Specific anion effects on the interfacial properties and aggregation of alkylphenol ethoxylate surfactants

The effect of Hofmeister anions on aggregation of nonionic surfactants and the formation of microemul-sion systems was evaluated. Added salt effects on the interfacial properties and aggregation of ethylene oxide condensates of nonylphenol were characterized by cloud point measurements, surface tension, flu-orescence spectroscopy, light scattering, and formulation scans. The specific effects of anions on the cloud point followed the trend predicted by the Hofmeister series: H2PO4- < Cl- < Br- < NO3 -< I- < SCN-, with the H2PO4- being the most kosmotropic anion and generating the most significant cloud point reduction. The specific effects of anions on the critical micelle concentration (CMC) also followed the Hofmeister ser-ies, with kosmotropic anions causing a decrease and chaotropic anions generating an increase in the CMC. Chaotropic anions decreased the size of the aggregates, while kosmotropic anions increased it, as evalu-ated by dynamic light scattering. The effect of Hofmeister anions on microemulsion formation in nonionic surfactant-oil-water (SOW) systems was assessed by formulation scans. Although the kosmotropicity of the anion did not influence the optimum formulation value, it did affect the phase behavior around the optimum formulation, pointing to the possibility of tuning microemulsion formulations via the choice of added electrolyte. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

The study evaluated the effect of Hofmeister anions on nonionic surfactants and microemulsion systems, finding that different anions have specific impacts on aggregation and microemulsion formation, with the order of ions affecting the size of aggregates and the process of microemulsion formation.