Effect of confinement on polymer chain movement
Collège de France, Paris
Liliane Léger is professor
at University Paris XI Orsay, and responsible of the group
Polymers at interfaces, adhesion and friction in the
laboratoire de Physique des Fluides Organisés at
Collège de France, Paris. Her present research interests
are on soft matter, complex fluids, colloids, polymers, polymer
interfaces, adhesion and friction. She has developed experimental
techniques based on fluorescence recovery after photobleaching to
characterize centre of mass diffusion of entangled polymer chains
and to confine such measurements to the immediate vicinity of an
interface by the use of evanescent waves to excite the
fluorescence. She has also a long practice of chemical surface
modification in order to manipulate wetting, adhesion and
friction. The proximity to a leading theoretical polymer physics
group (headed by Pierre Gilles de Gennes up to last September)
has promoted a way of defining model experiments specifically
designed to be discriminative between theoretical models. The
experimental work in her group always remains in close contact
with theoretical approaches.
In PolyFilm, we shall use
Fluorescence Recovery after Photobleaching techniques to
characterize how confinement affects the overall centre of mass
diffusion of polymer chains pertaining to films with nanometric
thickness deposited on solid surfaces with adjusted strength of
the polymer surface interactions. This will be performed with
polymers far from their glass transition temperature as a first
step, and then with polymers closer to the glass transition
temperature, in order to try to shed some light on the way
confinement affects dynamics and glass transition.
Above left: An unstabilised polypropylene film,
which has peeled from the polyamide 6 substrate after 45 minutes
annealing.
Above right: A film stabilised by the formation of diblock
copolymers in situ, by reaction of modified PP chains on the
NH2 end of PA6. Film annealed for 100 minutes without
peeling.
We shall also develop a program
to investigate the kinetics of chain relaxation first confined
(surface anchored chains with either end grafted or irreversibly
adsorbed, with a grafted layer thickness smaller than the natural
size of the chains) and put into contact with a crosslinked
elastomer of the same chemical specie. Such interfaces naturally
tend to heal progressively. The kinetics of the interdigitation
process will be followed by the associated adhesion and friction
enhancements. The mechanical response of the partially
interdigitated chains should be highly sensitive to the distance
to glass transition, providing an alternative way of trying to
understand the role of confinement and the glass transition
temperature.
Beyond the above fundamental
questions these studies should provide a guide to manipulate
adhesion and friction, which are of course of high practical
importance.
