疏水半柔性polymer刷包覆纳米通道中液滴传输：链刚度的影响
Droplet transport in a nanochannel coated by hydrophobic semiflexible polymer brushes: the effect of chain stiffness
摘要：
本文采用非平衡分子动力学模拟方法研究了链刚度对涂有半柔性疏水聚合物的纳米通道内液滴流动的影响。所研究的系统，然后是一个移动的液滴在狭缝通道中，与它的蒸汽共存，并受到周期性的边界条件的流动方向。由末端珠接枝到限制壁的聚合物链由粗粒模型描述，该模型考虑链连接性、排除体积相互作用和局部链刚度。刷的流变学，摩擦和动力学特性的探索在很宽的范围内的持久性长度。我们发现了丰富的行为的聚合物构象和伴随的变化，在广泛的研究聚合物刚度的摩擦性能。对于持久长度小于其轮廓长度的聚合物，随着链的刚性增加，观察到液滴速度的快速降低。我们发现刷的内部动力学和液滴传输特性之间有很强的关系，这可用于通过表面官能化来定制流动特性。刷层的单体，在液滴下，呈现集体的“跑步机带”样动力学，其只能由于接枝链的存在而存在。我们描述了它的变化，在聚合物刚度的变化，二维速度和密度分布的空间延伸。由于液滴的存在下的聚合物刷的变形进行了详细的分析。最后，通过改变液气比来研究液滴-气体相互作用，观察到与在连续液滴之间存在大间隙的液滴的训练相比，彼此靠近流动的液滴的速度增加16%。
英文摘要：
We study the influence of chain stiffness on droplet flow in a nano-channel, coated with semiflexible hydrophobic polymers by means of non-equilibrium molecular-dynamics simulations. The studied system is then a moving droplet in the slit channel, coexisting with its vapor and subjected to periodic boundary conditions in the flow direction. The polymer chains, grafted by the terminal bead to the confining walls, are described by a coarse-grained model that accounts for chain connectivity, excluded volume interactions and local chain stiffness. The rheological, frictional and dynamical properties of the brush are explored over a wide range of persistence lengths. We find a rich behavior of polymer conformations and concomitant changes in the friction properties over the wide range of studied polymer stiffnesses. A rapid decrease in the droplet velocity was observed as the rigidity of the chains is increased for polymers whose persistence length is smaller than their contour length. We find a strong relation between the internal dynamics of the brush and the droplet transport properties, which could be used to tailor flow properties by surface functionalization. The monomers of the brush layer, under the droplet, present a collective "treadmill belt" like dynamics which can only be present due the the existence of grafted chains. We describe its changes in spatial extension upon variations of polymer stiffness, with bidimensional velocity and density profiles. The deformation of the polymer brushes due to the presence of the droplet is analyzed in detail. Lastly, the droplet-gas interaction is studied by varying the liquid to gas ratio, observing a 16% speed increase for droplets that flow close to each other, compared to a train of droplets that present a large gap between consecutive droplets.
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