an introduction to microfluidics : lecture n°1 patrick tabeling, [email protected] espci,...
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AN INTRODUCTION TO MICROFLUIDICS :
Lecture n°1
Patrick TABELING, [email protected], MMN, 75231 Paris0140795153
1 - Past and present of microfluidics2 - Microfluidics, nanofluidics and macroscopic approach.3 - The changes in the balances of forces that result from miniaturization.
Outline of Lecture 1
SOME REFERENCES
Translation by Suelin CHENOxford University Press To appear, 20 Oct 2005
Oxford Univ Press
MEMS = MICRO ELECTROMECHANICHAL SYTEMS
Systems whose sizes lie in the range 1 -300 microns
A new situation arose in the seventies, further to the tremendous development of microelectronics : it became possible to fabricate all sorts of miniaturized objects : microcondensators, microvalves, micropumps, microresonators, microdispenser...by exploiting an important accumulation of technological knowledge, and taking advantage of the availability of sophisticated equipment.
This generated a substantial economicalactivity
Airbag SensorAirbag Sensor - - Analog DeviceAnalog Device
3 mm
m
Commercial Inkjet using MEMS technologyCommercial Inkjet using MEMS technology
2 mm
There's Plenty of Room at the Bottom
An Invitation to Enter a New Field of Physics
I would like to describe a field, in which little has been done, but inwhich an enormous amount can be done in principle. This field is not quitethe same as the others in that it will not tell us much of fundamentalphysics (in the sense of, ``What are the strange particles?'') but it ismore like solid-state physics in the sense that it might tell us much ofgreat interest about the strange phenomena that occur in complexsituations.Furthermore, a point that is most important is that it would have anenormous number of technical applications.
R Feynman, CALTECH, Dec 1959
Perhaps, everything started with a talk given by R. Feynman….
Micro-Electro-Mechanical -SystemMicro-Electro-Mechanical -System MEMSMEMS
Howe & Muller 1982
First Silicon Beams
1982Fan, Tai & Muller, 1988
Spring
1988
Insect spinning on a micromotor
Fan,Tai and Muller 1989
First micromotor(1989)
QuickTime™ et undécompresseur Cinepak Codec by Radiussont requis pour visionner cette image.
QuickTime™ et undécompresseur Cinepak Codec by Radiussont requis pour visionner cette image.
100 m
Craighead (Cornell)
HOW DO WE FABRICATE A MEMS ?
Microfabrication of a membraneSi
SiOxydation
Si
Depot de resine
SiAttaque par KOHSi
Insolation
masque
Si
Ouverture et strippage
DéveloppementSi
Microfluidics = Realization and study of flows and transfers in (artificial) microsystems
1970 - 1990 : Essentially nothing (apart from the Stanford gas chromatographer)
1990 : First liquid chromatograph (Manz et al)TAS concept (Manz, Graber, Widmer, Sens.Actuator, 1991)
1990 -1998 : First elementary microfluidic systems (micromixers, microréactors, separation systems,..)
1998-2004 : Appearance of soft lithography technology, which fostered the domain. All sorts of microfluidic systems with various levels of complexity are made, using different technologies
A few milestones
First microfluidic system : Terry (1975) (Stanford)
Canal de 1.5 m long
Injection valve
Thermalsensor
Reyes et al, Anal Chem, 74, 2623 (2002)
From Agilent-Caliper
Allow to characterize DNA Fragments with excellent resolution, and in a small time
A microfluidic system for DNA separation
A system which will probably have an impact in biology
(Quake et al, Science 2002)
Chargement, compartimentageMélange, purge.
Les opérations élémentaires
LAB-ON A CHIP
DIAGNOSESHEART ATTACKWITHIN 10 MN
BIOSITE
An elementary Lab-on-a-chip
PERSPECTIVES OF MICROFLUIDICS
Microfluidics is increasingly used in an impressive number of domains
- Food industry- Chemistry- Biotechnology- Oil industry- Drug discovery
In these domains, microfluidic systems of various complexities areneeded, and the challenge is to be able to respond to these needs.Current estimates indicate microfluidic demands will grow at a fast rate over the next 5 years, generating visible economical activity
One day, we’ll perhaps receive this strange watch as a birthday gift
It is not sure however we will be capable soon tomimick a number of natural systems
The spider
The tree
FLUIDS FLOWING IN NANOMETRIC DEVICES- NANOFLUIDICS
1nm 1m100nm m
Nanofluidics
10nm 1m 10m 1mm
MicrofluidicsSinglemolecule
Two admissible definitions of nanofluidics
Definition 1 (engineer definition) :Nanofluidics deals with fluids flowing in systems whose Characteristic sizes range between 10 and 300 nm
Definition 2 (physicist definition) :Nanofluidics deals with fluids flowing in conditions where interactions between micro and macroscopic scales play acrucial role.
