Propulsion of bullet- and cup-shaped nano- and microparticles by traveling ultrasound waves

TL;DR

This study uses acoustofluidic simulations to analyze how the propulsion of bullet- and cup-shaped nano- and microparticles by traveling ultrasound waves depends on their size and shape, revealing key factors influencing propulsion strength.

Contribution

It provides a detailed simulation-based analysis of how particle dimensions affect ultrasound propulsion, expanding understanding beyond previous experimental aspect ratio studies.

Findings

Propulsion strength increases with particle length and diameter.

Sign change in propulsion observed when varying particle diameter.

Flow field structure depends on particle shape and size.

Abstract

The propulsion of colloidal particles via planar traveling ultrasound waves has attracted increasing attention in recent years. A frequently studied type of particles is bullet-shaped and cup-shaped nano- and microparticles. Based on acoustofluidic simulations, this article investigates how the propulsion of bullet-shaped particles depends on their length and diameter, where cup-shaped particles are included as limiting cases corresponding to the smallest particle length. The structure of the flow field generated by the particles is discussed and it is shown that the particles' propulsion strength increases with their length and diameter. When varying the diameter, we observed also a sign change of the propulsion. This work complements previous experimental studies that have addressed such particles only for particular aspect ratios, and the provided understanding of how the propulsion of the particles depends on their dimensions will prospectively be helpful for the choice of particle shapes that are most suitable for future experimental studies.