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Abstract(s)
In this thesis we investigated the flow of flexible particles in complex environments, with a focus
on droplet-based emulsions driven by flow and the sedimentation of deformable capsules and
droplets in confined geometries. We used the lattice Boltzmann method (LBM) for fluid modelling
and employed a combination of intrinsic LB methods and coupling with other techniques
to simulate multicomponent droplets and flexible capsules. We conducted a comprehensive
review, summarising different approaches utilising LBM in simulating fluid-filled soft structures.
We highlight the relevance of these models in fields such as droplet microfluidics, drug
delivery, and microparticle synthesis, while categorising the methods into fluid-structure and
fluid-fluid methods, which consider interfacial boundaries and hydrodynamic interactions. We
emphasise the versatility of the lattice Boltzmann method in handling complex boundary conditions
and incorporating physical models. Additionally, we discussed benchmark tests for model
validation. In further studies, we extended a multicomponent LB method to 3D geometries and
simulated droplets flowing in a wetting channel. The results revealed a discontinuous shear
thinning transition as the external force increased. We examined the effect of surface tension,
directly related to droplet deformability, demonstrating that higher surface tension led to less
deformable droplets and thus require larger forces for shear thinning to occur. In the next study,
we looked at the shape transitions of sedimenting capsules and droplets. In the confined regime,
we found a transition to bullet shape consistent with experiments. Interestingly, we find that the
transition from oblate to bullet shaped droplets and capsules consistently occurs at a specific ratio
between the capsule size and confinement, regardless of the flexibility. A detailed analysis of
hydrodynamic stresses and forces provides valuable insights into the mechanisms driving these
shape transitions. Overall, the application of the lattice Boltzmann method, and the combination
of computational and experimental approaches (conducted by the Oppenheimer Group for Soft
Matter Physics at Tel Aviv University), sheds light into the dynamics of droplet-based systems
and deformable capsules. These findings have implications for a wide range of fields involving
soft matter systems, opening up new possibilities for designing and optimising processes in
droplet microfluidics, drug delivery, food & cosmetic industry and beyond.
Description
Keywords
fluid dynamics droplets capsules deformation lattice Boltzmann method dinâmica de fluídos gotas cápsulas deformação