Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Montag
can be induced and how it is identified and controlled by recording very
fast photoemission scans. A quantitative description based on successively
collected spectra is developed. The influence of different thin film
sample preparation methods on the photoemission signal is discussed as
well.
CPP 13 SYMPOSIUM: Understanding and Controlling Complex Structures: From
Synthetic Polymers to Biomaterials I
Zeit: Dienstag 09:30–12:30 Raum: H 37
Hauptvortrag CPP 13.1 Di 09:30 H 37
Hierarchical Structures in Biological Materials — •Peter
Fratzl — Max Planck Institute of Colloids and Interfaces, Department
of Biomaterials, D-14424 Potsdam
Natural mineralized tissues such as wood, collagen or bone are hierarchically
structured and optimized for mechanical performance at all
levels of hierarchy. The basic unit of bone is a collagen fibril reinforced
with calcium phosphate nanoparticles. Such fibrils are assembled into
a complex composite structure which is far from being completely understood.
The hierarchical structure in wood consists of parallel tubes
(the wood cells) with polymeric walls reinforced by thin cellulose fibrils.
Adaptive growth and remodelling are common denominators in biological
materials and responsible for functional adaptation all hierarchical
levels. A successful approach to study hierarchical structures and their
mechanisms of deformation is scanning microfocus x-ray scattering complemented
with scanning electron microscopy and nanoindentation. Size,
shape and arrangement of mineral nanoparticles in bone are found by
such methods to vary systematically with age or at interfaces. Their
detailed arrangement turns out to be essential for the mechanical performance
of the composite, since they seem to control both the rigidity
and the toughness of the tissue. Quite similarly, recent results show that
the exact geometrical arrangement of the cellulose fibrils in the plant cell
wall controls to a large extent its mechanical bahaviour. In conclusion,
mechanical behaviour seems to depend essentially on the complexity of
the structure which is controlled by functional adaptation.
Hauptvortrag CPP 13.2 Di 10:00 H 37
Polymer cystallization as an example for highly meta-stable
structure formation — •Jens-Uwe Sommer and Günter Reiter
— Institut de Chimie des Surfaces et Interfaces (CNRS-UHA), 15 rue
Jean Starcky, 68057 Mulhouse, FRANCE
Long chain molecules form crystalline structures by developing folded
conformations, thus incurring a large decrease of conformational entropy.
Generally, crystallization of polymers leads to structures far from thermodynamic
equilibrium. Many of the features of polymer crystallization
are thus only poorly understood and recent experiments show results
which are unexpected on the basis of existing theoretical models [1]. As
a general paradigm for complex structure formation, polymer crystals
develop through a series of intermediate states. We give an overview
about recent advances and open questions in the understanding of polymer
crystallization processes, considered from the point of view of nonequilibrium
structure formation processes. In particular the investigation
of crystallization processes in ultra-thin films sheds more light on these
complex systems. We have developed a generic lattice model which allows
us to understand and predict various aspects of morphogenesis and
non-equilibrium melting phenomena [2].
[1] J.-U. Sommer and G. Reiter: Polymer Crystallization: Observations,
Concepts and Interpretations, Lecture Notes in Physics , Vol. 606,
Springer Verlag (2003)
[2] J.-U. Sommer and G. Reiter: Morphogenesis of Polymer Chain Crystals,
Europhys. Lett. 56, 755 (2001)
CPP 13.3 Di 10:30 H 37
Melting and reorganization of polymer crystals on fast heating
(1,000 K/s) — •Christoph Schick 1 and Alexander Minakov 2 —
1 Universitaet Rostock, FB Physik, Universitaetsplatz 3, 18051 Rostock
— 2 Natural Science Center of General Physics Institute, Vavilov st. 38,
199911 Moscow, Russia
Reorganization of polymer crystals on heating is a well known phenomenon.
But kinetics of the process is mainly unknown because it is
very fast. Utilizing a thin film vacuum gauge as a calorimeter we are
able to extend the scanning rate range of commercial DSC’s (10E-6 K/s
to 10 K/s) to rates as high as 10,000 K/s. Because of the fast equilibration
time isothermal experiments can be performed after scanning at
several thousand K/s. The dead time after such a quench is in the order
of 10 ms and the time resolution is in the order of milliseconds. These
ultra fast calorimeters allow studying kinetics of crystal reorganization in
polymers, which appears on time scales in the order of 10 milliseconds.
Compared to crystallization from the isotropic melt at the same temperature
reorganization of existing polymer crystals is about two orders of
magnitude faster. For PET at highest rates only one single melting peak
is seen independent on crystallization temperature. This ’true’ melting
corresponds to the lowest endotherm in DSC curves.
CPP 13.4 Di 10:45 H 37
A model describing the tensile deformation properties of semicrystalline
polymers exemplified for a sample of low density
polyethylene — •Ke Hong, Ankur Rastogi, and Gert Strobl —
Physikalisches Institut, Albert-Ludwigs-Universität, Hermann-Herder-
Str.3, 79104 Freiburg, Germany
The tensile deformation behavior of a low density polyethylene was
studied with the aim of understanding the different contributing forces
and modelling the deformation properties of semicrystalline polymers.
The sample PEVA12 which was used is capable of uniform deformation.
In this way true stress-strain curves were obtained easily. Employing
stress-relaxation measurement, the viscous force included in the stress
was determined. The unrelaxable stress is quasi-stable and includes the
network force and the crystal skeleton contribution. The results so obtained
can be represented by means of a three components model in
which a first component describes the crystal skeleton behavior with
a spring combined with a finite-plastic element. Conventional Gaussian
chain statistics are employed in a second component which deals with
the stress arising from the entanglement network. A Hookean spring in
series with a Eyring dashpot represents as the third component the relaxatory
stress. Using this model experimental stress-strain curves, stress
relaxation curves, creep curves and load-unload-cycle-tests can be well reproduced.
15 min. Pause
CPP 13.5 Di 11:15 H 37
Quantifying and Controlling the Mechanical properties of polyelectrolyte
multilayer capsules: Towards mechanosensitive microcapsules
— •Andreas Fery, Frederic Dubreuil, Nils Elsner,
Julien Heuvingh, and Melmuth Möwald — MPI for Colloids
and Interfaces Golm
Quantifying the mechanical properties of microcapsules is of interest
for both a basic science understanding of those systems and for their
applications. Control of the mechanical properties could lead to new
”smart” materials like ”mechanosensitive” capsules that change their mechanical
properties in reaction depending on their environment.
In this context, hollow capsules made from polyelectrolyte multilayers
are promising, because they can be produced with well defined geometry,
wall thickness and from various materials.
We use AFM force-spectroscopy and optical microscopy to directly
probe the deformability of individual microcapsules in solvent environment.
Using continuum mechanics models, we can derive the elastic constants
of the wall material. We find that the Youngs-modulus of microcapsules
made from PAH (Polyallylamine)/PSS (Polystyrenesulfonate) is depending
on the solution salt concentration and pH. We discuss the effects
in terms of simple molecular pictures and present how this mechanosensitivity
can be used to control microcapsule adhesion properties.
CPP 13.6 Di 11:30 H 37
The Mobility of the Amorphous Phase in Polyethylene as a Determining
Factor for Slow Crack Growth — •Yongfeng Men 1 ,
Jens Rieger 1 , Hans-Friedrich Enderle 2 , and Dieter Lilge 2 —
1 BASF Aktiengesellschaft, Polymer Physics, 67056 Ludwigshafen, Germany
— 2 Basell Polyolefine GmbH, R&D, 65926 Frankfurt, Germany