Volume dependent forces in charge stabilized colloidal crystals

The existence of an equilibrium lattice with a small shear modulus G in charge stabilized colloidal suspensions is examined through a classical analogy with metallic systems. The inclusion of a non-configurational volume dependent term in the total energy associated with the presence of a plasma of small screening ions, is seen to contribute to G and the elastic constants. This is in addition to the familiar configurational contribution which arises from pairwise interactions between the macroions. It also suggests a simple physical interpretation of the sharp G→0 transition accompanied by a loss of crystalline order that is observed on the addition of electrolyte.