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Behavior of cationic surfactants in poly(styrene sulfonate) brushes / Akira Ishikubo in Industrial & engineering chemistry research, Vol. 47 N°17 (Septembre 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N°17 (Septembre 2008) . - p. 6426–6433 Titre : Behavior of cationic surfactants in poly(styrene sulfonate) brushes Type de document : texte imprimé Auteurs : Akira Ishikubo, Auteur ; Jimmy Mays, Auteur ; Matthew Tirrell, Auteur Année de publication : 2008 Article en page(s) : p. 6426–6433 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Cationic  surfactant  Adsorption  Electrostatic  interactions  Hydrophobic  interactions Résumé : The adsorption behavior of a cationic surfactant (cetyl trimethyl ammonium bromide, CTAB) in a sodium poly(styrene sulfonate) (NaPSS) brush in the presence of 1 mM NaNO3 was investigated by ellipsometry. The interactions between surfactants and brush chains determined from these results are compared with data from other types of experiments on similar systems. Four adsorption regimes were found, including regimes dominated by electrostatic interactions and by hydrophobic interactions. As the concentration of the surfactant increased from zero in the bulk solution surrounding the PSS brush, (1) surfactant monomers replaced Na+ ions reversibly, in a manner analogous to ion exchange, until β (the ratio of the number of bound surfactants to the total number of negatively charged monomers of PSS) reached 0.2−0.3 (1 × 10−6 M CTAB), (2) surfactants in the brushes interacted with each other hydrophobically, making adsorption irreversible and producing contraction of the brush (0.3 < β < 0.4), (3) the rate of adsorption increase was suppressed, by the squeezing out of available volume in the shrinking brush (β = 0.4), (4) additional uptake of surfactants took place above 1 × 10−4 M CTAB in bulk solution (still 1 order of magnitude lower than the critical micelle concentration (cmc) of CTAB), because of the hydrophobic aggregation of surfactants on surfactant−polyelectrolyte complexes in the brushes. The overall conclusion and insight gained from this work is that surfactants are taken up, even at micromolar concentrations, extensively and in a nonlinear, cooperative fashion, in polyelectrolyte brushes. These data imply that the properties expected from highly hydrated polyelectrolyte brushes (steric protection, lubricity) are strongly modified by the presence of oppositely charged surfactants. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800004w [article] Behavior of cationic surfactants in poly(styrene sulfonate) brushes [texte imprimé] / Akira Ishikubo, Auteur ; Jimmy Mays, Auteur ; Matthew Tirrell, Auteur . - 2008 . - p. 6426–6433. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N°17 (Septembre 2008) . - p. 6426–6433 Mots-clés : Cationic  surfactant  Adsorption  Electrostatic  interactions  Hydrophobic  interactions Résumé : The adsorption behavior of a cationic surfactant (cetyl trimethyl ammonium bromide, CTAB) in a sodium poly(styrene sulfonate) (NaPSS) brush in the presence of 1 mM NaNO3 was investigated by ellipsometry. The interactions between surfactants and brush chains determined from these results are compared with data from other types of experiments on similar systems. Four adsorption regimes were found, including regimes dominated by electrostatic interactions and by hydrophobic interactions. As the concentration of the surfactant increased from zero in the bulk solution surrounding the PSS brush, (1) surfactant monomers replaced Na+ ions reversibly, in a manner analogous to ion exchange, until β (the ratio of the number of bound surfactants to the total number of negatively charged monomers of PSS) reached 0.2−0.3 (1 × 10−6 M CTAB), (2) surfactants in the brushes interacted with each other hydrophobically, making adsorption irreversible and producing contraction of the brush (0.3 < β < 0.4), (3) the rate of adsorption increase was suppressed, by the squeezing out of available volume in the shrinking brush (β = 0.4), (4) additional uptake of surfactants took place above 1 × 10−4 M CTAB in bulk solution (still 1 order of magnitude lower than the critical micelle concentration (cmc) of CTAB), because of the hydrophobic aggregation of surfactants on surfactant−polyelectrolyte complexes in the brushes. The overall conclusion and insight gained from this work is that surfactants are taken up, even at micromolar concentrations, extensively and in a nonlinear, cooperative fashion, in polyelectrolyte brushes. These data imply that the properties expected from highly hydrated polyelectrolyte brushes (steric protection, lubricity) are strongly modified by the presence of oppositely charged surfactants. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800004w