Chain segment dynamics in polymer thin films
Université de Paris Sud
Confinement of many molten
polymer films (grafted, adsorbed, spin-coated polymer films) is
ensured by the presence of impenetrable and interacting surfaces
(which limit chain re-configurations) and/or by anchor junctions
(which fix the chain extremities). The film thickness and the
mean distance between the junctions may be much lower than the
overall dimension of the polymer chains, i.e. lower than 10
nm.
Chain dynamics in polymer films
has been investigated much less than structural properties (film
morphology, interface thickness, and so on) but it is very
important to properly appreciate how segment fluctuations, chain
motions and the averaged chain conformations are affected by the
confinement and deviate from the bulk behaviour. Various relevant
properties or questions about chain dynamics in polymer films
remain unanswered. The properties induced by confinement may
concern the following points:
distribution and values of correlation times characterising
the local dynamics (segmental fluctuations) and large scale
motions (sub-chains or chain motions).
the presence of slow motions in the vicinity to interfaces
and close to linkage junctions.
the degree of anisotropy of segmental motions.
the presence of collective motion and the occurrence of
segmental ordering around one particular (microscopic or
macroscopic) direction.
heterogeneity of the segmental dynamics: coexistence of
domains of slow dynamics with domains of rapid dynamics,
coexistence of domains of various degree of local order
(magnitude and direction).
chain reconfigurations and the chain diffusion (magnitude and
anisotropy) inside the polymer films.
During the past few years some
preliminary experiments have demonstrated the ability of the
Nuclear Magnetic Resonance (NMR) approach to probe the dynamics
at interfaces. A major NMR contribution to this field is its
ability to measure the anisotropy (laterally and perpendicular to
the surface) of chain segment dynamics whenever the chain
conformation is modified by the presence of surfaces.
For a deeper understanding of
polymer dynamical behaviour in thin films, NMR will be used in
conjunction with some other techniques available in the framework
of the RTN, mainly inelastic neutron scattering (Saclay),
fluorescence recovery after photo-bleaching (Paris) and broadband
dielectric spectroscopy (Delft).
Relevant publications
Some remarks on the chain segment dynamics in confined
polymers, B. Deloche, Eur. Phys. J.E. 12, s01 (2003) 027.
Chain segment order in polymer films on a non-adsorbing
surfaces : a NMR study. S. Rivillon, P. Auroy and B. Deloche,
Phys. Rev. Lett. 84 (2000) 233.
Chain segment order and dynamics in a grafted polymer melt :
a deuterium NMR study. M. Zeghal, B. Deloche, P.A. Albouy and P.
Auroy, Phys. Rev. E 56 (1997) 5603.
