Electrokinetic Phenomena of Colloid Polymer Complex and Flocs

概要

Electrokinetic Phenomena of Colloid Polymer
Complex and Flocs
SAHA SANTANU
Student ID: 201936028
Supervisor: Adachi Yasuhisa
A Dissertation Submitted to the Graduate School of Life and Environmental Sciences,
the University of Tsukuba
in Partial Fulfillment of the Requirements
for the degree of Doctor of Philosophy in Bioresource Engineering
(Doctoral Program in Appropriate Technology and Sciences for Sustainable Development)

Summary of the Dissertation
Throughout this thesis, I have addressed some fundamental issues relating to electrokinetic
transport of a colloidal complex which includes environmental as well as biological entries such
as soil colloidal particles are turbid in an aquatic environment, living cells, and microorganisms
exist in nature. Such colloidal complex exist in the form of dispersed particle, soft particles i.e.
particle covered by some flocculant mostly polymer and porous formed. Thus, the transport
characteristics of the colloidal complex is important is necessary to evaluate.In the introductory
chapter, I reviewed the principle fluid mechanics and the fundamental mechanisms of electrokinetic transport. Additionally, the basic equations governing the transport of such particles
are described. In the following chapters, I present the major contribution in electrophoretic
transport phenomena of charged particle covered by uncharged polymer and colloidal porous
aggregate.

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Four chapters (Chapter-2 to Chapter-5) comprise this thesis, as well as an introductory
chapter (Chapter-1).
In an introductory chapter (Chapter-1), electrohydrodynamics of charged particles is described by the basic equations of electro-hydrodynamics. I have also illustrated mainly the
electrophoretic transport of colloids covered by neutral polymer and porous aggregate. Each
chapter begins with a description of the problem, followed by a bibliographic review, a discussion of the motivation for the problem, and an outline of its applicability. The experimental or
theoretical methods are then presented. A discussion of the results has been conducted with
the assistance of relevant data and plots. I have given a concise summary of the results of each
study at the end of each chapter. Below are the outlines of the problems I investigated.
In Chapter-2, Chapter-3 and Chapter-4, I have investigated the adsorption and electrophoretic study of of a colloidal particle adsorbed by a polymer. In Chapter-2, I have studied
the shielding properties of negatively charged polystyrene latex with sulfate/sulfonate group
adsorbed by electrically neutral polyethylene oxide (PEO). The study is conducted with various
ionic strength to control the ion cloud around the particle and different molecular weight of the
polymer PEO. Our findings emphasis that the expectation of producing electrically neutral colloid by adsorption of uncharged polymer should be revised. The stability of colloid characterizes
by electrophoretic mobility decreases while developing the adsorbed layer thickness and reaches
a plateau form has been revisited. This tendency is the same as formation of adsorbed layer
thickness on particle resulting steric stabilization. And that the absolute value of mobility decreases more sharply at higher ionic concentrations regardless of molecular weight reflecting the
shift of slipping plane outward from the surface. Furthermore, the dependency of the mobility
of latex particles on the molecular weight of the polymer is also clearly found. That is adsorbed
with higher molecular weighed polymer results lesser electrophoretic mobility. However, most
interestingly, in any cases, it can be observed that the absolute value of EPM never reaches zero,
which concluded the electrokinetic shielding can not be completed even though the adsorbed
neutral polymer layer is much saturated.
In Chapter-3 I have extended the experimental work presented in Chapter-2 in order to
validate our results of non zero mobility even though the adsorbed neutral polymer layer is
much thick. I have introduced a simple mathematical model and derived a analytical solution
for electrophoretic mobility of a charged colloidal particle adsorbed by uncharged polymer. The
scaling relation for the distribution of hydrodynamic drag for the structure of adsorbed polymer
layer is been treated as an extension. We restrict ourselves in this study to the low charge density
and weak applied electric field assumptions where the double layer relaxation and polarization
effects are negligible and the Debye-Huckel approximation for the distribution of ions which obeys
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Poisson-Boltzmann. The linearized Poisson-Boltzmann equation is used to obtain the electric
potential distribution. Solving the Navier and Stokes equations, respectively, determines the
fluid velocity field inside the polymer and that in the portion of the cell filled with electrolyte
solution. Our results show that due to the presence of open pores in the polymer layer, particles
in suspensions with net non-zero charge cannot achieve zero electrophoretic mobility. Stokes
drag is a measure of permeability in the polymer layer, which is a result of the solvent flowing
inside. This analytical expression of electrophoretic mobility of such colloid complex is therefore
successful in describing the shielding of electrokinetics by the adsorption of neutral polymers
and validating the experimental data in Chapter-2.
In Chapter-4, the electrophoretic mobility of the negatively charged polystyrene latex (PSL)
with sulfate/sulfonate group under trace amount of electrically neutral polyethylene oxide (PEO)
adsorption has been studied intensively. Various ionic strengths and different molecular weights
of the polymer PEO were used in the study as Chapter-2. It is noted that PSL is hydrophobic in
nature and significant velocity slip appears at the close vicinity of the hydrophobic surface when
a liquid flows over it. In Chapter-2 and 3 I found that the he mobility decreases with increasing
polymer concentration regardless the type of polymer but at smaller dosage of polymer, at very
beginning electrophoretic mobility starts to enhance as polymer dosage increases and reaches
to a local maximum at some certain polymer amount before they decrease and the shielding
occurs. The similar tenancy of increasing EPM for different ionic strength was pointed. Such
loss in the electrophoretic mobility is explained by the hydrophobicity of the particle surface
and the increasing of EPM phenomena occurred due to the elimination of hydrophobicity by flat
like adsorption of hydrophilic polymer onto it. Such unusual phenomena for very dilute polymer
dosage is been discussed throughout the study.

