Abstract
The self-assembly behaviors of sodium oleate (NaOL), dodecylamine (DDA), and their mixtures in aqueous solution were systematically investigated by large-scale molecular dynamics simulations, respectively. The interaction mechanisms between the surfactants, as well as the surfactants and solvent, were revealed via the radial distribution function (RDF), cluster size, solvent-accessible surface area (SASA), hydrogen bond, and non-bond interaction energy. Results showed that the molecules more easily formed aggregates in mixed systems compared to pure systems, indicating higher surface activity. The SASA values of DDA and NaOL decreased significantly after mixing, indicating a tighter aggregation of the mixed surfactants. The RDF results indicated that DDA and NaOL strongly interacted with each other, especially in the mixed system with a 1:1 molar ratio. Compared to van der Waals interactions, electrostatic interactions between the surfactant molecules were the main contributors to the improved aggregation in the mixed systems. Besides, hydrogen bonds were found between NaOL and DDA in the mixed systems. Therefore, the aggregates in the mixed systems were much more compact in comparison with pure systems, which contributed to the reduction of the repulsive force between same molecules. These findings indicated that the mixed NaOL/DDA surfactants had a great potential in application of mineral flotation.
Highlights
Mixed surfactants have attracted a great deal of attention from researchers in various fields, including flotation, oil recovery, drug delivery, daily cosmetics, textiles, and pesticide emulsifiers [1,2,3,4,5,6]
Many researchers found that the anionic/cationic mixed systems show much higher surface activity compared to other mixed systems due to the strong electrostatic interactions between surfactants [17,18]
We found that the increasing simulation time led to a higher level of aggregation in both pure systems and mixed system
Summary
Mixed surfactants have attracted a great deal of attention from researchers in various fields, including flotation, oil recovery, drug delivery, daily cosmetics, textiles, and pesticide emulsifiers [1,2,3,4,5,6]. As a result, investigating the collective behavior of NaOL/DDA in water is very important for improving flotation performance. The self-aggregation behaviors of NaOL, DDA, and their mixture in aqueous solution were investigated using large-scale molecular dynamics’ simulation. Mixed surfactants of anionic-rich system shows excellent flotation and separation performance on silicate minerals [8,19,30,32,33] In this regard, the effects of a total molecular number and a range of varied molar ratios on the self-aggregation of mixed NaOL/DDA (NaOL-rich) surfactants in aqueous solution were discussed, respectively. All molecules were randomly added to the box, which may cause anomalous contact between atoms and improper shape These defects of initial structures could be eliminated by energy minimization to obtain optimized geometry. The stable tendency for potential energy of all systems indicated the energy of systems was minimum
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