The effects of finite amplitude drop shape oscillations on the inference of material properties

Acoustic levitation of drops provides a non-contact means of isolation, stable positioning and static and dynamic manipulation. Despite a long history of the use of drop shape oscillations to infer both surface and bulk material properties, and an equally long history of observing behaviors that result in incorrect inference of material properties, researchers continue to employ finite amplitude oscillations for their experimental observations. In this study we use the inference of surface tension and viscosity of known samples of glycerin-water mixtures to illustrate the fact that finite-amplitude oscillations are the dominant mechanism for many reports of ill-behaved drop dynamics, including modal peak-splitting, vorticity, and strong field-coupling. Since this “bad” behavior leads to incorrect inferences of surface tension and viscosity, we show that small amplitude oscillations yields recovery of correct inferences for these properties for known samples. Finally, we show results from experiments with bovine and human blood. [Work supported by NSF grant # 1438569.]