Ejected microcrystals probe jammed states of droplets in cyclodextrin-based emulsions

Abstract

The cyclodextrin (CD)-based emulsions exhibit complex instability behaviors such as rapid flocculation and creaming, and how to capture droplet dispersion states of the emulsions remains a great challenge. Here we prepare the CD-based emulsions with different oil-water volume ratios and CD concentrations by using high-pressure homogenization, and characterize the emulsion droplets by using optical microscopy and confocal laser scanning microscopy. We evaluate the effects of homogenization pressure on the stability of the emulsions, identify armored droplets with different surface features, measure interfacial concentrations of adsorbed ICs microcrystals, and observe ejection of the oil/CD inclusion complexes (ICs) microcrystals from the droplet surface. The droplet dispersion states are sensitive to the dynamic buildup and evolving morphologies of the interfacial microcrystals, and there are clear correlations between the properties of the ejected microcrystals and the characteristics of the emulsions. We ascribe the subsequent ejection of ICs microcrystals from the droplet surface to consolidation and deformation of the films formed between neighboring droplets. The ejection of the ICs microcrystals affords a simple method to detect the droplet-droplet interactions and phase transitions in the CD-based emulsions, which might be a generic feature in the broader context of the creaming processes of emulsions.