Berlin 2012 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 27: Poster: (Hydrogels) and Elastomers
CPP 27.12: Poster
Wednesday, March 28, 2012, 11:00–13:00, Poster A
Elastic anomalies at the volume phase transition of PNIPAM solutions — •Martine Philipp1, Ulrich Müller2, Olga Astasheva2, Jan Krüger2, and Peter Müller-Buschbaum1 — 1TU München, Physik-Department, LS Funktionelle Materialien, Garching, Germany — 2Université du Luxembourg, Laboratoire de physique des matériaux avancés, Luxembourg, Luxembourg
The molecular collapse of poly(N-isopropyl acrylamide) (PNIPAM) in aqueous solution at the lower critical solution temperature has been intensively investigated in basic and applied research. On a macroscopic scale, this phase transition is reflected in an anomalous behavior of the mass density and elastic properties. Particularly in case of chemical PNIPAM hydrogels, the longitudinal elastic modulus is considered as the order parameter susceptibility of the highly complex volume transition. In the current contribution the evolution of elastic anomalies at the discontinuous volume transition of PNIPAM solutions is presented in dependence of temperature and PNIPAM concentration. Brillouin spectroscopy permits a novel and unique perspective on the static, dynamic and kinetic aspects of the phase separation occurring at about 32°C. In particular the qualitative changes of the acoustic phonon spectrum at the phase transition reflect the formation of macroscopic PNIPAM-rich agglomerates embedded in the PNIPAM-poor phase.