Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Dienstag
the chain length. Furthermore we show how the kinetics of microphase
ordering can be studied on large time and length scales, where entanglement
effects are negligible.
[1] F. Eurich and P. Maass, J. Chem. Phys. 114, 7655 (2001).
[2] F. Eurich, P. Maass, and J. Baschnagel, J. Chem. Phys. 117, 4564 (2002).
CPP 15.29 Di 17:00 B
Changes in the mechansim during isothermal polymer crystallizations:
Indications in scattering experiments on P(E-co-O)
andPεCL — •Barbera Heck, Peter Kohn, and Gert Strobl —
Physikalisches Institut der Albert-Ludwigs-Universität, 79104 Freiburg,
Germany
The kinetics of crystallization in polymer systems can be followed in
different experiments, and a comparison of the corresponding isotherms
provides special insights with regard to the mechanism. We carried
out such comparative studies for samples of poly(ethylene(0.86)-cooctene(0.14))
and poly(ε-caprolactone), employing time-dependent absolute
intensity SAXS coupled with WAXS, density measurements by
dilatometry and optical microscopy.
The measurements on P(E-co-O) showed a strict proportionality of the
Porod-coefficient P and a Bragg-reflection intensity I, but strong deviations
of the development of the density. Optical microscopy shows objects
with constant size but increasing birefringence rather then growing
spherulites. Obviously some densification occurs prior to the formation
of crystals.
For PCL it was found that the power-laws describing the increase in P
and I during the initial stage differ from each other, which is indicative for
a change of the inner order of the growing lamellae. The WAXS-pattern
includes in addition to contributions associated with melt-like regions and
crystals also a third contribution associated with a mesomorphic phase.
CPP 15.30 Di 17:00 B
Orientation of the Microdomains in Concentrated Block
Copolymer Solutions using Electric Fields: Confinement
Effects and Mechanisms — •Kristin Schmidt 1 , Helmut
Hänsel 1 , Frank Schubert 1 , Heiko Zettl 1 , Thomas Weiss 2 ,
Franz Fischer 3 , Volker Abetz 4 , Alexander Böker 1,5 , and
Georg Krausch 1 — 1 Physikalische Chemie II, Universität Bayreuth,
Bayreuth, Germany — 2 ESRF, Grenoble, France — 3 Kristallographie,
Universität Bayreuth, Bayreuth, Germany — 4 Makromolekulare Chemie
II, Universität Bayreuth, Bayreuth, Germany — 5 Department of
Polymer Science & Engineering, University of Massachusetts, Amherst,
USA
We investigate the microdomain orientation of concentrated block
copolymer solutions exposed to a DC electric field by time-resolved synchrotron
SAXS. As a model system, we use a lamellar polystyrene-bpolyisoprene
block copolymer dissolved in toluene. Depending on the
polymer concentration we can identify two different microscopic mechanisms
which dominate the orientation process, i.e. nucleation and growth
of domains and grain rotation. The former dominates close to the ODT,
while the latter prevails under more strongly segregated conditions.
Reduction of the electrode spacing from 2mm to 200µm leads to a
dramatic increase in the time constant of the orientation process, i.e.
it is slowed down significantly. This finding is attributed to a confinement
effect which finally results in complete trapping of the process.
Furthermore, in the case of highly segregated samples we observe that
increasing confinement suppresses the grain rotation mechanism, favoring
nucleation and growth for highly confined systems.
CPP 15.31 Di 17:00 B
Evidence of pre-order in polymer melts revealed from dielectric
spectroscopy — •Andreas Wurm, Ragab Soliman,
and Christoph Schick — Universität Rostock, Fachbereich Physik,
Universitätsplatz 3, 18051 Rostock
Existence and formation of pre-ordered structures as the initial step of
polymer crystallization are discussed controversially. Most of the findings
and interpretations are based on scattering experiments, which test small
density differences between the assumed precursors of the crystals and
the surrounding melt. Because of the low contrast the interpretation of
experimental results becomes often speculative. Contrary relaxation experiments
are probing motions in the sample and are therefore independent
on density contrast. During crystallization material is transformed
from the liquid to the solid state. Consequently, motions (fluctuations)
typical for a liquid become impossible and do not longer contribute to
the measured relaxing signal. For pre-ordered structures we expect some
decrease in mobility too because of the changes in conformation on preordering.
On the other hand due to the formation of regions with different
order new internal surfaces will be formed. At such surfaces Maxwell-
Wagner-Sillars charge carrier relaxation may occur and contribute to the
measured dielectric signal.
