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Beyond Microfluidics: Measuring Nanoscale Fluid Dynamics

Beyond Microfluidics: Measuring Nanoscale Fluid Dynamics. Christopher Limbach University of Arizona Physics Department. Overview. Motivation Atomic Force Microscopy Samples and Equipment Fluid Mechanics Experimental Results Convolution Effects Pipes vs. Screens

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Beyond Microfluidics: Measuring Nanoscale Fluid Dynamics

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  1. Beyond Microfluidics: Measuring Nanoscale Fluid Dynamics Christopher Limbach University of Arizona Physics Department

  2. Overview • Motivation • Atomic Force Microscopy • Samples and Equipment • Fluid Mechanics • Experimental Results • Convolution Effects • Pipes vs. Screens • Future Research and Applications

  3. Motivation • Development of AFM as a microflow probe • Applications • Porous media characterization • Microfiltration • Study of non-continuum behavior • Biology Bacterial flagellum http://coris.noaa.gov/ Microfluidic gene sorter www.sinc.stonybrook.edu

  4. Atomic Force Microscopy nano.tm.agilent.com www.llnl.gov

  5. Samples and Equipment 20 μm Hole Micro-channel Plate Track-Etch Membrane Lacey Carbon Film Large Single Pipe Small Pipe Array Screen 50μm scan 50μm scan 20μm scan 10μm scan

  6. Expectations(Continuum Fluid Mechanics) ScreenPipe “Poiseuille Flow Profile” (parabolic shape) “No-Slip” Condition Fox, McDonald & Pritchard

  7. Expectations(Molecular Flows) Rarified flows can be parameterized by the Knudsen number, Kn=λ/L λ=mean free path No-slip condition breaks down Pipe Flow Profiles

  8. Experimental Setup Sample

  9. Single 20μm Hole 100μm x 100μm non-contact AFM image. 100μm x 100μm simulated image of cantilever/flow convolution.

  10. Hole Array Image Data(Track Etch Membrane) 10 μm contact image Without airflow High imaging force 10 μm contact image With airflow High imaging force 10 μm non-contact image With airflow Low imaging force

  11. Flow Profiles Height [nm] x [microns] 10 μm contact image With airflow Is this a velocity profile? What happened to convolution effects?

  12. Poiseuille Flow?(Parabolic Profiles?) 1. Convolution effects decrease at small scales

  13. Poiseuille Flow?(Parabolic Profiles?) 2. All observed profiles are parabolic -profile vertices aligned -data rescaled Data re-scaling y = ax2 x’ = xa-1/2 y = x’2 Overlay of 14 non-contact flow profiles

  14. Poiseuille Flow?(Parabolic Profiles?) Convolution with an idealized cantilever tip can reproduce parabolic flow profiles.

  15. Flow Through Screens No airflow Airflow

  16. Conclusions and Future Efforts Micro-fluidic measurements are possible with the Atomic Force Microscope. Approaching direct profile measurement in Knudsen flow regime. Mean free path ~ 0.1μm (room temperature) Both continuum and Knudsen profiles are parabolic Higher Knudsen number needed Experimental challenges

  17. Acknowledgements Dr. Srinivas Manne Elaine Ulrich

  18. Resonant Frequency Shifts Resonance shifts can detect the presence of different gases. Damped Harmonic Motion ω’=(ω02-(b/2m)2)1/2 (Halliday and Resnick)

  19. Contact Flow Profile Data

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