The observation of formation and annihilation of solitons and standing strain wave superstructures in a two-dimensional colloidal crystal.

Confining a colloidal crystal within a long narrow channel produced by two parallel walls can be used to impose a mesoscale superstructure of a predominantly mechanical elastic character [Chui et al., EPL 83, 58004 (2008)]. When the crystal is compressed in the direction perpendicular to the walls, we obtain a structural transition when the number of rows of particles parallel to the walls decreases by one. All the particles of this vanishing row are distributed throughout the crystal. If the confining walls are structured (say with a corrugation along the length of the walls), then these extra particles are distributed neither uniformly nor randomly; rather, defect structures are created along the boundaries resembling "soliton staircases," inducing a nonuniform strain pattern within the crystal. Here, we study the conditions of stability, formation, and annihilation of these solitons using a coarse grained description of the dynamics. The processes are shown by comparing superimposed configurations as well as molecular animations obtained from our simulations. Also, the corresponding normal and shear stresses during the transformation are calculated. A study of these dynamical processes should be useful for controlling strain wave superstructures in the self-assembly of various nano- and mesoscaled particles.