Colloidal stability

This chapter is dedicated to the principles that govern colloidal stability. We start by calculating the van der Waals interaction between atoms in vacuum and, then, see how to implement the equations to bigger particles of different shapes, sizes, and materials, introducing, as well, the effect of the solvent. Subsequently, we describe the electrostatic potential profile associated to the electrical double layer (EDL) for charged surfaces. This will allow us to understand the forces that arise when two charged particles approach in solution. The balance between the EDL and the van der Waals interactions provides a quantitative explanation to colloidal stability as described by the DLVO theory. The main principles of this theory are discussed passing from the interaction between two particles of identically charged densities to opposite charges, passing through the charged-neutral case. Eventually, depletion and steric forces in colloidal solutions are discussed.