Dynamics of capillary surfaces at the nano and meso scale and their impact on dispensing devices: development of a free surface dissipative particle dynamics method

目前，在集成微流控和片上实验室设备中，毛细管作用对于简单和复杂流体的高效被动液体处理起着至关重要的作用。在微观尺度上，被动阀门、断口或剂量单位等部件的设计可以完全依赖于毛细管效应的经典描述，而对于介观尺度上的部件则不一定如此。流动和毛细管界面的波动以及大分子的布朗运动对流动的影响可能变得重要。现有的模拟方案只能对这些现象的相互作用提供部分见解。为了得到一个完整的描述，我们采用了耗散粒子动力学（DPD）的方法，它能够描述流体动力流动以及热波动及其对复杂悬浮物体的影响。DPD方案将首先得到增强，以包括自由毛细管表面的非平衡动力学。其次，改进后的DPD将通过低水平分子动力学模拟和亚微米通道中简单流体的毛细管流动行为的系统实验进行校准。在此之后，该方案可以应用于探索毛细驱动流在处理单个大分子中的潜在用途。

At present, in integrated microfluidic and lab-on-chip devices, capillarity plays a vital role for efficient passive liquid handling of simple and complex fluids. On the microscale, the design of components like passive valves, breaks or dosage units can entirely rely on a classical description of capillary effects, whereas this is not necessarily the case for components on a mesoscopic scale. Fluctuations on flow and capillary interfaces as well as the impact of brownian motion of macromolecules on flow are likely to become important. Existing simulation schemes can each provide only partial insight into the interplay of these phenomena. To arrive at a complete description, we employ the method of Dissipative Particle Dynamics (DPD), capable of describing hydrodynamical flow together with thermal fluctuations and their impact on complex supended objects. The DPD scheme will first be enhanced to include nonequilibrium dynamics of free capillary surfaces. Second, the modified DPD will be calibrated by low level molecular dynamics simulations and systematic experiments on capillary flow behaviour of simple fluids in sub-micron channels. After this, the scheme can be applied to explore the potential use of capillarity driven flows in handling even single macromolecules.