Industrial applications of water-based surfactant systems often require the use of chelating agents to deal with water hardness. Nevertheless, including chelating agents reduces surfactant solubility preventing the formulation of concentrated systems. With current trends aiming to transport less water and develop more efficient cleaning products, understanding how to overcome stability issues in common formulations is of utmost importance.

In this work, specific interactions between chelating agents and surfactants are hypothesized to influence both the self-assembly process and the macroscopic properties of surfactant formulations.

To investigate these interactions and their relationship to the chemical structures of the surfactant and chelating agent, NMR spectroscopy was employed, focusing on 13C chemical shift and line shape analysis. Moreover, the impact of these interactions on the formulation properties was assessed by measuring cloud point, viscosity, surface tension, and contact angle on hydrophobic surfaces.

The study reveals that interactions between the head group of amphoteric surfactants and chelating agents of the aminopolycarboxylate types, such as GLDA and MGDA, lead to the formation of oligomeric surfactant analogues with larger hydrophilic moieties. The interaction between the species results in smaller, more spherical micelles, that can be used to increase the solubility of nonionic ethoxylated surfactants in mixed micellar systems. The interaction offers possibilities for tuning the aggregation behavior of systems containing surfactants and chelating agents, and consequently, the macroscopic properties of the formulation.

References:
Velásquez, J., Evenäs, L., & Bordes, R. (2024). The role of chelating agent in the self-assembly of amphoteric surfactants. Journal of Colloid and Interface Science, 676, 1079-1087.
Velásquez, J., Lundgren, S., Evenäs, L., & Bordes, R. Amphoteric Surfactant-Chelating Agent Interactions: Impact on Bulk and Surface Properties. Available at SSRN 5120630.