B05

In this project the interaction of transport and wetting phenomena is to be investigated at the molecular level. In addition, it provides macroscopic model parameters by molecular analysis of the matter in their physico-chemical behavior. The focus will be the fluid-solid interaction on smooth homogeneous or chemically heterogeneous surfaces. Molecular dynamic simulations will yield boundary conditions at the solid surfaces (e.g. slip length) e.g. in fluids with surfactants which can be formulated for a continuum description, suitable for implementation in OpenFOAM. Together with other projects from B (esp. B01, B02), a hierarchical multiscale modeling should ultimately be developed.

Static and dynamic properties of three-phase contact lines (TPCLs) are poorly understood. The picture shows the molecular simulation of a liquid bridge between two solid surfaces with a vertical dimension of ~ 70 nm. The static electro-wetting contact angles are indicated as well. Molecular Dynamics (MD) simulations (F. Taherian et. al. , 2015, DOI: 10.1021/acs.langmuir.5b00625)indicate that the static contact angle responds asymmetrically upon switching the sign of the surface charge density, while the bulk interfacial (solid-liquid) free energy remains unchanged. The observed effect is caused by differences in the molecular structure and free energies of the two TPCLs on oppositely polarised surfaces. The implications of these differences for contact line friction and dynamics will be investigated in TP B05 (amongst other effects and systems). The MD simulations performed in TP B05 provide atomic-level understanding of TPCL properties and provide information on hydrodynamic boundary conditions in continuum fluid mechanics models for fluid mixtures.