Simulation studies of adsorption of circular discs on a substrate with pre-adsorbed circular defects by using Random Sequential Adsorption (RSA)

Abstract

The Random sequential adsorption of circular discs on a two dimensional continuum substrate with pre-adsorbed circular defects is carried out using computer simulations. The defects are randomly distributed, and the adsorbing discs do not overlap with the defects. Simulations are run for different values of the fractional coverage of defects, \(\rho \), and the size ratio of defect particles to depositing particles, \(\sigma \). The kinetics of deposition follow a power law \({(\theta }_{max}-\theta (t)) \sim { t}^{-\eta }\), where \({\theta }_{max}\) and \(\theta (t)\) are maximum and instantaneous surface coverage, respectively. The value of \({\theta }_{max}\) is found to vary from 0.370 to 0.483 for \(\rho =0.1\), from 0.283 to 0.451 for \(\rho =0.15\) and from 0.194 to 0.415 for \(\rho =0.2\) when \(\sigma \) increases from 0.2 to 10. In general, the exponent \(\eta \) is found to increase with \(\sigma \) for a given value of \(\rho \). Also, it is found that for a given \(\sigma \), the value of the exponent, \(\eta \), is found to decrease with the increase in \(\rho \). Pair correlation functions of deposited discs and the pore size distribution are calculated to study the microstructural properties of monolayers of discs upon deposition. The minimum porosity condition for the deposited monolayers is determined in terms of specific parameters \(\rho \) and \(\sigma \). For a given value of \(\rho \), the value of the \(\sigma \) can be adjusted to achieve minimum porosity. The deviation from minimum porosity condition increases the porosity of the surface. Hence, one can tune the porosity of the adsorbed layer at a desired surface coverage. Pair correlation between adsorbed particles shows the increase in number of nearest neighbours with \(\sigma .\)