Investigation on Drop Formation Process by CaBER ‘Hanging Drop’ Experiments

Abstract

We use a commercial apparatus, the Capillary Breakup Extensional Rheometer (CaBER from ThermoFisher Scientific), in an unconventional way, and present the CaBER “hanging drop” experiment as a possible tool for studying drop formation process. In the CaBER ‘hanging drop’ experiments a microsyringe is used to place a drop of liquid onto the upper plate to create a drop hanging in the air. The volume of the drop is sufficiently small (up to a couple of tenths of microliters), so that surface tension of the liquid successfully overpowers the gravity and the formed hanging drop has a more or less, hemispherical shape. Then, the upper plate is suddenly moved in vertical direction, at a given speed, to reach the maximum distance the instrument allows. Inertial and gravity forces resist the sudden movement of the drop, caused by its adhesion to the moving plate. Thus, the continuous extension, deformation and movement of the drop take place. The drop movement and the shape evolution are monitored by a high speed video camera. The drop movement and the shape evolution depend on experimental conditions (i.e. the drop volume, the speed of the upper plate movement) and on the physicochemical properties of the liquid. The presented method is especially suited for studying influence of the free surface curvature effects and drop shape evolution on the breakup process.