Robert E. Apfel
R. Glynn Holt
Yuren Tian
Ctr. for Ultrasonics and Sonics, Yale Univ., New Haven, CT 06520-8286
Droplet shape oscillations induced by acoustic radiation force can be applied to investigate liquid surface rheology. During experiments performed on the United States Microgravity Laboratory missions, the droplet shape was recorded both by video and by film cameras. In order to determine the free oscillation frequency and damping constant of droplets, an automatic image analysis system was developed to evaluate the variations of droplet shape versus time. With this system the edges of drops are automatically located frame by frame, and then matched by a polynomial function. The geometric center point, the maximum and minimum diameters, and the droplet aspect ratio are calculated from the fitting results, which give the droplet free oscillation frequency and damping constant. From these two parameters and the droplet size, the surface elasticity and viscosity of surfactant solutions can be evaluated. [Work supported by NASA through JPL, contract 958722.]