RESUMO
A simple model for amorphous solids, consisting of a triangular lattice with a fraction of attenuated bonds randomly distributed (which simulate the presence of defects in the surface), is used here to find out, by using grand canonical Monte Carlo simulations, how the adsorption thermodynamics of repulsively interacting monomers is modified with respect to the same process in the regular lattice. The degree of disorder of the surface is tunable by selecting the values of (1) the fraction of attenuated bonds ρ (0 ≤ρ≤ 1) and (2) the attenuation factor r (0 ≤r≤ 1), where r is defined as the ratio between the value of the lateral interaction associated to an attenuated bond and that corresponding to a regular bond. Adsorption isotherm and differential heat of adsorption calculations have been carried out showing and interpreting the effects of the disorder. A rich variety of behavior has been observed for different values of ρ and r, varying between two limit cases: bond-diluted lattices (r = 0 and ρ≠ 0) and regular lattices (r = 1 and any value of ρ). In addition, the critical behavior of the system was studied, showing that the order-disorder phase transition observed for the regular lattice survives, though with modifications, above a critical curve (ρ-r-temperature).
RESUMO
The adsorption of gases on patchwise heterogeneous bivariate surfaces is studied. These surfaces are characterized by a collection of strong and weak adsorbing patches with a typical length scale l. Different forms and spatial arrangements of these patches determine different topographies characterized by an effective length, l(eff) = sigmal, where sigma takes values from 1 to 4 for the different topographies considered here. Previous studies showed that the mean square deviation between isotherms corresponding to different values of l(eff) scaled as a power law with exponent alpha, without providing any physical interpretation of such behavior. In the present work, we introduce a different scaling function, chi(l), which is shown to be twice the difference in free energy per site between a reference isotherm and the given isotherm, at half coverage. With this function the scaling behavior and the value of the scaling exponent alpha are determined over the whole range of interparticles interaction energy and adsorptive energy, and for different temperatures, through Monte Carlo simulations. The results are similar to those obtained in previous studies, with a value of alpha which is half the one obtained before due to the different definition of the scaling function, but the present analysis provides a full understanding of the scaling behavior based on the physical significance of the scaling function and the scaling exponent.
RESUMO
The adsorption of particles with nearest-neighbor attractive and repulsive interactions is studied through Monte Carlo simulation on bivariate surfaces characterized by patches of weak and strong adsorbing sites of size l. Patches are considered to have either a square or a strip geometry and they can be either arranged in a deterministic ordered structure or in a random way. Quantities are identified that scale obeying power laws as a function of the scale length l. The consequences of this finding are discussed for the determination of the energetic topography of the surface from adsorption measurements.