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诸如通过多孔介质或在芯片上的实验室设备中的流动等应用非常重要。在求解流过固体表面的液体的流体动力学方程时，通常假设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”。对复杂流体的实验以及最近对简单（牛顿）液体的实验表明，在边界处确实可能存在非零速度（“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纳米级。因此，在同样的尺度上，我们将确定移动的液体锋的速度和形状。两者都被认为是极其敏感的“纳米流变仪”。从理论上可以预料，光滑和低表面能的衬底会发生滑移。在我们的实验中，我们会改变这些系统的性质，也会改变液体的性质，比如粘度和粘弹性。由于滑移在宏观上也能提高流量，因此在混合器等微流控装置的设计中，滑移是一个重要的问题。因此，我们的愿景是能够调整表面的能力，以增强滑动。

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.