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

TL;DR

This study uses computer simulations to analyze film growth and surface roughness in aqueous solutions with hydrophobic and hydrophilic groups, revealing how temperature influences film properties and roughness dynamics.

Contribution

It introduces a novel simulation model for film growth considering fluctuating covalent bonds and compares hard-core and interacting particles across temperatures.

Findings

Film thickness and roughness follow power-law growth in initial stages.

Surface roughness and film thickness scale linearly with temperature for hard-core particles.

Interacting groups show rapid decay and slow increase in film properties with rising temperature.

Abstract

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 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 ($h_s, W_s$) 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 hard-core system, 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.