Dresden 2009 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 13: POSTERS Polymer Physics
CPP 13.20: Poster
Tuesday, March 24, 2009, 14:00–16:30, P3
Temperature-resolved structures and kinetics of deswelling in PNIPAM hydrogels and solutions — •Andreas Meier-Koll1, Anastasia Golosova1, Joseph Adelsberger1, Weinan Wang1, Peter Busch2, Vitaliy Pipich2, Christine M. Papadakis1, and Peter Müller-Buschbaum1 — 1TU München, Physik-Department E13, Garching — 2JCNS at FRM II, Garching
The deswelling behavior as well as its kinetics of highly concentrated aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions are investigated with small angle neutron scattering (SANS) and are discussed in terms of spinodal decomposition. The phase transition is shown to be of second order. After a temperature jump from the swollen to the deswollen state, three different time regimes of the decomposition process are observed: In the early stage, small fluctuations of the density are reinforced by the negative curvature of the Gibbs free energy, which lead to a negative diffusion coefficient and an exponential increase of the scattering intensity. Within this time, well-defined interfaces between both species are formed. The corresponding strong forward scattering can be described by a Porod behavior. The coarsening in the intermediate and late stage manifests itself in a decrease of the forward scattering intensity which follows a power law behavior with an exponent below 1 in the intermediate, whereas an unusual exponent above 1 is observed in the late stage.