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Location of Pinacyanol in Micellar Solutions of N-Alkyl Trimethylammonium Bromide Surfactants

✍ Scribed by Raimon Sabaté; Montserrat Gallardo; Joan Estelrich

Book ID
102585721
Publisher
Elsevier Science
Year
2001
Tongue
English
Weight
79 KB
Volume
233
Category
Article
ISSN
0021-9797

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✦ Synopsis

The interaction of pinacyanol (PIN), a cationic dye formed by monomer and dimer species, with three cationic surfactants (DTAB, TTAB, and HTAB) has been studied spectroscopically and by acidbase equilibrium in the micellar concentration range. In the presence of surfactants, the absorption maximum of the two main peaks undergoes bathochromic shifts. The spectral shifts suggest a hydrophobic environment of the chromophore. The presence of micelles favors the monomer species; i.e., it reduces the extent of dimerization. The pK a of PIN in micellar medium is similar to the value in pure water. When acid-base equilibrium was considered, the changes in the interfacial pK a allowed to us to determine the constant dielectric for the interfacial region (ε = 69). This led to the conclusion that the dye must be solubilized between the solution and the hydrocarbon chain core, i.e., in the aqueous micellar interface. This location can be explained by a cation-π interaction between the uncharged ring system of the dye and the cationic headgroups of the surfactants.

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