| Summary: | The colloidal state has long been of interest to physicists, both in its own right and as a model for atomic systems. In particular, colloidal suspensions with low size-polydispersity have been widely used as model hard spheres. Optical microscopy can resolve detail at the larger end of the colloidal length scale, and to image suspensions at an individual particle level of resolution would allow the investigation of local behaviour in a way denied to the established techniques of light-scattering. To achieve high-contrast, single-particle resolution in dense suspensions that are thick enough to show behaviour the same as would be expected in the bulk, is not a trivial exercise, however. This work builds on established advanced techniques of the light microscopy of phase objects, to develop an effective method of achieving this aim, addressing issues of imaging technique, suspension mounting and the interpretation of image data. The usefulness of this newly developed experimental protocol is demonstrated by, amongst other results, a detailed study of the structure of the colloidal crystals found in hard-sphere suspensions and an investigation of the nucleation of such crystals from the metastable colloidal fluid.
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