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Rigid particles (402-407)
COLL
402: Electric birefringence and dichroism
measurements on synthetic clays in the presence of adsorbed amphiphilic
compounds
Heinz Hoffmann, Physical Chemistry I, University of Bayreuth, 95440
Bayreuth, Germany, Heinz.Hoffmann@uni-bayreuth.de
Abstract
Adsorption isotherms of surfactants, blockcopolymers, dyes, watersoluble
polymers and proteins adsorbed on clays can be determined via surface
tension measurements. We did electric birefringence and dichroism
measurements on such systems to elucidate the influence of adsorption on
the electric birefringence anomaly. The concentration of clay particles
was adjusted such that the solutions showed large, anomalous signals.
Under these conditions two birefringence or dichroism processes were
induced by a rectangular electric field (E) pulse. The two
processes have different signs and somewhat different rates. The faster
process (FP) is due to alignment of the clay particles parallel to E
while in the second process (SP) they align perpendicular. During SP, the
clay particles act as apparent permanent dipoles. With increasing
adsorption the amplitude of SP disappeared at saturation while FP was
little effected. Disappearance of SP is due to slowing down of the
mobility of condensed counter-ions by the adsorbed molecules.
COLL
403: Anisotropy of electric polarizability of
fractionated bentonite particles in aqueous media
Mistuhiro Matsumoto, Keiko Yamamoto, Saori Fushitani, Kouji Nitta,
and Shinji Yoshima, Department of Chemistry/Faculty of Integrated Arts and
Sciences, University of Tokushima, Minami-Josanjima 1, 770-8502 Tokushima,
Japan, Fax: 088-656-7249, mitsu@ias.tokushima-u.ac.jp
Abstract
The anisotropy of electric polarizability is related to the initial slope
of the intensity of the transmitted light through crossed Nicols after
applying an electric pulse to the flowing solution between parallel
platinum electrodes. Using the theoretical build-up expression up to the
third power of time, we have evaluated the anisotropy of electric
polarizability and the permanent dipole moment for fractionated bentonite
particles suspended in aqueous media. The results show that the anisotropy
of electric polarizability rapidly decreases with an increase of electric
field. On the other hand, the permanent dipole moment is almost constant
but slightly decreases at low fields. We will discuss the relations of the
anisotropy of electric polarizability and the permanent dipole moment with
the electric field and try to analyze the steady-state electric
birefringence.
COLL
404: Interactions between nanoparticles and
between nanoparticles and substrates
Eliza Hutter1, Dipankar Roy2, and Janos H.
Fendler1. (1) Department of Chemistry, Clarkson University,
Center for Advanced Materials Processing, Box 5814, Potsdam, NY
13699-5814, Fax: 315-268-4416, huttere@clarkson.edu, fendler@clarkson.edu,
(2) Department of Physics, Clarkson University
Abstract
Optical, spectroscopic electron- and scanning force microscopic
investigations have demonstrated that the molecular interactions in
nanostructured materials are highly specific and depend on the nature, the
size and the surface characteristics of the components and their
environments. Two examples of our recent work will be used for
illustration. In the first, details will be provided on the size dependent
formation of gold encased silver nanoparticles in aqueous dispersions and
in self-assembled films on gold substrates. In the second example, effects
of the substrate on the formation of self-assembled monolayers (SAMs) and
on the attachment of metallic and semiconducting nanoparticles onto these
SAMs will be discussed.
COLL
405: Electro-optical method of determination of
the type of aggregation kinetics
Alexandar M. Zhivkov, and Stoyl P. Stoylov, Institute of Physical
Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev str., bl. 11,
1113 Sofia, Bulgaria, zhivkov@ipc.bas.bg
Abstract
The light scattering for two types of aggregation of small particles or
macromolecules is numerically analysed for aggregates of spheroidal shape.
In the first type of aggregation all initial particles have formed
clusters, which further coalesce, the number of aggregates decreasing with
time (cluster-cluster aggregation). In the second type of aggregation the
number of aggregates remains constant, while the size of the aggregates
grows through attachment of the initial particles. The dependence of the
light scattering intensity coefficient on the size of the aggregates has a
maximum, whose position is determined by the type of aggregation.
Polydispersity influences only the amplitude of the maxima but not their
positions. Thus measuring the time variation of the intensity of the
scattered light and the variation of the size of the aggregates (e.g., by
the electro-optic relaxation time) it is possible to determine the type of
the aggregation kinetics.
COLL
406: Counterion dynamics in the presence of
polymers as studied by electric light scattering
Ivana B. Petkanchin, Institute of Physical Chemistry, Bulgarian
Academy of Sciences, Acad. G. Bontchev str., bl. 11, Sofia 1113, Bulgaria,
petkanch@ipchp.ipc.bas.bg
Abstract
Important information on the dynamics of counterions, i.e. the relaxation
time of electric polarizability, could be obtained from electric light
scattering studied in the frequency domain. The electro-optical results
obtained for various particles (ferric oxide, SiO2, mica, g-Al2O3), when neutral polymers or
polyelectrolytes are adsorbed on them, are reviewed. The presence of an
adsorbed neutral polymer layer leads to a decrease of polarizability
relaxation time (tg).
In contrast, the adsorption of charged polymers gives rise to an increase
of that time, irrespective of the substrate and polyelectrolyte charge. In
the case of neutral polymer adsorption conformational changes could be
supposed to cause the changes in counterion dynamics. When
polyelectrolytes are adsorbed, the observed increase of tg
is explicable with reduced counterion mobility because of their binding
(“condensation”) on the adsorbed polymer.
COLL
407: Electro-optic and electrokinetic studies of
laponite nanoparticles
Maria Buleva, Alexandar M. Zhivkov, and Stoyl P. Stoylov, Institute
of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Abstract
Electric birefringence measurements on the highly advanced electro-optic
instrument of Dietmar Pörschke have confirmed electron microscopy,
neutron scattering and quasielastic light scattering results that primary
laponite particles may be approximated by thin discs of 30-50 nm diameter.
Further studies on composite b-FeOOH
needle-like particles covered with laponite particles allowed us to
investigate their interfacial electric properties by electric light
scattering. Moreover this made possible to measure the electrophoretic
mobility of the laponite particles by the classical method of
microelectrophoresis. In contrast to composite b-FeOOH-Ludox
particles, in this case the rotational relaxation time and the electric
polarizability considerably increase at pH=5.5. At higher pH (=9.5), the
electric polarizability of b-FeOOH-Laponite
is almost twofold higher than that of b-FeOOH-Ludox,
and the saturated electric light scattering effect is 30% higher. The
authors acknowledge the great help of D. Pörschke in the electric
birefringence measurements.
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