Beyond Microfluidics: Measuring Nanoscale Fluid Dynamics

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24 Οκτ 2013 (πριν από 4 χρόνια και 20 μέρες)

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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


Future Research and Applications

Motivation


Development of AFM as a microflow probe


Applications


Porous media characterization


Microfiltration


Study of non
-
continuum behavior


Biology




Microfluidic gene sorter

www.sinc.stonybrook.edu

Bacterial flagellum

http://coris.noaa.gov/

Atomic Force Microscopy

nano.tm.agilent.com

www.llnl.gov

Samples and Equipment


Large Single Pipe


Small Pipe Array


Screen

50μm scan



50μm scan





20μm scan




10μm scan


20 μm Hole



Micro
-
channel Plate Track
-
Etch Membrane

Lacey Carbon Film

Expectations

(Continuum Fluid Mechanics)


Screen









Pipe

Fox, McDonald & Pritchard

“Poiseuille Flow Profile”


(parabolic shape)

“No
-
Slip” Condition

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

Experimental Setup

Sample

Single 20μm Hole

100μm x 100μm non
-
contact

AFM image.

100μm x 100μm simulated image

of cantilever/flow convolution.

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

Flow Profiles

Is this a velocity profile? What happened to convolution effects?

Height [nm]

x [microns]

10 μm contact image

With airflow

Poiseuille Flow?

(Parabolic Profiles?)

1. Convolution effects decrease at small scales

Poiseuille Flow?

(Parabolic Profiles?)

2. All observed profiles are parabolic


-
profile vertices aligned

-
data rescaled


Data re
-
scaling


y = ax
2


x’ = xa
-
1/2


y = x’
2

Overlay

of 14 non
-
contact flow profiles

Poiseuille Flow?

(Parabolic Profiles?)


Convolution with an idealized cantilever tip
can reproduce parabolic flow profiles.

Flow Through Screens

No airflow




Airflow

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

Acknowledgements


Dr. Srinivas Manne


Elaine Ulrich


Resonant Frequency Shifts


Resonance shifts can detect the presence of
different gases.

Gas

Air

Nitrogen

Helium

Freq. [kHz]
(
±
0.01)

308.62

308.65

309.19

Damped Harmonic
Motion

ω’=(ω
0
2
-
(b/2m)
2
)
1/2


(Halliday and Resnick)

Contact Flow Profile Data