Repulsive bubble-bubble interaction in ultrasonic field*

The bubble–bubble interaction (BBI) is attractive in most cases, but also could be repulsive. In the present study, three specific mechanisms of repulsive BBI are given. The great contribution to the repulsive BBI is derived from the large radius of the bubble catching the rebound point of the other bubble. For "elastic" bubble and "inelastic" bubble, with the increase of the phase shift between two bubbles, the BBI changes from attractive to repulsive, and the repulsion can be maintained. For both "elastic" bubbles, the BBI alternates between attractive interaction and repulsive interaction along the direction where the ambient radius of one of bubbles increases. For stimulating bubble and stimulated bubble, the BBI can be repulsive. Its property depends on the ambient radii of bubbles. In addition, the distribution of the radiation forces in ambient radius space shows that the BBI is sensitive to the size of bubble and is complex because the bubbles are not of the same size in an ultrasonic field. Finally, as the distance increases or decreases monotonically with time, the absolute value of the BBI decreases or increases, correspondingly. The BBI can oscillate not only in strength but also in polarity when the distance fluctuates with time.