Abstract
A binary mixture of oppositely charged particles with additional short-range attraction between like particles and short-range repulsion between different ones in the neighborhood of a substrate preferentially adsorbing the first component is studied by molecular dynamics simulations. The studied thermodynamic states correspond to an approach to the gas–crystal coexistence. Dependence of the near-surface structure, adsorption and selective adsorption on the strength of the wall–particle interactions and the gas density is determined. We find that alternating layers or bilayers of particles of the two components are formed, but the number of the adsorbed layers, their orientation and the ordered patterns formed inside these layers could be quite different for different substrates and gas density. Different structures are associated with different numbers of adsorbed layers, and for strong attraction the thickness of the adsorbed film can be as large as seven particle diameters. In all cases, similar amount of particles of the two components is adsorbed, because of the long-range attraction between different particles.
Highlights
Adsorption in Mixtures withPhenomena associated with adsorption on solid surfaces have been studied for decades for systems ranging from noble gases to liquid crystals and polymers [1,2,3,4]
We focus on the adsorption on the selective surface interacting with the particles of the first and the second component with the potentials (3) and (4), respectively, at thermodynamic states given by T = 0.25 and the density of gas ρ g < 0.0027
Before describing the adsorption in the mixture, we show as a reference the near-surface structure in the case of the one-component system with particle–particle and wall–particle interactions given by (1) and (3), respectively
Summary
Phenomena associated with adsorption on solid surfaces have been studied for decades for systems ranging from noble gases to liquid crystals and polymers [1,2,3,4]. Attractive and repulsive Casimir interactions between like and different surfaces, respectively, are induced by concentration fluctuations in a binary solvent close to a critical point of the demixing phase transition, and were studied by theory and experiment [24,25,26]. Our theoretical model is motivated by the Casimir and screened electrostatic potentials, but this type of interactions in binary mixtures may be present in different complex systems as well. Molecules 2021, 26, 4532 confirmed experimentally yet, since the studies of the self-assembly of particles interacting with the Casimir and screened electrostatic potentials were limited to one-component systems [29,31].
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