Thoughts on the ideal behavior of mixed micelles and the appropriate application of regular solution theory (RST)

Abstract

Solutions of mixed surfactants are often considered as solvent mixtures. Usually, mixed micellar aggregates are considered as a homogeneous mixture of solvents dispersed in a solution. But the transposition of the usual thermodynamic models of solvent mixtures to mixed micelles is not always so obvious. We discussed this point in this paper by considering several cases of surfactant mixtures. A major problem is to define the molar fraction of each surfactant in the aggregate especially when a charged surfactant is employed in the mixture, because possible dissociation of the components of the mixture must be considered in the bulk as well in the micelle. This definition is crucial especially for the characterization of the ideal behavior which is usually described by the Clint relation, as well as for the application of regular solution theory (RST) which is the most frequently applied model for interpreting the behavior of surfactant mixtures. We show in this paper how the definition of the molar fraction can change the equations and the interpretations.

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

“…The equations and interpretations get varied according to the molar fraction definition (Letellier et al, 2011;Poša, 2014Poša, , 2019.…”

“…In the case of mixed surfactant systems, the determination of the molar fraction of each surfactant in the aggregate iss difficult, which is needed to interpret the behavior of surfactant mixtures by using Clint relation as well as regular solution theory (RST). The equations and interpretations get varied according to the molar fraction definition (Letellier et al, 2011 ; Poša, 2014 , 2019 ). In the case of ideal mixing, there is no net interaction between the components of the mixed system.…”

Specific ion effects on the micellization of aqueous mixed cationic/anionic surfactant systems with various counterions

“…The dissociated Margules model proposed in our previous paper [41] has been used to calculate the nonideal mixed cmc of the binary oppositely charged surfactant mixtures. According to the approach of Turmine et al [70] and the dissociated Margules model, the possible dissociation of ionic surfactant must be considered when treating the mixed micellization. For the mixtures formed by cationic surfactant 1 and anionic surfactant 2, we suppose that surfactant 1 generates r 1 particles, and surfactant 2 generates r 2 particles.…”

The effect of micellization-induced deprotonation on the associative behavior of a carboxyl modified Pluronic P85

“…The micelles formed from the CAE85 polymer are therefore mixed micelles, which have been studied extensively and which include neutral surfactants, charged surfactants and polymers. 8 The control of acid-base properties of this macromolecular surfactant is important for applications, in which ion-binding processes take place. 2 In general, the use of surfactant mixtures is advantageous in cosmetics, pharmacology and biological systems.…”

“…2 In general, the use of surfactant mixtures is advantageous in cosmetics, pharmacology and biological systems. 8,9 The mixed micelles are oen assumed to behave like a homogenous mixture of solvents, which is dispersed in a solution and is in equilibrium with it. Following this assumption, phenomenological thermodynamic models such as regular solution theory, originally developed for mixtures of solvents, are applied also to the mixed micelles.…”