Film Formation with Reactive Hydrophobic and Polar Groups in Aqueous Solution: A Bond-Fluctuating Computer Simulation Model

We study film formation with reactive hydrophobic ($H$) and polar ($P$) components in evaporating aqueous ($A$) solution by Monte Carlo simulation to model the polyurethane film growth. Each component is represented by mobile particles with appropriate molecular weight, interaction, and reaction functionality on a simple three-dimensional lattice $L_x \times L_y \times L_z$ with an adsorbing substrate. $H$ and $P$ react by forming fluctuating covalent bonds proceeding from the substrate with probability $P_B$. Bonds may also be formed between $H$ and $A$ when $A$ is considered reactive. Growth of the film thickness ($h$) and surface roughness ($W$) are studied at a range of temperature ($T$). With non-reactive $A$, the saturated film thickness ($h_s$) and roughness ($W_s$) decay first before increasing linearly on raising the temperature. With reactive $A$, a fast increase of $h_s$ at low temperature is followed by a slow increase at high temperature. $W_s$ also shows non-monotonic dependence on temperature.