High-Velocity Impact of Polymer Aerosol Particles on Soft Substrates: Experiments and Simulations.

We study the high-velocity impact of spherical polystyrene (PS) particles on polymer substrates to gain insight into the initial stages of powder aerosol deposition (PAD), a sustainable, solvent-free technique for polymer and ceramic thin film deposition with promising application potential for single functional or multilayered, multimaterial coatings. Single-particle impacts were investigated experimentally using a PAD setup and compared to molecular dynamics simulations, in which the particle diameter and impact velocity were systematically varied. The simulated particle shapes show good agreement with those observed experimentally via atomic force microscopy. After impact, the initially spherical particles deform into shapes resembling cylindrical domes, similar to those known from the impact of yield-stress fluids. Scaling behavior extracted from the simulations provides estimates of the otherwise not directly measurable experimental impact velocities and reveals key aspects of the particles' deformation mechanism during impact, which is driven by a temperature increase causing viscoplastic flow. Our results suggest that both adhesion and deformation of PS on polymer substrates during PAD are primarily governed by viscoplastic deformation rather than by fragmentation as typically observed in ceramic systems, or jetting due to adiabatic shear instabilities, as found in the closely related cold spray process. The insights gained in our study suggest that efficient PAD of polymers is easier for materials with good plastic deformability and thereby contribute to identifying material properties and design principles for future polymer PAD systems.