Influence of the drying conditions on the particle distribution in particle-filled polymer films: Predictive simulation of the particle distribution during drying

For coating applications, particles are frequently added to a polymer solution, and then the dispersion is deposited onto a substrate and dried to make the composite coating. To engineer its microstructure, it is essential to understand how drying conditions and dispersion composition influence the distribution of components. In this work a 1D-simulation model is proposed to predict the component distribution during drying of a particle–polymer–solvent mixture not undergoing a phase change. It uses a quasi-binary approach to describe diffusion in the multicomponent system. Only binary and pure component data for solvent–polymer and particle dispersion systems are needed. Comparison of the model to others in the literature shows good agreement. The model was used to explore particle distribution during drying of a base case dispersion with an initial solvent, polymer, and particle contents of 95, 3.5, and 1.5 vol%, respectively. Under the conditions explored, the polymer remains uniformly distributed in the solvent phase during drying, but the particle distribution varies. Depending on the dominance of evaporation, particle sedimentation or diffusion, three different component distributions through the thickness occur: a particle-rich sediment at the bottom and polymer enriched layer on the top, a particle-rich layer on the top and polymer accumulation at the top or uniform distributions of particles and polymer. The different regimes are mapped as function of relevant dimensionless numbers. The effect of changing the solvent concentration and relative amounts of polymer and particles are explored.