Table Of ContentNanofluidics and
Microfluidics
Nanofluidics and
Microfluidics
Systems and Applications
Shaurya Prakash and Junghoon Yeom
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Preface
Microfluidics and nanofluidics span a broad array of disciplines including
mechanical, materials, and electrical engineering, surface science, chemistry,
physics, and biology. The interplay of all these disciplines has led to several
topics being covered by this multidisciplinary area and has consequently led to
several different types of devices and systems for myriad applications. Our intent
in writing this book is to present a comprehensive resource that integrates essen-
tials of microfluidic and nanofluidic systems in a single text. Therefore, the goal
is to present the underlying theory, discuss the main (and a large variety of) fabri-
cation methods that are commonly used and finally present a snapshot of the vari-
ety of applications. Throughout the book several case studies are presented to
highlight the development of systems and subsequent use in applications.
Therefore, the rationale behind the book is to demonstrate the use of multiple
disciplines and topics for constructing a broad array of systems for solving sci-
ence, engineering, andtechnology challenges.
The microfluidics and nanofluidics community comprises a growing group of
active, creative, and pioneering researchers. Therefore, this area has seen tremen-
dous growth inthe pastdecade evidencedby the large number ofscientific papers
and books that have been published. Our book presents a unique look at this vast
body of scientific literature from a systems perspective with the underlying
assumption that fundamental theories and fabrication go hand in hand for con-
structionandoperationofmanypractical devices. Therefore,itwouldbeuseful to
view the advances through the prism of “global” advances in science and technol-
ogy using our case studies as an example rather than advances in individual disci-
plines. The direct consequence of our approach is that this book covers a large
rangeoftopics.Itislikelythatwehaveomittedsomematerialeitherforclarityor
lack ofspace butwe assist the interestedreader by pointing them to aselect bibli-
ography at the end of each chapter. Finally, we expect the book to be adopted in
introductory courses on microfluidics and nanofluidics as it covers all the essen-
tials. Therefore, some chapters present exercises in the text with additional pro-
blems available on the companion website. In addition, the companion website
(which includes all chapters in digital form) presents a unique advancement in
sharing knowledge through books. We present a purely digital chapter that dis-
cusses several experimental methods relevant to microfluidics and nanofluidics.
The goal of this e-chapter is to demonstrate a variety of laboratory scale techni-
ques that are usually lost in the print format. Therefore, our book presents a first
comprehensive effort at viewing the discipline of microfluidics and nanofluidics
from an application standpoint driven by a systems approach by drawing upon
underlyingtheoriesandadvancesinfabrication.
Shaurya Prakash and JunghoonYeom
ix
About the Authors
Shaurya Prakash received his B.S. in mechanical engineering from the
University of Arkansas, Fayetteville, in 2001, and went on to receive his M.S.
and Ph.D. degrees also in mechanical engineering from the University of Illinois,
Urbana-Champaign, in 2003 and 2007, respectively. He has been on the faculty at
the Ohio State University since 2009 in the Department of Mechanical and
Aerospace Engineering. He is the director of the Microsystems and Nanosystems
Laboratory at OSU, and has published over 20 archival journal articles, 50
conference papers, and 4 book-chapters on various aspects of microsystems and
nanosystems. His research focuses on developing microsystems and nanosystems
for applications in water purification, renewable and alternate energy, and health-
care systems. His group addresses fundamental scientific questions and strives to
develop new technologies for problems important to modern societal needs. The
research work is multidisciplinary and often requires bridging several fields
includingmechanical engineering, surface chemistry, andmaterials science.
JunghoonYeomreceivedhis B.S. inmechanicaldesignandproductionengineer-
ing from Yonsei University, Seoul, Korea, in 2000, and his M.S. and Ph.D. in
mechanical engineering from the University of Illinois, Urbana-Champaign, in
2003 and 2007, respectively. He is an assistant professor in the Department of
Mechanical Engineering at Michigan State University and the director of
Nanomaterials, Nanomanufacturing, Nanodevice Laboratory. Prior to joining
MSU, Dr. Yeom was an NRC research associate at Naval Research Laboratory in
Washington DC and a research scientist at Cbana Labs Inc. in Illinois. He was
also a visiting scholar in the Department of Mechanical Science and Engineering
at University of Illinois, Urbana-Champaign, and affiliated with the nano-
CEMMS center. His research group focuses on developing unconventional nano-
manufacturing platforms, photocatalysis, and gas sensing and separation. He is a
coauthor of a book chapter, over 20 journal publications, and more than 50 con-
ference proceedings in the field of chemical sensors, NEMS/MEMS, micro/nano-
fluidics, fuel cells, and gas sorbents technology.
xi
Acknowledgments
Any authorof abookwill disclose thatwriting abook,even asingle volume such
as this one, is an arduous task. We acknowledge the support of many key indivi-
dualsincompleting this task.
We owe many thanks to several special people. We would like to thank our
familiesfortheirenormouspatienceandconstantencouragementduringtheentire
process, from the initial concept to writing and going through all the details of
publishing. Shaurya’s wife, Ruchika, and Jung’s wife, Hyokyoung, have been a
pillar of strength and have provided wonderful feedback on several aspects of
writing, while managing many responsibilities and allowing us the time to under-
take this academic exercise. No words can express our heartfelt thanks to both of
them. We also appreciate the support of our parents who nurtured the curiosity in
us to grow as a scientist and an engineer, which was instrumental in initiating this
effort and taking itto completion.
