Microfluidic structures from nematic liquid crystalsKos, Žiga (Avtor) Ravnik, Miha (Mentor) nematic liquid crystalsnematodynamicsmicrofluidicsfield structuresflow generationmicroswimmersactive nematicstopological defectsNematicity is an exciting material property, which in complex fluids relies on the orientational ordering of passive or active (self-driven) building blocks. Here, I present the results of my research on microfluidic structures in passive and active nematic fluids that are characterised by geometrically distinct and often topologically protected profiles of the relevant material fields (such as the orientational field and the velocity field). The results are obtained through numerical and analytical efforts, with the main methodological approach being the mesoscopic continuum nematodynamic modelling based on the order paramter tensor which is solved by the hybrid lattice Boltzmann method. The used mesoscopic approach fully accounts for the backflow effects --- i.e. strong coupling between the orientational ordering and the material flow --- that underlies the explored structures. Structural properties of the flow and the orientational field are investigated and controlled through externally induced (electric, optic, or pressure) fields , topology-inducing confinement, or material activity. In junctions of microchannels, I characterize an effective interaction between topological defect structures in the orientational and in the velocity field of a flowing nematic. The topic is further explored in porous networks of cylindrical channels, where a variety of stationary structures and the transition processes between them is observed. In a single microchannel, flow field is used as a control mechanism for growth or annihilation of structural domains. A twist instability in nematic microchannels is shown, and a phase diagram is obtained, from which the expected nematic structure at a given speed in the channel and at a given elastic anisotropy can be identified. In nematic cells with patterned anchoring profiles, stability of Skyrmion-like structures is explored in view of elastic anisotropy and saddle-splay elasticity. Generation of flow patterns for confined nematics is proposed, based on using external electric or optic fields to continually deform the nematic structure and generate backflow. The process of structure formation during a temperature quench is examined. Lastly, nematics driven by active materials or inherent activity are studied. An analytical approximation of the flow field generated by a microswimmer in a nematic liquid crystal is provided. Structural properties of unconfined and confined three-dimensional (3D) active nematics are investigated and a variety of regimes is identified. Main modes of coupled oscillations of active and passive defects in emulsions of active nematic droplets in the passive nematic medium are explored. The thesis is aimed towards control of the emergent properties and functionality of non-equilibrium soft matter through the manipulation of the underlying structural organization.20192019-02-20 07:45:33Doktorsko delo/naloga106362sl