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Colloidal transport within nematic liquid crystals with arrays of obstacles

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Abstract

We have investigated the gravity-driven transport of spherical colloids suspended in the nematic liquid crystal 4-cyano-4′-pentylbiphenyl (5CB) within microfluidic arrays of cylindrical obstacles arranged in a square lattice. Homeotropic anchoring at the surfaces of the obstacles created periodic director-field patterns that strongly influenced the motion of the colloids, whose surfaces had planar anchoring. When the gravitational force was oriented parallel to a principal axis of the lattice, the particles moved along channels between columns of obstacles and displayed pronounced modulations in their velocity. Quantitative analysis indicates that this modulation resulted from a combination of a spatially varying effective drag viscosity and elastic interactions engendered by the periodic director field. The interactions differed qualitatively from a sum of pair-wise interactions between the colloids and isolated obstacles, reflecting the distinct nematic environment created by confinement within the array. As the angle α between the gravitational force and principal axis of the lattice was varied, the velocity did not follow the force but instead locked into a discrete set of directions commensurate with the lattice. The transitions between these directions occurred at values of α that were different from those observed when the spheres were in an isotropic liquid, indicating the ability of the liquid crystal forces to tune the lateral displacement behavior in such devices.

Graphical abstract: Colloidal transport within nematic liquid crystals with arrays of obstacles

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Publication details

The article was received on 21 Aug 2017, accepted on 24 Oct 2017 and first published on 24 Oct 2017


Article type: Paper
DOI: 10.1039/C7SM01681F
Citation: Soft Matter, 2017, Advance Article
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    Colloidal transport within nematic liquid crystals with arrays of obstacles

    K. Chen, O. J. Gebhardt, R. Devendra, G. Drazer, R. D. Kamien, D. H. Reich and R. L. Leheny, Soft Matter, 2017, Advance Article , DOI: 10.1039/C7SM01681F

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