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Interfacial ion exchange between monovalent and divalent anions in cationic micelles, revised in the light of correlation analysis
Author(s) -
Blagoeva Iva B.,
Ouarti Nadia,
El Seoud Omar A.,
Ruasse MarieFrançoise
Publication year - 2005
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.953
Subject(s) - chemistry , counterion , divalent , pulmonary surfactant , aqueous solution , cationic polymerization , inorganic chemistry , salt (chemistry) , ion exchange , micelle , base (topology) , chloride , ion , organic chemistry , mathematical analysis , biochemistry , mathematics
The pH changes of an aqueous carbonate buffer solution (9 × 10 −3 M Na 2 CO 3 , 10 −3 M NaHCO 3 , p H o 10.79), induced by addition of cetyltrimethylammonium chloride (CTA + Cl − ) in concentrations varying from 10 −3 to 10 −1 M , are employed to determine the concentration of dianionic base in the water pseudophase. The pH decreases markedly up to −0.6 pH units at 0.1 M CTA + . The pH profile is analysed in terms of the pseudophase ion‐exchange model from which the equations for mono‐/divalent anion exchanges are derived. The fit of the pH data to these equations is satisfactory only when a [CTA + ] dependence of β (the degree of counterion binding) is considered: β = 0.5 + 2[CTA + ]. The resulting exchange constant, K ex CI/CO 3 = (6.75 ± 0.22) × 10 −2 , is markedly larger than that measured previously at only one surfactant concentration without taking into account the β variation. This surfactant concentration dependence of β is discussed in terms of recent results on salt effects on the composition of micellar interfaces, which also show that β depends on the surfactant concentration in the presence or absence of any added salt. Copyright © 2005 John Wiley & Sons, Ltd.