A photographic study of bubble coalescence

The coalescence of nitrogen bubbles in liquid was studied by using a high-speed motion picture camera at speeds up to 3,000 frames per second. Examination of the films frame by frame reveals that the general process of bubble coalescence is growth-touching- coalescence-vibrating-detachment. A small amount of surface active additive influences the time of coalescence significantly: 0.9ppm of sodium lauryl sulfate (SLS), 1.6 ppm of sodium laury benzene sulfonate (SLBS) or 1.8 ppm of n-octanol inhibits the bubble coalescence completely. This phenomenon is attributed to the dynamic surface effect or the departure from static surface tension caused by extension of the gas-liquid interface.