Regensburg 2016 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 57: Polymer Dynamics and Rheology (joint session CPP/DY, organized by CPP)

CPP 57.13: Vortrag

Donnerstag, 10. März 2016, 18:15–18:30, H40

PNIPAM dynamics in water-methanol mixtures — •Konstantinos N. Raftopoulos¹, Konstantinos Kyriakos¹, Olaf Holderer², Oxana Ivanova², Michael Ohl³, Peter Müller-Buschbaum¹, and Christine Papadakis¹ — ¹Physik-Department, Technische Universität München, Garching, Germany — ²JCNS at Outstation MLZ, Garching, Germany — ³JCNS at Outstation Oak Ridge, Tennessee, USA

In aqueous solutions, at low temperatures, the hydrophilic groups of Poly(N-isopropylacrylamide) form H-bonds with the water molecules and the polymer dissolves. Above the cloud point, the chain dehydrates and phase-separates. Although the polymer dissolves well in methanol too, the cloud point in water-methanol mixtures decreases considerably with respect to that in aqueous solutions. The phenomenon is termed cononsolvency. The physical mechanisms behind the process are still not clear and even less is known about the dynamics. Aiming to shed some light in this question, we followed the segmental dynamics of the polymer in water-methanol mixtures by neutron spin echo spectroscopy. The experiments were performed 2 and 5 K below the cloud points, in a temperature region where the solution is in θ-conditions. Methanol slows down the segmental dynamics of the polymer, but there is no evidence for a change of the mobility mechanism. The deceleration is more pronounced at higher polymer concentrations.