Emulsion droplets — What can we learn from them?
Interactions between oil droplets and solid surfaces control many applications of emulsions. The project SLIDING DROPLETS aimed to study the interaction between droplets and solid surfaces undergoing sliding contact. The project focused on hydrodynamics, surface forces, and the role of surfactants and polymers in sliding droplets' behaviour. Combining force measurements and spectroscopy allowed the scientists to 'see' and 'feel' the interaction between the droplets and the solid surfaces under sliding conditions. The team used dynamic surface tension measurements, quartz crystal microbalance and the advanced form of atomic force microscopy (AFM), interferometric AFM. The first part of the project focused on understanding how droplets or bubbles interact with solid surfaces in a liquid environment. The scientists studied droplet attachment to solid surfaces, performed for free-rising and captive droplets in solutions of varying composition. These interactions were affected by electrostatic, van der Waals and other surface forces. Results demonstrated the ability to control the interactions between a droplet and a solid surface by choosing the conformation of polymers and surfactants at the interface. Emulsion droplets are also often used as models to study the mechanics of living cells. The interaction of a surfactant-coated oil droplet with a solid surface is a useful model system for understanding cell-surface interactions. For that purpose, the second part of the project investigated the motion of emulsion droplets in microfluidic channels. The work involved design of custom microfluidic devices for the creation and surface modification of droplets, controlling the flow and monitoring droplet velocity. The scientists understood the mechanisms controlling the behaviour of droplets in microfluidic channels, which enabled very precise manipulation on droplets in microfluidic circuits. Achieving precise microfluidic droplet manipulation has an array of applications in chemistry, physics, biology and medical diagnostics. Better understanding of microfluidic droplet behaviour can advance the design of rapid, simple and low-cost diagnostic tests.
Keywords
Emulsion, droplets, hydrodynamics, surface forces, surfactants
