Collaborative Research: Separation of nanoparticles using gradient surfaces: multiscale simulations and experiments

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National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)Proposal Number: 0731032 Principal Investigators: Drazer, German Affiliation: Johns Hopkins University Proposal Title: Collaborative Research: Separation of nanoparticles using gradientsurfaces: multiscale simulations and experiments The ability to guide particles to a desired location in a fluidic device while allowing them to remain suspended in solution is challenging since micro- and nano-particles undergo Brownian motion. We have conceived a technique that exploits Brownian motion itself to focus particles spatially by controlling the energy landscape on the bounding surfaces of a device. We exploit this particle focusing technique to create separation units for the continuous fractionation of suspended colloids. The conceived devices provide a novel approach to the separation of suspended particles based on the differential interaction of the species with affinity gradients created on the bounding walls of the device. The overall result is the vector separation of the mixture, in which different species move in different directions, thus allowing for continuous operation with higher separation power and peak capacity compared to one-dimensional systems. The strategy is to combine state-of-the-art microfabrication, with multiscale modeling and simulation, to design and experimentally test these micro- and nanofluidic separation devices.Intellectual merit: A deep understanding of particle-surface interactions is crucial to a successful design and optimization of the proposed separation devices. In contrast to the significant activity and advances in developing and refining experimental techniques needed to fabricate nanoscale materials or devices, the framework for understanding transport phenomena at nanometer scales is less developed, particularly in cases with significant geometric confinement as in the case of interest here, in which the channel dimension is comparable to the size of the suspended particles. Therefore, we propose a collaborative effort, combining critical experiments with multiscale modeling and simulations, all aimed at understanding the dominant aspects of particle-surface interactions under flow conditions with geometric confinement.Broader Impact. Scientific aspects: Brownian excursions of particles hamper applications in which one wants to address specific particles at specific positions within a fluidic device. The focusing scheme investigated in this work could be used to overcome those complications, and could be widely exploited in lab-on-a-chip devices. In this context, the potential extensions of this work are broad, given the high activity in the field of particle manipulation in fluidic devices, and in the field of active control of surface properties.Broader Impact. Education and Outreach aspects: The fundamental issues resulting from particle-surface interactions in our project, as well as the potential impact of harnessing molecular phenomena for technological applications, will be incorporated in modules designed for undergraduate and graduate level courses in "Molecular simulations" and "Interfacial Phenomena in Nanomaterials", which are currently part of IGERT programs in the participating institutions. These modules will provide the students with a clear example of the need for multidisciplinary teams in order to understand complex problems in nanoscale science and to be able to address challenging issues in nanotechnology. In addition, the present project will provide hands-on experience to undergraduate and high school students drawn from the different outreach and educational programs available at both institutions. The students will be part of a diverse team of researchers and, as a result, will be better prepared for the increasingly interdisciplinary field of biomolecular and chemical engineering. The students will present their results in conferences and workshops and will be responsible for maintaining a research webpage that will present the results in a timely manner and for the general public.