Nonionic surfactants are widely used in many industrial applications ranging from emulsion polymerization to crude oil production. The solubility of a nonionic surfactant in water, however, decreases with increasing temperature, until the surfactant becomes insoluble when reaching the cloud point temperature. Moreover, the presence of electrolyte in aqueous solutions suppresses the cloud point of a nonionic surfactant. The decrease in aqueous solubility with increasing temperature and electrolyte concentration makes it particularly challenging for application of nonionic surfactants in this type of environment. In order to enhance the solubility of nonionic surfactants in electrolyte solutions and at elevated temperatures, additives such as hydrotropes, solvents, and co-surfactants are used in surfactant formulations. In this presentation, we will describe an approach to enhance the solubility of polyethoxylated nonionic surfactants in electrolyte solution by addition of di-sulfonated anionic surfactants. Although it is generally accepted that the solubility of polyethoxylated nonionic surfactants in water increases linearly with increasing the level of ethylene oxide units in the molecule, our studies show that in the presence of a di-sulfonated anionic hydrotrope in solutions containing high levels of electrolyte, the dependence of cloud point on the ethylene oxide chain length departs from this linear trend. Our results suggest that optimal solution stability can be achieved by tailoring the number of ethylene oxide units in the nonionic surfactant molecule to an optimal length, by decreasing the length of the hydrocarbon tail of the di-sulfonated anionic surfactant, and by varying the concentration of the anionic surfactant in solution. Finally, we will present diffusion NMR studies performed to obtain fundamental insights into the self-assembly of these surfactant systems, which suggest that anionic surfactants with different molecular structures lead to enhanced solubility of polyethoxylated nonionic surfactants in electrolyte solution by different mechanisms.

Enhanced solubility and self-assembly of nonionic surfactants in electrolyte solution

251st National Meeting (2016)

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