Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Dienstag
Essentially non-adiabatic conditions were taken into account to get sample
properties. A time resolution of better than 10 ms was achieved in
calorimetric measurements.
CPP 16.26 Di 17:00 B
Calorimetry on thin films — •Heiko Huth — Universität Rostock,
Fachbereich Physik, Universitätsplatz 3, 18051 Rostock
There is an increasing interest in the behavior of confined geometries
as small samples and thin films in the last years. Interesting questions are
the influence on glass transition or the change in crystallization behavior
in the nm range. Beside dielectric methods and structural investigations,
calorimetric data as heat capacity are of interest in such systems.
For small sample mass as thin films in the µm...nm range we run into
problems with the standard calorimetric methods like commercial DSC
because of the limited sensitivity. One method to solve these problems
are thin film calorimeter used by different authors. These systems are
developed to achieve fast heating rates not possible with usual commercial
DSC. To realize this, small samples and sensors are used. This idea
can also be applied for measuring frequency dependent heat capacity of
small samples. We present a measuring system based on thin film sensors
which makes it possible to measure heat capacity of thin films down to
the nm range with sample mass in the µg range or below. First results
are presented.
CPP 16.27 Di 17:00 B
Sum-Frequency Generation Spectroscopy: Monitoring the Hydrophobic
Recovery of PDMS Stamps after Plasma Etching
— •Dominik M.P. Hoffmann, Klaus Kuhnke, and Klaus Kern
— Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-
70569 Stuttgart
Polydimethylsiloxane (PDMS) is a polymer widely employed in the
fabrication of stamps for micro-contact-printing, as substrates for microfluidic
cells, and water-proof protection layers. The PDMS surface, which
is hydrophobic in its native state, becomes hydrophilic by oxygen plasmaetching.
Contact angle measurements have established that the hydrophobicity
recovers on the time scale of a few weeks.
Sum-frequency generation (SFG) spectroscopy can access the preferential
orientation of a specific chemical group near an interface. We monitor
the hydrophobic recovery by SFG vibrational spectroscopy of the methyl
groups. For typical plasma etching parameters (15 s etching time at nominally
190 W plasma power) the contact angle decreases from 110 ◦ to 0 ◦
reflecting the substantial decrease of hydrophobicity while SFG spectroscopy
finds that only one third of the preferentially oriented methyl
groups disappear. In addition, the characteristic time for the hydrophobic
recovery observed by SFG is shorter than the time observed by contact
angle measurements. The observations will be discussed in terms of a
model with two different recovery processes.
CPP 16.28 Di 17:00 B
Solvation and Solvation Dynamics of Hydrogen Bonding Dyes
Solvation and Solvation Dynamics of Hydrogen Bonding Dyes
— •Dzmitry Starukhin 1 , Frank Cichos 2 , and Christian von
Borczyskowski 1 — 1 Institut für Physik 122501, TU Chemnitz, 09107
Chemnitz — 2 Institut für Physik 123705, TU Chemnitz, 09107 Chemnitz
Hydrogen bonding is a key element of many biological macromolecules
to ensure function and structure. To study hydrogen bonding effects in
relation to solvent dynamics, we employ a resorufin dye, which is sensitive
to solute-solvent hydrogen bonds. We show that the dye emission wavelength
in different solvents is not governed by dielectric effects such as
dipolar solvation but rather completely determined by hydrogen bonds.
Steady state spectroscopy of the dye in protic solvents shows, that ground
and excited state of the dye possess the same number of hydrogen bonds,
but at different positions of the molecule. This results in two spectroscopically
distinguishable forms of the molecule, which exchange upon photoexcitation.
Due to the exchange the fluorescence decay of the dye studied
by time correlated single photon counting shows mainly two different
timescales. One very fast component is due to a braking and making of
hydrogen bonds and is accompanied by a structural relaxation of the solvent.
The structural relaxation shows time constants which are close to
the typical time constants found in dipolar solvation dynamics measurements.
These experimental findings are further supported by quantum
chemical calculations as well as molecular dynamics simulations.
CPP 16.29 Di 17:00 B
Two-photon single-molecule spectroscopy on a ladder type conjugated
polymer — •Richard Hildner 1 , Uli Lemmer 2 , Ullrich
Scherf 3 , and Jürgen Köhler 1 — 1 Experimentalphysik IV, Universität
Bayreuth — 2 Lichttechnisches Institut, Universität Karlsruhe —
3 Makromolekulare Chemie, Bergische Universität Wuppertal
Conjugated polymers are interesting both for basic and applied research
owing to their high potential for applications in optoelectronic
devices as in organic light emitting diodes and polymer displays. However,
the nature of their electronically excited states is unclear as yet.
