Jet formation and break-up in inkjet printing has been studied and understood mainly for pure liquids. Questions remain as to the role of surfactants on the inkjet printing process at the microsecond timescale. Here, numerical and experimental results demonstrating the effects of surfactants on jet break-up and drop formation at the scales relevant to drop-on-demand inkjet printing are presented. The rapid expansion of the free surface during the fast jetting process results in a depletion of surfactants along the air–liquid interface, resulting in surface tension gradients. During ejection, surfactants are concentrated toward the head of the droplet, while the trailing ligament is found to be almost devoid of surfactants. As a consequence, the initial evolution and pinch-off of the jet from the nozzle are found to be very similar to that of pure water, even though the equilibrium surface tension of the surfactant solution is lower by a factor of two. However, particularly for strong surfactants, Marangoni forces arising from surface tension gradients between the head drop and the ligament are found to delay and can even prevent the break-up of the main drop from the ligament thereby inhibiting the formation of satellite drops.

中文翻译：

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表面活性剂对按需喷墨打印中射流破裂的影响

喷墨印刷中的射流形成和破裂主要针对纯液体进行了研究和理解。关于表面活性剂在微秒时间尺度上的喷墨印刷过程中的作用仍然存在问题。在这里，数值和实验结果展示了表面活性剂在与按需喷墨打印相关的尺度上对喷射破裂和液滴形成的影响。在快速喷射过程中自由表面的快速膨胀导致沿气-液界面的表面活性剂耗尽，导致表面张力梯度。在喷射过程中，表面活性剂集中在液滴的头部，而尾部韧带几乎没有表面活性剂。作为结果，发现喷嘴射流的初始演变和夹断与纯水非常相似，即使表面活性剂溶液的平衡表面张力低了两倍。然而，特别是对于强表面活性剂，发现由头部液滴和韧带之间的表面张力梯度产生的 Marangoni 力会延迟甚至可以防止主液滴从韧带断裂，从而抑制卫星液滴的形成。