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Counterion effect on the solution and thermodynamic properties of lithium perfluoroalkanoates

2005; Taylor & Francis; Volume: 103; Issue: 24 Linguagem: Inglês

10.1080/00268970500290284

1362-3028

Elena Blanco, Paula V. Messina, Juan M. Ruso, Gerardo Prieto, Félix Sarmiento,

Chemical and Physical Properties in Aqueous Solutions

Abstract The isotherms of conductivity of lithium perfluorooctanoate and perfluoroundecanoate were measured and the critical micelle concentration, cmc, degree of ionization of the micelles, β, determined in a range of temperatures above the Krafft point. The thermodynamic parameters, Gibbs free energy, , enthalpy , and entropy of micelle formation, were determined from a proposed thermodynamic model. Apparent molar volume and the apparent molar adiabatic compressibility for both surfactants have been calculated over a wide concentration range from density and ultrasound velocity measurements. Positive deviations of the apparent molar volume from the Debye–Hückel limiting law in dilute solutions indicate the existence of premicellar aggregation. Changes in the slope of adiabatic compressibility of lihium perfluoroundecanoate from positive to negative have been interpreted in terms of solute solvent interactions. Dynamic surface tension measurements allow us to calculated diffusion coefficients, areas and aggregation numbers. These values are discussed comparing the corresponding sodium compounds. Acknowledgements This research was funded by the Spanish Ministry of Science and Technology, through the Project MAT2002-00608 (European FEDER support included) and by Xunta de Galicia (Project PGIDIT03 PXIC 20615 PN). Paula Messina thanks Fundación Antorchas and Banco Río, Argentina (Project 4308-110) for her grant. Additional informationNotes on contributorsP. Messina††Permanent address: Grupo de Ciencia de Superficies y Coloides, Departamento de Química, Universidad Nacional del Sur, 8000 Bahía Blanca, Argentina. §Permanent address: Department of Chemistry, Quaid-i-Azam University, Islamabad, 45320, Pakistan †Permanent address: Grupo de Ciencia de Superficies y Coloides, Departamento de Química, Universidad Nacional del Sur, 8000 Bahía Blanca, Argentina.