The Dynamic Scaling Study of Vapor Deposition Polymerization: A Monte Carlo Approach

Abstract

The morphological scaling properties of linear polymer films grown by vapor deposition polymerization (VDP) are studied by 1+1D Monte Carlo simulations. The model implements the basic processes of random angle ballistic deposition ($F$), free-monomer diffusion ($D$) and monomer adsorption along with the dynamical processes of polymer chain initiation, extension, and merger. The ratio $G=D/F$ is found to have a strong influence on the polymer film morphology. Spatial and temporal behavior of kinetic roughening has been extensively studied using finite-length scaling and height-height correlations $H(r,t)$. The scaling analysis has been performed within the no-overhang approximation and the scaling behaviors at local and global length scales were found to be very different. The global and local scaling exponents for morphological evolution have been evaluated for varying free-monomer diffusion by growing the films at $G$ = $10$, $10^2$, $10^3$, and $10^4$ and fixing the deposition flux $F$. With an increase in $G$ from $10$ to $10^4$, the average growth exponent $\beta \approx 0.50$ was found to be invariant, where as the global roughness exponent $\alpha_{g}$ decreased from $0.87(1)$ to $0.73(1)$ along with a corresponding decrease in the global dynamic exponent $z_g$ from $1.71(1)$ to $1.38(2)$. The global scaling exponents were observed to follow the dynamic scaling hypothesis, $z_g=\alpha_{g}/\beta$. With a similar increase in $G$ however, the average local roughness exponent ${\alpha_{l}}$ remained close to $0.46$ and the anomalous growth exponent ${\beta}_{\ast}$ decreased from 0.23(4) to 0.18(8). The interfaces display anomalous scaling and multiscaling in the relevant height-height correlations. The variation of $H(r,t)$ with deposition time $t$ indicates non-stationary growth.