Quasielastic neutron scattering study of dynamics at the crossover from dilute to semidilute behavior in polymer solutions

Dynamics at the Temperature Crossover in Dilute Polymer Solutions Investigated by Neutron Spin-Echo Spectroscopy

Applying ultrahigh-resolution neutron spin-echo spectroscopy the existence of a $q$-dependent temperature crossover in the dynamics of dilute polymer solutions was proved. It is associated with the transition from $\ensuremath{\theta}$ to good solvent conditions. At small momentum transfers $q$ a nearly stepwise increase of the reduced quasielastic linewidth versus the reduced temperature was observed. With increasing $q$, both the sharpness of the transition and the step height decrease.

Analyse der Temperaturabhängigkeit der dielektrischen α-Relaxation am Modell eines Paraffin-Keton-Mischkristalls

Am Modell einer festen Losung von C35H70O in n-C36H74 wurde durch parallel gefuhrte dielektrische und rontgenographische Experimente die Aktivierungsenergie des dielektrischen α-Prozesses (Flip-flop-Sprunge) und ihre Abhangigkeit von den Gitterkonstanten gemessen. Die Untersuchungen machen deutlich, das der Anstieg der Relaxationsfrequenz mit wachsender Temperatur wesentlich durch den Abfall der Aktivierungsenergie infolge der thermischen Ausdehnung des Gitters mitbestimmt wird und die ubliche Arrhenius-Auftragung deshalb stark verfalschte Werte liefert. Eine Analyse der Daten unter Berucksichtigung dieses Einflusses fuhrt bezuglich der Aktivierungsenergie des flipflop-Prozesses und ihrer A…

Chemical structure and internal diffusion within polymer chains in the melt

The single chain dynamics of polydimethylsiloxane in the melt is studied by means of quasielastic neutron scattering. For this polymer the wave vector range 0.03 A−1≦q≦0.30 A−1 covers the regime of universal modes as well as local diffusive processes. A model is described which incorporates the specific chemical structure of the macromolecule and allows to interpret our data in the full wave vector regime. The only parameter which enters the model, the monomer diffusion constantDm, is found to be (1.2±0.2)·10−5 cm2s−1.

Richteret al.Respond

Dynamical Scaling in Polymer Solutions Investigated by the Neutron Spin-Echo Technique

Chain dynamics in polymer solutions was investigated by means of the recently developed neutron spin echo spectroscopy. — By this technique, it was possible for the first time to verify unambiguously the scaling predictions of the Zimm model in the case of single chain behaviour and to observe the cross over to many chain behaviour. The segmental diffusion of single chains exhibits deviations from a simple exponential law, indicating the importance of memory effects. Mit Hilfe der erst kurzlich entwickelten Neutronen-Spin-Echo-Spektroskopie wurde die Kettendynamik von Polymermolekulen im gelosten Zustand untersucht. - Die Methode eroffnete die Moglichkeit, zum ersten Mal fur das Einzelkette…