Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Dienstag
Polyethylene (PE) pipes generally exhibit a limited life-time, which is
considerably shorter than their chemical degradation period. Slow crack
growth failure occurs when pipes are used in long distance water or gas
distribution though being exposed to a pressure lower than the corresponding
yield stress. This slow crack growth failure is characterized by
localized craze growth and craze fibril rupture. In literature, the life-time
of PE pipes is often considered as being determined by the density of tie
chains connecting adjacent crystalline lamellae. But this consideration
cannot explain the excellent durability of the recent bimodal grade PE
for pipe application. We show the importance of the craze fibril length as
determining factor for the pipe life-time. The conclusions are drawn from
stress analysis. It is found that longer craze fibrils sustain lower stress
and are deformed to a lesser degree. The mobility of the amorphous phase
is found to control the amount of material that can be sucked in by the
craze fibrils and thus the length of the craze fibrils. The mobility of the
amorphous phase can be monitored by dynamic mechanical analysis measurements.
Excellent agreement between the mobility thus derived and
life-times of PE materials as derived from FNCT-tests (full notch creep
test) is given, thus providing an effective means to estimate the life-time
of PE pipes by considering well defined physical properties.
CPP 13.7 Di 11:45 H 37
Thermal Fluctuations of Individual Actin Filaments in Confined
Geometry — •Sarah Köster 1 , Alexander Otten 1 , Stephan
Herminghaus 1,2 und Thomas Pfohl 1 — 1 Angewandte Physik,
Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm — 2 Max-Planck-
Institut für Strömungsforschung, Bunsenstraße 10, 37073 Göttingen
The investigation of individual semiflexible biopolymers will bring new
insights concerning microfluidic in vitro applications as well as the understanding
of biomechanical processes within the cell. The chosen system,
F-actin, is experimentally accessible quite well and it is one of the most
important proteins in eucaryotic cells. Thermal fluctuations of individual
fluorescently labeled actin filaments in confined geometry can directly
be observed using microfluidic devices fabricated by soft lithography.
Analyzing the fluorescence microscopy images of the contour line of the
fluctuating biopolymers we have access to macromolecular characteristics
such as the mean square end-to-end distance, the bending energy, and the
tangent correlation function. While the tangent correlation function of
free semiflexible polymers shows a simple exponential decay, a completely
different behaviour can be observed when investigating individual actin
polymers in confining microchannels. In this case the decay is superposed
by an oscillation which allows for the determination of the deflection
length λ in addition to the persistence length LP.
CPP 13.8 Di 12:00 H 37
Synthetic collagen peptides give clues to triple helix stability —
•Christian Renner, Dirk Barth, Alexander Milbradt, Barbara
Sacca, Hans-Juergen Musiol, and Luis Moroder — MPI
fuer Biochemie, 82152 Martinsried
Collagen is the most abundant protein in mammals. It gives mechanical
strength to tissue through its unique molecular structure: In the
collagen triple helix three protein strands that each form a left-handed
helix pack together resulting in a right-handed super helix. Although collagens
have been investigated by biologists, chemists and physicists for
many decades, the rules governing triple helix stability and thus collagen
function have not yet been fully elucidated. Surprisingly, repetition of the
simple amino acid triplet (Gly-Pro-Pro/Hyp) is sufficient for generating
the supramolecular organisation of the collagen helix with high stability.
We have used synthetic collagen peptides, where one hydrogen atom of
each triplet is substituted by fluorine, to study the influence of the fluorinated
position on structure and stability (1). We found that current
explanations of triple helix stability are inadequately simple and have to
be replaced by a detailed and quantitative view of the combination of interactions
involved. Additional means for investigation and stabilisation
of triple helices are natural (2) or synthetic cystine knots (3).
(1) Barth, D., Milbradt, A. G., Renner, C. and Moroder, L. (2003)
ChemBioChem, in press. (2) Barth, D., Kyrieleis, O., Renner, C. and
Moroder L. (2003) Chem. Eur. J. 9, 3703-3714. (3) Renner, C., Sacca, B.
and Moroder, L. (2003) Biopolymers, in press.
CPP 13.9 Di 12:15 H 37
Structural modifications and electromechanical properties of inflated
cellular polypropylene films — •Michael Wegener, Enis
Tuncer, Werner Wirges, and Reimund Gerhard-Multhaupt —
University of Potsdam, Department of Physics, Am Neuen Palais 10, D-
14469 Potsdam
Voided space-charge electrets with internal charge layers show significant
piezoelectrical properties. In such materials, e.g. cellular polypropylene,
the piezoelectric coefficient strongly depends on the cell-size and
-shape distributions. The electrically charged cells represent macroscopic
dipoles. The typically air-filled cells can be deformed very easily by a
mechanical stress or an electrical field, which represents the direct and
inverse piezoelectric effects, respectively. By means of controlled inflation,
cell sizes and shapes can be varied over a rather large range. This
is achieved by altering pressure and temperature. Here, we describe various
inflation procedures with several different pressures, temperatures
and treatment times. After optimization the procedure yields high piezoelectric
coefficients that may be due to the low elastic moduli of the
inflated samples. The results are discussed with respect to the observed
micro-structure of cellular films (as seen in SEM cross-sections), and are
compared to the finite element analysis. The comparison to numerical
simulations explains the micro-structural changes during the inflation
process.
CPP 14 SYMPOSIUM: Understanding and Controlling Complex Structures: From
Synthetic Polymers to Biomaterials II
Zeit: Dienstag 14:00–17:00 Raum: H 37
Hauptvortrag CPP 14.1 Di 14:00 H 37
Competition of order in liquid crystalline/isotropic block
copolymers — •Bernd Stühn 1 , Wolfram Gronski 2 , Rosina
Staneva 1 , Sergei Zhukov 1 , and Steffen Geppert 2 — 1 Technische
Universität Darmstadt, Physics of Condensed Matter, D-64289
Darmstadt — 2 Albert Ludwigs Universität Freiburg, Institute of
Macromolecular Chemistry, D-79104 Freiburg
The formation of structure in block copolymers consisting of an
isotropic and a liquid crystalline block is governed by two factors. One is
the domain ordering caused by the strong repulsive interaction between
both blocks. As a second factor the orientational order of the mesogens
in the liquid crystalline block is to be considered.
We have investigated a series of di- and triblock copolymers with the
liquid crystalline block either confined within spherical, cylindrical or
lamellar domains or forming the continuous matrix. Small and wide angle
X-ray scattering has been applied to study structure on a wide range
of length scales. The dependence of domain order on the orientational
order is studied by variation of temperature and crossing the transition
temperature of the liquid crystalline phase. The nematic order of the
LC clearly favours the cylindrical over the spherical domain form thus
causing a variation of structure with temperature at the LC phase transition.
For one example we find a order-to-order transition in the domain
structure triggered by the nematic-isotropic phase transition of the liquid
crystalline matrix.
Hauptvortrag CPP 14.2 Di 14:30 H 37
Bio- and biomimetic mineralization — •Helmut Cölfen —
Max-Planck-Institute of Colloids and Interfaces, Colloid Cemistry, Am
Mühlenberg, D-14476 Golm
Nature is able to produce highly optimized materials by the process of
biomineralization at ambient temperature in water. These materials like
bones and teeth are organic-inorganic hybrid systems with hierarchical
order. Some basic principles of biomineralization will be introduced to illustrate
how these materials are formed. Biomineralization processes can
be successfully mimicked to produce advanced synthetic materials from
simple inorganic systems. Examples will be given, how polymers can be
used to direct crystallization processes resulting in hybrid materials with
complex shape.