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Dynamical and topological singularities cross-talk in flowing nematic liquid crystals | | Luca Giomi
; Žiga Kos
; Miha Ravnik
; Anupam Sengupta
; | | Date: |
1 Dec 2016 | | Abstract: | Dynamical singularities in fluids, also known as stagnation points, have been
extensively studied in flows of isotropic liquids, yet, how, and to what
extent, a stagnation point can influence the molecular ordering, or the
topology of a nematic liquid crystal (NLC) is largely unknown. Here we
investigate the emergence of topological singularities in the nematic director
field, or a disclination, arising due to a hydrodynamic stagnation in an NLC
flowing through star-shaped microfluidic junctions. The regular alternation of
inlets and outlets at the junction drives the formation of a stagnation point
of topological charge $1-n$, where $2n$ is the number of arms of the star
junction. Using a combination of microfluidic experiments, numerical modeling,
and analytical calculations we demonstrate that such a hydrodynamic singularity
can nucleate a disclination of equal topological charge. In the case of a
simple $4-$arm junction ($n=2$), this central $-1$ defect forms due to the
merging of a pair of traveling $-1/2$ disclinations in each of the inlet arms.
At microfluidic junctions with $6-$ and $8-$arm, topological defects of charge
$-2$ and $-3$ initially nucleate and eventually decay into multistable
arrangements of $-1$ defects. Finally, we demonstrate that manipulating the
hydrodynamic stagnation points allows us to dynamically control the spatial
arrangement of the nematic disclinations. We attribute this to a coupling
interplay between the hydrodynamic stagnation point and the emergent
topological defect, and explore the microfluidic setting to quantify the
strength of the coupling between dynamical and topological defects. | | Source: | arXiv, 1612.0095 | | Services: | Forum | Review | PDF | Favorites | |
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