Lightning-Like Charged Jet Cascade in Bubble Electrospinning with Ultrasonic Vibration

Lightning is a natural phenomenon caused by an atmospheric electrical discharge, and lightning strikes are of hierarchical structure. Similar phenomenon is first observed in a charged jet in the presence of a high electrostatic field, the process is widely adopted for fabrication of superfine fibers, and its mechanism of lightning-like charged jet is still unknown. Our observation reveals that a daughter jet can be ejected from the surface of a micro/nanoscale charged jet to form an initial two-stage cascade, whereby the daughter charged jet can reduce size over three orders of magnitude, while at the ultimate stage, the jets have almost same size from several nanometers to dozens of nanometers. The origin of this phenomenon might be central to nanotechnology. Here we demonstrate that an electrostatic field can accelerate a charged jet, and the surface charge repels each other. When the repelling force reaches a threshold to overcome its surface tension, one or more daughter charged jets are ejected from the surface. The daughter jets behave similarly to the initial jet, the process is iterative, creating a lightning-like multi-stage cascade. This observation opens the door to mimicking the lightning to produce two dimensional superfine fiber web with hierarchical structure.