Some notions on the ranges of influence of Intermolecular microscopic forces
MOSY OF WHAT MOSY OF WHAT WE KNOW ON WE KNOW ON THE BEHAVIOURTHE BEHAVIOUROF SIMPLE OF SIMPLE LIQUIDS AT THE LIQUIDS AT THE NANOSCALE NANOSCALE COMES FROM COMES FROM THIS MACHINETHIS MACHINE(Tabor, (Tabor, Israelachvilii Israelachvilii ~1980) ~1980)
This is not the case for the Van der Waals forces between surfaces in the vacuum, whose extent lies in the nm range
FORCES LINKED TO THE PRESENCE OF ADSORBED LAYERS
Debye layers may have sizes comparable toSubmicrometric channels.
In the presence of an electrolyte, Debye layers develop
DEBYE-HUCKEL layers - typically 100 nmup to 1m thick in pure water
1nm 10m100nm km
Nanofluidics
10nm 1m 100m
MicrofluidicsSingleMoleculestudies
VdW force range
Fluctuation forces range
Debye layer thickness
Bubble nucleation barrier
Mean free path in gases
Thermal capillarity length Nanofluidics is a host of Many novel phenomena,Involving interactions betweenMicroscopic and macroscopic scales
BREAKUP OF A NANOJET ( NUMERICAL EXPERIMENTS)
M. Moseler, U. LandmanScience, 289, 5482, 1165 - 1169 (2000)
Microjet Nanojet
Nanojets do not behave like ordinary jets
The reason is that capillary thermal scale matters : l=(kT/)1/2
Working with negative pressures becomes feasible
Macroscopic approach generally assumes that the interfacesare infinitely thin
Laplace law
Boundary conditions
Speculating about possible effects in nanochannels
Laminar flow are not parabolic; they probe the natureof the surfaces exposed to the fluidFree interfaces behave in a strange way in nanochannelsHydrodynamic instabilities behave differentlyFabricate superfluid hydrogen.
500 nm
Nanofluidics is not just an exotic subject : we alreadyuse nanofabricated nanochannels in a number of applications
Separation of long strands of DNS by usine nanopillars (Baba et al, Univ. Tokyo)
A broad prospective on nanofluidics (from A. Van den Berg)
Physical aspects of microfluidics
1nm 10m100nm km
Nanofluidics
10nm 1m 100m
MicrofluidicsSingleMoleculestudies
VdW force range
Fluctuation forces range
Debye layer thickness
Bubble nucleation barrier
Mean free path in gases
Thermal capillarity length There exists interactions betweenmicroscopic and macroscopic scalesin microfluidic systems
Experiment by S. Chu et al (1994)
The cell and a number of its components have sizes comparable to microsystems
Cells can be manipulated individually in microfluidic systems.
PLAYING WITH CELLS ANDCONCENTRATIONGRADIENTS
Cell sorting (Quake et al, 2000)
There exist microscopic scales which are comparable to microsystem sizes
The mean free path in gases may reach micrometers
The notion of fluid particle in hydrodynamics
(According to Batchelor)
should be much smaller than the system size for ordinaryHydrodynamics to apply :
Kn=λL
<<1
Gas flow regimes
Kn0.1 0.6 20« Ordinary »hydrodynamicregime
Slip flow regime
Transitionnalregime
Rarefied gasregime
MICROFLUIDICS
Pressure sensor I
Pressure sensor O
PI
vacuum pump
Mercury column
PO
Pressurized gas tank
Variableresistance
(4)
(3)(2)
(1)
J.Maurer et al (2002)
1
2
3
4
5
6
7
8
9
0 0,2 0,4 0,6 0,8 1Kn
Théory with~ 0.9
S=12μRTLQmΔPPmwb
3
1+6Kn
S=1“Ordinary” hydrod.
