基于磁性纳米复合棒的“咖啡环”效应

Coffee ring effect based on magnetic nanorods

研究了含有不溶性纳米复合棒的液滴在蒸发过程中出现的"咖啡环"效应,证实了"咖啡环"现象的形成和抑制与液滴体积、液滴浓度、基底温度、表面活性剂添加量及外加磁场等因素有关,并根据实验数据拟合"咖啡环"宽度与实验参量间的关系.证实了减小液滴体积、增大液滴浓度或升高基底温度,导致"咖啡环"变宽,而添加表面活性剂或施加外磁场则能够抑制"咖啡环"效应的出现.建立了磁性纳米复合棒在液滴蒸发过程中的受力模型,探讨了液滴重力、毛细流引起的牵引力、马兰戈尼流引起的牵引力及外加磁场提供的牵引力对"咖啡环"的形成及其宽度的调控影响规律.

The coffee ring effect in the evaporation process of droplets containing insoluble nanorods was studied. The formation and inhibition of the coffee ring were regulated by changing the experimental conditions, such as the volume and concentration of the droplet, the temperature of the substrate, the amounts of the surfactant and the external magnetic field. The relationship between the width of the coffee ring and these parameters was fitted according to the experimental data. The reduction of the droplet volume, the increase of the nanorod concentration or the rise of the substrate temperature increased the width of the coffee ring. The addition of surfactant in the droplets or the introduction of external magnetic field reduced the width of the coffee ring and even eliminated it. The force analysis model of the magnetic nanorods was established during the droplet evaporation. The droplet gravity, the capillary flow, the Marangoni flow and the tractive force of the external magnetic field played important roles in the formation of the coffee ring and the control of its width.