Friday, 30th October 2020

Online Symposium

For information on how to access the event, please contact Henning Reinken via: henning.reinken(at)itp.tu-berlin.de

Guests are welcome!

Friday, 30th October 2020

Gradient dynamics models for thin films - how to break them and other new challenges

Uwe Thiele, Universität Münster, Germany

In the first part, I review a number of established gradient dynamics formulations of mesoscopic hydrodynamics (or thin-film models) [1] when two density/height fields are involved. Particular considered cases are two-layer films of nonvolatile simple liquids on solid substrates [2], films of mixtures and suspensions [3], and liquid drops on brush-covered substrates [4].
Second, I discuss what to expect when the gradient dynamics structure is broken looking at a number of recent examples. This includes specific (bio-)active systems where a core gradient dynamics thin-film model is amended by nonvariational terms [5], or more abstract generic models like two Cahn-Hilliard equations with nonreciprocal coupling [6].

[1] U. Thiele, Colloids Surf. A 553, 487 (2018).
[2] A. Pototsky, M. Bestehorn, D. Merkt and U. Thiele, Phys. Rev. E 70, 025201(R) (2004); J. Chem. Phys. 122, 224711 (2005).
[3] U. Thiele, A. Archer, L. Pismen,  Phys. Rev. Fluids 1, 083903 (2016); U. Thiele, D. Todorova, H. Lopez, Phys. Rev. Lett. 111, 117801 (2013).
[4] U. Thiele, S. Hartmann, Eur. Phys. J.-Spec. Top. 229, 1819 (2020).
[5] S. Trinschek, K. John, U. Thiele, Soft Matter 14, 4464 (2018); Phys. Rev. Lett. 119, 078003 (2017); S. Trinschek, F. Stegemerten, K. John, U. Thiele, Phys. Rev. E 101, 062802 (2020).
[6] T. Frohoff-Hulsmann, J. Wrembel and U. Thiele, arxiv.org/abs/2009.14287 (2020).

Rheology of dense granular suspensions

Elisabeth Guazzelli, Université de Paris, France

Suspensions are composed of mixtures of particles and fluid and are ubiquitous in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing) and in natural phenomena (e.g. flows of slurries, debris, and lava). The present talk focusses on the rheology of concentrated suspensions of non-colloidal particles. It addresses the classical shear viscosity of suspensions but also non-Newtonian behaviour such as normal-stress differences and shear-induced migration. The rheology of dense suspensions can be tackled via a diversity of approaches that are introduced. In particular, the rheometry of suspensions can be undertaken at an imposed volume fraction but also at imposed values of particle normal stress, which is particularly well suited to yield examination of the rheology close to the jamming transition. The influences of particle roughness and shape are discussed.
This work has been done in collaboration with J. E. Butler, O. Pouliquen, S. Shaikh, F. Tapia.

Phase separation on evolving surfaces

Charles Elliott, University of Warwick, Great Britain

We discuss some mathematical models of phase separation on evolving surfaces involving Cahn-Hilliard functionals. Particular concerns are models of two phase biomembranes, well posedness of Cahn-Hilliard equations on evolving surfaces and free boundary problems on surfaces.