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The wetting dynamics of liquid particles, from coated droplets to soft capsules, holds significant technological interest. Motivated by the need to simulate liquid metal droplet with an oxidize surface layer, in this work we introduce a computational scheme that allows to simulate droplet dynamics with general surface properties and model different levels of interface stiffness, describing also cases that are intermediate between pure droplets and capsules. Our approach is based on a combination of the immersed boundary (IB) and the lattice Boltzmann (LB) methods. Here, we validate our approach against the theoretical predictions in the context of shear flow and static wetting properties and we show its effectiveness in accessing the wetting dynamics, exploring the ability of the scheme to address a broad phenomenology., Comment: 14 pages, 6 figures

Membrane viscosity is known to play a central role in the transient dynamics of isolated viscoelastic capsules by decreasing their deformation, inducing shape oscillations and reducing the loading time, that is, the time required to reach the steady-state deformation. However, for dense suspensions of capsules, our understanding of the influence of the membrane viscosity is minimal. In this work, we perform a systematic numerical investigation based on coupled immersed boundary -- lattice Boltzmann (IB-LB) simulations of viscoelastic spherical capsule suspensions in the non-inertial regime. We show the effect of the membrane viscosity on the transient dynamics as a function of volume fraction and capillary number. Our results indicate that the influence of membrane viscosity on both deformation and loading time strongly depends on the volume fraction in a non-trivial manner: dense suspensions with large surface viscosity are more resistant to deformation but attain loading times that are characteristic of capsules with no surface viscosity, thus opening the possibility to obtain richer combinations of mechanical features.

Wetting dynamics may significantly impact technological applications involving some liquids, from coated droplets to soft particles. Indeed, in some cases, external conditions can trigger alterations in the interface properties of simple droplets, leading to variations in the mechanical interface response, even resulting in the acquisition of rigidity. This work explores the wetting dynamics of hydrophobic coated droplets with generic interface properties by combining the immersed boundary (IB) and the lattice Boltzmann (LB) methods. The presented model allows to explore different situations, corresponding to different levels of droplet interface stiffness. We first validate our methodology with the theoretical predictions in the context of shear flow and wetting experiments. Then, we show the effectiveness of our numerical framework to access the hydrophobic wetting dynamics, also providing a theoretical prediction for contact angles. Model limits are also discussed. To generalise the application of our methodology, we present a numerical framework to study a wide spectrum of coated droplets and soft particles with varying interfacial properties. It can serve as an initial approximation to investigate the wetting dynamics of specific coated droplets, like liquid metal droplets, which are observed to exhibit large contact angles on any solid surface and whose wetting properties can be altered when entering into contact with oxygen because of forming a solid-like oxide layer on the top of the interface., 13 pages, 6 figures

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2022). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022, The study of the mechanical properties of red blood cell (RBC) membrane spreads between several and somehow different fields: from the development of medical devices to the biological understanding, from applications to theory. In this thesis work, we investigate the effects of membrane viscosity on transient RBC dynamics, focusing on the tumbling to tank-treading (TB-TT) transition, as well as on the loading and relaxation dynamics of a single RBC, highlighting the key role played by the membrane viscosity to provide a realistic numerical simulation of the RBC dynamics; we also investigate the effect of the viscosity at the interface for viscous droplets and we propose a reduced model to describe its deformation. Mesoscale numerical simulations are carried out in the framework of the immersed boundary - lattice Boltzmann (IBLB) method., Published by RWTH Aachen University, Aachen

14 Seiten (2021).