Departamento de Física de la Materia Condensada, Centro Atómico Constituyentes, CNEA, Av. Gral. Paz 1499, 1650 Pcia. de Buenos Aires, Argentina.
Soft Matter. 2019 Jan 30;15(5):937-946. doi: 10.1039/c8sm02388c.
We study by coarse-grained molecular-dynamics simulations the liquid flow in a slit channel with the inner walls coated by semiflexible polymer brushes. The distance between walls is close enough such that polymers grafted to opposing walls interact among each other and form bundles across the channel in poor solvent conditions. The solvent is simulated explicitly, including particles that fill the interior of the channel. The system is studied in equilibrium and under flow, by applying a constant body force on each particle of the system. A non-linear relation between external force and flow rate is observed, for a particular set of parameters. This non-linear response is linked to a morphological change of the polymer brushes. For large enough forces, the bundle structures formed across the channel break as the chains lean in the direction of the flow, and clear the middle of the channel. This morphological alteration of the polymer configurations translates in a sudden increase in the flow rate, acting as a pressure-responsive gate. The relation between flow and external force is investigated for various parameters, such as grafting density, quality of the solvent and polymer bending rigidity. We observe a non-monotonic dependence of the flow as a function of the polymer rigidity, and find an optimum value for the persistence length. We also find that the force threshold at which the morphological changes happen in the polymer brush, depends linearly on the grafting density. These findings can lead to new flow control techniques in micro and nano-fluidic devices.
我们通过粗粒化分子动力学模拟研究了带有涂覆半刚性聚合物刷的内壁的狭缝通道中的液体流动。壁之间的距离足够近，以至于接枝到相对壁上的聚合物在不良溶剂条件下相互作用并在通道中形成束。溶剂被明确模拟，包括填充通道内部的粒子。通过对系统中的每个粒子施加恒定的体力，在平衡和流动条件下研究该系统。对于特定的参数集，观察到外力和流速之间的非线性关系。这种非线性响应与聚合物刷的形态变化有关。对于足够大的力，当链在流动方向上倾斜并清除通道中间时，形成的跨通道束结构会断裂。聚合物构型的这种形态改变会导致流速突然增加，充当压力响应门。我们研究了各种参数（例如接枝密度、溶剂质量和聚合物弯曲刚度）下的流速与外力之间的关系。我们观察到流速随聚合物刚度的非单调依赖性，并找到了最佳的持久长度值。我们还发现，聚合物刷中形态变化发生的力阈值与接枝密度呈线性关系。这些发现可以为微纳流控装置中的新流量控制技术提供依据。
