  Electrostatic repulsions can drive crystallization in many-particle systems.
For charged colloidal systems, the phase boundaries as well as crystal
structure are highly tunable by experimental parameters such as salt
concentration and pH. By using projections of the colloid-ion mixture to a
system of (soft) repulsive spheres and the one-component plasma (OCP), we study
the hitherto unexplained experimentally observed reentrant melting of
electrostatically repelling colloids upon increasing the colloid density. Our
study shows that the surface chemistry should involve a competition between
adsorption of cations and anions to explain the observed density-induced
reentrant melting.
