Elastic properties of colloidal crystals and glasses

We have measured the shear modulus of lattices of charged polystyrene spheres. We describe a simple apparatus used in this study for determining the frequency of standing shear modes. For the monodisperse lattices, crystals form, stabilized by the repulsive Coulomb interaction, producing a classical ’’Wigner crystal’’ characterized by Bragg scattering and finite rigidity. We studied the rigidity as a function of volume fraction and electrolyte concentration for several particle diameters. Mixtures of colloids with different particle diameters form classical ’’Wigner glasses’’ characterized by the absence of long range order and Bragg scattering but the presence of a finite shear rigidity. We have studied the shear properties of these solids as a function of composition and electrolyte concentration.