Electro-Osmosis of Polymer Solutions: Linear and Nonlinear Behavior

84 Pages·2017·3.167 MB·English

by  Yuki Uematsu (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Yuki Uematsu

Electro-Osmosis of
Polymer Solutions
Linear and Nonlinear Behavior
Springer Theses
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Yuki Uematsu
Electro-Osmosis of Polymer
Solutions
Linear and Nonlinear Behavior
Doctoral Thesis accepted by
Kyoto University, Kyoto, Japan
123
Author Supervisor
Dr. YukiUematsu Prof. TakeakiAraki
Department ofChemistry KyotoUniversity
Kyushu University Kyoto
Fukuoka Japan
Japan
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-981-10-3423-7 ISBN978-981-10-3424-4 (eBook)
DOI 10.1007/978-981-10-3424-4
LibraryofCongressControlNumber:2016962038
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’
Supervisor s Foreword
Electro-osmotic flow is the motion of liquid that results when an external electric
fieldisapplied.Itwasfirstreportedmorethan200yearsagoandhasbeenutilized
in a variety of applications in chemical engineering and biotechnology.
Electro-osmoticflowiscausedbymobileelectrolytesnearchargedwalls,sothatit
ismostsignificantwhentheliquidisconfinedinnarrowchannels.Theflowisoften
argued with a coarse-grained theory based on the hydrodynamic equation and the
Poisson–Boltzmann equation, which describes the distributions of the electrolytes.
Itpredictsthattheelectro-osmoticflowisproportionaltotheexternalfieldstrength
and the electrostatic potential at the surfaces.
In recent years, interest in its application has been growing significantly. It can
be used to pump liquids in microfluidic devices, as it is more easily implemented
thanpressure-drivenflows.Also,itsapplicationtoanelectricalpowerconversionis
of great interest in chemical engineering. In order to improve the efficiency of
devicesusingelectro-osmosis,thestructuresofliquidinterfacesincontactwiththe
charged surfaces are modified by grafting polymers or adding polyelectrolytes. In
them, some detailed experimental observations demonstrated linear and non-linear
behaviors beyond the conventional theory. For example, it was reported that the
electrokinetic mobility changes with the polyelectrolyte concentration.
Furthermore,thedirectionoftheelectrokineticmotioncanbereversedinasolution
of high polyelectrolyte concentrations.
This thesis was written by Yuki Uematsu, who has tackled these classical and
new problems on the electro-osmosis of polymer solutions theoretically and
numerically.Inthisthesis,hedemonstratedtwoofhismainachievements.(1)The
effect of polyelectrolytes on electro-osmosis is considered. He solved the spatial
distribution of the polyelectrolyte monomer near the surface and the resultant
non-uniformityofthesolutionviscosity.Hefoundthattheelectro-osmoticmobility
changes with the polyelectrolyte and small ions, and demonstrated a possibility of
mobility reversal. (2) He considered the effect of uncharged polymer chains on
electro-osmosis. In the electro-osmotic flow, the shear gradient of the flow is
localized near the surface within the Debye screening length. Under the localized
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vi Supervisor’sForeword
shear gradient, the theoretical analysis of a kinetic theory and the corresponding
numerical simulations with hydrodynamic interactions showed that the polymer
conformations are changed and the polymers are expelled from the surface.
Althoughtheelectricexternalfielddoesnotactonthepolymerchains,theyleadto
non-linear dependence of the electro-osmotic flow.
The schemes and results in this thesis are based on theoretical physics but will
provide simple and clear insight for understanding experimental results on