Channel1.14±0.02 min heigth200 m wide
RECENT NUMERICAL SIMULATIONSINDICATE THAT ORDINARY HYDRODYNAMICS IS RECOVERED IN THE SUBMICRON RANGE
THE PHYSICS OF MINIATURIZATION
The spectacular changes of the balances of forces aswe go to small scales.
Scaling laws
Remarks
- Animal maximum speeds do not depend on the scale
- But the fluid velocity, at low Reynolds numbers, varies as the scale.
All animals run at the same speed
Lower members oscillate with a periodT ~ l
Velocity is V~l/T ~l0, size independent
A mechanical example of a scaling law
Vibration frequency of a Cantilever beam
f ≈hc
2πL2
f ~l−1
hL
At what speed does the Thyrannosaurus run ?
20 m/s ?11 m/s
J.R. Hutchintson, M. Garcia, Nature, 415, 1018 (2002)
An apparently controversial issue
Méthod 1 : Compare the exponents of the scaling laws. The smallest “wins”.
Example : Insects are easily caught by water drops
Fmusc~ l2, Fcap ~ l Fmusc << Fcap
Reasonings on the physics of miniaturization
Méthod 2 : More accurate : using theorem
Consider a physical quantity function of n other quantities a = f(a1,a2,…..an)In a system with k dimensions.We are thus dealing with n+1 quantities
The physical law reduces to a simpler expression :
=g(1, 2,…. n+k-1)
Involving n-k+1 variables instead of n+1
Example :
Hydrodynamic flows, characterized by a single scale, have a velocity field which satisfies :
u = U g(x/l,Re)Reynolds number = Ul/
As we miniaturize, the Reynolds number goes to zero, and thus one may conclude that in microfluidic systems, flows are laminar and stable.
Argument :
u(x) = f(x,U,,,l)
n+1=6k=3
On peut donc définir 6-3 nombres sans dimensions
uU
=gxl,Re
⎛ ⎝ ⎜
⎞ ⎠ ⎟
Avec Re=Ul/, le nombre de Reynolds
100 m
Analysis of a microjet
Re=Uaν
≈10 ; Ca=μUγ
≈10−2 ; Bo=ρa2gγ
≈10−3
Conclusion : le jet est laminaire (donc facilement controlable), les gouttes sont sphériques et la gravité est négligeable
Scaling laws in nature
Reasonings on scaling laws are often used to explain a number of apparently strange phenomena in nature
Thermal power lossed by conduction with the environnement, for a fixed T ~ T l
Power extracted from the digestion of the food ~ N l3
To reach a steady temperature, loss and gain must balance :l ~ (T/N)1/2
Since one cannot take an infinite number of meals per day, one cannot miniaturize mammifers at will
Smallest mammifer is ~2 cm
The smallest size of the mammifers
The shred
Smallest mammifer : The pygmee shred
2cm
Advantages being miniaturized : jump high (H~ l0),
walk on water
Disadvantage : being easily caught by a water drop
Scaling laws for the electrostatic micromotor
Small torque, small power(unless we rotate fast)
TorqueC~Fl ~l3
P=CΩ ~Ωl3
EScheme of the electrostatic micromotor
Réalisation d’un micro moteurRéalisation d’un micro moteur
Sacrificial Etching
Sacrificial Layer Structure Layer
MIT micro-turbine project
- Diameter-heigth : 12 mm/3mm- Air flow-rate : 0.15 g/s- Outlet temperature : 1600 K-Rotation speed: 2.4 106 tr/mn- Power : 16W- Weight : 1g- Fuel consumption : 7g/h
Some words….
Limits of the scaling arguments
1)- The detailed factors coming with the scaling lawsTheir analysis allows to determine the range of validity of the reasoning.
2) The spatial structure of the forces at hand.
CONCLUSIONS OF LECTURE 1
1 - Microfluidics is an interdisciplinary domain, driven by applications (existing or potential), in which interesting physics can be done
2 - Most of the phenomena taking place in microsystems can be described in a macroscopic framework; however, for a number of systems (gases, macromolecules,..) the microscopic scales interfere directly with the microsystem size.
3 - Balances of forces are deeply modified as we go from the ordinary to the micro world. Reasoning on scaling laws is a powerful approach to anticipate the changes one may expect from miniaturizing a given system.