Recent advances in microfabrication techniques have enabled the development of the field of microfluidics. As these techniques become more sophisticated, devices are now being scaled down to the nanoscale, bringing about a new wealth of physical phenomena to be exploited in lab-on-chip devices for instance. The use of electrokinetics in these devices has proven particularly useful in a wide range of applications, and specifically to manipulate fluid, particles and macromolecules. Yet, the modeling of these flows at the nanoscale still suffers from limitations, owing to the inability of classical models to capture certain non-continuum effects, and to the high-cost of direct molecular simulations, which are only able to resolve very short time scales. These observations emphasize the need for renewed modeling efforts in the field of electrokinetics in highly confined environments. In this project, we propose to study electrochemical and macromolecular transport in confined devices using a new simulation approach for diffuse charge dynamics based on a Langevin model and Brownian dynamics for the electrolyte species. This new method will incorporate features from classical continuum models, but will also allow one to capture non-continuum effects without the high cost of atomistic methods. It can be applied to study both electroosmosis and electrophoresis with electrical double layers of arbitrary sizes, and can easily account for complex geometries. A new polymer model based on slender-body theory for a fluctuating elastic filament will also be developed to study the dynamics of polyelectrolytes with arbitrary Debye lengths. These new models and tools will be applied to study a number of technological applications, including: (i) the electrophoretic separation of oligonucleotides in nanochannels, (ii) electrochemical transport through nanocapillary array membranes, and (iii) the electrically driven translocation of biological polymers through nanopores.
The proposed research activities will serve to enhance the fundamental understanding and modeling of electrokinetic flows and macromolecular transport in highly confined geometries, where non-continuum effects may become important. The new models and simulation tools implemented as part of the research will be applicable to a wide range of problems in the fields of physics, engineering, and medicine, among which: biochemical assays on lab-on-chip devices, electrohydrodynamic stretching of DNA for genomic analysis, electrochemical transport through polymer electrolyte membranes in PEM fuel cells, and many others. Educational and outreach activities will also be integrated in this program. A new graduate-level course on fundamentals and applications of micro- and nanofluidics, including electrokinetic flows, will be introduced at the University of Illinois. A tutorial website on electrokinetics and its applications will be designed for use by students and non-specialists, and a visualization software for diffuse charge dynamics and electrochemical transport will be developed and made available online to students and researchers in the field under a public license.
