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David Y.H. Pui, Associate Fellow and Da-Ren Chen, Co-Principal Investigator

Nanoparticle Collision with a Surface

Collisions of nanoparticles (particles smaller than about 50 nm in diameter) with surfaces are relevant to many applications, including material synthesis, microcontamination, and health effects. One of the interesting applications is the filtration of nanoparticles. It is often thought that filtering nanoparticles is relatively easy, since such particles have a very high diffusion coefficient, thus easily migrating to and being collected by the filter surface. However, Wang and Kasper (1991) predicted that, if the particle size is very small, say, less than 5 nm, particles may bounce on filter surfaces due to their large thermal velocity, thus penetrating the filter. This could be a serious problem since nanoparticles are believed to have seriously adverse health effects because of their enormous total surface area. However, the prediction was based on a macroscopic theory of particle adhesion onto surfaces. In fact, properties of nanoparticles are expected to be different from those of large particles (e.g., micrometer range) due to the size effects or high proportion of atoms exposed to the surface. Accordingly, the interaction of nanoparticles with surfaces should be understood considering such effects. This study led these researchers to do a theoretical study on nanoparticle-surface collisions.

The most straightforward way of analyzing those phenomena is to use a classical molecular dynamics (MD) method. Namely, to follow individual atoms of a particle and a surface using equations of motion. Although being computationally intensive, MD methods are known to be a powerful simulation method to study material properties or dynamic phenomena from the first principles. The MD method, with a proper choice of interatomic potentials, allows an understanding of particle-surface collisions from a microscopic viewpoint.

This project is studying collision dynamics as a function of the incident velocity of the particles. Materials of particles and surfaces are chosen such that they can simulate actual situations in filtration processes. The simulation using the classical MD methods is the main part of the study.

This information is available in alternative formats upon request by individuals with disabilities. Please send email to alt-format@msi.umn.edu or call 612-624-0528.

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