We have studied the complex dielectric permittivity of polycaprolactone
(PCL) and polypropylene (sPP) during non-isothermal and isothermal
crystallization in the frequency range from 0.01 Hz to 10 MHz.
CPP 15.32 Di 17:00 B
Electric field induced structural fluctuations in lamellar block
copolymers — •Xiuli Jiang 1 , Thomas Thurn-Albrecht 1 ,
Thomas Gutberlet 2 , Mukul Gupta 2 , and Daniel Clemens 2 —
1 Martin-Luther-Universitaet Halle-Wittenberg,Fachbereich Physik,D-
06099 Halle — 2 Paul Scherrer Institut,Lab. f. Neutron Scattering,5232
Villigen PSI,Switzerland
Lamellar microphase structures formed in symmetric diblock copolymers
[1], as well as cylindrical microdomains formed in asymmetric diblock
copolymers [2], can be oriented by an external electric field. Though
the mechanism of the orientation is not fully understood yet, it is believed
that the electric field induces an instability connected with structural
fluctuations or undulations leading eventually to a disruption of
the original structure which facilitates alignment to set in. Using neutron
reflectometry the current study investigates these undulations in
films of different thicknesses with and without application of an electric
field. To map the intensity in the relevant range of reciprocal space we
use the newly established time-of-flight (TOF) mode on the AMOR neutron
reflectometer at the Paul-Scherrer-Institute. Our results show that
thermally excited fluctuations always exist. The film thickness was shown
to be an important parameter governing the length scale as well as the
amplitude of the undulations. As expected the electric field leads to an
amplification of undulations with smaller wavelengths. [1] K. Amundson,
E. Helfand, D. D. Davis, X. Quan, S. S. Patel and S. D. Smith, Macromolecules
24, 6546 (1991). [2] T. Thurn-Albrecht, J. DeRouchey, T. P.
Russell and R. Kolb, Macromolecules 35, 8106 (2002).
CPP 15.33 Di 17:00 B
Phase Diagram and Morphologies of Crystalline/Crystalline
Poly (Vinylidene Fluoride)/Poly (3-Hydroxybutyrate) Blends
— •Jieping Liu and Bernd-J Jungnickel — Deutsches Kunststoff-
Institut, Schlossgartenstr. 6, D-64289 Darmstadt, Germany
The melting point depression and a single glass transition in the
phase diagram evidence that PVDF and PHB are completely miscible
in the melt. PVDF crystallizes first and PHB second upon cooling. At
isothermal two-step crystallization, the components behave quite different.
Crystallization temperature and rate, respectively, of PVDF decrease
with increasing PHB content since PHB acts as a diluent; the PVDF crystallization
is ruled only by crystallization temperature and initial composition.
In contrast, PHB crystallization depends on the already existent
PVDF morphology since PHB may be included in or rejected from the
PVDF spherulites depending on the PVDF crystallization temperature.
The inclusion of PHB into PVDF dendrites reduces the available dimension
for PHB crystal growth (Avrami exponent n = 2) whereas the
PHB crystallizes undisturbed tri-dimensionally with athermal nucleation
in the surroundings of globular PVDF spherulites (n = 3). At a given
temperature, the crystallization rate of PHB inside the PVDF spherulites
is distinctly larger than that of PHB outside. These results underline the
microscopic findings on the complex supermolecular structure in that
blend.
CPP 15.34 Di 17:00 B
Charakterisierung der Strukturbildung in Blockcopolymeren
mit Minkowskifunktionalen — •S. Scherdel 1 , A. Horvat 1 , K.
R. Mecke 2 und R. Magerle 1 — 1 Physikalische Chemie II, Universität
Bayreuth — 2 Max-Planck-Institut für Metallforschung, Heisenbergstr. 3,
70569 Stuttgart
Blockcopolymere sind langkettige Moleküle, die aus zwei unterschiedlichen
Komponenten bestehen. Durch Mikrophasenseparation bilden
Blockcopolymere komplexe Strukturen mit Mikrodomänen im 10-100 nm
Bereich. Die physikalischen Eigenschaften des Materials hängen wesentlich
von seiner räumlichen Struktur ab. Häufig ist diese unregelmäßig,
was die Analyse und Interpretation der Struktur-Eingeschafts-Beziehung
sehr erschwert. Wir verwenden die aus der Integralgeometrie bekannten
Minkowskimaße, um Mikrodomänenstrukturen zu charakterisieren.