2016-03-24
10:15 at HCP F43.4

Thermodynamically consistent gradient dynamics models for interface-dominated evolution of thin films

Johannes Kemper

Institute of Theoretical Physics, WWU Münster, Germany

The talk begins with an introduction of the two simplest types of gradient dynamics equations for single scalar order parameter fields that are often employed to describe interface evolution. Here we use the example of evolution equations for the profile of a thin liquid film without and with evaporation, respectively. For a conserved field it has the structure of the Cahn-Hilliard equation while the non-conserved equation is of Allen-Cahn type [1,2]. The underlying free energy (or Lyapunov functional) includes geometric interfacial energy contributions as well as a film-substrate interaction potential that accounts for wettability. The gradient dynamics approach will then be extended towards the case of two order parameter fields and I will shortly discuss the Onsager character of the mobility matrix. Then I will show that these models are able to describe different systems involving simple and complex liquids. In particular, I focus on the description of films of mixtures and suspensions and present the underlying energies and mobilities [3,4]. In addition, the model even allows one to study the evolution in certain non-equilibrium settings like, for instance, drops sliding down an inclined surface. Based on my master thesis, I will further illustrate how a general viscoelastic description of a soft layer that incorporates an additional elastic energy contribution can be simplified by a local approximation [5]. A two-layer model can then be extended to include such a local elastic energy to describe a liquid film and drops on top of a viscoelastic material. References: [1] U. Thiele, J. Phys.-Cond. Mat. 22, 084019 (2010). [2] U. Thiele, Eur. Phys. J. Special Topics, 197 213-220 (2011). [3] U. Thiele, A. J. Archer and M. Plapp, Phys. Fluids 24, 102107 (2012). [4] U. Thiele, D. V. Todorova and H. Lopez, Phys. Rev. Lett. 111, 117801 (2013). [5] J. Kemper, “Modeling of viscous drops on soft substrates”, Masterthesis, WWU Müns-ter (2015).