Abstract
The bulk and interfacial properties of solutions formed by a polycation (i.e., poly(diallyl-dimethylammonium chloride), PDADMAC) and two different zwitterionic surfactants (i.e., coco-betaine (CB) and cocoamidopropyl-betaine (CAPB)) have been studied. The bulk aggregation of the polyelectrolyte and the two surfactants was analyzed by turbidity and electrophoretic mobility measurements, and the adsorption of the solutions at the fluid interface was studied by surface tension and interfacial dilational rheology measurements. Evidence of polymer–surfactant complex formation in bulk was only found when the number of surfactant molecules was closer to the number of charged monomers in solutions, which suggests that the electrostatic repulsion associated with the presence of a positively charged group in the surfactant hinders the association between PDADMAC and the zwitterionic surfactant for concentrations in which there are no micelles in solution. This lack of interaction in bulk is reflected in the absence of an influence of the polyelectrolyte in the interfacial properties of the mixtures, with the behavior being controlled by the presence of surfactant. This work has evidenced the significant importance of the different interactions involved in the system for controlling the interaction and complexation mechanisms of in polyelectrolyte–surfactant mixtures.
Highlights
The physico-chemical behavior of solutions combining charged polyelectrolytes and oppositely charged surfactants both in bulk and close to interfaces—either fluid or solid—has received growing interest in the past two decades [1,2,3,4]
It is worth mentioning that the complexation process is strongly affected by non-equilibrium effects, with the protocol used during polyelectrolyte–surfactant mixing being critical for the properties and Molecules 2019, 24, 3442; doi:10.3390/molecules24193442
It is expected that theit combined of the interaction occurring in solution occurring solution between a polycation anddifferent two chemically different zwitterionic surfactants with between in a polycation and two chemically zwitterionic surfactants with the interfacial the interfacial properties, equilibrium, and dynamics of the layers resulting from the adsorption of properties, equilibrium, and dynamics of the layers resulting from the adsorption of the pseudothe pseudo-binary polymer–surfactant mixtures may help to draw a comprehensive picture of the binary polymer–surfactant mixtures may help to draw a comprehensive picture of the behavior of behavior typewhich of system, which presents technological a growing technological this typeof ofthis system, presents a growing interest. interest
Summary
The physico-chemical behavior of solutions combining charged polyelectrolytes and oppositely charged surfactants both in bulk and close to interfaces—either fluid or solid—has received growing interest in the past two decades [1,2,3,4]. Delgado et al [23] investigated the interaction of PSS with two different carboxybetaines, combining bulk characterization with surface-sensitive techniques They found that the formation of complexes in solution occurs as result of the electrostatic interaction between the surfactant and the polymer chains; no effect of such complexes on the interfacial properties of the water/vapor interfaces was reported. This work tries to contribute to the knowledge on the physico-chemical bases underlying the behavior of polyelectrolyte–zwitterionic surfactant solutions For this purpose, we studied the self-assembly in solution and the adsorption to the water/vapor interface of mixtures formed by PDADMAC and two different carboxybetaines. It is expected that theit combined of the interaction occurring in solution occurring solution between a polycation anddifferent two chemically different zwitterionic surfactants with between in a polycation and two chemically zwitterionic surfactants with the interfacial the interfacial properties, equilibrium, and dynamics of the layers resulting from the adsorption of properties, equilibrium, and dynamics of the layers resulting from the adsorption of the pseudothe pseudo-binary polymer–surfactant mixtures may help to draw a comprehensive picture of the binary polymer–surfactant mixtures may help to draw a comprehensive picture of the behavior of behavior typewhich of system, which presents technological a growing technological this typeof ofthis system, presents a growing interest. interest
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