Low‐Field High‐Resolution PFG‐NMR to Predict the Size Distribution of Inner Droplets in Double Emulsions

Monitoring the Early Stages of Formation of Oil-Water Emulsions Using Flow Cytometry

Characterization of complex oil emulsions is critical yet challenging both in science and in many industrial applications. Here we demonstrate for the first time the use of flow cytometry as a fast method for characterizing complex, polydisperse oil-water emulsions. Owing to our interest in understanding how the presence of specific ions might affect the properties of oil-water emulsions including size, polydispersity, and complexity, we present a systematic study of oil emulsions in deionized water and various brines of different ionic strength. Forward scatter (FSC) and side scatter (SSC) intensities associated with detailed statistics were judiciously combined to provide a better understanding of these complex systems. We find that the type and concentration profiles of ions around the oil droplets affect significantly the properties of the emulsion. Weakly hydrated cations NH₄⁺ and Ca²⁺ appear to be more effective in screening the charge of oil droplets compared to the monovalent Na⁺ and divalent Mg²⁺ ions, respectively. As a result, coalescence and formation of larger droplets are seen in the case of NH₄Cl and CaCl₂ compared to NaCl and MgCl₂, respectively. In addition, weakly hydrated anions such as Cl^- can come closer to the oil surface and, thus, decrease the effective screening that the Na⁺ ions provide as compared to SO₄^2- ions, which leads to more stable emulsions in NaCl compared to Na₂SO₄. In addition to these specific findings, the work demonstrates the utility of the technique as a new tool for characterizing oil emulsions in a wide spectrum of fields ranging from food to oil and gas applications.