  Physical properties of colloidal materials can be modified by addition of
nanoparticles. Within a model of like-charged mixtures of particles governed by
effective electrostatic interactions, we explore the influence of charged
nanoparticles on the structure and thermodynamic phase stability of
charge-stabilized colloidal suspensions. Focusing on salt-free mixtures of
particles of high size and charge asymmetry, interacting via repulsive Yukawa
effective pair potentials, we perform molecular dynamics simulations and
compute radial distribution functions and static structure factors. Analysis of
these structural properties indicates that increasing the charge and
concentration of nanoparticles progressively weakens correlations between
charged colloids. We show that addition of charged nanoparticles to a
suspension of like-charged colloids can induce a colloidal crystal to melt and
can facilitate aggregation of a fluid suspension due to attractive van der
Waals interactions. We attribute the destabilizing influence of charged
nanoparticles to enhanced screening of electrostatic interactions, which
weakens repulsion between charged colloids. This interpretation is consistent
with recent predictions of an effective interaction theory of charged
colloid-nanoparticle mixtures.
