Charge–Dipole Attraction as a Surface Interaction between Water Droplets Immersed in Organic Phases

Abstract

The dynamic behavior of emulsion droplets during their interactions with one another or with solid surfaces plays a paramount role in their ultimate stability in various applications. While the interaction of oil droplets through a surrounding aqueous phase is well understood, recent studies on the interaction of water droplets through a surrounding pure organic phase showed the presence of an unexplained attraction between water droplets at relatively long ranges. In this research study, we propose fixed-surface-charge−bulk-dipole attraction as a new interaction force between water-in-oil droplets and then derive an equation for its disjoining pressure. The behavior of water droplets in the presence and absence of this charge−dipole interaction was numerically quantified using the Stokes− Reynolds−Young−Laplace model and compared to the experimental data. Numerically calculated net force curves are in excellent agreement with experimental data from the literature when charge−dipole attraction is included, while they deviate in its absence. In addition, the water droplet and thin oil film profiles in the presence and absence of charge−dipole attraction were calculated and compared. This research indicates that charge−dipole attraction can adequately explain the mysterious force observed in some studies, which demonstrates its unexplored potential to capture the physical properties and dynamic behavior of water droplets in organic phases with useful implications to unravel unidentified interactions between emulsion droplets in different industries.

Effect of Oil-Soluble/Water-Soluble Surfactants on the Stability of Water-in-Oil Systems, an Atomic Force Microscopy Study

“…When two droplets were driven close enough, they tend to coalesce into one droplet. As for the source of the attraction between water droplets, Afsaneh et al 30 suggested that the attraction originates from the charge−dipole interaction by building a model and fitting data from the published literature. 31 Further research is still demanded.…”

Drop‐on‐Demand Electrohydrodynamic Printing of Nematic Liquid Crystals

“…[45][46][47] As the entire EHD printing process was conducted at room temperature and standard atmospheric pressure, we do not anticipate any potential instability caused by such external factors on the droplet profiles after the printing process has been completed. [48,49] This is because the shape of the droplets is determined by the interplay between the interfacial tension, gravitational force, and droplet size. The droplet sizes presented in this work are consistently less than 1 mm, where surface tension forces dominate compared to other external factors such as atmospheric pressure and the gravitational force.…”

Variability of entropy force and its coupling with electrostatic and steric hindrance interactions

“…The potential of mean force, or effective interaction potential (EIP), between particles (where the term 'particle' encompasses molecules, colloidal particles, and clusters) plays a crucial role in various contexts, such as collision rates [1,2], dispersion stability [3][4][5], ion-ligand association [6,7], particle assembly [8], enrichment and fractionation during hydrothermal transport process [9,10]. Although the EIP acquires distinct names in different situations, the underlying phenomena share common features.…”