Article (Scientific journals)
Surface anchoring mediates bifurcation in nematic microflows within cylindrical capillaries
Paul, Steffen; Eric, Stellamanns; Sengupta, Anupam
2021In Physics of Fluids, 33 (072005), p. 072005-1-072005-13
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Keywords :
Liquid Crystal Flows; Complex Fluids; Microfluidics; Simulations; Topological Defects
Abstract :
[en] Capillary microflows of liquid crystal phases are central to material, biological and bio-inspired systems. Despite their fundamental and applied significance, a detailed understanding of the stationary behavior of nematic liquid crystals (NLC-s) in cylindrical capillaries is still lacking. Here, using numerical simulations based on the continuum theory of Leslie, Ericksen, and Parodi, we investigate stationary NLC flows within cylindrical capillaries possessing homeotropic (normal) and uniform planar anchoring conditions. By considering the material parameters of the flow-aligning NLC, 5CB, we report that instead of the expected, unique director field monotonically approaching the alignment angle over corresponding Ericksen numbers (dimensionless number capturing viscous vs elastic effects), a second solution emerges at a threshold flow rate (or applied pressure gradient). We demonstrate that the onset of the second solution, a nematodynamic bifurcation yielding distinct director configurations at the threshold pressure gradient, can be controlled by the surface anchoring and the flow driving mechanism (pressure-driven or volume-driven). For homeotropic surface anchoring, this alternate director field orients against the alignment angle in the vicinity of the capillary center; while in the uniform planar case, the alternate director field extends throughout the capillary volume, leading to reduction of the flow speed with increasing pressure gradients. While the practical realization and utilization of such nematodynamic bifurcations still await systematic exploration, signatures of the emergent rheology have been reported by the authors previously within microfluidic environments, under both homeotropic and planar anchoring conditions.
Research center :
University of Luxembourg, Department of Physics and Materials Science
Disciplines :
Physics
Author, co-author :
Paul, Steffen
Eric, Stellamanns
Sengupta, Anupam  ;  University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
External co-authors :
yes
Language :
English
Title :
Surface anchoring mediates bifurcation in nematic microflows within cylindrical capillaries
Publication date :
July 2021
Journal title :
Physics of Fluids
ISSN :
1089-7666
Publisher :
American Institute of Physics, Woodbury, United States - New York
Volume :
33
Issue :
072005
Pages :
072005-1-072005-13
Peer reviewed :
Peer Reviewed verified by ORBi
Focus Area :
Physics and Materials Science
FnR Project :
FNR11572821 - Biophysics Of Microbial Adaptation To Fluctuations In The Environment, 2017 (15/05/2018-14/05/2023) - Anupam Sengupta
Name of the research project :
ATTRACT Investigator Grant (No. A17/MS/11572821/MBRACE), FNR-CORE Grant (No. C19/MS/13719464/TOPOFLUME/Sengupta)
Funders :
FNR - Fonds National de la Recherche [LU]
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since 22 January 2022

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