Liquids on switchable pre-structured substrates - from microscopic to mesoscopic models

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In this project we will study the static and dynamic properties of a simple liquid on a switchable pre-structured substrate from a numerical/theoretical perspective in close contact to the both experimental and theoretical projects of the SPP. Whereas the wetting behavior on homogeneous and pre-structured substrates is well-understood, we aim to obtain a thorough understanding of the resulting non-equilibrium effects upon switching, involving new time-scales as in the case of periodic switching. Prominent effects are expected, e.g., for the wetting of close-by hydrophilic stripes, involving liquid bulge as well as bridge configurations.For a comprehensive understanding of the system in question we are convinced that an analysis of different length- and time-scales is of utmost importance. For example, in order to take into account the switching process itself, a microscopic analysis is required and, indeed, we will explicitly study the switching of photoactive molecules via Molecular Dynamics simulations (MD) and its impact on the liquid. In contrast, to study the long-time behavior to new equilibrium states, a continuum perspective will be most appropriate where, e.g., the dynamical behavior and arising instabilities can best be analyzed. For specific questions, and fully related to the scientific expertise of the two PIs, we will combine force field and lattice gas simulations, on the one hand, and mesoscopic thin film models studying the gradient dynamics on interface Hamiltonians, on the other hand.In order to have a quantitative matching among these approaches, we employ specific multiscale bridging techniques to perform the parameter passing to the mesoscopic thin film approach, i.e. the estimation of the tension and the wetting potential. For MD simulations, the information can be directly obtained from the calculation of appropriate virials whereas for the case of a LGM, a bridging microscopic Density Functional Theory will be employed, as developed in a recent collaboration of both PIs. The matched hierarchy of models shall allow us to quantitatively understand crucial aspects of non-equilibrium deposition and rearrangement processes of the molecules across several length and time scales.During this three year period we aim (i) to gain full experience with the relevant theoretical tools, (ii) to obtain a good physical understanding of non-equilibrium effects upon switching, and (iii) to apply these results, in close collaboration with the corresponding experimental groups of the SPP, to the specific interaction parameters of their experiments (e.g., for given pre-structuring and contact angles).