Stabilisation of Emulsions by Trapped Species

TL;DR

This paper develops a theoretical framework to determine the stability conditions of emulsions containing trapped species, extending previous models to account for polydispersity and different coarsening mechanisms, with implications for emulsion stabilization.

Contribution

It derives a general stability condition for emulsions with trapped species, considering polydispersity and distinguishing coarsening types, advancing understanding of emulsion stabilization strategies.

Findings

Derived a stability condition based on initial droplet volume

Identified differences between nucleated and spinodal coarsening

Showed how trapped species can be used to restabilize emulsions

Abstract

We consider an emulsion whose droplets contain a trapped species (insoluble in the continuous phase), and study the emulsion's stability against coarsening via Lifshitz-Slyozov dynamics (Ostwald Ripening). Extending an earlier treatment by Kabalnov et al(Colloids and Surfaces, 24,(1987), 19-32), we derive a general condition on the mean initial droplet volume which ensures stability, even when arbitrary polydispersity is present in both size and composition of the initial droplets. We distinguish "nucleated" coarsening, which requires either fluctuations about the mean field equations or a tail in the initial droplet size distribution, from "spinodal" coarsening in which a typical droplet is locally unstable. A weaker condition for stability, previously suggested by Kabalnov et al., is sufficient only to prevent "spinodal" coarsening and is best viewed as a condition for metastability. The coarsening of unstable emulsions is considered, and shown at long times to resemble that of ordinary emulsions (with no trapped species), but with a reduced value of the initial volume fraction of dispersed phase. We discuss the physical principles relevant to the stability of emulsions with trapped species, describing how these may be exploited to restabilise partially coarsened emulsions and to "shrink" previously formed emulsion droplets to form "miniemulsions".