Structure and phase transitions at interfaces
ICSI, Mulhouse
The research interests of Dr
Dimitri Ivanov focus on studies of the structure and phase
transitions of polymers and liquid crystals in thin films and at
surfaces. It is well known that the polymer-substrate
interactions can induce substantial modification of the structure
and thermodynamics of polymer crystals confined in thin films.
For example, the melting temperature of a thin deposited film can
be increased by several tens of degrees due to a specific
interaction with the substrate.
The figure shows the lamellar
organization in a thin alkane layer deposited on graphite, which
was visualized by atomic force microscopy (AFM). The
topographical images show the details of the nano-scale
organization of this material in the proximity of the substrate.
High temperature AFM imaging shows that the structure of the
alkane is preserved at temperatures far above its bulk melting
temperature. In addition, AFM successive imaging of the same
region reveals the mobility of the alkane lamellae, which
gradually change their orientation. Note the lamellar stacks with
almost vertically oriented lamellae growing in the upper right
part of the image. The alkane lamellae lose their mobility when
the temperature is decreased and a second layer starts to
crystallize on top of the monolayer.
Above right: Tapping mode topography AFM images
(1x1mm2) of a mono-molecular layer of
C122H246. The same region was successively
imaged at 135°C. The images show that the lamella structure
of the alkane undergoes modification with annealing time: the
chains orientation is changed in the central and upper right part
of the image.
In PolyFilm we shall study the
thermodynamics and organisation of hierarchical semicrystalline
polymer structures in thin films and in the bulk. The
direct-space information on polymer structure will be
complemented with results time- and temperature-resolved small-
and wide-angle X-ray scattering, which will be performed with
laboratory equipment or using synchrotron sources. The structure
and orientation of polymer close to the surface layers will be
studied with grazing incidence small- and wide-angle X-ray
scattering.
The French groups participating in POLYFILM are all affiliated via a
national network, the French Groupement de Recherche (GDR2637 PolyFUM).
The overall co-ordinator of the French contribution to POLYFILM is led
by Dr Günter Reiter, who is a Directeur de Recherche at the
ICSI Mulhouse.
