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

在这个项目中，我们将从数值/理论的角度研究简单液体在可切换的预结构衬底上的静态和动态特性，与SPP的实验和理论项目密切相关。尽管均匀和预结构衬底上的润湿行为已经得到了很好的理解，但我们的目标是全面了解切换时产生的非平衡效应。涉及新的时间尺度的，如在周期转换的情况下。预期会有显著的影响，例如，对附近的亲水条纹的润湿，包括液体凸起和桥的结构。为了全面了解有关系统，我们深信，对不同长度和时间尺度的分析是极为重要的。例如，为了考虑到开关过程本身，需要进行微观分析，实际上，我们将通过分子动力学模拟（MD）明确研究光活性分子的开关及其对液体的影响。相比之下，为了研究新平衡状态的长期行为，连续体视角将是最合适的，例如，动态行为和产生的不稳定性可以最好地分析。对于具体的问题，并充分涉及到两个pi的科学专长，我们将结合力场和晶格气体模拟，以及研究界面哈密顿量梯度动力学的介观薄膜模型。为了在这些方法之间进行定量匹配，我们采用特定的多尺度桥接技术来执行向介观薄膜方法传递的参数，即张力和润湿势的估计。对于MD模拟，可以直接从适当的病毒数计算中获得信息，而对于LGM的情况，将采用桥接微观密度泛函理论，这是由两个pi最近合作开发的。匹配的模型层次结构将使我们能够定量地了解分子在几个长度和时间尺度上的非平衡沉积和重排过程的关键方面。在这三年的时间里，我们的目标是(i)获得相关理论工具的充分经验，（ii）获得对开关时非平衡效应的良好物理理解，以及（iii）与SPP相应的实验组密切合作，将这些结果应用于他们实验的特定相互作用参数（例如，给定的预结构和接触角）。

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).