Dynamic Colloidal Stabilization by Nanoparticle Halos
  We explore the conditions under which colloids can be stabilized by the addition of smaller particles. The largest repulsive barriers between colloids occur when the added particles repel each other with soft interactions, leading to an accumulation near the colloid surfaces. At lower densities these layers of mobile particles (nanoparticle halos) result in stabilization, but when too many are added, the interactions become attractive again. We systematically study these effects --accumulation repulsion, re-entrant attraction, and bridging -- by accurate integral equation techniques. 
S. Karanikas and A.A. Louis