Coalescence characteristics of water droplets in W/O emulsion under ultrasonic irradiation

Under ultrasonic irradiation, the displacement effect of water droplets in W/O emulsion occurred. The water droplets moved to the wave loop or wave node, then gathered and collided into one. The coalescence characteristics of water droplets in W/O emulsion under ultrasonic irradiation were analyzed by using microscopic high-speed camera system combined with image processing technology. The results indicated that ultrasonic mechanical vibration could reduce the oil-water interfacial film strength, thus promoted the coalescence of droplets in W/O emulsion, and the water droplets took the similar sine oscillation movement before coalescence. Under ultrasonic intensity of 4.89 W/cm2 and ultrasonic frequency of 20 kHz, the water droplets with 200-400 μm diameters in the W/O emulsion with 13.62 mN/m interfacial tension took severe oscillation movement with the best coalescence effect. The oscillation frequency and coalescence time of water droplets were mainly affected by ultrasonic intensity, ultrasonic frequency, droplet size, oil viscosity and oil-water interfacial tension. With the increase of ultrasonic intensity, the coalescence time of water droplets decreased. With the increase of ultrasonic frequency, the coalescence time of water droplets increased. With the decrease of droplet size and oil viscosity, the oscillation frequency of water droplets increased and the coalescence time decreased. With the decrease of oil-water interfacial tension, the oscillation frequency of water droplets increased to the maximum and then decreased, while the change of coalescence time was inverse. ©, 2015, Science Press. All right reserved.