Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: INTERNAL SYMPOSIUM Scattering Experiments I

CPP 10.3: Talk

Tuesday, March 27, 2007, 10:15–10:30, H37

Starlike dendrimers in solutions: Structural properties and internal dynamics — •Silke Rathgeber¹, Michael Mokenbusch², James L. Hedrick³, Mikael Trollsas³, and Alice P. Gast⁴ — ¹Max-Planck Institut für Polymerforschung, Polymer Physik, D-55128 Mainz, Germany — ²Forschungszentrum Jülich GmbH, Institut für Festkörperforschung, D-52425 Jülich, Germany — ³IBM Almaden Research Center, San Jose, California 95120-609, USA — ⁴Department of Chemical Engineering, Masschusetts Institute of Technology, Cambridge, Massachusetts 0213, USA

We measured the shape and the internal dynamics of starlike dendrimers under good solvent conditions with small-angle neutron scattering and neutron spin-echo spectroscopy, respectively. [1] Architectural parameters such as the spacer length and generation were varied in a systematic manner. Structural changes occurring in the dendrimers as a function of these parameters are discussed. A first cumulant evaluation of the NSE spectra for each scattering vector q separately yields the length scale dependent relaxation rates Ω (q). We observe a local minimum in the normalized relaxation rates Ω (q)/q³ on length scales corresponding to the overall dendrimer dimension. The dynamics is discussed within a Rouse-Zimm approach generalized to the case of starlike dendrimers of arbitrary geometry. The model allows an identification of the modes contributing to the relaxation of the dendrimer. The local minimum is due to collective breathing motions of (parts of) the dendrons relative to each other. Shape fluctuations are not observed. [1] S. Rathgeber et. al., J. Chem. Phys. 125, 204908 (2006)