Slippage and Nanorheology of Simple and Complex Fluids in Confinement

与固体界面接触的液体的性质对于涉及例如流过多孔介质或在芯片实验室装置中的应用是非常重要的。在求解液体流过固体表面的流体动力学方程时，通常假定流体和固体之间的相对速度为零。这就是所谓的“无滑移边界条件”。复杂流体的实验和最近简单（牛顿）液体的实验表明，在边界处确实可以有非零速度（“滑移”）。在这个项目中，我们将通过实验研究为什么以及在什么条件下会发生这种情况。所涉及的尺寸预计为nm级。因此，在同样的尺度上，我们将确定运动液体前缘的速度和形状。两者都被认为是非常敏感的“纳米流变仪”。从理论上可以预期，对于光滑和低表面能的基材，滑移是强制性的。在我们的实验中，我们将改变这些系统特性以及液体的特性，如粘度和粘弹性。由于滑移也可以在宏观尺度上提高流速，因此滑移是微流体装置（如混合器等）设计中的一个重要问题。因此，我们的愿景是能够调整表面以提高滑移的能力。

The properties of a liquid in contact with a solid interface are very important for applications involving e.g. the flow through porous media or in lab-on-a-chip devices. Solving the hydrodynamic equations for a liquid flowing over a solid surface, one usually assumes the relative velocity between fluid and solid to be zero. This is the so-called "no-slip boundary condition". Experiments with complex fluids and, very recently, with simple (Newtonian) liquids have shown that there can indeed be a non-zero velocity ("slippage") at the boundary. In the project we will study experimentally why and under which conditions this can take place. The sizes involved are expected to be of nm-scale. On the same scale we will therefore determine the velocity and the shape of a moving liquid front. Both are known to serve as extremely sensitive "nano-rheometers". It is expected from theory that slippage is enforced for smooth and low surface-energy substrates. In our experiments, we will vary these system properties and also properties of the liquid like viscosity and viscoelasticity. Since slippage can enhance the flow rate also on a macro-scale, slippage is an important issue in the design of microfluidic devices such as mixers etc. The vision thus is to be able to tailor surfaces in their ability to enhance slippage.