Colloidal brazil nut effect in sediments of binary charged suspensions

TL;DR

This paper predicts a novel 'brazil nut' sedimentation effect in charged colloidal suspensions, where heavier particles can float above lighter ones due to charge and mass interactions, confirmed by simulations and theory.

Contribution

It introduces the colloidal 'brazil nut' effect in binary charged suspensions, combining computer simulations and density functional theory to predict this counterintuitive sedimentation behavior.

Findings

Heavy particles can sediment above lighter ones under certain charge conditions

The effect is predicted for deionized samples and is experimentally verifiable

Simulation and theoretical results agree on the sedimentation pattern

Abstract

Equilibrium sedimentation density profiles of charged binary colloidal suspensions are calculated by computer simulations and density functional theory. For deionized samples, we predict a colloidal ``brazil nut'' effect: heavy colloidal particles sediment on top of the lighter ones provided that their mass per charge is smaller than that of the lighter ones. This effect is verifiable in settling experiments.