electro-osmosis and improving their application properties. I am confident that not
only graduate students in theoretical physics but also researchers in many fields
suchasbiology,chemistry,andengineeringwillenjoyreadingthisSpringerThesis.
Kyoto, Japan Takeaki Araki
October 2016 Associate Professor
Kyoto University
Parts of this thesis have been published in the following journal articles:
1. Y. Uematsu and T. Araki, Electro-Osmotic Flow of Semidilute Polyelectrolyte
Solutions, J. Chem. Phys. 139, 094901 (2013).
2. Y. Uematsu, Nonlinear Electro-Osmosis of Dilute Non-Adsorbing Ploymer
Solutions with Low Ionic Strength, Soft Matter 11, 7402–7411 (2015).
vii
Acknowledgements
ItismygreatpleasuretoacknowledgeProf.TakeakiArakiasthesupervisorofmy
research.Duringmymaster’sandPh.D.coursesinKyoto,hecontinuedtosupport
me.Withouthissupport,thisthesiscouldnothavebeenaccomplished.Iwouldalso
like to thank the members of my group: A. Onuki, R. Okamoto, T. Kawasaki,
K.Takae,M.R.Mozaffari,andT.Uchida.Theyhelpedmeinmydailylifeandheld
many discussions with me. I very much enjoyed the life in that group at Kyoto
University. I would also like to thank members of the Electrokinetic Society of
Japan: H. Ohshima, Y. Adachi, M. Kobayashi, H. Washizu, H. Yoshida, and
T.Sugimoto.Itwasagreatopportunityformetomeetthemanddiscussmyinterest
inelectrokinetics.Inaddition,Ithanktheseresearchersabroad:R.R.Netz,C.Holm,
F. Zhang, O.A. Hickey, J.F. Joanny, D. Andelman, and D.J. Bonthuis. I have had
several long stays overseas to visit them. I truly enjoyed experiencing foreign
cultureandtheacademicatmosphere,especiallyinGermany.NowIfeelthatthese
experiencesledmetoworkasapost-docinBerlin.Finally,Ithankmyparentsand
wife for their warm support.
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Contents
1 Introduction .... .... .... .... .... ..... .... .... .... .... .... . 1
1.1 General Introduction .. .... .... ..... .... .... .... .... .... . 1
1.2 Electrolyte Solution... .... .... ..... .... .... .... .... .... . 6
1.3 Structure of Electric Double Layer..... .... .... .... .... .... . 8
1.4 Electrokinetic Transport.... .... ..... .... .... .... .... .... . 12
1.5 Theory of the Stern Layer .. .... ..... .... .... .... .... .... . 17
1.5.1 Gouy-Stern Double-Layer Model with Specific
Adsorption of Ions.. .... ..... .... .... .... .... .... . 17
1.5.2 Shear Plane and Saturation of Electrokinetic Charge . .... . 19
1.5.3 Continuum Model Using Nonuniform Permittivity
and Viscosity .. .... .... ..... .... .... .... .... .... . 21
1.6 Basis of Polymer Physics... .... ..... .... .... .... .... .... . 23
1.6.1 Gyration Radius of a Polymer .. .... .... .... .... .... . 23
1.6.2 Continuum Model of Polymer Solution ... .... .... .... . 25
1.6.3 Polymer at an Interface .. ..... .... .... .... .... .... . 28
1.6.4 Charged Polymers .. .... ..... .... .... .... .... .... . 29
References .. .... .... .... .... .... ..... .... .... .... .... .... . 30
2 Linear Electro-Osmosis of Charged and Uncharged Polymer
Solutions ... .... .... .... .... .... ..... .... .... .... .... .... . 33
2.1 Mean-Field Equations for Concentrations, Electrostatic
Potential and Flow.... .... .... ..... .... .... .... .... .... . 33
2.2 Electrically Neutral Polymer Solution with Chemically
Repulsive Surfaces.... .... .... ..... .... .... .... .... .... . 37
2.3 Polyelectrolyte Solution with Chemically Repulsive Surfaces .... . 39
2.3.1 Relationship Between Electro-Osmosis and Static
Properties. .... .... .... ..... .... .... .... .... .... . 40
2.3.2 Relationship Between Electro-Osmosis
and Dynamical Properties. ..... .... .... .... .... .... . 43
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