Emulsification in binary liquids containing colloidal particles: a structure-factor analysis

TL;DR

This study uses confocal microscopy and structure-factor analysis to quantitatively investigate the microstructure and droplet formation mechanisms in particle-stabilized emulsions during phase separation.

Contribution

We developed a novel image-analysis method based on structure factors to analyze emulsion microstructures from confocal images, capturing early nucleation and droplet size evolution.

Findings

Emulsions are stabilized by interfacial particles over experimental times.

Droplet size distributions are likely bimodal due to coalescence and creaming.

Droplet growth is influenced by creaming during early emulsification stages.

Abstract

We present a quantitative confocal-microscopy study of the transient and final microstructure of particle-stabilised emulsions formed via demixing in a binary liquid. To this end, we have developed an image-analysis method that relies on structure factors obtained from discrete Fourier transforms of individual frames in confocal image sequences. Radially averaging the squared modulus of these Fourier transforms before peak fitting allows extraction of dominant length scales over the entire temperature range of the quench. Our procedure even yields information just after droplet nucleation, when the (fluorescence) contrast between the two separating phases is scarcely discernable in the images. We find that our emulsions are stabilised on experimental time scales by interfacial particles and that they are likely to have bimodal droplet-size distributions. We attribute the latter to coalescence together with creaming being the main coarsening mechanism during the late stages of emulsification and we support this claim with (direct) confocal-microscopy observations. In addition, our results imply that the observed droplets emerge from particle-promoted nucleation, possibly followed by a free-growth regime. Finally, we argue that creaming strongly affects droplet growth during the early stages of emulsification. Future investigations could clarify the link between quench conditions and resulting microstructure, paving the way for tailor-made particle-stabilised emulsions from binary liquids.