Both of us thank the entire microfluidics and nanofluidics community of
researchers for providing us with ample creative and wonderful scientific material
to discuss. Among this group, a few select individuals have influenced us both
professionally and personally that made the task of writing this book an enjoyable
journey. In particular, we thank our Ph.D. advisor, Prof. Mark Shannon at the
University of Illinois, for teaching us the value of communicating scientific
results and sharing our knowledge with the broad scientific community. He also
was instrumental in training us with all the fundamentals on building successful
systems. We are both deeply indebted to Mark. We also would like to take this
opportunity to thank our graduate students, co-workers, collaborators, research
mentors, and friends who made numerous contributions to the book and whose
work appearsinseveral places includingthe Select bibliography.
Without all these wonderful people,this book would notbepossible.
Shaurya Prakash and JunghoonYeom
xiii
Nomenclature List
Symbols
γ interfacial energy the liquid(cid:1)fluid interface
LF
γ interfacial energy for the solid(cid:1)fluid interface
SF
γ interfacial energy for the solid(cid:1)liquid interface
SL
ΔW adhesionenergy per unit area of contact
SLF
ε
permittivity offreespace
0
ε
complexdielectric permittivity ofthe medium
m
ε
complexdielectric permittivity ofthe particle
p
ε
dielectric permittivity
r
ζ
zeta potential
η
liquid viscosity
θ
fraction ofsurface sites occupied
θ
contact angle
c
θ
contact anglefor a rough surface
c,R
κ
inverse of the Debyelength
λ
Debye length
D
μ
electroosmotic mobility
EOF
μ
ionic mobility
i
μ-Nafl microfluidic and nanofluidic
ρ
fluid density
ρ
liquid density
l
ρ
charge density
e
ρ
gas (other fluid in the capillary)density
F
σ
surface tension
σ
surface charge
s
τ
shear stress
shear
ϕ
surface potential at the wall
s
A fractionalarea of phase i
Fi
Bo Bond number
b aconstant related tothe adsorbent
c concentration ofthe adsorbing species near the surface
C differentialcapacitance
d
D binary diffusion coefficient of the species of interest
AB
De Dean number
xv
xvi Nomenclature List
D diffusioncoefficient
i
E electric field
F force
F Faraday’s constant
f applied body forces
B
f Clausius(cid:1)Mossottifactor
CM
F drag force
D
F dielectrophoreticforce
DEP
g acceleration due togravity
I ionic strength of electrolyte
J total current density
A
J molar flux ofthe ithspecies
i
k adsorption rate constants
a
k Boltzmann constant
B
k desorption rate constants
d
L length
l characteristic length
c
n local concentration
i
p applied pressure
q charge
q elementary charge
e
R gas constant
R and R radii ofcurvatureof the surface along anytwo
1 2
orthogonal tangentsdifferential capacitance, C
d
Re Reynolds number
SA surface area
S surface roughness factor
R
St Strouhal number
S Stokesnumber
t
T absolute temperature
t diffusiontime scale
d
u bulk fluid velocity
u, v, w beingthe x, y, andz componentsofthe velocityvector
V volume
V applied potential
z valence
i
Nomenclature List xvii
Common Abbreviations
AFM atomic force microscope
Al aluminum
Au gold
Cr chromium
CVD chemical vapor deposition
DRIE deep reactiveion-etching
EDL electricdouble layer
FTIR Fourier transform infrared
IPA isopropanol
NCAM nanocapillary arraymembrane
PDMS poly dimethylsiloxane
PI polyimide
PMMA poly (methylmethacrylate)
PR photoresist
RIE reactive ion-etching
SEM scanningelectron microscope
Si silicon
SSN solid-state nanopore
TEM transmission electronmicroscope
XPS X-ray photoelectron spectroscopy
CHAPTER
1
Introduction
CHAPTER OUTLINE
1.1 Lengthscales......................................................................................................1
1.2 Scopeandlayoutofthebook...............................................................................6
1.3 Futureoutlook......................................................................................................7
References.................................................................................................................8
Selectbibliography.....................................................................................................8
1.1 Length scales
Microfluidicandnanofluidic(µ-Nafl)systemsaredefinedassystemswithfunctional
components with operational or critical dimensions in the 1(cid:1)100µm range for
microfluidicsand1(cid:1)100nmfornanofluidics,respectively.Therefore,wenowhave
the ability to study and systematically manipulate exceedingly small volumes
(approaching the order of zeptoliters or 10221l has been discussed in literature and
listed in several bibliographic references throughout this book) of fluids and
other species. Consequently, the ability to engineer processes and phenomena that
operateatfundamentalmolecularlengthsdrivingahostofapplicationsinchemical,
biological,andparticleseparations,sensors,energygenerationandharvesting,envi-
ronmentalremediation,waterpurification,andattheinterfaceofseveralscienceand
engineering disciplines is being pursued. Figure 1.1 shows a conceptual plot that
depicts how the interplay between critical length scales and subsequent device
volumescandriveseveralapplicationsforµ-Naflsystems.
An identifying feature of all µ-Nafl systems is the surface-area-to-volume
(SA/V) ratio. Consider two examples: (1) a simple circular cross-section nanopipe
with a diameter of 10nm and a length of 1µm will have a SA/V ratio on the
order of 107m21 and (2) a microchannel with a rectangular cross-section with a
width of 100µm, depth of 20µm, and a length of 1mm will have an SA/V ratio
on the order of 105m21. The discussion for SA/V ratios is pertinent because sev-
eral forces and related phenomena important to fluid transport at these length
scales change as SA/V ratios increase, as the governing principles dominating
these phenomena assume different relative magnitudes. For example, in the
1
S.Prakash&J.Yeom:NanofluidicsandMicrofluidics.DOI:http://dx.doi.org/10.1016/B978-1-4377-4469-9.00001-9
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