电润湿作用下水在石墨烯表面流动的边界滑移及界面摩擦

Boundary slip and interfacial friction properties of confined-water flow on graphene under electrowetting

采用分子动力学方法结合流体边界滑移理论对电润湿作用下水在石墨烯表面流动的边界滑移及摩擦特性进行数值模拟和理论分析。采用石墨烯-水Couette剪切模型,获取电润湿作用下和不带电情况下的剪切速率轮廓、石墨烯表面的剪切应力、边界滑移速率、滑移长度及界面摩擦系数,着重研究界面滑移长度和界面摩擦系数与剪切应变率之间的变化。结果表明:当剪切应变率超过临界剪切应变率时,滑移长度迅速增加,且电润湿作用下的临界剪切应变率明显高于不带电情况下的临界剪切应变率,而界面摩擦系数随着剪切应变率的增大而减小;石墨烯电润湿作用明显增强了石墨烯-水界面的摩擦。无论在电润湿作用下还是不带电情况下,石墨烯-水Couette模型中水的黏性系数与剪切应变率无关。

The boundary slip and interracial friction properties of confined-water flow on two parallel single-layer graphene sheets with a separation of 6 nm under electrowetting conditions were investigated by molecular dynamics simulation and boundary slip the- ory. For both electrowetted and uncharged graphenes, the flow velocity profiles perpendicular to the flow direction, shear stress, boundary slip velocity, slip length and interfacial friction coefficient were obtained with a graphene-water Couette flow model. Re- suits show that the slip length increases abruptly when the shear rate is above a critical value. The critical shear rate in the elec- trowetted graphenes is obviously larger than that in uncharged ones. The interfacial friction coefficient between graphene and water decreases with the shear rate and is increased by electrowetting the graphenes. The water viscosity is independent of the shear rate in both eletrowetted and uncharged graphenes.