Prsentation PowerPoint

1
AN INTRODUCTION TO MICROFLUIDICS Lecture n3
Patrick TABELING, patrick.tabeling_at_espci.fr ESPCI,
MMN, 75231 Paris 0140795153
2
Outline of Lecture 1
1 - History and prospectives of microfluidics 2 -
Microsystems and macroscopic approach. 3 - The
spectacular changes of the balances of forces
as we go to the small world.
Outline of Lecture 2
- The fluid mechanics of microfluidics - Digital
microfluidics
3
Outline of Lecture 3
1 - Basic notions on diffusive processes 2 -
Micromixing 3 - Microreactors.
4
Diffusion time for a 100 mm wide channel (for a
molecule such as fluorescein) This time
may be too long, especially if one develops
several chemical reactions on the same chip
5
Equation de diffusion advection

• Dans le cas incompressible, l équation de
  diffusion advection est

Ordre de grandeur Pe 105 pour un colorant
dans l eau agitée à des vitesses de 1cm/s
Un nombre sans dimension analogue au nombre de
Reynolds est
6
Quelques propriétés de léquation de
diffusion-advection
La variance de la concentation décroit avec le
temps
- si les CL sont périodiques ou si lécoulement
est confiné dans un volume avec parois rigides
imperméables.
7
Le nombre de Peclet nest pas nécessairement
petit dans les systèmes miniaturisés
.donc petit
8
Un problème fondamental la diffusion d une
petite tache dans un fluide au repos
C
C
t0
t
x
x
Écart type s(2Dt)1/2
9
Dispersion dans un écoulement uniforme

• A t 0, on impose CC0 en x0 sur une couche
  d épaisseur d

U
x
x0
Avec s22Dt
10
Dispersion de TAYLOR-ARIS
d
d doit etre très fin
11
Origine microscopique de la diffusion moléculaire

• On introduit un  marcheur  effectuant des sauts
  de longueur li le long d une ligne (mouvement
  brownien)

li
On démontre
La poxition du marcheur est
Mouvement diffusif et front gaussien
12
Mixing in microsystems
- Mixing is difficult in microsystems
13
There has been some clever and less clever ideas
FLOW
Poor transverse mixing for microfluidic systems
14
HYDRODYNAMIC FOCUSING ALLOWS
On the order of 30 nm in the extreme cases
TO MIX IN TENS OF MICROSECONDS Austin et
al, PRL (2002)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
Circular micromixer
Quake, Scherer (2001)
22
Transformation du boulanger
23
In chaotic regimes, two close particles separate
exponentially In confined systems, this property
is extremely favorable to mixing,
24
From Ottinos book  Chaotic Advection 
25
The first chaotic micromixer was designed at
Berkeley (1997)
Thermal actuator
Micromixer
J. Evans, D. Liepmann, D., and A.P. Pisano, 1997,
Planar Laminar Mixer, Proceeding of the IEEE
10th Annual Workshop of Micro Electro Mechanical
Systems (MEMS 97), Nagoya, Japan, Jan, pp.96-101.
26
Cross-channel micro-mixer(UCLA,1999)
Fluid A
V
time
-V
Fluid B
400 mm
investigated by Y.K. Lee, C.M.Ho (1999), Mezic et
al (1999)
27
How it works (from a kinematical viewpoint)
U
Perturbation is applied Line is stretched
U
U
Perturbation is stopped Line is folded
28
EXPERIMENT
Micro-valve
25mm
200mm
Microvalve
1mm
29
(No Transcript)
30
200 mm
A.Dodge, P. Tabeling, A. Hountoundji, M.C.Jullien
(2004)
31
Under resonance conditions, the interface is
stretched in the active zone, and returns flat
afterwards
A.Dodge, P. Tabeling, A. Hountoundji, M.C.Jullien
(2004)
32
DETERMINING A PHASE DIAGRAM, USING THE
VARIANCE OF THE PDF OF THE CONCENTRATION FIELD
- Well mixed the variance is small - Unmixed
the variance is large
33
EXPERIMENTAL PHASE DIAGRAM, REPRESENTING ISOLINES
OF s2
Actuation pressure (bar)
Frequency (Hz)
34
An efficient particle sorter, using resonance
RESONANCES MAY BE USED TO SORT PARTICLES BY
CHANGING THE FREQUENCY OF THE PERTURBATION,
ONE OBTAINS A SYSTEM WHICH MIXES FLUIDS, FILTERS
PARTICLES, OR SIMPLY TRANSPORTS MATERIALS SIDE BY
SIDE.
35
A.Dodge, P. Tabeling, A. Hountoundji, M.C.Jullien
(2004)
36
CHEMICAL MICROREACTORS
37
EXPERIMENTAL STUDY OF A CHEMICAL REACTION AB
C IN A T MICROREACTOR
B
A
Channels 10mm deep, 500mm wide, various
flow-rates System made in glass, covered by a
silicon wafer, or in PDMS
38
One may also measure the kinetics without mixing
thoroughly
A
y
The T reactor
x
U
Diffusion-reaction zone where the product C is
formed
B
39
EXPERIMENT
Reaction Ca-CaGreen
C.Baroud, F Okkels, P Tabeling, L Menetrier,
Phys. Rev E67, 60104 (2003) 
40
Fluorescence intensity fields obtained for the
reaction CaGrCa2 (CaGr,Ca2)
Ca
U
U
CaGreen
C.Baroud, F Okkels, P Tabeling, L Menetrier,
Phys. Rev E67, 60104 (2003) 
41
Theory of the T-reactor for a second order
reaction
The product C is governed by the following
equation
42
C
Agreement between theory and experiment is good
width
Location of the max Conc.
y
Location of the max.
x
Typical structure of a concentration profile of
the product across the channel
Width
x
Maximum Conc.
THEORY with one fitting
parameter k 105 lM-1 s-1 (t 1 ms)
x
C.Baroud et al, Phys. RevE (2003)
43
EXPERIMENT IS WELL INTERPRETED BY THE THEORY
mm
mm
THEORY
THEORY
y (mm)
y (mm)
X
Fitting the experiment with one free parameter k
105 LM-1 s-1 (t 1 ms)
y
C.Baroud et al Phys. Rev E67, 60104 (2003) 
44
Digital microfluidics is interesting for chemical
analysis, protein cristallization, elaborating
novel emulsions,
Ismagilov et al (Chicago University)
45
Can we produce much using microreactors ?
Can we move a mountain with a spoon ?
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
The end