Vibration and development of pearl-chain-type tree in silicone gel under AC voltage

Pearl-chain-type trees under AC voltage have been observed using a high-speed camera. When AC voltage (60Hz) was applied, a bubble was appeared at a tip of needle electrode in silicone gel. The bubble oscillated with 120Hz. After increasing the applied voltage, a linear tree/tube proceeded ahead a certain distance and stopped. Then the bubble was formed at the tips of the tree/tube. The speed of the part of the bubble was slower than the speed of the linear tube. The branching also occurred. This kind of tree is called pearl-chain-type tree. It was observed that the center of the bubble was located slightly from the tip inward.