Enhanced Saturation Coverages in Adsorption-Desorption Processes

TL;DR

This paper investigates how introducing a desorption step in adsorption processes affects the saturation density, revealing an enhancement and a maximum saturation point, supported by theoretical and simulation results.

Contribution

It introduces a theoretical model for adsorption-desorption processes that predicts increased saturation densities and identifies optimal conditions, advancing understanding of layered adsorption.

Findings

Desorption steps increase saturation density compared to continuous adsorption.

Maximum saturation density occurs when the depleted density is two-thirds of the initial density.

Theoretical predictions align qualitatively and semi-quantitatively with numerical simulations.

Abstract

Many experimental studies of protein deposition on solid surfaces involve alternating adsorption/desorption steps. In this paper, we investigate the effect of a desorption step (separating two adsorption steps) on the kinetics, the adsorbed-layer structure, and the saturation density. Our theoretical approach involves a density expansion of the pair distribution function and an application of an interpolation formula to estimate the saturation density as a function of the density at which the desorption process commences, $\rho_1$, and the density of the depleted configuration, $\rho_2$. The theory predicts an enhancement of the saturation density compared with that of a simple, uninterrupted RSA process and a maximum in the saturation density when $\rho_2={2/3}\rho_1$. The theoretical results are in qualitative and in semi-quantitative agreement with the results of numerical simulations.