CHARGED COLLOIDAL SYSTEMS

Using photon correlation spectroscopy we study the various modes of mo tion of a colloidal crystal and the properties of charged colloidal sy stems in general. We have designed a dynamic light scattering experime nt that is suited to study fast relaxation times. In order to obtain u nambiguous results it is always operated in the heterodyne scattering mode. We provide experimental evidence for a longitudinal mode that is due to the relaxation of Debye clouds that surround moving crystal pa rticles. Measuring the structure factor of our colloidal system leads to a value of Z = 360 +/- 20e for the effective charge on the spheres.