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Geometry of defects in nematic opals

Simon Čopar, Miha Ravnik, and Slobodan Žumer, in collaboration with Noel Clark from University of Colorado, investigate defect networks that occur in a synthetic opal, permeated by a nematic liquid crystal. Their work, inspired by experimental results by the research group from Colorado, blends numerical modeling with topological methods to create a geometrical model for microscopic states of the nematic opal. Their findings, presented in the article Elementary building blocks of nematic disclination networks in densely packed 3D colloidal lattices (PDF), were featured on the Back Cover of the Soft Matter journal (image created by Simon Čopar), and appeared in the "Hot Paper" selection at RSC blog. The same issue of the Soft Matter journal also feature a Front Cover by Simon Čopar, associated with a review article by Uroš Tkalec and Igor Muševič from the "Jožef Stefan" Institute.

The disclination lines that thread the space between the silica spheres in the opal, follow a geometric pattern, composed from tetrahedral and cubic unit cells. The system, that appears disordered on the macroscopic scale, is in fact combinatorially composed from a small number of local states, which suggests the system is capable of storing information.

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