Our approach is to use single-molecule spectroscopy, which avoids ensemble
averaging and disorder induced inhomogeneous broadening of the
spectral lines of conjugated polymers. Hence single-molecule spectroscopy
allows a direct verification of theoretical models.
In this contribution we present the first results of two-photon excitation
spectroscopy on single chains of a methyl substituted ladder type
poly(para-phenylene) (MeLPPP) at low temperatures. These results are
discussed in the context of current models of conjugated polymers.
CPP 16.30 Di 17:00 B
Fluorescence Correlation Spectroscopy Investigations of Watersoluble
Polymers — •Tune B. Bonné 1 , Karin Lüdtke 2 , Rainer
Jordan 2 , Petr ˇ Stěpánek 3 , and Christine M. Papadakis 1 —
1 Faculty of Physics and Earth Sciences, University of Leipzig, D-04103
Leipzig, Germany — 2 Faculty of Chemistry, Technische Universität
München, D-85747 Garching, Germany — 3 Institute of Macromolecular
Chemistry, Academy of Sciences of the Czech Republic, Prague
Fluorescence correlation spectroscopy (FCS) is a method to study the
self-diffusion of fluorescence-labeled molecules. The detection volume is
very small (∼ 1 µm 3 ), and the measurements are carried out on the basis
of very few molecules in the detection volume.
Using FCS, we have studied the micellization of fluorescence-labeled
poly(methyloxazoline)-poly(nonyloxazoline) diblock copolymers in aqueous
solution. This polymer system is very versatile with respect to the
degree of hydrophobicity of the blocks. In order to investigate the influence
of the dye on the aggregation behavior, polymers with the dye
attached to either the hydrophilic or the hydrophobic end were investigated.
The critical micelle concentrations were determined with FCS. By
comparing with results from dynamic light scattering (DLS), it is shown
that the hydrodynamic radius of the micelles can reliably be determined
using FCS. Temperature-resolved DLS showed, however, that after dissolution
of the polymers in water at room temperature, large aggregates
are formed, and stable micelles form only after heating the solutions.
CPP 16.31 Di 17:00 B
Photoelectron Spectroscopy on Thin Films of Metal-Free and
Copper Extended Porphyrazines — •D. Pop 1 , B. Winter 1 , W.
Freyer 1 , I. V. Hertel 1 , and W. Widdra 2 — 1 Max-Born-Institut,
Max-Born Str. 2A, D-12489 Berlin — 2 Martin-Luther-Universität Halle-
Wittenberg, D-06099 Halle
We report photoemission measurements using synchrotron radiation
for a series of metal-free and copper benzo-annelated porphyrazines, respectively.
Such systems of molecules allow to investigate the evolution
of the electronic structure with the increasing π-electron system of the
molecule. For the copper set of compounds information about metal-toligand
and ligand-to-metal charge transfer processes are inferred from
the ratios between the copper satellites and main lines. The results are
discussed for both the Cu2p and valence regions of the photoemission
spectra.
CPP 16.32 Di 17:00 B
Fluorescence Correlation Spectroscopy (FCS) of Single Dye-
Labelled Polymers in Organic Solvents — •Heiko Zettl 1 , Wolfgang
Häfner 1 , Alexander Böker 2 , Holger Schmalz 3 , Michael
Lanzendörfer 3 , Axel H.E. Müller 3 , and Georg Krausch 1 —
1 Physikalische Chemie II, Universität Bayreuth, 95440 Bayreuth, Germany
— 2 Department of Polymer Science and Engineering, University of
Massachusetts, Amherst, MA 01003, USA — 3 Makromolekulare Chemie
II, Universität Bayreuth, 95440 Bayreuth, Germany
We discuss the use of fluorescence correlation spectroscopy (FCS) to
study the diffusion of single, dye-labelled polymer chains in organic solvents.
Monodisperse batches of polystyrenes labelled with a single Rhodamine
B molecule have been synthesized via anionic polymerisation of
styrene and ethylene oxide end capping followed by a polymer analogous
coupling reaction. MALDI-ToF mass spectrometry is used to character-