Polyhedral oligomeric silsesquioxane as co-surfactant in stabilizing highly concentrated emulsion with an overcooled dispersed phase

Abstract

This study investigated water-in-oil (w/o) super-concentrated emulsions used as pumpable explosives. The aqueous phase of the emulsions is a supersaturated nitrate salt solution (at room temperature), with a mass fraction of approximately 0.9. Instability of such emulsions arises either from crystallization of the dispersed phase in the system during ageing or under high shear conditions. Here, we report an alternative approach to stabilize emulsion explosives by using Polyhedral Oligomeric Silsesquioxane (POSS) as a co-surfactant to PIBSA (i.e. polyisobutylene succinic anhydride), in replacement of conventional co-surfactants, Span 80 or Tween 80. The interfacial tension, interfacial elasticity, refinement time, stability under high shearing as well as stability during storage have been investigated. It has been found that first, conversely to the standard co-surfactant Span 80, POSS can generate a more complex and very resistant interfacial film that has no tendency to induce crystallization in the system. Second, unlike conventional mixtures, PIBSA-MEA/POSS mixture confers outstanding stability to the emulsion not only under high shearing but most importantly during storage. In presence of POSS the emulsion explosives stabilization occurs through a reinforced interfacial skin rather than the usual mechanical barrier of reverse micelles in the inter-droplet layer. This new mechanism is much more effective than the conventional one and allows for a significant reduction in the total surfactant concentration required to stabilize the sheared as well as un-sheared emulsions. We propose that through the synergetic interaction POSS occupy the free spaces between the bulky polymeric PIBSA molecules and create a reinforced condensed layer at the interface.