The innovation engine for new materials

Alexandra Paul


Saarland University, Germany




John Frostad

Faculty Sponsor(s): 

Gary Leal

Faculty Sponsor's Department: 

Chemical Engineering

Project Title: 


Project Description: 

Many everyday items such as shampoo, mayonnaise and beauty crèmes are emulsions. An emulsion consists of two or more immiscible liquids that have been mixed together to form drops of one liquid suspended in the other. Coalescence, flocculation and sedimentation can lead to phase separation of the two liquids and thereby decrease the product’s quality. Investigated herein, was a fundamental study of the time required for the coalescence of two drops interacting via a constant force. First a theoretical model that allows the compression of the drops to be treated as Hookean springs was validated. Hence it was possible to calculate the force, which was actually applied between the drops. With a Cantilevered-Capillary Force Apparatus (CCFA) it was possible to create small drops with a volume of a few nanoliters and to compress them together with a constant force. It was observed that the time required for coalescence, or drainage time, increases as the radius of the drop increases. However, after considering fifty measurements for each radius it could also be noticed that the drainage time varied substantially more for droplets with larger radii. Furthermore the dependence of the drainage time on a dimensionless force parameter (D) for the special case when the Capillary number is equal to D was reported. This study allows a fundamental understanding of the coalescence, forming a background for further improvements on the stability of emulsions.