Shape, vibrations, and effective surface tension of water marbles

The surface of water "marbles" obtained with hydrophobic lycopodium and polyvinylidene fluoride particles was investigated first with environmental scanning electron microscopy. The shape of water marbles was studied both experimentally and theoretically. The mathematical model describing the deformation of marbles by gravity is proposed. The model allowed the calculation of the effective surface tension of marbles and gives 0.09 J/m ² for marbles coated with PVDF and 0.06 J/m² for marbles coated with lycopodium. The effective surface tensions of marbles calculated independently by the horizontal vibration of marbles were in semiquantitative agreement with the above values (0.07 J/m² for marbles coated with PVDF and 0.055 J/m² for marbles coated with lycopodium).