Investigation of Dielectrophoresis-directed Fluidic Assembly

Dielectrophoresis (DEP)-based fluidic self-assembly of nanoscale building blocks, such as nanoparticles and nanowires, is a promising alternative to the current micro/nanofabrication techniques to manufacture functional micro/nanodevices. While individual particles can be manipulated with reasonable precision, it remains a grand challenge to scale up the assembly process to reproducibly assemble a large number of particles. This is partially due to the lack of a quantitative understanding of the complex fluid-particle dynamics when numerous nanostructures are interacting both electrically and hydrodynamically. In this work, both experiment and numerical study were conducted to explore the electrohydrodynamic effects during the assembly of multiple nanostructures driven by DEP. Direct numerical simulations were conducted that combine the Maxwell Stress Tensor (MST) approach and the Distributed Lagrange Multiplier/Fictitious Domain (DLM/FD) method to solve the conjugate fluid-particle interaction problem. The MST approach was used to compute the DEP forces and torques exerted on the particles, which yields rigorous solutions even for highly non-uniform electric field and for particles of irregular shapes. The DLM/FD method was then employed to simulate the hydrodynamic equations of the particle-fluid system involving multiple particles. The motion of the individual particles and the subsequent aggregation of adjacent particles under three major driving mechanisms for directed self-assembly, namely, DEP, traveling-wave DEP and electrorotation, were studied in details. In addition, microfluidic DEP devices were fabricated and self-assembly experiments were carried out for polystyrene microparticles suspended in colloidal solutions. The observed particle motion and the assembly patterns were compared to the numerical simulation results. The good agreement suggests the comprehensive numerical framework developed in this work can be used as a powerful tool for the fundamental study of colloidal hydrodynamics with coupled electrokinetic effects.
With further advancement, this work will help to push forward the development of more effective and robust fluidic assembly techniques, and lay the foundation towards large-scale parallel manufacturing of functional nanostructures for various engineering applications.