Shape and structure formation of mixed nonionic–anionic surfactant micelles

  • Aqueous solutions of a nonionic surfactant (either Tween20 or BrijL23) and an anionic surfactant (sodium dodecyl sulfate, SDS) are investigated, using small-angle neutron scattering (SANS). SANS spectra are analysed by using a core-shell model to describe the form factor of self-assembled surfactant micelles; the intermicellar interactions are modelled by using a hard-sphere Percus–Yevick (HS-PY) or a rescaled mean spherical approximation (RMSA) structure factor. Choosing these specific nonionic surfactants allows for comparison of the effect of branched (Tween20) and linear (BrijL23) surfactant headgroups, both constituted of poly-ethylene oxide (PEO) groups. The nonionic–anionic surfactant mixtures are studied at various concentrations up to highly concentrated samples (ϕ ≲ 0.45) and various mixing ratios, from pure nonionic to pure anionic surfactant solutions. The scattering data reveal the formation of mixed micelles already at concentrations below the critical micelle concentration of SDS. At higher volume fractions, excluded volume effects dominate the intermicellar structuring, even for charged micelles. In consequence, at high volume fractions, the intermicellar structuring is the same for charged and uncharged micelles. At all mixing ratios, almost spherical mixed micelles form. This offers the opportunity to create a system of colloidal particles with a variable surface charge. This excludes only roughly equimolar mixing ratios (X≈ 0.4–0.6) at which the micelles significantly increase in size and ellipticity due to specific sulfate–EO interactions.

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Author:Michael LudwigORCiDGND, Ramsia GeislerORCiDGND, Sylvain PrévostORCiDGND, Regine von KlitzingORCiDGND
Parent Title (English):Molecules
Place of publication:Basel
Document Type:Article
Date of Publication (online):2021/07/07
Date of first Publication:2021/07/07
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2022/10/18
Tag:Brij 35; BrijL23; SDS; Tween20; micelles; mixed micelles; polysorbate 20; small-angle neutron scattering; surfactant
Issue:14, art. 4136
Page Number:23
First Page:1
Last Page:23
Institutes:Medizin / Medizin
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 4.0