title: STAND: Surface Tension for Aggregation Number Determination.
abstract: Taking advantage of the extremely high dependence of surface tension on the concentration of amphiphilic molecules in aqueous solution, a new model based on the double equilibrium between free and aggregated molecules in the liquid phase and between free molecules in the liquid phase and those adsorbed at the air/liquid interface is presented and validated using literature data and fluorescence measurements. A key point of the model is the use of both the Langmuir isotherm and the Gibbs adsorption equation in terms of free molecules instead of the nominal concentration of the solute. The application of the model should be limited to non ionic compounds since it does not consider the presence of counterions. It requires several coupled nonlinear fittings for which we developed a software that is publicly available in our server as a web application. Using this tool, it is straightforward to get the average aggregation number of an amphiphile, the micellization free energy, the adsorption constant, the maximum surface excess (and so the minimum area per molecule), the distribution of solute in the liquid phase between free and aggregate species, and the surface coverage in only a couple of seconds, just by uploading a text file with surface tension vs concentration data and the corresponding uncertainties.
authors.affiliation: Departamento de Física Aplicada, Facultade de Física, Universidade de Santiago de Compostela , 15782 Santiago de Compostela, Spain.
authors.forename: Pablo F
authors.initials: PF
authors.lastname: Garrido
authors.affiliation: Departamento de Física Aplicada, Facultade de Física, Universidade de Santiago de Compostela , 15782 Santiago de Compostela, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: Brocos
authors.affiliation: Departamento de Física Aplicada, Facultade de Física, Universidade de Santiago de Compostela , 15782 Santiago de Compostela, Spain.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Amigo
authors.affiliation: Departamento de Química Física, Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Facultade de Química, Universidade de Santiago de Compostela , 15782 Santiago de Compostela, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: García-Río
authors.affiliation: Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria , 04510 México D.F., Mexico.
authors.forename: Jesús
authors.initials: J
authors.lastname: Gracia-Fadrique
authors.affiliation: Departamento de Física Aplicada, Facultade de Física, Universidade de Santiago de Compostela , 15782 Santiago de Compostela, Spain.
authors.forename: Ángel
authors.initials: Á
authors.lastname: Piñeiro