Characterization of ion distribution around the surface of micelles under high salt conditions using small angle neutron scattering and resonant soft x-ray scattering*

Surfactants can self-assemble into micelles once reaching critical micellar concentration. Industrially, high concentration of inorganic salts are frequently employed as additives for surfactant systems to depress the CMC of the system, enhance further growth of micelle and eventually alter the rheological behavior of targeted systems. Although frequently employed in commercial surfactant products and in biological systems, little was known about how ions behave around these aggregates under high salt condition. An ion cloud model was recently developed based on the screening effect observed in small angle neutron scattering for the high salt condition. To verify this model, resonant soft x-ray scattering was performed by setting the energy of the incident x-ray close to the absorption edge of Cl atom, which allows the manipulation of the scattering length density. The scattering contribution of the ion cloud layer can thus be obtained through the subtraction of scattering curves measured at different energies. This also allows verification of the forcefield and other protocols applied in micelle simulations and enhance the predictability of micelle behavior.
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