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 enable a myriad of engineering applications, including fabricating engineered materials with patterns of nanoscale inclusions.