18 October 2004 Statics and dynamics of colloidal particles in periodic traps
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We show with computer simulations that a rich variety of static and dynamical colloidal phases can be realized for colloids interacting with two-dimensional periodic substrates. For the static case a new type of colloidal state that we term colloidal molecular crystals occurs when there is an integer number of colloids per substrate minima. Here there is a novel orientational ordering in addition to the positional ordering of the colloids. The colloidal molecular crystals exhibit a multi-step melting in which the orientational ordering is lost first, followed by the positional ordering. This multi-step melting phenomenon agrees well with recent experiments. Additionally we show that at fillings where the number of colloids is an incommensurate fraction of the number of substrate minima, as a function of temperature there is a transition to a state in which local incommensurations become thermally activated. With an applied drive we find that a remarkable number of distinct dynamical phases can be realized, including ordered and disordered flows. We also illustrate flow phases in which the colloidal motion locks to a symmetry direction of the underlying lattice.
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Charles M. Reichhardt, Charles M. Reichhardt, Cynthia J. Olson Reichhardt, Cynthia J. Olson Reichhardt, "Statics and dynamics of colloidal particles in periodic traps", Proc. SPIE 5514, Optical Trapping and Optical Micromanipulation, (18 October 2004); doi: 10.1117/12.558964; https://doi.org/10.1117/12.558964

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