Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1,...
-
date post
22-Dec-2015 -
Category
Documents
-
view
221 -
download
0
Transcript of Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1,...
![Page 1: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/1.jpg)
Steric effects on AC electroosmosis in dilute electrolytes
Brian D. Storey1, Lee R. Edwards1, Mustafa Sabri Kilic2, Martin Z. Bazant2
1Olin College of Engineering2MIT
Storey, Edwards, Kilic, Bazant PRE 2008Bazant, Kilic, Storey, Ajdari, arXiv, 2007
![Page 2: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/2.jpg)
Motivation – ICEO microfluidics• For engineers, ICEO operates at low voltage (portable microfluidics). • For electrokinetic theorists, ICEO operates at high voltage ~100 kT/e.• Current simulations of ICEO microfluidic devices rely on classical
electrokinetic theory.• What’s complicated about ICEO? Large voltage, dynamics, long range
flow patterns, complex geometry.• Can we develop a simple theory that can be implemented as
boundary conditions in commercial finite element codes for predicting macro-scale flows?
Bazant & Squires PRL & JFM2004
![Page 3: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/3.jpg)
Ramos, Morgan, Green, Castellenos 1998
AC Electroosmosis
![Page 4: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/4.jpg)
ACEO PumpAjdari, PRE 2000
Exp. data from Urbanski et al, MIT
![Page 5: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/5.jpg)
ln iiii eczckT
Near a wall, steady state, 1D:
Chemical potential of dilute point ions:
0 1 2 3 4 50
0.5
1
1.5
2
2.5
3
X
C
0 1 2 3 4 510
-20
10-10
100
1010
1020
X
C
Applied voltage =.025 V Applied voltage =0.75 V
kT
ez
i
i
ec
Would need ions to be 0.01 angstrom
Classical electrokinetics
![Page 6: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/6.jpg)
Bikerman (1942)
Kilic, Bazant, Ajdari – PRE 2007
iii
i eczc
kT
1
ln kT
ze
ec
c
1 C, dimensionless, ν, volume fraction in bulk
@ equilibrium
![Page 7: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/7.jpg)
Linearized, DH
Non-linear, GCS
Bikerman model
Model applied to ACEO
![Page 8: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/8.jpg)
Flow contours – different ion size
![Page 9: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/9.jpg)
Theory and experiment
Ion is 4 nm to best fit data.
Exp. from Studer, Pepin, Chen, Ajdari Analyst 2004
![Page 10: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/10.jpg)
Better steric models
Carnahan Starling (2 nm)
“volume effects can be underestimated significantly” using Bikerman model.
We can reduce to ~1 nm if we assume ε changes in double layer
(Biesheuvel & van Soestbergen, JCIS 2007).
![Page 11: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/11.jpg)
Concentration effects-ACEO experiments
Urbanski et al. 2007 Studer et al, 2004
![Page 12: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/12.jpg)
Concentration effects - simple model
ts bEU
b
bdbD
0
cb
b
1
Electroosmotic mobility
Valid for any continuum model
Simplest model of a viscoelectric effect
(Bazant, Kilic, Storey, Ajdari 2007 arXiv)
![Page 13: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/13.jpg)
Viscoelectric model applied to ACEO
10-1
100
101
102
-1
0
1
2
x 10-3
Frequency
Vel
ocit
y
Increasing concentration
Need an ion size of ~4 nm to fit forward flow dataLose the flow reversal when we combine models
![Page 14: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/14.jpg)
What’s missing?
• Correlations effects.• Faradaic reactions (recall talk of Ramos et al on TWEO).• …..
What’s needed?• Experiments designed to study these effects.• Multi-scale modeling
![Page 15: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/15.jpg)
Conclusions
• ICEO applications has opened new avenues for study in theoretical EK.
• Crowding of ions, increased viscosity, and decreased permittivity are not new ideas (Bikerman, 1970).
• Accounting for steric effects can effect qualitative and quantitative predictions in ACEO.
• Still more work is needed for a truly useful theory based on first principles.
![Page 16: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/16.jpg)
![Page 17: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/17.jpg)
Induced charge electroosmosis (ICEO)
Bazant & Squires PRL & JFM2004
![Page 18: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/18.jpg)
Theory & experiment
Exp. from Studer, Pepin, Chen, Ajdari Analyst 2004
![Page 19: Steric effects on AC electroosmosis in dilute electrolytes Brian D. Storey 1, Lee R. Edwards 1, Mustafa Sabri Kilic 2, Martin Z. Bazant 2 1 Olin College.](https://reader031.fdocuments.us/reader031/viewer/2022020111/56649d805503460f94a64d25/html5/thumbnails/19.jpg)
AC Electroosmosis
Ramos, Morgan, Green, Castellenos 1998*simulations account for EK through BC.