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

Summary: 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 $L_x \times L_y \times L_z$ 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 hardcore and interacting particles for a range of temperature ( $T$ ). Simulation data show a rapid increase in $h$ and $W$ followed by its non‐monotonic growth and decay before reaching steady‐state and near equilibrium ( $h_{\rm s}, W_{\rm s}$ ) in asymptotic time step limit. The growth can be described by power laws, e.g., $h \propto t^{\gamma}, W \propto t^{\beta}$ with a typical value of $\gamma \approx 2, \beta \approx 1$ in initial time regime followed by $\gamma \approx 1.5, \beta \approx 0.8$ at $T = 0.5$ . For hardcore system, the equilibrium film thickness ( $h_{\rm s}$ ) and surface roughness ( $w_{\rm s}$ ) seem to scale linearly with the temperature, i.e., $h_{\rm s} = 6.206 + 0.302 T, W_{\rm s} = 1\,255 + 0.425 T$ at low $T$ and $h_{\rm s} = 6.54 + 0.198 T, W_{\rm s} = 1.808 + 0.202 T$ at higher $T$ . For interacting functional groups in contrast, the long time (unsaturated) film thickness and surface roughness, $h_{\rm s}$ and $W_{\rm s}$ decay rapidly followed by a slow increase on raising the temperature.Growth of the average film thickness at a temperature $T=5$ .