Stabilization of Silicone Oil-in-Water Emulsions by Ionic Surfactant and Electrolytes: The Role of Adsorption and Electric Charge at the Interface

Abstract

The stability of silicone oil-in-water emulsions in the presence of a cationic surfactant (viz. cetyltrimethylammonium bromide) and salts containing mono-, di-, and trivalent ions (viz. NaCl, CaCl 2 , and AlCl 3 ) is reported in this work. Addition of salt enhanced the adsorption of surfactant at the oil−water interface and had a significant effect on the zeta potential. The evolution of droplet size with time was measured by dynamic light scattering. The experimental data were fitted by a model based on drop coalescence. The stability of the emulsions increased in the presence of salt. The effectiveness of the salts investigated was in the sequence AlCl 3 > CaCl 2 > NaCl. Coalescence of a single silicone oil drop at a flat oil−water interface was studied. Addition of salt increased the drop coalescence time.

Mechanistic studies of droplet electrophoresis: A review

“…The surface charge of a droplet can be measured using standardized ‐potential measurements. The surfactant type in the system [76, 88], or the nature of the interface‐stabilizing nanoparticles [94, 95], pH [12, 38, 87], and ionic strength of the solution [96, 97] are contributing factors to the apparent surface charge or ‐potential at the droplet interface.…”

“…The influence of different surfactants (anionic, cationic, and amphoteric) on ‐potential [96–98] and EP mobility of droplets has been investigated in several studies [36, 90, 99]. Initially, the droplet interface in an O/W emulsion exhibits a negative surface charge.…”

“…It has been shown that, by adsorption of surfactant molecules at the droplet interface in O/W emulsions, the surface charge of the oil droplet changes and consequently the intensity of the EP mobility or the direction of motion is affected. Increasing the concentration of cationic surfactants changes the initially negative surface charge at the oil–water interface to a less negative value, and can even lead to charge sign reversal [96]. Contrarily, by increasing the concentration of anionic surfactants, the already negative surface charge becomes more negative.…”

“…Contrarily, by increasing the concentration of anionic surfactants, the already negative surface charge becomes more negative. In these studies, the maximum surface charge was observed near the CMC of surfactants and reached a plateau at higher concentrations [96–98]. Using an experimental study, Tuvcek et al.…”

Development of Nanoemulsion of Silicone Oil and Pine Oil Using Binary Surfactant System for Textile Finishing

“…As the surfactant concentration increased, maintaining all other parameters constant, increased viscosity of the emulsion was observed (Table 1) due to water molecules becoming trapped in the long alkyl chain of surfactant molecules increasing the effective volume fraction due to an electrical double layer of surfactant as surfactant concentration increases [24,25].…”