Dynamics of particles suspended in field-enhanced microscale flows

Understanding the dynamics of particles suspended in a flowing liquid is a fundamental fluid mechanics problem. Over the last several decades, significant advances in our theoretical and experimental understanding of these particle-laden flows have been used to manipulate particles in a variety of applications. In particular, recent developments in micro- and nanoscale fabrication and nanotechnology have increased the range of applications, as well as requirements, for manipulating suspended particles with radii less than a few micrometers. We focus here on the surprising and largely unexplained dynamics of neutrally buoyant particles suspended in two common microscale flows, namely Poiseuille and electroosmotic flows, where the particles are subject to both surface forces (e.g., due to pressure gradients) and body forces (e.g., due to electric fields). This perspective review summarizes current developments and identifies opportunities for future advances. Particles suspended in flows can demonstrate both individual and collective behaviors that lead to unusual and unexpected physicochemical hydrodynamics. These dynamics are a long-standing subject of interest, and there has been significant research on the fundamentals of particle-fluid interactions and suspension dynamics because of their relevance to nano- and microscale robotics, drug delivery, biosensing, nanomaterials, optical systems, and biotechnology. The review focuses on the dynamics of nanoscale colloidal particles within confined microscale flows, discussing past discoveries and current state-of-art research, and concluding with suggestions for future research directions.