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Advances in methodology (152-159)
COLL
152: Colloidal electro-optics in nanotechnology
research: Characterization of composite nanoparticles (Kerr Medal
Address)
Stoyl P. Stoylov1, Maria Buleva1, Galina Bila2,
and Ivana B. Petkanchin1. (1) Institute of Physical Chemistry,
Bulgarian Academy of Sciences, Sofia 1113, Bulgaria, (2) Institute of
Biocolloid Chemistry, Ukrainian Academy of Sciences
Abstract
Recently, nanocomposites and hybrid nanoparticles have attracted the
attention of investigators. This concerns their formation to obtain
materials with desired properties and methods for their characterization.
Determination of the surface electric properties (dipole moments), the
optical anisotropy and size distribution of nanocomposite particles would
help clarify the processes of their formation and would advance the
development of on-line control for their production. In composite
particles, adsorption of small and/or spherical particles on larger
anisometric particles renders the former particles accessible to
electro-optical characterization. Thus it becomes possible to attack some
fundamental problems such as the mechanisms of build-up of permanent
dipole moment and slow electric polarizability, and the mechanism of
electrical charging of nanoparticles as well. Experimental results,
obtained on ferric oxide/silica nanoparticles, illustrate the utility of
electro-optic methods for characterizing such objects. These methods are
extremely useful in following the “construction” of composite and/or
hybrid nanoparticles.
COLL
153: Frequency-domain electric birefringence study
on the deformation dynamics of microemulsion droplets
Takeshi Shimomura, and Kohzo Ito, Graduate School of Frotier
Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656,
Japan, Fax: +81-3-5841-6853, simo@exp.t.u-tokyo.ac.jp
Abstract
Electric birefringence has been applied widely to solutions of polymers,
micelles and colloids in order to investigate the microscopic
electro-optical properties closely related to the conformation and
polarization of molecules. Further, a time-dependent electric field yields
electric birefringence relaxation, which provides information on the
dynamic behavior of molecules, such as molecular rotation, deformation and
polarization. So we applied the frequency-domain electric birefringence
(FEB) method to deformable droplets in order to investigate their
deformation dynamics. At first, we derived theoretically the second-order
nonlinear response function from the diffusion equation of the deformable
droplet with induced dipole moment. Further, we applied this formula to
the experimental results obtained by the FEB method for water/AOT/isooctane
(w/o) microemulsion system (L2 phase) and obtained the bending modulus of
the amphiphilic layer, which plays an important role in the stability of
the microemulsion structure.
COLL
154: Wide-band spectroscopy of dynamic
electrophoretic mobility and its application to microrheology
Daisuke Mizuno, Yasuyuki Kimura, and Reinosuke Hayakawa, Department
of Applied Physics, School of Engineering, University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, Fax: +81-3-5841-6853, mizuno@exp.t.u-tokyo.ac.jp
Abstract
We developed a novel method for measuring wide-band spectrum of dynamic
electrophoretic mobility m*(w)
of charged colloids. This method has been verified to provide rich
information on 1)surface electrical properties of charged colloids,
2)local viscoelastic properties of solvent surrounding a
well-characterized colloidal particle (microrheology). As a typical
example of latter case, we report on the m*(w)
of nanometer-sized particles dispersed in a dilute lamellar phase of a
nonionic surfactant. Its frequency dispersion shows two relaxation
processes around 1kHz(HF) and 1Hz(LF). It is quantitatively shown that
these processes are caused by trapping of particles within the two
characteristic local structures of lamellar phase. That is, interbilayer
distance for HF and persistence length for LF, respectively. Our findings
on the transport properties of particles in complex fluids may be
applicable to the transport phenomena of proteins and secretions in
biological system.
COLL
155: Electro-optic and electrophoretic research of
colloid dispersions of high electric conductivity
Oksana Kolesnikova, Anatoli Trusov, Alexei Voitylov, Vladislav Vojtylov,
and Tatiana Zernova, Department of Physics, St. Petersburg State
University, Ulianovskaja 1, Sankt-Petersburg 198504, Russia, Fax:
07-812-4287240, o_kolesn@mail.ru, Vladislav.Voitylov@paloma.spbu.ru
Abstract
While studying the electric properties of colloid particles we developed
new methods and equipment which allowed us to study electrophoretic and
electrooptic properties of the system simultaneously. We made the
following conclusions: 1. Change of the electrooptic effect due to
electrophoresis allows to determine the correlation between charge,
polarizability and size of the particles, and also check the
Helmholtz-Smoluchowski equation for colloid systems. 2. Drop of volume of
colloid systems does not influence some electro-optic dependencies. This
changes the experimental conditions from adiabatic to isothermal and
allows us to study nonlinear electrooptic effects (that requires strong
electric field) in systems of high electric conductivity. Existing theory
of electrokinetic phenomena corresponds to the results of electrophoretic
experiments on such systems. 3. Determination of particle distribution
functions on their parameters from the electrooptic experiment allows us
to study the electrooptic and electrokinetic properties of colloid
particles in more details.
