title: Sphere to rod transitions in homologous alkylpyridinium salts: a Stauff-Klevens-type equation for the second critical micelle concentration.
abstract: In the present paper, we analyze the dependence of the second critical micelle concentration (second cmc) of ionic amphiphiles on the number of atoms in the hydrocarbon molecular chain, n(c). A molecular thermodynamic model for the interaction energy between the end caps of rodlike micelles, g(N), is introduced and the linear dependence of this object on n(c) analyzed, thus leading to a Stauff-Klevens-like behavior of the second cmc. The predictions agree with previously reported data for n-alkyldimethylbenzylammonium chloride (C(n)BACl) for n-alkylpyridinium chloride (C(n)PyCl) and n-alkyltrymethylammonium bromide (C(n)TABr) at 35 degrees C. These conclusions are reinforced by the conductivity, density, and ultrasound velocity measurements of the second cmc of several C(n)PyCl (n=12, 14, 16) and n-alkylpyridinium bromides (C(n)PyBr, n=12, 14, 15, 16) presented in this paper.
authors.affiliation: Grupo de Materia Condensada Blanda, Departamento de Física de la Materia Condensada, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
authors.forename: A
authors.initials: A
authors.lastname: González-Pérez
authors.forename: L M
authors.initials: LM
authors.lastname: Varela
authors.forename: M
authors.initials: M
authors.lastname: García
authors.forename: J R
authors.initials: JR
authors.lastname: Rodríguez