Observation of a smecticlike crystalline structure in polydisperse colloids

We present the results of crystallographic measurements on samples of two latexes: one with a relatively symmetric particle size distribution, and another with a highly skewed pseudobimodal distribution. For the skewed latex, crystallites are clearly visible, but they exhibit only a single Bragg reflection, indicating long-range order in only one direction. We propose a schematic model that explains this result in terms of stacks of planes, which are unregistered due to a high incidence of stacking faults caused by the incorporation of a large number of small particles.