Regensburg 2004 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
CPP: Chemische Physik und Polymerphysik
CPP 1: Polymer Surfaces I
CPP 1.2: Vortrag
Montag, 8. März 2004, 10:00–10:15, H 37
Volume Phase Transition of PNIPAM-Microgel Paricles Studied with Laser-AFM — •Lothar Zitzler1, Frieder Mugele1, and Stephan Herminghaus1,2 — 1Angewandte Physik, Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm — 2Max-Planck-Institut für Strömungsforschung, Bunsenstraße 10, 37073 Göttingen
Poly(N-isopropylacrylamide) (PNIPAM) is a polymer with a lower critical
solution temperature (LCST) of TLCST ≈ 32˚C. It shows a
conformational change from a coil to a globule state upon increasing the
temperature above TLCST. Here we present AFM-studies (in aqueous
environment) of PNIPAM-co-poly(vinyl acetic acid) microgel particles
adsorbed on glass substrates. Like in solutions the adsorbed particles also
show a pronounced change in volume of approximately 200% with respect to
the globular state. The different elastic properties of the particles in
the coil and globular states could be distinguished clearly in amplitude-
and phase-distance curves, obtained by AFM in Tapping Mode.
To study the dynamics of this coil to globule transition we combined the
AFM with an intense cw-laser (5W at 532 nm). We generated laser pulses of
variable width (10ns-100µs) with an
acousto-optical modulator. The laser pulses were used to trigger
the volume phase transition by heating the particles above
TLCST. By synchronizing the laser pulses with the cantilever
oscillation and by varying the relative time delay one can obtain
information on the dynamics of the phase transition.