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Title: Frank-Read Mechanism in Nematic Liquid Crystals
In a crystalline solid under mechanical stress, a Frank-Read source is a pinned dislocation segment that repeatedly bows and detaches, generating concentric dislocation loops. We demonstrate that, in nematic liquid crystals, an analogous Frank-Read mechanism can generate concentric disclination loops. Using experiment, simulation, and theory, we study a disclination segment pinned between surface defects on one substrate in a nematic cell. Under applied twist of the nematic director, the pinned segment bows and emits a new disclination loop which expands, leaving the original segment intact; loop emission repeats for each additional 180° of applied twist. We present experimental micrographs showing loop expansion and snap-off, numerical simulations of loop emission under both quasistatic and dynamic loading, and theoretical analysis considering both free energy minimization and the balance of competing forces. We find that the critical stress for disclination loop emission scales as the inverse of segment length and changes as a function of strain rate and temperature, in close analogy to the Frank-Read source mechanism in crystals. Lastly, we discuss how Frank-Read sources could be used to modify microstructural evolution in both passive and active nematics.  more » « less
Award ID(s):
1663041
PAR ID:
10509753
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
American Physical Society
Date Published:
Journal Name:
Physical Review X
Volume:
14
Issue:
1
ISSN:
2160-3308
Subject(s) / Keyword(s):
Disclinations and dislocations Polymers and soft matter Line defects Topological defects Nematic liquid crystals Coarse graining Polarized optical microscopy
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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