assist. dr. Žiga Kos



Research

Active matter

Active matter consist of self-propelled active agents that consume energy from its environment. My research on active matter is linked to anisotropic active systems, such as bacterial collonies, tissues, and microtubule-kinesin mixtures. Using a mesoscopic approach and hybrid lattice Boltzmann numerical modelling, we show the non-equilibrium dynamics of 3D active nematics and focus specifically on the dynamics of topological defects that form spontaneously under sufficient activity or under geometrical constraints.

Selected publications:

  • J. Binysh, Z. Kos, S. Copar, M. Ravnik, and G. P. Alexander, Three-Dimensional Active Defect Loops, Phys. Rev. Lett. 124, 088001 (2020) [abstract] [PDF].

  • S. Čopar, J. Aplinc, Ž. Kos, S. Žumer and M. Ravnik Topology of three-dimensional active nematic turbulence confined to droplets, Phys. Rev. X, 9, 031051 (2019). [Link] [PDF].

  • P. Guillamat, Ž Kos, J. Hardoüin, J. I. Ignés-Mullol, M. Ravnik and F. Sagués Active nematic emulsions, Sci. Adv. 4, eaao1470 (2018). [Link] [PDF].

  • Ž. Kos and M. Ravnik Elementary Flow Field Profiles of Micro-Swimmers in Weakly Anisotropic Nematic Fluids: Stokeslet, Stresslet, Rotlet and Source Flows, Fluids 3, 15 (2018). [Link]

Non-equilibrium liquid crystals

Nematic liquid crystals flowing inside microchannels show a rich variety of structures and are an ideal testing ground for non-equilibrium behaviour of nematic fluids. We explore analytically the structural dynamics of flowing nematic liquids due to flow-aligning interaction with the velocity field. By numerical modelling, we are also able to explore the nematic structure in junctions of microchannels and stabilize higher order defects. We also show, how optical fields can be used to periodically deform the director field, which could serve as a adjustable micropump with no moving parts.

Selected publications:

  • S. Čopar, Ž. Kos, T. Emeršič, U.Tkalec, Microfluidic control over topological states in channel-confined nematic flows, Nat. Comm. 11 59 (2020) [Link] [PDF].

  • T. Emeršič, R. Zhang, Ž. Kos, S. Čopar, N. Osterman, J. J. de Pablo, and U. Tkalec, Sculpting stable structures in pure liquids, Sci. Adv. 5, 2 (2019) [Link] [PDF].

  • Ž. Kos and M. Ravnik, Field generated nematic microflows via backflow mechanism, Sci. Rep. 10, 1446 (2020). [Link] [PDF].

  • L. Giomi, Ž. Kos, M. Ravnik and A. Sengupta Cross-talk between topological defects in different fields revealed by nematic microfluidics , Proc. Natl. Acad. Sci., 114, 29 (2017). [Link] [PDF].


Soft matter logic

Most computers today are based on electronic digital circuts that manipulate binary sequences such as 0011001 with logic gates. Alternative computation methods are explored in soft matter, such as DNA-based computation, computation in cells, microfluidics and mechanical networks. Liquid crystals allow for production of large arrays of tunable structures and formation of complex topological states. We explore how such nematic liquid crystal states could be used as bits for computation and how logic operations could be applied to them.

Selected publications:

  • Ž. Kos and J. Dunkel , Nematic bits and universal logic gates, Sci. Adv. 8, eabp8371 (2022). [Link] [PDF]

  • V. P. Patil, Ž. Kos and J. Dunkel, Harmonic flow field representations of quantum bits and gates, arXiv:2202.03941 (2022). [Link]