Electrochimica Acta 85 (2012) 659–664 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Electrochemical study of the interfacial behavior of cationic polyelectrolytes and their complexation with monovalent anionic surfactants Julieta S. Riva a,b , Karina Bierbrauer b,c , Dante M. Beltramo b,c , Lidia M. Yudi a,b,∗ a Instituto de Investigaciones en Fisicoquímica de Córdoba (INFIQC). Departamento de Físico Química, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ala 1, Pabellón Argentina, Ciudad Universitaria, 5000 Córdoba, Argentina b Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, Argentina c Centro de Excelencia en Productos y Procesos de Córdoba (CEPROCOR), Ministerio de Ciencia y Tecnología de Córdoba, Pabellón CEPROCOR, CP 5164, Santa María de Punilla, Córdoba, Argentina a r t i c l e i n f o Article history: Received 4 June 2012 Received in revised form 7 August 2012 Accepted 13 August 2012 Available online 30 August 2012 Keywords: Liquid/liquid interfaces Hydroxyethylcellulose Perfluorate acids Polyelectrolites Cooperative binding a b s t r a c t The complexation of two hydroxyethylcellulose, of different molecular weights, SC230 and SC240, with the anionic surfactants perfluorodecanoic acid, PFDA, and perfluorooctanoic acid, PFOA, has been studied. For this purpose, the anions transfer current across a water/1,2-dichloroethane interface was employed to quantify PFDA and PFOA concentration in the absence or in the presence of the polyelectrolyte. When polymers were added in increasing amounts to solutions containing PFDA or PFOA, a gradual decrease in current values was observed, evincing the binding of the anions to the polymer. Peak Current values for the transfer, were used for the drawing up the binding isotherms, which were fitted by Satake and Yang theory. Cooperative binding was observed, but all fluorinated acids gave a similar cooperativity parameter, and it was found that both the overall constant as well as the cooperative binding process, increases with the molecular weight of the polymer. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Cationic polyelectrolytes are polymers carrying positively charged ionizable groups. The properties of these species in aque- ous solutions and at charged surfaces depend on the fraction of dissociated ionic groups, salt concentration and polymer-substrate interactions. Dobrynin and Rubinstein summarized in a review article the theoretical models describing the properties of poly- electrolyte solutions and the adsorption at surfaces and interfaces [1]. Aqueous mixtures of ionic surfactants with oppositely charged polyelectrolyte have been extensity studied for the last decades due to numerous applications of the systems in the pharmaceutical formulations, personal care and food products, and in others indus- trial areas [2,3]. Moreover, the layer by layer technique, based upon the alternate adsorption of cationic and anionic species, provides a simple and affordable route in creating new active electrodes and electrolytes with high control of materials selection (polyelec- trolytes, clays, nanoparticles, proteins) and with specific properties ∗ Corresponding author at: Instituto de Investigaciones en Fisicoquímica de Cór- doba (INFIQC). Departamento de Físico Química, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ala 1, Pabellón Argentina, Ciudad Universitaria, 5000 Córdoba, Argentina. Tel.: +54 0351 4334169/80; fax: +54 0351 4334188. E-mail addresses: mjudi@fcq.unc.edu.ar, mabelyudi@hotmail.com (L.M. Yudi). for potential applicability in proton-exchange membranes, fuel- cells, batteries, electrochromic devices, solar cells, and sensors [4,5]. Many investigations have focused on the binding isotherms and their thermodynamic analysis, and it was determined that the primary nature of the interaction between polyelectrolyte and sur- factant is electrostatic, but specific and hydrophobic interactions are also important. The strength of the specific and the hydropho- bic interactions depends on the properties of both, the surfactant and the polyelectrolyte [6]. Recently, the interaction between polyquaternium cellulose PQ10, also known as SC230, and perfluorodecanoic acid, PFDA, was characterized by spectroscopy and rheological techniques [7]. There, it was found that the binding of PFDA to PQ10 produces a strong hydrogel structure which is maintained in a wide range of conditions: PFDA molar ratio (0.1–1), ionic strength (0–300 mM), temperature (15–120 ◦ C) and pH (3–11). The nature of the interac- tions was demonstrated to be of electrostatic type but it was also suggested that some hydrophobic interaction could be contributing to the stiffness of the hydrogel. The phenomenon of hydrogel formation by the interaction between a cationic polymer in the presence of an anionic surfac- tant has been reported in previous works. Such is the case reported by Kästner et al. [8] who studied the effect produced by the addi- tion of different surfactants to a cationically modified hydroxyethyl cellulose. They observed the formation of a strong hydrogel in the 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.08.049