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Superchaotropic or Hydrophobic Behavior? How Borate Clusters Assemble with Nonionic Surfactants
Max Hohenschutz1, Sanyukta Bhattacharje1, Olivier Diat1
1ICSM, CEA, CNRS, ENSCM, Univ. Montpellier, Marcoule, France, Centre de Marcoule, 30207Bagnols-sur-Cèze, France.
The Journal of Physical Chemistry Letters
|August 3, 2026
Summary
Anionic borate clusters interact with surfactant systems, extending the Hofmeister series. Their binding affinity and structural effects on micelles reveal new insights into ion-surfactant interactions.
Area of Science:
- Colloid and interface science
- Supramolecular chemistry
- Physical chemistry
Background:
- The Hofmeister series describes how ions affect the properties of aqueous solutions.
- Anionic borate clusters and cobaltabisdicarbollide (COSAN) are nanometer-sized ions with potential applications in various fields.
- Surfactant self-assembly into micelles is crucial for solubilization and delivery systems.
Purpose of the Study:
- To investigate the interaction of anionic borate clusters with self-assembled surfactant systems.
- To determine the binding affinity of various borate clusters and COSAN to nonionic surfactant micelles.
- To elucidate the structural consequences of these interactions on micellar systems.
Main Methods:
- Cloud point measurements to assess binding affinity.
- Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) for structural analysis.
- Synthesis and characterization of anionic borate clusters (closo-dodecaborates B12X122- and COSAN).
Main Results:
- A continuous series of binding affinity was observed, from chaotropic to superchaotropic and hydrophobic ions, extending the Hofmeister series.
- Superchaotropic ions formed interfacial monolayers, while hydrophobic ions localized within the micelle core.
- Hydrophobic ions induced micellar curvature transitions into bilayer structures, leading to destabilization and phase separation.
Conclusions:
- Anionic borate clusters and COSAN act as chaotropic, superchaotropic, or hydrophobic ions, expanding the known Hofmeister series.
- The structural behavior of these ions at the micelle interface dictates their effect on surfactant self-assembly.
- This study provides a structural basis for understanding the interaction of large anionic ions with surfactant systems.
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