Formation and stability of highly concentrated emulsions (gel emulsions): influence of aromatic aliphatic hydrocarbon interactions

Abstract

Gel emulsions are high-internal-phase-ratio emulsions which form in ternary water/nonionic surfactant/oil systems. Their structure resembles that of foams, they possess a gel appearance and their visual aspect can vary from transparent to translucent or white depending on composition variables and temperature. Because of these peculiar properties, gel emulsions are interesting materials both for scientific studies and applications.

In previous investigations it was found that the PIT of the ternary system had a great influence on the formation and stability of these emulsions. Formation of w/o gel emulsions was only possible at temperatures above the PIT and maximum stability was found at temperatures higher than the PIT by 20–25 °C. PIT values of ternary systems containing aromatic hydrocarbons are much lower than those of systems containing aliphatic hydrocarbons. However, gel emulsions did not form using aromatic hydrocarbons and polyethylene glycol alkyl ether derivatives as emulsifiers. This had been attributed to a specific interaction between aromatic hydrocarbons and ethylene oxide with increased oil penetration in the surfactant layer. Nevertheless, gel emulsion formation with aromatic hydrocarbons was achieved using sorbitan derivatives or monoglycerides but failed with ethoxylated sorbitan derivatives. The specific interaction of aromatic hydrocarbons with polyethylene-oxide can be overcomed by using mixtures of aromatic and aliphatic hydrocarbons. This interaction has been studied using equilibrium phase behavior, interfacial tension, conductivity and H¹ NMR. In this paper we present results concerning the formation and stability of gel emulsions formed with mixtures of aromatic and aliphatic hydrocarbons. These results are discussed on the basis of equilibrium and nonequilibrium properties of the system, in particular the structure of the continuous phase.