Highly parallel acoustic assembly of microparticles into well-ordered colloidal crystallites

Abstract

The precise arrangement of microscopic objects is critical to the development of functional materials and ornately patterned surfaces. Here, we present an acoustics-based method for the rapid arrangement of microscopic particles into organized and programmable architectures, which are periodically spaced within a square assembly chamber. This macroscale device employs two-dimensional bulk acoustic standing waves to propel particles along the base of the chamber toward pressure nodes or antinodes, depending on the acoustic contrast factor of the particle, and is capable of simultaneously creating thousands of size-limited, isotropic and anisotropic assemblies within minutes. We pair experiments with Brownian dynamics simulations to model the migration kinetics and assembly patterns of spherical microparticles. We use these insights to predict and subsequently validate the onset of buckling of the assemblies into three-dimensional clusters by experiments upon increasing the acoustic pressure amplitude and the particle concentration. The simulations are also used to inform our experiments for the assembly of non-spherical particles, which are then recovered via fluid evaporation and directly inspected by electron microscopy. This method for assembly of particles offers several notable advantages over other approaches (e.g., magnetics, electrokinetics and optical tweezing) including simplicity, speed and scalability and can also be used in concert with other such approaches for enhancing the types of assemblies achievable.

Local Acoustic Fields Powered Assembly of Microparticles and Applications

“…To date, tremendous efforts have been devoted to study the assembly mechanisms, such as attractive or repulsive interactions and mechanical constraints, among others. Conventional and efficient organized assembly methods have been investigated for specific applications based on diverse physical or chemical effects, including the hydrophobic interactions and ionic interactions [12], templated dewetting [6], external electronic [13], magnetic field [14], and acoustic waves [15,16].…”

Modeling and Analysis of the Two-Dimensional Axisymmetric Acoustofluidic Fields in the Probe-Type and Substrate-Type Ultrasonic Micro/Nano Manipulation Systems

“…For SAW-based devices, diverse manipulation functions, such as trapping [26,27], patterning [28,29], separation [30,31], concentration [32,33], mixing [34,35], and rotation [36,37] have been implemented by various groups. For BAW-based devices, manipulation functions such as levitation [38,39], assembly [40,41], focusing [42,43] and sorting [44] have also been realized by many researchers.…”

Separation efficiency maximization in acoustofluidic systems: study of the sample launch-position

“…Acoustouidics has been successfully applied to many different research studies, ranging from micro-droplet production and manipulation to micro-particle (or cell) sorting, focusing, separation, mixing and arraying. [16][17][18][19][20][21][22][23][24][25][26][27] Among these possible applications, cell separation has attracted a lot of attention including substantial effort devoted towards enabling the isolation of circulating tumor cells from human blood samples. [28][29][30][31][32][33][34][35][36] Several groups have demonstrated the possibility of isolating target cells from a given sample containing a mix of cells with different characteristics using acoustouidics.…”