Ultrasound directed self-assembly of user-specified patterns of nanoparticles dispersed in a fluid medium

Abstract

We employ an ultrasound wave field generated by one or more ultrasound transducers to organize large quantities of nanoparticles dispersed in a fluid medium into two-dimensional user-specified patterns. To accomplish this, we theoretically derive a direct method of calculating the ultrasound transducer parameters required to assemble a user-specified pattern of nanoparticles. The computation relates the ultrasound wave field and the force acting on the nanoparticles to the ultrasound transducer parameters by solving a constrained optimization problem. We experimentally demonstrate this method for carbon nanoparticles in a water reservoir and observe good agreement between experiment and theory. This method works for any simply closed fluid reservoir geometry and any arrangement of ultrasound transducers, and it enables using ultrasound directed self-assembly as a scalable fabrication technique that may facilitate a myriad of engineering applications, including fabricating engineered materials with patterns of nanoscale inclusions.

Nanomaterial Patterning in 3D Printing

“…Acoustic force patterning leverages pressure waves often directed through the ink to drive the assembly of nanoparticles 98,99. For example, Figure 1diii shows nanoparticles concentrated at the displacement nodes of a bulk acoustic wave.…”

“…“Acoustic patterning” refers to the organization of particles dispersed in a fluid medium through the application of acoustic energy 99. Acoustic radiation forces generated by the acoustic waves transfer momentum to the particles and fluid.…”

Acoustic Fabrication via the Assembly and Fusion of Particles

“…The attainable shapes depend on acoustic modes of the chamber or superpositions of those. Attempts to move this concept toward higher complexity of the patterns increase the number of transducers around the chamber boundary, but due to multiple reflection inside the chamber these methods also create undesired ghost traps . Phased array transducers (PATs) are the norm to shape acoustic fields via controlled excitation of many individual transducer elements, but the necessary drive and control circuits limit available systems to <1000 elements.…”

Particle separation by phase modulated surface acoustic waves

“…1 Multiple frequencies excitation of a single transducer alleviates the problem of single patterns at the expense of reduced focusing efficiency. 21 In multi-transducer bulk devices, the control of the trapping position can either be achieved by a carefully designed matching layer 2,4,22 or by calculations of the required phase and amplitude of the transducers' signals, 23,24 providing thereby the possibility to pattern any user-specified pattern in 2D 25 or even in 3D. 26 Surface acoustic wave devices offer flexibility, as no matching layer or complex design is required to achieve patterning by frequency or phase control, and such devices can produce one-dimensional, 3,5,18,[27][28][29][30][31][32] two-dimensional, 3,5,33,34 or three-dimensional 35 patterns.…”