Limits of oscillation frequencies in drop and bubble shape tensiometry

To determine the dilational rheology of surface layers, the profile analysis tensiometry can be used with oscillating drops or bubbles. The methodology limits for these oscillations depend on the liquids' properties, such as density, viscosity and surface tension. For the most frequently studied water/air interface, the maximum oscillation frequency is of the order of 1 Hz, although much higher frequencies are technically feasible by the existing profile analysis tensiometers. For f > 1 Hz, deviations of the drops/bubbles from the Laplacian shape mimic non-zero dilational elasticities for the pure water/air and ethanol/air interface. For liquids of higher viscosity, the critical frequency is much lower.