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Polymers and polyelectrolytes (437-442)
COLL
437: Electric birefringence of stiff-chain
polymers in solution
Wilhelm Oppermann, Institute of Physical Chemistry, Technical
University of Clausthal, Arnold-Sommerfeld-Strasse 4, 38678
Clausthal-Zellerfeld, Germany, Fax: 49-5323-722863, wilhelm.oppermann@tu-clausthal.de
Abstract
Dilute aqueous solutions of stiff-chain polyelectrolytes having a
poly(p-phenylene) (PPP) backbone were studied by means of electric
birefringence and some supplementary conductivity measurements. The PPP
polyelectrolytes form molecular solutions, whose electrically induced
birefringence rises with field strength according to Kerr's law. From an
estimate of the optical anisotropy of the chain backbone it becomes clear
that the anisotropy of the ionic polarizability responsible for the
orientation in an electric field is about 5-6 orders of magnitude larger
than that of the electronic (optical) polarizability. It increases
markedly with rising molecular weight (rod-length) of the polyelectrolyte.
The anisotropy of the electric polarizability seems to be due to the ion
cloud and not to the condensed ions. This interpretation is obtained from
a comparison of the changes of electric birefringence and electric
conductivity upon addition of a low molecular weight electrolyte.
COLL
438: Polymer alloys with colloidal-size phases
prepared in electric fields
Sonja Krause, Jing Li, and Nikolaos Bentenitis, Department of
Chemistry, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY
12180-3590, Fax: 518-276-4887
Abstract
Polymer alloys with colloidal sized inclusions were prepared in two ways:
(1) After two immiscible polymers were dissolved in a mutual solvent, the
solvent was evaporated in an electric field, and (2) a polymer or
nanoparticles were dissolved in a monomer and the monomer was polymerized
in an electric field. Method 2 generally formed smaller dispersed phases
than method 1. Also, in method 2, the dispersed phase was not always the
same polymer as obtained when the alloy was prepared in the absence of an
electric field. Both AC and DC fields were used. The dispersed phases were
elongated either parallel or perpendicular to the field direction,
depending on the conductivities and dielectric constants of the dispersed
and the matrix phases. An existing theoretical treatment for the dispersed
phase distortions in small electric fields was extended to high electric
fields. A few of its predictions will be compared with experiment.
COLL
439: Nanoscale charge nonuniformity on colloids in
the presence of surfactants and polyelectrolytes
Darrell Velegol, and Jason Feick, Chemical Engineering, Penn State
University, University Park, PA 16802, Fax: 814-865-7846, velegol@psu.edu
Abstract
The classical models for colloidal forces have assumed uniform charge
distributions on the particle surfaces. Recent papers have shown that a
nonuniform charge distribution on two colloidal particles will
significantly reduce colloidal stability from predictions based on a
uniform charge distribution. Thus, nonuniform charge distributions can
cause unexpected suspension stability, structure, and rheology. But using
the technique of “rotational electrophoresis” (which combines video
microscopy measurements of electrophoretic angular velocities with
interpretations from electrokinetic theory), we have previously obtained
data showing that particles are nonuniformly-charged on a nanoscale. Now
we have examined the effects of adding surfactants (e.g., SDBS) and
polyelectrolytes (e.g., sodium polystyrene sulfonate) on charge
nonuniformity on polystyrene latex particles with sulfate charge groups.
These additives have been found to reduce charge nonuniformity on the
particles.
COLL
440: Microfabrication of polymers for
optoelectronics and biomedical applications
Toshiyuki Watanabe, Youmei Lu, Fuyuki Hasegawa, Fumiko Chiba,
Noriko Kimura, Mari Tsubouchi, and Kenro Totani, Department of Oraganic
and Polymeric Material Systems Engineering, Tokyo University of
Agriculture and Technology, 2-24-16 Nakacho, Koganei-shi, Tokyo 184-8588,
Japan, Fax: +81-42-388-7289, toshi@cc.tuat.ac.jp
Abstract
Recent progresses in mesoscopic pattern formation of polymers are reviewed
from the view point of nanotechnology of bottom-up materials function. The
radical photoinitiation characteristics of novel chromophores under
two-photon excitation are reported. Photo-crosslinkable resins were
formulated with these initiators and were used to fabricate a variety of
complex three-dimensional structures by two-photon induced polymerization
(TPIP). These structures illustrate that TPIP can be a highly versatile
technique for the rapid single-step fabrication of complex microstructures
and devices. The new two photon resins were found to be as much as 100
times more sensitive than resins containing conventional UV initiators.
TPIP was applied to produce photonic crystals, photoresposive micromachine
and elastic substrate for tissue engineering.
COLL
441: Unraveling an old mystery: The anomalous
electric birefringence of concentrated polyelectrolytes
Tommaso G. Bellini, Dpt Chimica, Biochimica e Biotecnologie per la
Medicina, University of Milano, via Cervi 93, Segrate (MI) 20090, Italy,
Fax: +39 02 50330365, tommaso.bellini@unimi.it, and Francesco Mantegazza,
Dpt Medicina Sperimentale, University of Milano "Bicocca"
Abstract
For over 60 years encompassing about 100 reports, "anomalous
birefringence" has been observed in concentrated aqueous solutions of
nonspherical polyelectrolytes: their electro-optic susceptibility (e.g.,
electric birefringence) changes its sign upon increasing the particle
concentration. This indicates that at high concentration the particles
align, on average, their longest axis perpendicular to the electric field
– without satisfactory explanation. In this work we present an
experimental and theoretical investigation of the phenomenon aimed at
giving a common denominator to the whole body of recent and older
observations. At variance with previous understanding, we show that the
origin of this effect can be described in terms of single particle
mechanisms, and we propose a theoretical model to interpret the results.
Anomalous birefringence is a pseudo-collective electrokinetic phenomenon:
the high concentration of polyelectrolytes effectively modifies the
mobility of co-ions and counter-ions, in turn changing the anisotropy of
the polarizability of each single particle.
COLL
442: Electro-optics of self-assembled multilayers
of strong polyelectrolytes
Tsetska Radeva, Viktoria Milkova, and Ivana B. Petkanchin,
Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia
1113, Bulgaria, radeva@ipc.bas.bg
Abstract
Electrical properties and structure of polyelectrolyte multilayers
prepared by layer-by-layer deposition of poly(sodium 4-styrenesulfonate)
(PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) on ellipsoidal b-ferric
hydrous oxide particles are examined in situ using electric light
scattering method. In the initial nonlinear growth regime, the
electro-optical effect is found to increase almost in the same manner as
the thickness of the multilayer film. This reveals an increase in the
multilayer surface charge due to the nonlinear increase in the
polyelectrolyte adsorption. Above five deposition cycles, the
electro-optical effect reaches a plateau and the thickness increment per
layer becomes constant, thus indicating regular film growth. Evidence is
given that the concentration of small residual ions, incorporated into the
PSS/PDADMAC film, is negligible. Polarization of counterions, bound near
to the surface of the last-adsorbed polyion, is supposed to explain the
relaxation of the electro-optical effect in the 103-105
Hz frequency range.
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