This work reports a Dynamic Light Scattering study on aqueous micelles formed by tetradecyl dialkylammonium propanesulfonate surfactants (sulfobetaines; with alkyl = methyl, ethyl, n‑propyl and n‑butyl) within a range of surfactant concentrations (0.01–0.40 M) both in pure water and in the presence of various concentrations of NaBr, NaOH and NaClO4 (0.02–0.50 M NaBr; 0.10–1.00 M NaOH; 0.005–0.50 M NaClO4). From values of diffusion coefficients, D, we obtained micellar hydrodynamic radii, Rh, by application of the Stokes-Einstein relation. Plots of D vs. sulfobetaine concentrations can be qualitatively explained with a model based on a linear interaction theory, which allowed to separate thermodynamic and hydrodynamic perturbations to D. Results show that: i) formally neutral sulfobetaine micelles become negatively charged by preferential interaction with strongly interacting, “soft” anions; ii) the surface negative charge increases with the hydrophobicity of the anions; iii) bulkier alkyl substituents on the sulfobetaine head groups lead to less charged, less hydrated aggregates, which result in opposite perturbations to D; (iv) highly hydrated, high charge density hydroxide ions lead to an increase of micellar sizes through a disc-like growth pattern.

Surface charge modulation of sulfobetaine micelles by interaction with different anions: A dynamic light scattering study

Di Profio, P.
Primo
;
Fontana, A.
Penultimo
;
Canale, V.
Ultimo
2019

Abstract

This work reports a Dynamic Light Scattering study on aqueous micelles formed by tetradecyl dialkylammonium propanesulfonate surfactants (sulfobetaines; with alkyl = methyl, ethyl, n‑propyl and n‑butyl) within a range of surfactant concentrations (0.01–0.40 M) both in pure water and in the presence of various concentrations of NaBr, NaOH and NaClO4 (0.02–0.50 M NaBr; 0.10–1.00 M NaOH; 0.005–0.50 M NaClO4). From values of diffusion coefficients, D, we obtained micellar hydrodynamic radii, Rh, by application of the Stokes-Einstein relation. Plots of D vs. sulfobetaine concentrations can be qualitatively explained with a model based on a linear interaction theory, which allowed to separate thermodynamic and hydrodynamic perturbations to D. Results show that: i) formally neutral sulfobetaine micelles become negatively charged by preferential interaction with strongly interacting, “soft” anions; ii) the surface negative charge increases with the hydrophobicity of the anions; iii) bulkier alkyl substituents on the sulfobetaine head groups lead to less charged, less hydrated aggregates, which result in opposite perturbations to D; (iv) highly hydrated, high charge density hydroxide ions lead to an increase of micellar sizes through a disc-like growth pattern.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11564/701221
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