedly, even in their sign, implying that the electrostatic interaction between the two chemically identical surfaces can be attractive instead of repulsive. Moreover, an initial symmetry with equal charge densities on both surfaces can also be broken spontaneously upon decreasing the separation between the two surfaces. The origin of this phenomenon is a competition between the adsorption of ions from the solution to the surface and the interaction between the adsorbed ions already on the surface.These findings are fundamental for the understanding of the forces between colloidal objects and, in particular, they are bound to strongly influence the present picture of protein interaction.