Nano and Microfluidics Laboratory

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Large-Area 3-D Nano-Patterning and Nanostructure Fabrication

As scientific quests and engineering applications reach down to a nanometer scale, there is a strong need to fabricate nanostructures with good regularity and controllability of their pattern, size, and shape. In many applications, furthermore, the nanostructures are not useful unless they cover a relatively large area and the manufacturing cost is within an acceptable range. While several nanoscale patterning techniques are available, it should be noted that serial lithography methods do not cover a large area needed for non-electronic applications. Other non-lithographic methods, for example, the use of nanotemplates or the direct growth of nanoscale structures do not provide good regularity over a large area. One of our research interests is to develop a simple but efficient nanofabrication method with superior control of pattern regularity, size, and shape over a large area, which will open new application possibilities in many scientific and engineering domains.

References

1. I. Wathuthanthri, C.-H. Choi, “Tunable Lloyd-Mirror Interferometer for Large-Area Nanopatterning”, in Proceedings of ASME IMECE, November 15-19, 2009, Orlando, FL, USA.

2. C.-H. Choi, C.-J. Kim, “Design, Fabrication, and Applications of Large-Area Well-Ordered Dense-Array Three-Dimensional Nanostructures”, in Nanostructures in Electronics and Photonics, Ed. Faiz Rahman, Pan Stanford Publishing (2008) (invited).

3. C.-H. Choi, C.-J. Kim, “Fabrication of Dense Array of Tall Nanostructures over a Large Sample Area with Sidewall Profile and Tip Sharpness Control”, Nanotechnology 17, 5326-5333 (2006).

Nanoscale Interfacial Phenomena

Fundamental scientific quests, which were unexplored before due to the lack of experimental precision, can now be explored with the recent development of nanotechnology. Especially, various interfacial phenomena at nanoscale can now be explored by using well-tailored nanomechanical properties of nanostructures. One of our research interests is to investigate the nanoscale interfacial phenomena including friction, adhesion, and fluid/thermal transport phenomena.

References

Interfacial liquid slip:

1. C. Lee, C.-H. Choi, C.-J. Kim, “Structured Surfaces for a Giant Liquid Slip”, Physical Review Letters 101, 064501 (2008).

2. C.-H. Choi, C.-J. Kim, “Large Slip of Aqueous Liquid Flow over a Nanoengineered Superhydrophobic Surface”, Physical Review Letters 96, 066001 (2006).

3. C.-H. Choi, U. Ulmanella, J. Kim, C.-M. Ho, C.-J. Kim, “Effective Slip and Friction Reduction in Nanograted Superhydrophobic Microchannels”, Physics of Fluids 18, 087105 (2006)

4. C.-H. Choi, K. J. A. Westin, K. S. Breuer, “Apparent Slip Flows in Hydrophilic and Hydrophobic Microchannels”, Physics of Fluids 15, 2897-2902 (2003).

Cell adhesion:

1. C.-H. Choi, S. H. Hagvall, B. M. Wu, J. C. Y. Dunn, R. E. Beygui, C.-J. Kim, “Cell Growth as a Sheet on Three-Dimensional Sharp-Tip Nanostructures”, Journal of Biomedical Materials Research 89A, 804-817 (2009).

2. S. Heydarkhan-Hagvall, C.-H. Choi, J. Dunn, S. Heydarkhan, K. Schenke-Layland, W. R. MacLellan, R. E. Beygui, “Influence of Systematically Varied Nano-Scale Topography on Cell Morphology and Adhesion”, Cell Communication & Adhesion 14, 181-194 (2007).

3. C.-H. Choi, S. H. Hagvall, B. M. Wu, J. C. Y. Dunn, R. E. Beygui, C.-J. Kim, “Cell Interaction with Three-Dimensional Sharp-Tip Nanotopography”, Biomaterials 28, 1672-1679 (2007).

Droplet evaporation kinetics and wetting dynamics:

1. R. Leeladhar, W. Xu, C.-H. Choi, “Effects of Nanofluids on Droplet Evaporation and Wetting on Nanoporous Superhydrophobic Surfaces”, in Proceedings of ASME MNHMT, December 18-22, 2009, Shanghai, China.

