Break | AIChE


The wetting of a solid surface by the drop of an emulsion has been traditionally thought to be mediated by the formation of a liquid bridge that connects the drop and the surface. In the current work, we experimentally show that the spreading of a drop on a surface follows a different, new mechanism. Drops of glycerol were allowed to settle under gravity in a lighter polymeric liquid phase (silicone oil) under conditions of small Bond numbers. The approach of the drop towards the substrate was visualized using Reflection Interference Contrast Microscopy (RICM), and the details of the film drainage dynamics and the spreading process of the drop on the surface were recorded. The film shapes obtained were compared with predictions from scaling analysis. The temporal variation of the minimum film heights matched theoretical expectations, until the height reached few tens of nanometers, at which point a stable film was formed. Following this, islands were observed to grow on the substrate, one of which eventually merged with the parent drop to complete spreading. The reasons for these observations and their implications on the calculation of drainage times will be discussed.