Synergistic Effect of Binary Surfactant Mixtures in Two-Phase and Three-Phase Systems.

Agata Wiertel-Pochopien,Jan Zawala,Piotr Batys,Przemyslaw B Kowalczuk

doi:10.1021/acs.jpcb.1c00664

Abstract

Cationic alkyltrimethylammonium bromides (CnTAB, with n = 8, 12, 16, 18) and their mixtures with n-octanol as a nonionic surfactant were chosen as a model system to study the synergistic effect on foamability (two-phase system) and floatability (three-phase system) of quartz in the presence of binary mixtures of ionic/nonionic surfactants. The foam height of one-component solutions and binary mixtures and floatability of quartz particles were characterized as a function of the surfactant concentration and the number of carbons (n) in the alkyl chain of CnTAB. The experimental results of foamability and floatability measurements in one-component and mixed solutions revealed the synergistic effect, causing a significant enhancement in the foam height and recovery of quartz. In the presence of n-octanol, the height of foam increased remarkably for all CnTAB solutions studied, and this effect, whose magnitude depended on the CnTAB hydrophobic tail length, could not be justified by a simple increase in total surfactant concentration. A similar picture was obtained in the case of flotation response. The mechanism of synergistic effect observed in mixed CnTAB/n-octanol solutions was proposed. The discussion was supported by molecular dynamics simulations, and the probable mechanism responsible for synergism was discussed. In addition, an analysis allowing accurate determination of the concentration regimes, where the synergistic effect can be expected, was given. It was shown that for the two-phase system, the n-octanol molecule preadsorption at the liquid/gas interface causes an increase in CnTAB adsorption coverage over the level expected from its equilibrium value in the one-component solution. In the case of the three-phase system, the synergistic effect was related to the ionic surfactants serving as an anchor layer for n-octanol, which, in water/n-octanol solution (one-component system), do not adsorb on the surface of quartz.

Highlights

Multiphase systems with interfaces of complex adsorption layers are ubiquitous in nature, as well as in numerous technical applications
The increased interest in multiphase systems is based on their importance for various applications in pharmaceuticals, cosmetics, food production, biotechnology, biomedicine, and mineral processing.3−7 The dynamic behavior of such systems is complex because it depends on the composition, structure, and various internal relaxation processes within the interfacial layers, which in turn strongly depend on the dynamics of the contacting fluid phases
The vertical line represents the critical synergistic concentration (CSC)12,35 determined from the equation dσeq = σwater − σ(c) where σwater and σ(c) are the equilibrium surface tensions of water and surfactant solution of a given concentration, respectively

Summary

Introduction

Multiphase systems with interfaces of complex (mixed) adsorption layers are ubiquitous in nature, as well as in numerous technical applications Important examples of such systems are foams, emulsions, paints, surfactant solutions, complicated microemulsions, foamed emulsions, double emulsions, biological cells, liposomes, etc.. Important examples of such systems are foams, emulsions, paints, surfactant solutions, complicated microemulsions, foamed emulsions, double emulsions, biological cells, liposomes, etc.1,2 The properties of such complex multicomponent systems are largely determined by the dynamic properties of the interfacial layers, which can be composed of surfactants, polymers, biopolymers, nanoparticles, and their mixtures. In the case of a multicomponent interface, the interactions between mixed adsorption layer molecules can result in better macroscopic system properties than expected from each component separately This enhancement of the considered effects is called synergism. Mixed surfactant systems are Received: January 25, 2021 Revised: March 31, 2021 Published: April 13, 2021

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Conclusion