Effect of interparticle interactions on colloidal film formation during the drying process: A study using Brownian dynamics simulation

Drying conditions must be controlled to achieve high-quality films in various manufacturing processes. In this study, the influence of particle interactions on colloidal film formation during drying was investigated using Brownian dynamics simulations. The film structures formed under three different interparticle interaction conditions—attractive, weakly attractive, and repulsive—were quantitatively analyzed using various structural metrics, including porosity distribution, porosity heterogeneity, pore size distribution, and tortuosity. As drying progressed and the concentration increased, attractive interactions between particles resulted in aggregates in the skin layer, which hindered the diffusion of concentrated particles in the top layer. This led to a more heterogeneous film structure in both the vertical and horizontal directions, characterized by significant porosity heterogeneity and a broader pore size distribution. Moreover, the film formation of attractive particles at three different drying rates was studied for a comprehensive understanding of the interplay between attractive interactions and drying rate. At higher drying rates, a more heterogeneous structure was observed in the vertical direction, whereas the horizontal structure appeared to be less heterogeneous. We further investigated the relationship between the film structure under various drying conditions and mass-transport properties by examining the diffusion behavior of small virtual particles through the dried film. The results demonstrated that the structural heterogeneity induced by attractive interactions and rapid drying is positively correlated with tortuosity, thereby disrupting mass transport through the film. The insights obtained from this study provide valuable guidance for optimizing colloidal suspensions to control the film formation and refining processes.