Deposition patterns of nanoparticles in a small S/W ratio impactor: measurements and physics

The deposition pattern for an impactor with a small nozzle-to-plate ratio (S/W) is a ring whose diameter is related to the particle diameter, among other quantities. The extant literature on impactors has focused on devices where S/W is of order unity and what literature exists for small S/W impactors has focused on micron-scale particles. Herein deposition patterns were obtained for particles ranging in diameter from 50 nm to 3 µm using scanning electron microscopy (SEM) where S/W was 0.09. Particle trajectory simulations mimicking the experimental conditions were also conducted to reveal the underlying physics. These showed the important role of the Hamaker constant, A and the coefficient of restitution, e as well as the importance of bounce, particle interception, and inertial effects (notwithstanding the small size of the particles considered). An improved relationship between the ring diameter and particle diameter is presented, and the relevance of this work to potential improvements in the diameter resolution of impactors is discussed. Copyright © 2026 American Association for Aerosol Research