Loading in 5 sec....

AN INTRODUCTION TO MICROFLUIDICS : Lecture n°2PowerPoint Presentation

AN INTRODUCTION TO MICROFLUIDICS : Lecture n°2

- By
**roddy** - Follow User

- 106 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' AN INTRODUCTION TO MICROFLUIDICS : Lecture n°2' - roddy

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

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

microfluidics

Reynolds numbers are small in microsystems

Re = Ul/n ~ l2

One thus may think in the framework of Stokes equations

Stokes regime : inertial terms are neglected

Acceptable approximation in most case. Exceptions are

Micro-heat pipes and drop dispensers

This solution cannot be Stokes Reynolds

U

Hele Shaw flows Reynolds

Darcy law governs Hele Shaw cells Reynolds

In a Hele Shaw cell, flows are potential

An important notion : the hydrodynamic resistance Reynolds

Increases as the system size decreases

Analogy with electrokinetics

Flows in rectangular ducts Reynolds

Another important notion : the hydrodynamic capacity Reynolds

Deformable tube :

dP=k-1 dV/V

Example :

Volume V

Pressure P

Now Qm=rdV/dt

Thus Qm=mkdP/dt and hence C=km

Question Reynolds: Show that the time to reach a steady state is given by

The expression

Response : C=m/E=πD2Lr/4E et R=12nl/b3w

with t=RC

Experiment in a microchannel, 1.4 Reynoldsmm deep

Expérience effectuée au MMN (2001)- Matthieu Cécillon

Beware of dead volumes Reynolds

Because to reach a steady state, it takes a time t equal to

t ≈ RC then t ≈ kmR

One must avoid dead volumes, bubbles, etc..

A PDMS actuator, based on Multi-layer Soft Lithography Reynolds

Actuation channel

Glass slide

Working channel

PDMS

A. Unger, H-P. Chou, T. Thorsen, A . Scherer et S. R. Quake, Science, 288, 113, (2000).

V ReynoldsC

R

R

From the electrical point of view, pneumatic actuators are

represented by a capacitance/non linear resistance system .

They are not just diodes

Non linear

resistances

R=f(VC)

J.Goulpeau, A. Ajdari

P. Tabeling,J. Appl.Phys.

May 2005

No actuation : Large localized gradient Reynolds

Actuation : Producing different

Concentration gradients

by changing the actuaction

parameters

Mechanical actuators dedicated to the generation of concentration gradients

Passive concentration

gradient generator (1)

The same, using mechanical

actuators

(1)Jeon et al, Nature Techn., 20, 826 (2002))

ELECTRICAL REPRESENTATIONS OF ELEMENTARY ACTIVE SYSTEMS concentration gradients

Mixer - Extractor

Microdoser

Mixer

Gradient concentration generator

Microdoser

Integrated actuators can be used to make progress in the realization of complex systems : an example is a chip for proteomics

The boundary conditions realization of complex systems : an example is a chip for proteomics

for liquids

The slip length realization of complex systems : an example is a chip for proteomics

z

u

Navier Boundary Conditions

Slip length (or extrapolation length)

Pressure drop with a slip length realization of complex systems : an example is a chip for proteomics

DP

Flow rate Q

Depth b

Slip length LS

Microfluidics and capillarity realization of complex systems : an example is a chip for proteomics

Two or three things important realization of complex systems : an example is a chip for proteomics

to know in microfluidics

Laplace’s law realization of complex systems : an example is a chip for proteomics

S

R

V

At mechanical equilibrium : dE=0

Bubble

Capillary phenomena are important in microsystems realization of complex systems : an example is a chip for proteomics

Pressure drops

caused by capillarity

are ~ l-1 while

those due to

viscosity behave

like l0

THE PATTERNS WHICH DEVELOP IN “ORDINARY” TWO PHASE FLOWS realization of complex systems : an example is a chip for proteomics

…OFTEN PRODUCE COMPLEX MORPHOLOGIES; THIS IS DUE

TO HYDRODYNAMIC TURBULENCE

IN MICROFLUIDIC SYSTEMS, WE OBTAIN MUCH SIMPLER realization of complex systems : an example is a chip for proteomics

MORPHOLOGIES : ESSENTIALLY DROPLETS

Laure MENETRIER, 2004

Wetting are exceedingly important in microsytems geometry

3 cases

Complete wetting

Partial wetting

Desorption

When S is non homogeneous, droplets spontaneously geometry

move on the surfaces

qA<qB

Good wetting (S ≈ 0)

Poor wetting (S <0)

Wetting properties of the walls are geometry

important in microfluidic multiphase flows

Oil with or without surfactant (Span 80)

Water

Water

R Dreyfus, P.Tabeling, H Willaime, Phys Rev Lett, 90, 144505 (2003))

When oil fully wets the surface geometry

Oil flow rate

(L/min)

Isolated water drops

Stratified regime

Pear necklace

Large-pearl necklace

Pears

Coalescence

Pearl necklace

Water flow rate (L/min)

WHEN THE FLUIDS PARTIALLY WET THE WALLS geometry

Oil flow-rate (mL/mn)

Water flow-rate (mL/mn)

(R Dreyfus, P.Tabeling, H Willaime, Phys Rev Lett (2003))

Rayleigh instability is the most geometry

important instability to be aware of

Surface energy of a column

d

Surface energy of N spherical droplets

l

UNSTABLE

Applications :Digital microfluidics geometry

- Liquid liquid flows are used in microsystems, in several circumstances.

Producing drops of one liquid into another liquid

so as to generate emulsions, or perform screening

Producing bubbles in a microchannel flow so as

to increase heat exchange, or simply because the

liquid boils.

Digital microfluidics geometry

1 - In air

2 - In a liquid

The drop moves in air over a flat surface

The drop moves in a liquid

in a microchannel

Digital microfluidics is interesting for chemical geometry

analysis, protein cristallization, elaborating novel emulsions,…

Ismagilov et al

(Chicago University)

AN EXAMPLE OF AN INTERESTING PROBLEM : REDUCING THE DROP SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

10mm

Suppose we are willing to reduce the drop size of an emulsion

One possibility is to cut the drops one by one SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

in a microfluidic system

Water drop

10mm

U

L0

u

DIFFERENT REGIMES, FOR INCREASING SIDE FLOWS SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

WHITE = WATER DROP, BLACK (IN THE CHANNEL) = HEXADECANE

We would like also to control the drop break-up SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

Lf

VS

Finger

To break or not to break SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

Curve

suggested by

the theory

(Navot, 1999)

BREAKING

VS

(mm/s)

NON

BREAKING

0 1 2 3 4 5 x102

Lf (mm)

Laure MENETRIER, 2004

Side where the contact angle SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

is smaller

qA<qB

Électrode

+V

qB=qA +1/2CV2

AN IMPORTANT PART OF DIGITAL MICROFLUIDICS

IS BASED ON ELECTROWETTING

A microfluidic network along which drops are driven SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

C.J.Kim (2001)

Digital microfluidic devices based on electrowetting SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

Liquid-liquid flows in microsystems may be used to produce SIZE OF AN EMULSION BY USING DIGITAL MICROFLUIDICS TECHNOLOGY

well controlled drops, emulsions,…

… provided the wetting properties of the exposed surfaces,

with respect to the working fluids, are appropriately chosen.

Download Presentation

Connecting to Server..