2. W. Xu, C.-H. Choi, “Effects of Structural Topography on Nanofluids Droplet Evaporation on Multifarious Superhydrophobic Surfaces”, in Proceedings of ASME MNHMT, December 18-22, 2009, Shanghai, China.

3. C.-H. Choi, C.-J. Kim, “Droplet Evaporation of Pure Water and Protein Solution on Nanostructured Superhydrophobic Surfaces of Varying Heights”, Langmuir 25, 7561-7567 (2009).

Multifunctional Superhydrophobic Surfaces

Nature such as plants, insects, and marine animals uses micro- and nano-textured surfaces in their components (e.g., leaves, wings, eyes, legs, and skins) for multi-purposes such as self-cleanness. Such multi-functional surface properties are attributed to the 3-D surface structures. Especially, hydrophobic surface structures create a composite interface with liquid by retaining air between the structures, minimizing the contact area with liquid. Such non-wetting surface property, so-called superhydrophobicity, can offer numerous application potentials including anti-fogging, anti-snow adhesion, anti-frosting, anti-corrosion, low flow-friction, and anti-biofouling. One of our research interests is to develop multi-functional superhydrophobic surfaces of optimized de-wetting stability and adaptive self-healing capability for various applications.

References

1. C.-H. Choi, C.-J. Kim, “Nanostructured surfaces for anti-biofouling/anti-microbial applications”, in Proceedings of the SPIE Defense, Security, and Sensing, April 13-17, 2009, Orlando, FL, USA.

2. C.-H. Choi, C.-J. Kim, “Large Slip of Aqueous Liquid Flow over a Nanoengineered Superhydrophobic Surface”, Physical Review Letters 96, 066001 (2006).

3. C.-H. Choi, U. Ulmanella, J. Kim, C.-M. Ho, C.-J. Kim, “Effective Slip and Friction Reduction in Nanograted Superhydrophobic Microchannels”, Physics of Fluids 18, 087105 (2006).

Microfluidic Self-Assembly of Nanomaterials

Nanomaterials are promising building blocks for novel nanostructures and nanodevices. However, practical applications require precise arrangement of nanomaterials into hierarchical orders to construct desired geometry with controllable shape, location and direction on a large scale. Although several strategies had been explored for the controlled placement of nanoscale building blocks, the development of more efficient techniques is still essential to achieve well-ordered high-throughput nanoassembly. One of our research interests is to develop a simple and efficient nanoassembly mechanism based on various microfluidic techniques to result in site-specific self-assembly of nanomaterials.

References

1. R. Leeladhar, W. Xu, Y.-T. Tsai, E.-H. Yang, C.-H. Choi, “Nanowire Self-Assembly in Droplet Evaporation on Superhydrophobic Surfaces”, in Proceedings of the 13^th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2009), November 1-5, 2009, Jeju, Korea.

2. Y.-T. Tsai, W. Xu, E.-H. Yang, C.-H. Choi, “Interfacial-Tension-Directed Self-Assembly of Nanowires on a Superhydrophobic Surface”, in Proceedings of ASME IMECE, November 2-6, 2008, Boston, MA, USA.

Nanofluidic Energy Harvesting

This project is to develop a novel power generation device, utilizing a nanofluidic platform containing nanoenergetic materials, which are extremely mass-efficient in storing chemical energy. The stored chemical energy can be released rapidly, generating heat and pressure as a stimulus exists. These released energies need to be transformed to electricity and ultimately stored in energy storage devices, which can be used to power sensors, switches and fuzes. The technology will transform the energy created by energetic materials into electrical energy by using a nanofluidic system.

Optofluidic Waveguides and Sensors

Most optical systems are made with solid materials such as glasses, metals, and semiconductors. However, there are cases in which it will be advantageous to use fluids for optical systems. Whereas microfluidics has made it possible to integrate multiple fluidic tasks on a chip, most optical components, such as the light source, sensors, lenses, and waveguides, remained off the chip. In recent development of optofluidic integration, optics and microfluidics are combined on the same chip by building the optics out of the same fluidic toolkit. The advantage of optofluidics lies in the ease with which one can change the optical properties of the devices by manipulating fluids. The project is to study and develop new optofluidic waveguide architecture of liquid-core and air-cladding for multi-phase (liquid and gas) sensing with greater sensing efficiency.

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