Coupled continuum / dynamic Monte Carlo model of drying and curing in sol-gel silica films: cyclization effects
Multi-scale and/or multi-disciplinary approach to process-product innovation
Multiscale Modeling (T3-5)
Keywords: multiscale,coupling,molecular,continuum,coating
Modeling polymer curing in drying films prepared by processes such as sol-gel dip coating is important controlling the thickness, cracking and homogeneity of films. These films are of growing interest as engineered porous materials for controlled adsorption, membrane separations, sensor concentrators, and electronic materials. The sol-to-gel formation of porous ceramic coatings involves multiple length and time scales ranging from molecular to macroscopic. Therefore, a comprehensive model should link macroscopic flow and drying (controlled by process parameters) to film microstructure (which dictates the ultimate properties of the films). Here, we describe a multiscale model in which dynamic Monte Carlo (DMC) simulations are coupled to a continuum model of drying. The DMC approach is needed to simulate nonideal polymerization effects including first-shell substitution effects (FSSE) and, most importantly, cyclization. The simulation tracks the populations of differently connected sites and bond blocks to derive the rates of bimolecular reactions and cyclization reactions, respectively. Unlike statistical methods, DMC simulations track the entire molecular structure distribution to allow the calculation not only of molecular weight but also of topological indices related to molecular size and shape. These topological indices can be used for improved correlations of transport coefficients in polymers with different degrees of branching and cyclization. The entire DMC simulation (containing ~ 1,000,000 monomers) is treated as a particle of sol whose position and composition are tracked using a diffusion/evaporation finite difference calculation. By simulating a swarm of particles starting from different positions in the film and using variable parameters, we observe the effect of drying parameters on the gelation regime, predict different drying/gelation phenomena, and predict the occurrence of gradients of concentration, gelation, and structure in the films. In this contribution, we will focus on the modeling of cyclization and its effects on the evolution of the films.
Presented Tuesday 18, 09:05 to 09:25, in session Multiscale Modeling (T3-5).
