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

在这个项目中，我们将研究一个简单的液体的静态和动态特性的可切换的预结构基板从数值/理论的角度密切接触的SPP的实验和理论项目。而均匀和预结构化的基板上的润湿行为是很好的理解，我们的目标是获得一个彻底的了解所产生的非平衡效应切换时，涉及新的时间尺度的情况下，定期切换。预期会产生显著影响，例如，对于附近亲水性条带的润湿，包括液体膨胀以及桥结构。为了全面理解所讨论的系统，我们相信，不同长度和时间尺度的分析是至关重要的。例如，为了考虑开关过程本身，需要进行微观分析，实际上，我们将通过分子动力学模拟（MD）明确研究光敏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时间行为，连续统视角将是最合适的，例如，可以最好地分析动力学行为和产生的不稳定性。针对具体问题，充分结合两位PI的科学专长，我们将一方面结合联合收割机力场和晶格气模拟，另一方面结合介观薄膜模型研究界面Hamilton上的梯度动力学。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传递到介观薄膜方法的参数，即张力和润湿势的估计。对于MD模拟，信息可以直接从计算适当的维里，而对于LGM的情况下，桥接微观密度泛函理论将采用，在最近的合作开发的两个PI。匹配的模型层次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。在这三年期间，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）应用这些结果，与SPP的相应实验组密切合作，对其实验的具体相互作用参数（例如，对于给定的预结构化和接触角）。

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).