FREEZE-FRACTURE ELECTRON-MICROSCOPY OF POLYSTYRENE COLLOIDAL CRYSTALS

Colloidal crystals are suspensions of charged colloidal particles that spatially order in low ionic-strength solvents such as deionized water. The ordered arrays, stabilized by long-range electrostatic interparticle repulsions, display many cooperative phenomena inherent to atomic crystals, yet are uniquely amenable to both experimental manipulation and theoretical analysis. To date, the structures of colloidal crystals have been determined mainly by optical and X-ray diffraction methods, which reveal long-range order but not localized detail. Here a method is demonstrated for the visualization of colloidal-crystal structures in real space, employing freeze-fracture electron microscopy. It is shown that both long-range crystal structure and localized structures within the crystal can be identified in this manner. Information on crystal dynamics is available from analysis of the deviations of particles about their equilibrium lattice positions. The root-mean-square deviation is shown to be consistent with the Lindemann criterion for solid-liquid transitions. © 1993 Academic Press, Inc.