The effect of the surfactant hydrophilic groups and concentration of electrolyte in an internal aqueous phase on the interfacial interactions and rheology of highly concentrated emulsions

Abstract

Emulsion explosives are classified as highly concentrated Water-in-Oil emulsions with an internal phase volume fraction of approximately 94%, i.e. far beyond the close packing limit of spherical droplets of 74%. These emulsions are thermodynamically unstable compounds and their instability is related to the crystallisation in the dispersed phase, which is a supersaturated solution of ammonium nitrate salt in water. This presents a problem, because the emulsion weakens or becomes unstable, which results in droplet crystallisation, so that the explosive generally loses at least some of its sensitivity to detonation. Considerable effort has been applied to the improvement of emulsion stability by explosive manufacturers, but important aspects such as the effect of salt and surfactant content/type in emulsions are not fully understood and described in the literature. The purpose of this study was to investigate these shortcomings and to focus on the effect of surfactant nature and concentration and electrolyte concentration/type on the interfacial properties and interactions in emulsion explosives. Interfacial properties (interfacial tension and interfacial elasticity), thermal behaviour (freezing temperatures) of emulsions and rheological aspects (viscoelastic and flow properties) were investigated in terms of surfactant-electrolyte interactions.