Arrested coalescence

Project summary

Emulsions are mixtures of two immiscible liquid phases, where one phase exists as dispersed droplets in the second, continuous, phase as long as the system is stabilized against coalescence: the recombination of the dispersed phase into a single liquid region. Coalescence can be prevented by a number of mechanisms, but one common to many complex fluids like foods is the arrest resulting from colloids that provide an offsetting rheological resistance. Arrest occurs once coalescence is initiated but can not complete because of a halt in the ability to reduce droplet surface area or increase deformation to minimize system energy.

While both types of arrest play a role in practical microstructures, the surface, or Pickering, type can have significant limits on the number of connections formed between droplets because the end result is essentially a solid interfacial shell. Droplets with an internal viscoelastic resistance are more flexible in their ability to form multiple connections between droplets, even after an initial arrest event. Previous work showed that droplets containing an elastic network of crystals can initiate but not finish coalescence, creating a range of anisotropic intermediate droplet shapes, but only recently has a physical model of the process for uniform and non-uniform droplet pairs been developed. Essentially the interfacial pressure driving two droplets to minimize their area must be offset by the internal elasticity to stably arrest coalescence at an intermediate state: a liquid doublet rather than a sphere.

Project objectives

  • study the way such droplets come together in a food or consumer product microstructure
  • characterise the effects on rheology and product texture
  • model the structures formed and develop new approaches to efficient formulations