Multiscale simulation of irreversible deposition in presence of double layer interactions

Abstract

Sequential lattice Monte Carlo simulations, in which the transition probabilities are derived from the discrete form of the continuum-level mass conservation law, are used to predict the morphology of colloidal deposits. The simulations account for particle–surface (P–S) and particle–particle (P–P) electrostatic and van der Waals interactions. Simulation results for maximum coverage for monolayer deposition are in quantitative agreement with the hard-sphere RSA jamming limit. Moreover, as reported in earlier studies, monolayer simulations in the absence of P–S interactions qualitatively predict the monotonic increases in fractional coverage with increasing ionic strength, characterized by the Debye screening length ( κa). Monolayer simulations with P–S interactions show that the dependence of fractional coverage on κa is strongly influenced by the ratio of particle to surface potentials ( Ψ p / Ψ s ). P–S and P–P forces achieve their respective maximum at different values of κa leading to a nonmonotonic trend in surface coverage as a function of κa. These results indicate that the incorporation of P–S interactions into colloidal deposition studies allows more accurate interpretation of the experimental data. In multilayer deposition simulations, balance between long-ranged weak interactions and short-ranged strong interactions between P–P and P–S, coupled with physical screening effects, resulted in widely varying coverages with height of the deposit, ionic strength, and Ψ p / Ψ s . Moreover, fractal dimension of the deposit ranged from ≈1 ( κa⪡1) to 1.7 ( κa⪢1). Qualitative kinetic analysis showed widely varying deposition rates in different layers depending on Ψ p / Ψ s and ionic strength. The multilayer system approached the monolayer system in the limit κa→∞ and Ψ p / Ψ s →∞.