Abstract
By using surface tension and conductivity measurements, the colloid-chemical properties of the mixtures of cationic hexadecylpyridinium bromide with nonionic Triton X-100 surfactants were investigated both in the bulk solution and at air/solution interface at different pH values. The composition of mixed micelles and adsorption layers, parameters of molecular interactions in mixed micelles βm and adsorption layers βσ, as well as standard free energies of micelle formation ΔG0mic and adsorption ΔG0ads were calculated. It was found that molecules of the nonionic surfactant presumably dominate in the mixed micelles and adsorption layers. It was shown that βm and βσ have negative values, which indicate the strengthening of intermolecular interactions in the mixed micelles and adsorption layers. Based on the data obtained, it was suggested that ion-dipole interactions are involved in the formation of intermolecular structures between nonionic and cationic surfactants in aqueous solution and at the air-solution interface. It was shown that βm, βσ as well as ΔG0mic and ΔG0ads parameter depends on the solution pH value. The complex interplay of ion-dipole, protonation and chelation processes, which occur in the surfactant mixtures at different pH and affect the strength of intermolecular interaction, should be taken into account for data analysis.
Highlights
Due to surface tension reduction and micelle formation properties, surfactants are used as stabilizers, emulsifiers and foam forming agents in numerous industrial and domestic applications, including mineral flotation, oil recovery, surface coating, wetting, detergency, synthesis of nanoparticles, catalysis, cosmetic and food formulations [1, 2]
It was shown that βm and βσ have negative values, which indicate the strengthening of intermolecular interactions in the mixed micelles and adsorption layers
Based on the data obtained, it was suggested that ion-dipole interactions are involved in the formation of intermolecular structures between nonionic and cationic surfactants in aqueous solution and at the air-solution interface
Summary
Due to surface tension reduction and micelle formation properties, surfactants are used as stabilizers, emulsifiers and foam forming agents in numerous industrial and domestic applications, including mineral flotation, oil recovery, surface coating, wetting, detergency, synthesis of nanoparticles, catalysis, cosmetic and food formulations [1, 2]. One of the most widely accepted and used to study the nonideal intermolecular interactions in surfactant mixtures, is the Rubin-Rosen model, which is based on the theory of regular solutions [2, 8, 9]. In this model the intermolecular interactions between the surfactants molecules at interfaces or at micelle formation in the solution are evaluated by using molecular interaction β parameters, which can be estimated from surface tension (βσ) or critical micelle concentration (βm) data [10]
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