Surfactant–Chelating Agent Interplay: Effect on Self-Assembly, Surface Properties, and Performance
Doctoral thesis, 2026
Chelating agents are common components of aqueous surfactant formulations, yet they are typically regarded as passive additives whose role is limited to metal ion sequestration. This thesis challenges that assumption by showing that chelating agents such as glutamate diacetate and methylglycinediacetate actively interact with mixed surfactant systems and significantly influence micellar organization, dynamics, and formulation cleaning performance.
A systematic multi-scale investigation was conducted using mixed surfactant systems composed of nonionic and amphoteric surfactants with varied hydrophobic chain architectures. Diffusion NMR spectroscopy, small angle neutron scattering (SANS), cloud point measurements, viscosity analysis, and interfacial performance tests were employed to probe molecular dynamics, mesoscopic structure, and macroscopic behavior.
Diffusion NMR demonstrates that chelating agents undergo dynamic association with micellar environments, despite not forming aggregates themselves. Complementary SANS measurements reveal that this association is accompanied by changes in micellar size, shape, and internal organization, with the extent of restructuring strongly dependent on surfactant architecture, particularly hydrophobic chain branching. Linear amphoteric surfactants form mixed micelles that readily reorganize upon chelating agent addition, whereas branching reduces packing adaptability and limits structural response.
The macroscopic properties reflect these molecular interactions. Cloud point and viscosity measurements identify regimes in which chelating agents counteract classical salting-out behavior, particularly in amphoteric-stabilized systems. Changes in wetting, cleaning efficiency, and foam stability further demonstrate that chelating agent concentration governs the redistribution of surfactant between bulk and interfacial regions through micellar reorganization.
Complementary SANS measurements reveal that this association is accompanied by changes in micellar size, shape, and internal organization, with the extent of restructuring strongly dependent on surfactant architecture, particularly hydrophobic chain branching. Linear amphoteric surfactants form mixed micelles that readily reorganize upon chelating agent addition, whereas branching reduces packing adaptability and limits structural response.
A systematic multi-scale investigation was conducted using mixed surfactant systems composed of nonionic and amphoteric surfactants with varied hydrophobic chain architectures. Diffusion NMR spectroscopy, small angle neutron scattering (SANS), cloud point measurements, viscosity analysis, and interfacial performance tests were employed to probe molecular dynamics, mesoscopic structure, and macroscopic behavior.
Diffusion NMR demonstrates that chelating agents undergo dynamic association with micellar environments, despite not forming aggregates themselves. Complementary SANS measurements reveal that this association is accompanied by changes in micellar size, shape, and internal organization, with the extent of restructuring strongly dependent on surfactant architecture, particularly hydrophobic chain branching. Linear amphoteric surfactants form mixed micelles that readily reorganize upon chelating agent addition, whereas branching reduces packing adaptability and limits structural response.
The macroscopic properties reflect these molecular interactions. Cloud point and viscosity measurements identify regimes in which chelating agents counteract classical salting-out behavior, particularly in amphoteric-stabilized systems. Changes in wetting, cleaning efficiency, and foam stability further demonstrate that chelating agent concentration governs the redistribution of surfactant between bulk and interfacial regions through micellar reorganization.
Complementary SANS measurements reveal that this association is accompanied by changes in micellar size, shape, and internal organization, with the extent of restructuring strongly dependent on surfactant architecture, particularly hydrophobic chain branching. Linear amphoteric surfactants form mixed micelles that readily reorganize upon chelating agent addition, whereas branching reduces packing adaptability and limits structural response.
formulation behavior.
diffusion NMR
surfactant interactions
micellar structure
chelating agents
Lecture hall Vasa B in the Vasa Hus 2 building on Campus Johanneberg
Opponent: Professor, Gerardo Palazzo University of Bari, Italy.
Author
Josmary Alejandra Velasquez Cano
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Josmary Velásquez, Alexander Idström, Lars Evenäs, and Romain Bordes. Tail branching in mixed ionic/nonionic surfactant systems with chelating agents. Effect of branching of the ionic surfactant
Josmary Velásquez, Clémence Le Coeur, Lorenzo Metilli, Anne-Laure Fameau, Lars Evenäs, and Romain Bordes. Tail branching in mixed ionic/nonionic surfactant systems with chelating agents. Combined branching of amphoteric and nonionic surfactants
Josmary Velásquez, Lars Evenäs, and Romain Bordes. Amphoteric surfactant–chelating agent interactions governing emulsification, foaming, and cleaning behavior
Surfactants and chelating agents are key components of everyday products such as detergents and shampoos. Surfactants contain a water-attracting part and a part that prefers oily or greasy substances, enabling dirt and grease to be dispersed in water and removed. To achieve this, they spontaneously organize into small molecular assemblies called micelles, whose structure controls formulation performance. Chelating agents have traditionally been regarded as passive additives, with a role limited to neutralizing ions that interfere with cleaning efficiency. This thesis challenges that view by showing that chelating agents can actively interact with surfactant systems and influence their self-assembly, dynamics, and performance.
Using a combination of experimental techniques—including nuclear magnetic resonance spectroscopy (NMR), small-angle neutron scattering (SANS), and cloud point measurements—this work investigates mixed surfactant systems across multiple length scales. On the molecular scale, NMR measurements show that chelating agents dynamically associate with micellar environments in a manner that depends on chemical structures and concentrations, while SANS reveals how these interactions drive changes in micellar size and shape at the nanoscale. These molecular- and meso-scale differences explain variations in macroscale behavior, including cloud point, viscosity, wetting, foam stability, and cleaning efficiency.
Overall, this thesis demonstrates that chelating agents are not merely passive background components but active, structure-sensitive additives that influence micellar organization and formulation performance. Recognizing this role enables more rational and efficient formulation design.
Using a combination of experimental techniques—including nuclear magnetic resonance spectroscopy (NMR), small-angle neutron scattering (SANS), and cloud point measurements—this work investigates mixed surfactant systems across multiple length scales. On the molecular scale, NMR measurements show that chelating agents dynamically associate with micellar environments in a manner that depends on chemical structures and concentrations, while SANS reveals how these interactions drive changes in micellar size and shape at the nanoscale. These molecular- and meso-scale differences explain variations in macroscale behavior, including cloud point, viscosity, wetting, foam stability, and cleaning efficiency.
Overall, this thesis demonstrates that chelating agents are not merely passive background components but active, structure-sensitive additives that influence micellar organization and formulation performance. Recognizing this role enables more rational and efficient formulation design.
Hydrotroper i rengöringsformuleringar
Swedish Foundation for Strategic Research (SSF) (ID20-0039), 2021-06-01 -- 2026-05-31.
Subject Categories (SSIF 2025)
Physical Chemistry
DOI
10.63959/chalmers.dt/5826
ISBN
978-91-8103-369-4
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5826
Publisher
Chalmers
Lecture hall Vasa B in the Vasa Hus 2 building on Campus Johanneberg
Opponent: Professor, Gerardo Palazzo University of Bari, Italy.