Adsorption Behavior of Repulsive Molecules

Abstract

Recently, it has been shown that adsorption of gases on solid surfaces often leads to repulsive forces between adsorbate molecules. In this paper, adsorption of molecules on a one-dimensional lattice is considered for repulsive interactions between adsorbate molecules. Exact adsorption isotherms are calculated and analyzed for finite and infinite chains of active sites (i.e., a one-dimensional lattice). Although the mathematical solution for the one-dimensional lattice is known for attractive and repulsive systems, the effects of intermolecular repulsions on adsorption behavior have not been studied in detail previously. Similarly, though the mathematics for the one-dimensional lattice has been solved for any arbitrary lattice length, the effect of finite size on adsorption isotherms for repulsive adsorbate interactions has never been examined. This paper shows that spatial confinement and strong attraction to active sites can cause compression of an adsorbed phase and that repulsive interactions between adsorbed molecules result in steps in the adsorption isotherms. For higher chemical potentials, the density increases until saturating at the lattice capacity. These steps in the adsorption isotherm have not been observed in previous studies of lattice systems. For small lattices, the adsorption behavior was found to be fundamentally different for even and odd values of lattice length. Lattices with an even number of lattice sites can have two steps in the adsorption isotherm, whereas systems with an odd number of sites only have a single step occurring at a coverage slightly greater than half the lattice capacity.

Monomer Adsorption on Terraces and Nanotubes

“…We first considered homonuclear dimers on a square L × M lattice without any periodic boundary conditions and included only nearest neighbor interactions. , To first approximation, no distinction was made between step edge and bulk sites, thus neglecting edge effects. As an adsorbed dimer might be oriented either horizontally or vertically on the lattice, this was a finite width two-dimensional problem rather than an assembly of one-dimensional problems . In subsequent investigations of adsorption on square, rectangular, and isosceles triangular lattices, we only studied those cases that could be treated using the approach that was applied to the dimer problem on a square lattice.…”

Competitive Adsorption at the Air–Water Interface: A Second Harmonic Generation Study

“…The adsorption behavior for single adsorbed species can be modeled by Frumkin–Fowler–Guggenheim (FFG) isotherm which is a modification of the Langmuir isotherm incorporating lateral interaction between absorbed molecules. − The FFG equation is normalθ 1 − normalθ e − g normalθ = b c where θ is the fractional surface coverage of the absorbed species, b is the binding constant (adsorption equilibrium constant), c is bulk concentration, and g is a parameter representing the lateral interaction between the adsorbed species at the air–water interface. In the absence of lateral interaction ( g = 0), the model reduces to the Langmuir equation.…”

Configurational probabilities for monomers, dimers and trimers in fluids

“…All thermodynamic properties (density, number of monomers, dimers, and trimers) for the infinite lattice with finite width are calculated as derivatives of o max . 21,22 Fig. 14 shows a comparison between the probability of finding trimers on a 4 Â 2000 lattice from Monte Carlo simulations and analytical monomer based approximation.…”