Free-expansion melting of two dimensional colloidal crystals

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Abstract
Two-dimensional (2D) melting transitions have been observed in two freely expanding colloidal monolayer crystals formed from 1.01 μm polystyrene microspheres in an aqueous suspension between parallel optical flats, and with expansion rates differing by a factor of six. The data consist of digitized images of the 2D microsphere populations within a fixed sample area made from video records of the entire transition from ordered solid to liquid. The correlation functions computed from these data are consistent with a continuous two-step melting transition. However, direct observations of the time development of defect creation and evolution reveal that the systems may melt via a first order process. Although the melting rates differed appreciably, the results of the two melts are essentially the same.