Multiscale Modeling and Simulations of Micro- and Nano-Scale Electrokinetic Flows

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With the growing interests in bio-MEMS and bio-NEMS applications and fuel cell technologies, electrokinetic transport has received great attention in recent years. Electrokinetic flows have become one of the most important non-mechanical techniques in micro- and nano-systems and have been actively used for flow-controls, including pumping, separating and mixing. Modeling and simulations of electroosmotic phenomena based on the continuum Poisson-Boltzmann equation and the Navier-Stokes equations have been used to explain many experimental observations and guided the design of Micro-Total Analysis System. However, when the characteristic size of the flow system reaches the size comparable to submicron or the ion (molecule) size, the continuum assumption breaks down and the molecular effects cannot be ignored. Molecular-based methods have been used to model electroosmotic flows at nanoscale channels. However, because of the high computational cost, molecular dynamics simulations can only probe a very limited time (e.g., tens of nanoseconds) and lengthscale (e.g., a few nanometers) domain. The multiscale simulation capable of coupling molecular dynamics simulation of ions near material surfaces (molecular scale) and the continuum Poisson-Boltzmann simulation for the bulk region (micron scale) is an efficient way to solve this difficulty. The important thrust of the proposed research is to invent a new multiscale method to simulate micro- and nano-fluid dynamics in electrokinetic systems and to develop new algorithms for multiscale modeling that incorporate long-range Coulomb interactions in both atomistic and continuum regions. The distinguished feature in this approach is that only a small portion of the charged particles in the field near interfaces are simulated in MD, while in traditional particle-mesh based schemes all particles in the space must be followed. The research objectives in this proposal include: (i) develop an innovative multiscale (hybrid) method coupling molecular dynamics simulation with continuum method to simulate electrokinetic flows in micro and nano systems; (ii) investigate the multiscale effects on the electrokinetic flow; (iii) Investigate the flow mechanisms and characteristics of the micro- and nano-scale electrokinetic flows, including pumping, separation and mixing. Electrokinetic phenomena are the basis of many lab-on-a-chip concepts. The electrokinetic flow has many important applications in micro and nano systems, such as bio-chip or fuel cells. The proposed research will provide the mathematical foundations necessary for modeling the electrokinetic flows in micro- and nano-systems and develop multiscale numerical methods for simulating the electrokinetic flow. The algorithms developed in the project will be available to the community and can be extended for many studies of nano-technologies, such as nano-machines and their interface with charged biomolecules. A highly efficient parallel program will be developed and can be easily used by the research community. The proposed research will also provide an interdisciplinary training to postdocs, graduate and undergraduate students involved in the project, and bring basic material on numerical analysis, scientific computing, continuum fluid mechanics, nanomechanics and electokinetics into the general curriculum.