Micro- and Nanotechnologies

Fluidic Modeling

As microdevices advance in complexity and our ability to manufacture and exploit nano-scale phenomena grows, the need for physics-based computational and analytic capabilities increases. To support and augment concepts and designs for new devices, we develop new capabilities and leverage existing capabilities to elucidate the underlying complex interplay of physical phenomena/mechanisms governing system and subsystem performance. Our primary efforts have been in the areas of microfluidics, fluidics, chemical and biochemical reaction kinetics (stochastic and deterministic), and colloidal interactions. The portfolio of capabilities that we have developed and use include:

• µLatte3D
• Analytic Models
• StarCD
• Digital Particle Image Velocimetry (DPIV)

µLatte3D: a 3-D, parallel lattice Boltzmann simulation capability

This capability enables modeling of suspensions in micro- and nano-environments. It includes colloidal interactions, coupled external fields and coupled fluid and heat transfer.

Many of our applications in micro- and nanotechnology involve the separation of target species from other species in a liquid sample. Over the past few years, our experimental colleagues have developed prototype dielectrophoretic devices to effect the desired separations. In some cases, these devices have exhibited anomalous behaviors. To understand performance and augment device design, we have developed simulation capabilities to explore the complex interplay of forces involved during a dielectrophoretic (DEP) separations, e.g., coupled viscous colloidal and electromagnetic forces acting on multispecies suspensions in microenvironments. Simulation results enabled prediction of the range of effective separator Reynolds number for species capture as a function of species polarizability. Additionally, simulations elucidate anomalous DEP owing to concentration effects in multispecies separations with heterogeneity in species response.

We are also interested in how suspensions behave in filtration media to understand and quantify the effectiveness of filtration media and to help develop improved methods for sample preparation. For example, an array of pillars can perform size separation or purify samples. Shown here are µLatte3-D simulation results for different pillar geometries.

A µLatte3-D simulation of particles with fluid flow through a square array of pillars, displayed with the fluid velocity magnitude.

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Analytic Models

As a complement to µLatte3-D, we have developed analytic models to predict forces acting on particles suspended in electrolytic solutions. An example is DEP forces acting on suspended species. To explore various phenomena acting on target species, we developed analytic models to predict forces produced during separations for both standing and traveling-wave DEP. Additionally, we have developed various models to predict species polarizability for use in the DEP models. These models are also integrated with µLatte3-D to enable characterization of separation efficiencies while taking into account couple forces.

In addition to the DEP modeling efforts, we have developed analytic models to predict fluid, heat, and mass transport/separation with and without phase change in microenvironments, colloidal forces of interaction, and surface deposition.

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StarCD

We are coupling commercial computational software (StarCD) with custom tools to study aerosol transport in filtration media and shockwaves in rarefied gases. This effort has also helped improve the performance of biological pathogen detection instrumentation.

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Digital Particle Image Velocimetry (DPIV)

We have developed a digital particle image velocimetry (DPIV) capability to characterize flow behavior in microfluidic devices. Our system integrates a dualhead Nd:YAG laser with an inverted epi-fluorescent microscope and CCD camera to image fluorescent particles (0.25-5 µm diameter) with submicrometer resolution. Custom DPIV and particle-tracking software then measures velocity fields due to hydrodynamic, electrophoretic, and acoustic forces.

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January 30, 2008