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Hydrophobic Ion Pairing with Cationic Surfactant Modifies Surface Activity and Colloidal Behavior of PFAS
Bishnu Pandey1, Ligaya Manalastas1, Afaq Ahmad1
1Department of Civil & Environmental Engineering, New Jersey Institute of Technology, 323 Dr. Martin Luther King Jr. Blvd., Newark, New Jersey 07102, United States.
Abstract:
Quaternary ammonium compounds (QACs) are increasingly used to enhance the removal of per- and polyfluoroalkyl substances (PFAS), particularly short-chain compounds, through hydrophobic ion pairing (HIP). Here, we investigated how HIP with cetyltrimethylammonium chloride (CTAC) influences the interfacial and colloidal behavior of selected PFAS at low-micromolar concentrations below reported critical micelle concentrations (CMCs) and across varying solution chemistries (pH, ionic strength, and natural organic matter) using surface tension measurements, dynamic light scattering (DLS), ζ-potential analysis, and transmission electron microscopy (TEM). Relative to the corresponding PFAS-only controls, CTAC (6.66 μM) reduced the surface tension of PFBA, PFBS, and PFOA solutions (3.33 μM each) by 24.64, 45.71, and 70.17%, respectively. PFOS exhibited little additional surface-tension response to CTAC but responded strongly to a shorter-chain QAC (C12), indicating that interfacial behavior depends on fluorocarbon-hydrocarbon chain-length compatibility. Targeted DLS, ζ-potential, and TEM characterization identified detectable bulk coassembly in selected PFAS-QAC systems at concentrations of 3.33-33.30 μM. Electrolyte addition produced PFAS-dependent changes in interfacial behavior, while NOM reduced the interfacial activity of several mixtures. These findings provide mechanistic insight into PFAS-QAC behavior relevant to the development of QAC-assisted PFAS separation processes.
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The Colloidal State
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A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules, atoms, and/or ions)...
Intermolecular Forces

