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Title: Theory and Lattice Boltzmann simulation of active fluids
Author: De Magistris, Giulio
ISNI:       0000 0004 8497 5795
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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Active fluids are far from equilibrium systems, nominally highly dense suspensions of elongated elements that confer to the liquid orientational order, similar in nature to the one found in liquid crystals, and an internal stirring that they exert through the consumption of some fuel reservoir { typically AdenosineTriPhosphate(ATP). The interplay between the orientational order and the active behaviour gives rise to non-trivial dynamics, order-disorder out-of-equilibrium transitions, and dynamical transitions to non-equilibrium steady states. In this work we will discuss active fluids in the framework of the hydrodynamic theory of active nematics and active polar fluids, where the structural order is characterised by an elastic formalism drawn from the theory for liquid crystals, and the activity is obtained from the coarse graining of the microscopics. Our aim was to analyse and characterize large scale behaviours in multi-phase systems. We studied the dynamics of water phases embedded in active polar fluids, or rather 'inverse droplets', and considered how these move by effect of the surrounding active medium. We found two types of motile transitions, depending on the specifics of the boundary conditions of the orientation profile at the interface between the passive and the active phase. We also considered quenches of disordered mixtures of active nematic and passive isotropic fluids. In these systems we observed cases of arrested phase separation, with the coarsening saturating at finite length scales depending on the strength of the activity. We characterized this behaviour in terms of an active capillary number, resulting from the relative strength of active interface effects and surface tension.
Supervisor: Marenduzzo, Davide ; Brackley, Chris Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: active fluids ; active nematics ; active polar fluids ; elastic formalism ; inverse droplets ; passive isotropic fluids