Film Growth and Surface Roughness with Fluctuating Covalent Bonds in Evaporating Aqueous Solution of Reactive Hydrophobic and Polar Groups: A Computer Simulation Model

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A computer simulation model is proposed to study film growth and surface roughness in aqueous (A) solution of hydrophobic (H) and hydrophilic (P) groups on a simple three dimensional lattice of size Lₓ × Ly × Lz with an adsorbing substrate. Each group is represented by a particle with appropriate characteristics occupying a unit cube (i.e., eight sites). The Metropolis algorithm is used to move each particle stochastically. The aqueous constituents are allowed to evaporate while the concentration of H and P is constant. Reactions proceed from the substrate and bonded particles can hop within a fluctuating bond length. The film thickness (h) and its interface width (W) are examined for hard-core and interacting particles for a range of temperature (T). Simulation data show a rapid increase in h and W is followed by its non-monotonic growth and decay before reaching steady-state equilibrium (hₛ, Wₛ) in asymptotic time step limit. The growth can be described by power-laws, e.g., h ∝ tγ, W ∝ tβ with a typical value of γ≈ 2, β≈ 1 in initial time regime followed by γ≈ 1.5, β≈ 0.8 at T = 0.5. For hard-core system, the equilibrium film thickness (hₛ) and surface roughness (wₛ) seem to scale linearly with the temperature, i.e., hₛ = 6.206 + 0.302 T, Wₛ = 1,255 + 0.425 T at low T and hₛ = 6.54 + 0.198 T, Wₛ = 1.808 + 0.202 T at higher T. For interacting functional groups in contrast, hₛ and Wₛ decay rapidly followed by a slow increase on raising the temperature.