An enormous amount of effort has been dedicated to creating well-ordered structures from colloidal particles using magnetic fields, electric fields, capillary forces, and ionic interactions, for example. However, the potential of creating well-ordered structures from acoustic standing waves remains largely unexplored. Acoustic forces may offer numerous advantages compared to these techniques, including scalability, programmability, rapidity, and the ability to manipulate particles of various compositions (e.g., without a reliance on narrowly defined electromagnetic or surface properties). While a few studies have shown the ability to acoustically concentrate particles, the limitations to assemble particles of various sizes with precision and the morphology of these structures remains poorly understood. Here, we explore the flexibility and limitations of acoustophoresis for the rapid arrangement of micro- and nanoparticles into organized and programmable structures. We employ multi-dimensional bulk acoustic standing waves to propel particles toward the pressure nodes or antinodes, depending on their acoustic contrast factor, and can thus simultaneously create thousands of size-limited, assemblies within minutes. We pair these experiments with Brownian dynamics simulations to model the migration kinetics and assembly patterns of different particles. We also use simple analytical models to predict the limitations of this approach to manipulate particles of diminishing size, and we follow these predictions by concentrating gold nanoparticles into loosely packed clusters (unlike microparticles, which can arrange into tightly packed structures). Finally, to catalyze the assembly of these exceedingly small particles into tightly packed structures, we incorporated a simple light-based crosslinking approach that stabilizes the assemblies, which may provide utility in plasmonic and photonic applications.

Acoustic radiation forces for the rapid and programmable assembly of microparticles and nanoparticles

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.