COLL
156: Quantitative approach to molecular
electro-optics: Combined structure-dipole analysis
Dietmar Porschke, Biomolecular Dynamics, Max Planck Institut für
biophysikalische Chemie, Am Fassberg 11, Göttingen 37077, Germany, Fax:
-551-2011168, dpoersc@gwdg.de
Abstract
A quantitative approach to molecular electro-optics with automatic
calculation of electric dichroism data from known macromolecular
structures is reviewed. Examples for application of this procedure and its
use for structure analysis in solution to various examples are
demonstrated. – The electric dichroism of bacteriorhodopsin shows a
special pH-dependence with a lambda-point at pH 4.9 – close to the pH
where a reversal of the dipole moment has been reported. However, the
dichroism does not approach zero, which would be expected for a simple
dipole reversal. Stationary dichroism data demonstrate a minimum of the
dipole moment m at pH 4.9, but m-values
are far from zero. This is attributed to a fluctuating dipole moment.
Measurements using a field+pH-jump-instrument confirm reversal of the
dipole moment at pH 4.9. Comparison of experimental with calculated
dipoles demonstrate a large dipole component directed opposite to the
protein dipole. Implications of these results for biological function are
discussed.
COLL
157: Laser temperature jump experiments with
nanometer space resolution using rhodamine 101 anti-Stokes fluorescence
from nanoseconds to milliseconds for precise measurements of temperature
changes in liquid microenvironments
Josef F. Holzwarth, Physical Chemistry, Fritz-Haber-Institute, MPG,
Faradayweg 4-6, D-14195 Berlin, Germany, Fax: +49 30 8413 5385, holzwarth@fhi-berlin.mpg.de,
S. Couderc, Physical Chemistry, Fritz-Haber-Institut, MPG, Andrew Beeby,
Department of Chemistry, University of Durham, Ian P. Clark, Laser for
Science Facility, Rutherford Appelton Laboratories, and Anthony W. Parker,
Central Laser Facility, CLRC Rutherford Appleton Laboratory
Abstract
Measurement of temperature changes in nanoliter volumes is a serious
problem, especially if both high precision and nanosecond time resolution
are required. Exploitation of the anti-Stokes fluorescence of
laser-excited Rhodamine 101 dye offers a solution to the problem. We used
a pulsed dye laser (bandwidth 20 ns) for time resolved measurements. The
T-jump laser and the pulsed detection laser were aligned inside a 1 mm
spot of a liquid sample. A DT=4 K
caused 10% increase in fluorescence intensity. The detection was performed
with a variable delay between 10 ns and 100 ms after the heating. We could
observe special effects caused by shock-waves produced by the fast thermal
expansion of the liquid sample. This new technique of time resolved
anti-Stokes fluorescence measurements provides a convenient and precise
tool to measure small temperature changes in nano-volumes of liquid
samples under many different experimental conditions.
COLL
158: Development of a micronized electrical
field-flow fractionation instrument with an improved electrode system
Rik ter Veen1, Mats Jönsson2, Jesper
Gantelius1, Ulf Lindberg2, and Karin D. Caldwell3.
(1) Center for Surface Biotechnology, University of Uppsala, BMC, Box 577,
751 23 Uppsala, Sweden, Fax: +46-18-555016, Rik.Terveen@ytbioteknik.uu.se,
(2) Department of Materials Science, University of Uppsala, (3) Center for
Surface Biotechnology, Uppsala University
Abstract
Electrical Field-Flow Fractionation (ElFFF) is an analytical technique
that separates particles by an electrical field perpendicular to a laminar
flow field [1]. With increasing field strength, smaller particles can be
analyzed. In ElFFF, the field strength depends on the channel thickness
[2] and on the effectivity of the electrode system. We present a
micronized ElFFF channel with optimized electrodes and detection and
injection in the channel. In current electrode configurations, the
effective field strength is approximately 1% of the nominal field strength
due to a slow or an ion-producing electrode reaction. The new optimized
electrode system reacts fast with protons in the carrier liquid. This
leads to a strong increase in effective field strength. This should make
it possible to analyze particles as small as proteins.
1.
K.D. Caldwell, Y.-S. Gao, Anal. Chem., 48, 1834 (1993)
2.
B. Gale, et al., Anal. Chem., 73, 2345 (2001)
COLL
159: Polarization of the gas/liquid interface
Stoyl P. Stoylov, and Maria Buleva, Institute of Physical
Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev str., bl. 11,
1113 Sofia, Bulgaria
Abstract
The deformation of a gas-liquid interface in an inhomogeneous alternating
electric field (sharp electrode 30 micrometers above the interface) is
studied by micro-interferometry. A quadratic dependence of the magnitude
of deformation on the electric field strength in the range 0 to 4 x 106
V/m was found at all frequencies investigated. The magnitude of the
deformation at high electric field strengths showed a dispersion in the
range 160 kHz-2 MHz. This dependence together with the observed weak
dependence of the magnitude of deformation on the ionic strength, pH and
the addition of ionogenic surface active substances was interpreted as a
manifestation of the predominant role of Maxwell-Wagner polarization. The
relation of these results to the electro-optically determined interfacial
polarization, and the colloid forces connected with it, is discussed.
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