Cooperative Nature of Complex Formation in Mixed Polyelectrolyte−Surfactant Systems

Abstract

The binding of the cationic surfactant dodecylpyridinum chloride (DoPyCl) to different preformed anionic charged polyelectrolyte complexes consisting of cationic copolymers with varying charge density and poly-(acrylic acid, sodium salt) (PAA) has been investigated by using a potentiometric technique based on a surfactant ion solid-state electrode. The solid membrane used in the electrode consists of poly(vinyl chloride) plasticized by bis(2-ethylhexyl) phthalate. Binding isotherms are analyzed in terms of the nearest neighbor interaction model by Zimm and Bragg and for systems of reduced polyanion availability of the Scatchard plot, which indicates cooperative interactions at very low surfactant concentrations (∼0.01 mM). The binding constants decrease by decreasing the charge density of the cationic copolymer used. For selected systems the titration data have been complemented with static light scattering measurements.

pH-dependent polyampholyte SDS interactions

“…Moreover, charge neutralization occurs at c c,f of about 0.85 mM ($1.8 mM total surfactant concentration (c s,t )) and the system becomes turbid in a narrow concentration range without precipitation. As the surfactant concentration is further increased (region III) a strong rise in slope of binding isotherm could be related to a local overcrowding of surfactant molecules (n > 1), already reported for the poly(-acrylic acid)-dodecyl pyridinium chloride system [55]. Deviations from the 1:1 stoichiometry have additionally been published by other groups for oppositely charged PEL-surfactant systems [54,56,34].…”

Polymer–surfactant and protein–surfactant interactions

“…Later on, relevant contributions were reported by Tanford, who studied the phase behavior of some proteinsurfactant mixtures and developed the rigid-rod model of the resulting complexes [23,24]. More recent studies performed by Shirahama and co-workers [25][26][27], Kwak and co-workers [28][29][30], Zana and co-workers [31][32][33], Kabanov and co-workers [34,35], and Lund's group [36][37][38][39][40][41], focused on selected aspects pertinent to PSS and PrSS.…”

Phase Diagrams of Stoichiometric Polyelectrolyte−Surfactant Complexes

“…This point is evidenced by the fact that, in the presence of polyelectrolytes, critical aggregation concentrations (cac) of surfactants in dilute solution tend to be orders of magnitude lower than critical micelle concentrations (cmc). 30,31 Polyelectrolyte-surfactant complexation has been known for quite some time, and many studies have been devoted to characterizing the phase behavior of these systems. Previous work concerning stoichiometric complexes involved the study of morphological changes under various conditions, such as the variation of polymer charge density, 21,32,33 surfactant tail length, 19,[34][35][36] and temperature.…”