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In Chapter-5, I vigorously discussed about the electrokinetic transport of a different shaped
colloid complex which is the colloidal aggregate. The overall phenomena of electrokinetics of
a aggregate can be demonstrated mainly in three models namely, (a) Miller-Berg-O’Brien, (b)
Hermans-Fujita and (c) Velegol-Anderson-Solomentsev model. In Section 5.2, on the basis of
model proposed by Miller-Berg-O’Brien, I have studied the electrophoresis of concentrated aggregate porous complex of constituent particle by easing the limitation of thin double layer
which was considered by the mentioned model and inserting dimensional slip length of liquid on
the aggregate surface resulting tangential velocity which occurs due to the pore like structure.
A unit cell model introduced by Kuwabara is employed to take into account the effect of the
interaction between neighboring particles. Our restriction in this study to the low zeta potential
and weak applied electric field assumptions where the double layer relaxation and polarization
effects are negligible.The combined effects of double layer and the dimensional slip length of
liquid on the aggregate on the mobility are determined based spherical polar co-ordinate system
based on spherical symmetry. While agreeing with the results obtained by Miller-Berg-O’Brien
for electrophoretic mobility of the aggregate, our shows more realistic while in the situation of
double layer is low i.e. the mobility will be higher for high porosity. In Section 5.3, I have
investigate the electrophoresis of concentrated aggregate porous complex of constituent particle
on the basis of model proposed by Hermans-Fujita. By replacing the particle instead of polymer,
an analytic expression for the electrophoretic mobility, taking into account the surface charge
density of a single constituent particle and particle volume fraction is obtained. Surprisingly,
the expressed mobility data shows some diversity as that of Miller-Berg-O’Brien and the validity of the claimed data remains questionable. In Section 5.4, avoiding the porosity inside a
aggregate, I have considered an aggregate where the particles are rigidly connected resulting
no electroosmosis inside the aggregate since no fluid penetration inside th aggregate which is
the concept model by Velegol-Anderson-Solomentsev. Our motivation is to consider thick double layer (Huckel Limit) in Velegol-Anderson-Solomentsev model starting with doublet leads to
future work. ...