润滑聚合物刷上液滴运动的动力学
Dynamics of Droplets Moving on Lubricated Polymer Brushes
AI总结：
采用粗粒化模拟研究润滑聚合物刷基底上液滴在外力作用下的运动，发现液滴滚动而非滑动，且润滑剂对有效摩擦力影响甚微。
摘要：
理解聚合物涂层表面上液滴的动力学对于优化自清洁材料或微流控器件等应用至关重要。尽管沉积液滴的静态和动态性质已被充分表征，但对潜在动力学的微观理解仍然缺乏。特别是，液滴动力学如何依赖于刷中未交联链的数量尚不清楚，因为实验技术无法量化这些链。这里我们采用粗粒化模拟，研究在外力作用下润滑聚合物刷基底上液滴的运动。模拟模型基于多体耗散粒子动力学（mDPD）方法，旨在模拟水滴在聚二甲基硅氧烷（PDMS）刷上，并含有化学相同的PDMS润滑剂的系统。与实验一致，我们发现外力$F$与液滴速度$v$之间存在亚线性幂律关系，$F \propto v^α$，其中$α<1$；然而，指数不同（模拟中$α\sim 0.6-0.7$，实验中$α\sim 0.25$）。随着速度增加，液滴伸长，后退接触角减小，而前进接触角大致保持不变。分析液滴内部的流动轮廓表明，液滴并非滑动而是滚动，在基底表面无滑移。令人惊讶的是，添加润滑剂对液滴与基底之间的有效摩擦力影响甚微，尽管它对润湿脊的大小和结构有显著影响，尤其是在遮蔽转变之上。
英文摘要：
Understanding the dynamics of drops on polymer-coated surfaces is crucial for optimizing applications such as self-cleaning materials or microfluidic devices. While the static and dynamic properties of deposited drops have been well characterised, a microscopic understanding of the underlying dynamics is missing. In particular, it is unclear how drop dynamics depends on the amount of uncrosslinked chains in the brush, because experimental techniques fail to quantify those. Here we use coarse-grained simulations to study droplets moving on a lubricated polymer brush substrate under the influence of an external body force. The simulation model is based on the many body dissipative particle dynamics (mDPD) method and designed to mimic a system of water droplets on polydimethylsiloxane (PDMS) brushes with chemically identical PDMS lubricant. In agreement with experiments, we find a sublinear power law dependence between the external force $F$ and the droplet velocity $v$, $F \propto v^α$ with $α<1$; however, the exponents differ ($α\sim 0.6-0.7$ in simulations versus $α\sim 0.25$ in experiments). With increasing velocity, the droplets elongate and the receding contact angle decreases, whereas the advancing contact angle remains roughly constant. Analyzing the flow profiles inside the droplet reveals that the droplets do not slide, but roll, with vanishing slip at the substrate surface. Surprisingly, adding lubricant has very little effect on the effective friction force between the droplet and the substrate, even though it has a pronounced effect on the size and structure of the wetting ridge, especially above the cloaking transition.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
