We use confocal microscopy to study the three-dimensional (3D) structure of colloidal crystals formed by poly($N$-isopropylacrylamide)-co-(acrylic acid) microgels of diameter 1.0–1.5 $\mu$m. The confocal images are tracked to locate particle positions in 3D, which are used to compute pair-correlation functions $g$($r$), bond order parameters, and structure factors $s$($q$). We find that the structure remains fcc for a range of charge, size, and concentration of the particles. When the particles are weakly attractive and are at low concentrations, polycrystalline solids result. In addition, owing to the compressibility of the colloids, the crystals display remarkable structural stability when subjected to external stress.

• Received 8 November 2011

DOI:https://doi.org/10.1103/PhysRevE.85.021405