Multiscale simulation of irreversible deposition in presence of double layer interactions

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→∞.