| Description |
Engineered materials consisting of nano- or microparticles embedded in a matrix material may exhibit unique physical properties that are attributed to the specific type, geometry, and spatial pattern of the particles. However, existing techniques for fabricating such engineered materials are limited to laboratory scale, specific materials, and/or 2D implementations. We employ ultrasound directed self-assembly (DSA), which relies on the acoustic radiation force associated with an ultrasound wave field of wavelength significantly larger than the particle size, to organize particles of any material type dispersed in a fluid medium, into a user-specified pattern over a macroscale area or volume. We first derive the dynamics of a single particle in a fluid medium subject to a one-dimensional standing ultrasound wave field. We analyze the trajectory of the particle, driven to either a node or antinode of the ultrasound wave field by the acoustic radiation force, and we show that the particle oscillates around the node of the standing wave with an amplitude that depends on the ratio of the time-dependent drag forces and the particle inertia. We then theoretically derive and experimentally implement a method for single and multidimensional ultrasound DSA, which enables manipulating the position of a single particle and organizing user-specified patterns of nano- and microparticles dispersed in a fluid medium contained within a reservoir lined with ultrasound transducers, respectively. In contrast with existing ultrasound DSA techniques, this method works for any user-specified pattern of particles within a reservoir of arbitrary geometry and ultrasound transducer arrangement. Additionally, the method accounts for all ultrasound wave reflections in the reservoir, which allows for straightforward experimental implementation of the method. Finally, we integrate ultrasound DSA with stereolithography to fabricate engineered materials layer-by-layer via stereolithography, where in each layer we organize a user-specified pattern of particles using ultrasound DSA. This process enables manufacturing macroscale 3D materials with a user-specified microstructure consisting of particles of any material. We demonstrate 3D printing macroscale multilayer engineered materials containing a Bouligand microstructure of nickel-coated carbon fibers. Additionally, we fabricate engineered materials containing a pattern of electrically conductive nickel-coated carbon fibers, which illustrates the feasibility of 3D printing structures with embedded insulated electrical wiring. This process has implications for applications including manufacturing of metamaterials, and multifunctional composite materials. |
