Holographic microscopy of micron-sized droplets at liquid-liquid interfaces

When a millimetre-scale or larger bubble or droplet reaches a fluid-fluid interface, and after the liquid film between it and the interface has drained, it should form a three-phase contact line and change shape according to the surface tension and the viscosity of the fluids. Studies have mainly looked at the behaviour of these large drops using conventional imaging methods such as bright-field video microscopy. These conventional methods, however, are not suitable for smaller, micrometre-sized droplets. We describe how by using digital holography microscopy, we are able to obtain high precision, three dimensional information about the position and behaviour of droplets and bubbles. We also show an example demonstrating how this method can be used to look at the dynamic behaviour of a droplet before and after reaching a fluid-fluid interface.