Molecular dynamics simulations of surfactant and nanoparticle self-assembly at liquid–liquid interfaces

Abstract

We have performed molecular dynamics (MD) simulations to investigate self-assembly at water–trichloroethylene (TCE) interfaces with the emphasis on systems containing modified hydrocarbon nanoparticles (1.2 nm in diameter) and sodium dodecyl sulfate (SDS) surfactants. The nanoparticles and surfactants were first distributed randomly in the water phase. The MD simulations have clearly shown the progress of migration and final equilibrium of the SDS molecules at the water–TCE interfaces with the nanoparticles either at or in the vicinity of the interfaces. One unique feature is the ‘attachment’ of surfactant molecules to the nanoparticle clusters in the water phase followed by the ‘detachment’ at the water–TCE interfaces. At low concentrations of surfactants, the surfactants and nanoparticles co-equilibrate at the interfaces. However, the surfactants, at high concentrations, competitively dominate the interfaces and deplete nanoparticles away from the interfaces. The interfacial properties, such as interfacial thickness and interfacial tension, are significantly influenced by the presence of the surfactants, but not the nanoparticles. The order of the surfactants at the interfaces increases with increasing surfactant concentration, but is independent of nanoparticle concentration. Finally, the simulation has shown that surfactants can aggregate along the water–TCE interfaces, with and without the presence of nanoparticles.

Nanoparticle effects on the water-oil interfacial tension

“…However, as the concentration increases, adsorption onto the NP surface decreases the surfactant efficiency in lowering the interfacial tension, while concurrently preventing NP aggregation. Luo and Dai, 15 conducting simulations, found that surfactants and NPs compete for adsorption at liquid-liquid interfaces, and that as the surfactant concentration increased the NPs desorb from the interface. The thickness of the interface and the interfacial tension were found to depend significantly on the surfactant concentration, but not so on the NP adsorption.…”

Investigation of interfacial and structural properties of CTAB at the oil/water interface using dissipative particle dynamics simulations

“…Molecular orientations, structural variability of the peptide ring backbones, interfacial molecular areas, and the motion activities of surfactin derivatives were determined [28]. Dai et al reported the MD simulation of the in situ self-assembly of nanoparticles and SDS surfactants at a water/trichloroethylene (TCE) interface, highlighting the potential of using the liquid/liquid interface to produce novel nanomaterials [29]. Rivera et al simulated alkane/water systems containing methanol and reported the surfactant behavior of methanol molecules as they are preferably adsorbed at the interface and reduce the interfacial tension through a rearrangement of the molecules at the interface [30].…”

Molecular simulation of nanoparticle diffusion at fluid interfaces

“…Previous simulations have addressed the stability of nanoparticles at interfaces [13][14][15][16][17], interactions between nanoparticles [18], orientational behaviour of anisotropic nanoparticles [17,19], and the self-assembly of nanoparticles at fluid interfaces [20,21]. These simulations have largely focused on the static properties of nanoparticles at interfaces, while only recently has simulation be turned to the dynamic properties of nanoparticles at liquid interfaces [22].…”