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Elementary Edge and Screw Dislocations Visualized at the Lattice Periodicity Level in the Smectic Phase of Colloidal Rods

Topological defects such as dislocations play a major role in science, from condensed matter and geophysics to cosmology. These line defects present in periodically ordered structures mediate phase transitions and determine many distinctive features of materials, from crystal growth to mechanical properties. However, despite theoretical predictions, the detailed structure of dislocations remains largely elusive. By using a model system of tip-labeled rod-shaped particles enabling improved resolution and contrast by optical microscopy, in situ visualization and quantitative characterization of elementary dislocations has been performed at the lattice periodicity level in a colloidal smectic phase. Thanks to the micrometer layer spacing, the displacement field around an edge dislocation has been experimentally established and compared with the profile predicted by elastic theory. The local morphology of screw dislocations has also been evidenced, with the determination of the core size as well as the chiral handedness of the defect. Self-diffusion experiments performed at the individual particle level reveal for the first time nematiclike or “melted” ordering of the defect core.

Figure :Schematic representations of an edge and a screw dislocation in a lamellar system. The Burgers vector b is perpendicular to the dislocation line along y for an edge dislocation and it is parallel to the dislocation line along z in a screw dislocation.

PHYSICAL REVIEW LETTERS 121, 097801 (2018) 0031- Article published in Physical Review Letters :


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CRPP UMR 5031, Université de Bordeaux :

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Eric Grelet