Hunting Mermaids in Real Space: Known Knowns, Known Unknowns and Unknown Unknowns

TL;DR

This paper reviews the realization of mermaid interactions in 3D real space, highlighting the challenges and complexities arising from weak ion dissociation and non-centrosymmetric effects in colloidal systems.

Contribution

It provides a comprehensive review of experimental and simulation efforts to realize mermaid interactions, revealing new complexities due to ion dissociation effects.

Findings

Summation of attractive and repulsive components often deviates from experiments.

Weak ion dissociation causes non-centrosymmetric interactions.

Complex behaviors emerge in low dielectric constant solvents.

Abstract

We review efforts to realise so-called mermaid (or short-ranged attraction/long ranged repulsion) interactions in 3d real space. The repulsive and attractive contributions to these interactions in charged colloids and colloid-polymer mixtures, may be accurately realised, by comparing particle-resolved studies with colloids to computer simulation. However, when we review work where these interactions have been combined, despite early indications of behaviour consistent with predictions, closer analysis reveals that in the non-aqueous systems used for particle-resolved studies, the idea of summing the attractive and repulsive components leads to wild deviations with experiment. We suggest that the origin lies in the weak ion dissociation in these systems with low dielectric constant solvents. Ultimately this leads even to non-centro-symmetric interactions and a new level of complexity in these systems.