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

摘要

A computer simulation model is proposed to study film growth and surfaceroughness in aqueous ($A$) solution of hydrophobic ($H$) and hydrophilic ($P$)groups on a simple three dimensional lattice of size $L_x \times L_y \timesL_z$ with an adsorbing substrate. Each group is represented by a particle withappropriate characteristics occupying a unit cube (i.e., eight sites). TheMetropolis algorithm is used to move each particle stochastically. The aqueousconstituents are allowed to evaporate while the concentration of $H$ and $P$ isconstant. Reactions proceed from the substrate and bonded particles can hopwithin a fluctuating bond length. The film thickness ($h$) and its interfacewidth ($W$) are examined for hard-core and interacting particles for a range oftemperature ($T$). Simulation data show a rapid increase in $h$ and $W$ isfollowed by its non-monotonic growth and decay before reaching steady-stateequilibrium ($h_s, W_s$) in asymptotic time step limit. The growth can bedescribed by power-laws, e.g., $h \propto t^{\gamma}, W \propto t^{\beta}$ witha typical value of $\gamma \approx 2, \beta \approx 1$ in initial time regimefollowed by $\gamma \approx 1.5, \beta \approx 0.8$ at $T = 0.5$. For hard-coresystem, the equilibrium film thickness ($h_s$) and surface roughness ($w_s$)seem to scale linearly with the temperature, i.e., $h_s = 6.206 + 0.302 T, W_s= 1,255 + 0.425 T$ at low $T$ and $h_s = 6.54 + 0.198 T, W_s = 1.808 + 0.202 T$at higher $T$. For interacting functional groups in contrast, $h_s$ and $W_s$decay rapidly followed by a slow increase on raising the temperature.