In this study, the influence of NaCl on the cloud point of polyethoxylate surfactants from the family of lauryl alcohol polyethoxylates (C 12 EO n ) and nonylphenol polyethoxylates (NPEO n ) was investigated. Liquid-liquid equilibrium curves of the aforementioned aqueous surfactants system with the presence of NaCl were plotted and thermodynamic parameters based on the Flory-Huggins model were obtained. The visual method was used to determine the cloud point. Solutions containing surfactant concentrations between 0.5 and 20% (by weight) and NaCl between 4.9 and 12.1% (by weight) were prepared. Salt had a salting-out effect, decreasing surfactant solubility in water. Furthermore, the cloud point decreased with an increase of NaCl concentration. The Flory-Huggins model satisfactorily described the experimental data for all surfactant + NaCl aqueous mixtures studied. ---------

* autor a quién debe ser dirigida la correspondenciaRecibido Ago. 26, 2013; Aceptado Oct. 9, 2013; Versión final recibida Dic. 1, 2013 Resumen Se ha determinado los puntos de nube de distintos surfactantes polietoxilados y se han caliculado de parámetros termodinámicos como entalpía y entropía de la mezcla utilizando el modelo de Flory-Huggins. Los surfactantes no iónicos son compuestos que pueden ser utilizados como promotores de separación en procesos tales como extracción. Este proceso de separación es basado en un fenómeno químico que ocurre cuando una solución de surfactantes no iónico es sometida al calentamiento, aumentando la temperatura hasta quedar turbia. La temperatura en este momento se denominada punto de nube. La metodología experimental consideró tanto la preparación de soluciones de 0.25 hasta 20% en masa para cada surfactante estudiado y el calentamiento hasta alcanzar el punto de nube. Los parámetros en el modelo de Flory-Huggins fueron obtenidos usando el método de Levenberg-Marquardt y presentan un ajuste satisfactorio a los datos experimentales para todos los surfactantes estudiados en este trabajo. Palabras clave: Levenberg-Marquardt, surfactantes no iónico, Punto de nube, Grado de etoxilación, modelo Flory-Huggins Determination of the Parameters of the Flory-Huggins Model to estimate the Cloud Point of Nonionic Surfactants AbstractThe cloud point of different polyethoxylated surfactants have been experimentally determined and thermodynamic parameters such as enthalpy and entropy of mixing using the Flory-Huggins model have been determined. The non-ionic surfactants are compounds that can be used as separation aid in processes such as extraction. This separation process is based on a chemical phenomenon that occurs when a solution of non-ionic surfactants is subjected to warming, increasing the temperature until getting a turbid liquid. The temperature at this point is known as the cloud point. The experimental methodology considered the preparation of solutions of 0.25 to 20% by mass for each surfactant studied and the heating process until reaching the cloud point. The parameters in the Flory-Huggins model were obtained using the Levenberg-Marquardt method and presented a satisfactory adjustment to the experimental data for all the surfactants studied in this work.