Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Montag
by AFM and by grazing incidence x-ray small angle scattering (GISAX).
The LB-technique was found less effective than the gravity-sedimentation
method. Using the latter we could prepare samples with a nearly monolayer
covering (AFM).The GISAX measurement confirms that we produced
an almost homogeneous covering over a large sample area (2 mm
X 2 mm). Almost no agglomeration of colloidal spheres was observed.
CPP 11.6 Mo 15:15 H 39
Charged Interfaces of Colloidal Particles studied by Ellipsometric
Scattering — •Andreas Erbe, Reinhard Sigel, and Klaus
Tauer — Max Planck Institute of Colloids and Interfaces, D-14476
Potsdam-Golm
CPP 12 Colloids and Nanoparticles II
A combination of conventional light scattering equipment with polarization
optics can be used to obtain information about the interface
between a colloidal particle and the solvent.
Since charge-stabilized colloids are an important class of colloids, we
investigate the influence of the salt (NaCl) concentration on the colloid’s
interface. For this study, we use block copolymer particles with a
water-insoluble core of Poly(methyl-methacrylate) and a water soluble,
negatively charged layer consisting of Poly(styrenesulfonate).
In addition, the behaviour of Poly(styrene) colloids stabilized by the
surfactant perfluorooctancic acid (negatively charged under the chosen
conditions) are investigated with low amounts of salt present.
Zeit: Montag 15:45–17:15 Raum: H 39
CPP 12.1 Mo 15:45 H 39
SOLVENT-DEPENDENT CRYSTALLIZATION KINETICS
OF COLLOIDAL PARTICLES — •Roy Goldberg, Patrick
Wette und Thomas Palberg — Johannes Gutenberg-University
Mainz, Institute of Physics, Staudingerweg 7, D-55099 Mainz
For structural examinations of crystalline ordered particles and to avoid
aging (Ostwald-ripening) and later coagulation it is advantageous that
the crystals are kept in their original state. For this reason they will be
imbedded in polymer matrices.
By static light scattering we examined in which way the particleinteraction
in a monomer-solution compared to aquatic dispersions with
the same particle number density will change. Beside the investigation of
structural parameters, the determination and comparison of crystallite
sizes is possible and variations in the particle-interaction are thus directly
observable . Additionally, changes in lattice features of colloidal crystals
during imbedding in a polymer matrix and with further drying were investigated
with microscopical methods as atomic-force-microscopy and
electron-microscopy.
CPP 12.2 Mo 16:00 H 39
Wetting at the nanometric scale — •Hauke Schollmeyer 1 , Antonio
Checco 2 , Jean Daillant 1,3 und Patrick Guenoun 1 —
1 Service de Physique de l’Etat Condense, C.E.A. Saclay, F-91898 Orsay
Cedex, France — 2 Department of Physics, Brookhaven National Laboratory,
Upton, New York 11973 — 3 LURE, CNRS/CEA/MJENR, bat.
209D, Centre Universitaire Paris-sud, F-91898 Orsay Cedex, France
We have investigated the partial wetting of micrometric and nanometric
alkane droplets on model substrates using true non-contact atomic
force microscopy. The large droplet sizes accessible using this technique
allowed us to determine the contact line curvature dependence of contact
angle with unprecedented accuracy. Whereas previous studies aimed at
explaining such a dependence by a line tension effect, our results and
calculations on a model system exclude such an effect. Our results point
to an extreme sensitivity to weak substrate heterogeneities confirmed by
numerical simulations. Our goal is to prove this result for model substrates
without heterogeneities. For this we use self assembled monolayer
of long chained alkanes on silicon substrate. At room temperature these
form a smooth and solid surface.
