Numerical Investigation of Titanium Dioxide (TiO2) Nanoparticle Influence on the Operating Window in Slot-Die Coating

The effect of Titanium dioxide (TiO2) nanoparticles with different diameters (340, 100, 25, and 5 nm) integrated into the slot-die coating process is investigated. The study analyses the effects of particles on stability, the operating coating window, and coating regimes. The numerical simulation is conducted using the computational fluid dynamics (CFD) code to track particles’ motion and the free interface between the liquid and air. The study used 2.5% polyvinyl alcohol PVA solution with a constant 5 wt. % of TiO2 nanoparticles with different sizes. The results showed that decreasing the nanoparticle diameter from 340 nm to 25 nm expanded the operating coating window, increased the maximum substrate speed by 12.3%, and enabled coating of thinner layers by 12.5% while maintaining the coating stability. As particle size decreased, the likelihood of achieving higher substrate speeds increased, thereby increasing the production rate. Pure PVA solutions containing 340 nm exhibit Newtonian behavior, with stability limited to the surface-tension and viscous regions, and fail when entering the inertia region. At the same time, solutions of 100 and 25 nm particles showed a transition toward the inertia region, driven by changes in dynamic behavior caused by the smaller particles, leading to near shear-thinning rheological behaviour.