A colloidal suspension is an excellent model system for studying the structure and dynamics of classical condensed matter systems. We have used video microscopy and digital imaging to study the instantaneous particle positions and trajectories of uniform, highly charged submicron diameter polystyrene spheres in water. Brownian motion of the spheres creates a true thermodynamic temperature with a real thermal bath. The length and time scales of this system are perfect for video microscopy with an ordinary visible light microscope. We can easily follow the collective dynamics of the system as well as individual particle motions and the motions and rearrangements of topological defects.
Colloidal spheres arrange themselves into spectacular ordered structures.
We have studied the ordering transitions in two dimensions, in three dimensions and in thin layers, with and without modulated substrates. In a bidisperse system, where frustration is introduced by the random nature of the bond lengths, we observe a classical fluid-glass transition. Colloidal suspensions also have potential application as self-assembling new optical. Three-dimensionally microperiodic structures with lattice constantscomparable to the wavelength of light have potentially very interestingoptical properties. In particular, if the index of refraction contrast issufficiently large so-called photonic bandgaps appear.