CPP 12.3 Mo 16:15 H 39
Electrophoretic investigations of surface-modified silica nanoparticles
— •Holger Reiber and Thomas Palberg — Johannes
Gutenberg-Universität, Institut für Physik, Staudingerweg 7, D-55099
Mainz
Because of strong coulombic interactions, dispersions of electrostatically
stabilised colloidal silica particles show a characteristic behaviour
in the case of very low salt conditions. The strength of the interactions
between the single particles is a function of the surface charge, and therefore,
it also influences electrophoretic properties as for example the particle
mobility. For this reason, we investigate silica nano-particles which we
synthesised using a variation of the Stöber-syntheses by means of laser
Doppler velocimetry. The particles differ from each other only with respect
to number and/or type of the ionic surface groups, but not with
respect to typical properties such as diameter, density or polydispersity.
For this reason, our measurements can show the influence of a variable
surface charge on system properties of nano-particles such as the mobility.
CPP 12.4 Mo 16:30 H 39
Surface modification of carbon nanotubes: by deposition of
nanosized — •Miguel Correa-Duarte and Michael Giersig —
Caesar Research Center, Dept. Nanotechnology, Ludwig-Erhard Allee 2,
53175 Bonn
In this presentation we will discuss the covering of multi-walled carbon
nanotubes (MWCNTs) with nanosized metallic and semiconductor
nanoparticles. In the first step MWCNTs have been positively or
negatively charged (depending on the nanoparticles charge) by covering
with cationic poly(diallyldimethylammonium) chloride (PDDA) or
anionic poly(sodium 4-styrenesulfonate) (PSS) polyelectrolyte. The following
step was the deposition of nanosized metallic (Au, SiO2@Au) and
semiconductor (CdSe, CdTe) particles. The successive covering process
was optically registered and was correlated with the structural characterization
by high resolution transmission and scanning electron microscopy.
CPP 12.5 Mo 16:45 H 39
ION DISTRIBUTION AT CHARGED INTERFACES —
•Patrick Koelsch and Hubert Motschmann — Max-Planck-
Institute of Colloids and Interfaces, Am Muehlenberg, 14476 Potsdam
The distribution of ions close to a charged wall is a classical problem
in colloid and interface science. The traditional approach consists in a
mean field analysis of the counterion distribution leading to the Poisson-
Boltzmann theory. Recently this field has attracted renewed attention
with several theoretical papers addressing effects beyond the mean field
level such as fluctuations, discreteness of charges or 2D-correlations.
These papers reveal certain new features which are not captured in the
mean field picture. We already demonstrated, that the combination of
nonlinear (suface Second Harmonic Generation SHG) and linear optical
technics (Ellipsometry) allows a direct determination of the prevailing
ion distribution. A simple analytical expression was derived which can
be used to retrieve the number of condensed counterions within the compact
or so called Stern-layer. In this contribution we apply this formalism
on experimental data gained on aqueous cationic surfactants by varying
the counterions in order to quantify specific ion effects at the interface
following the Hofmeister series. The derived formalism relates the ellipsometric
signal to the surface charge and promises great potential in order
to discard or proof recently published theoretical approaches.
CPP 12.6 Mo 17:00 H 39
High-resolution photoemission study of CdS nanoparticles with
narrow size distribution: preparation, different sulfur components,
and beam damage effects — •Sanjeev Joshi 1 , L. Weinhardt
1 , C. Kumpf 1 , S. K. Kulkarni 2 , R. Fink 3 , C. Heske 1 , and
E. Umbach 1 — 1 Exp. Phys. II, Univ. Würzburg, 97074 Würzburg —
2 Dept. Physics, Univ. Pune, Pune 411 007, India — 3 Phys. Chem. II,
Univ. Erlangen, 91058 Erlangen
We report on high resolution X-ray photoemission data of very small
CdS nanoparticles of two different sizes, 1.4 nm and 2.7 nm diameter,
respectively. A detailed analysis is performed to identify the sizes and
their distribution and the various signal constituents. The signal is composed
of five S components, which can be assigned to the S atoms of
the particle in different environments. The peak assignment is done by
comparing the experimental data with intensity estimates, considering
the intensity attenuation and contributions of the various S atoms using
three structural models. Furthermore, it is discussed how beam damage