Topology of active and passive nematic defects

Miha Ravnik
University of Ljubljana

Microfluidics based on complex active and passive nematic fluids gives access to different mechanisms for controlling flow profiles, and especially gives access to various topological defect states and configurations. Here, we present our modelling study, in collaboration with partner experiments, that explores the coupling between geometry and orientational ordering in active and passive nematic microfluidics, especially on the role of topological and geometrical defects in both the flow and director profile. Specifically we use adapated hybrid Lattice Boltzmann modelling in both active and passive nematic flow regime. In more complex channels and geometries, we observe formation of different active and passive topological defects, as generated by the variable flow profiles and induced by the general confinement of space. The symmetry and topology of defects is shown to be controllable by the geometry of the confinement. For active microfluidics, we show that active defects act as local micro-pumps for the material flow. More generally, by designing the orientational profile of active or passive nematic we can control the profile and possibly topology of the material flow.

Selected related references:
[1] A. Sengupta, U. Tkalec, M. Ravnik, J.M. Yeomans, C. Bahr, S. Herminghaus, Phys. Rev. Lett. 110,
048303 (2013).
[2] M. Ravnik and J. M. Yeomans, Phys. Rev. Lett. 110, 026001 (2013).
[3] M. Nikkhou, M. Skarabot, S. Copar, M. Ravnik, S. Zumer and I. Musevic, Nature Phys. 11, 183 (2015).
[4] J. Aplinc, S. Morris and M. Ravnik, submitted to Phys. Rev. X

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