Regensburg 2010 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: Poster: Polymer Dynamics

CPP 31.4: Poster

Mittwoch, 24. März 2010, 17:30–19:00, Poster C

Probing macroscopic viscosity on a sub-nm scale in polymers — •Markus Selmke, Subhasis Adhikari, and Frank Cichos — Universität Leipzig, Exp. Physik I, mona

Well known are the results from hydrodynamics for the viscous drag spheres experience upon translation and rotation in a continuous medium. For each mode of Brownian motion in the respective degrees of freedom a diffusion equation may be setup with the well established diffusional parameters of the Stokes-Einstein Relation (SER) and the Debye-Stokes-Einstein Relation (DSER). Our recent results show for the first time that these relations accurately predict the measured rotational diffusion time constants of sub-nm sized single fluorescent probe molecules in the complex environment of a glass-forming polymer (PMA) close to its glass transition temperature. Dielectric spectroscopy however does not and shows a different temperature dependence of relaxation times. Simulations of log-normal distributed time-traces of time-constants which describe normal rotational diffusion explain the observed distributions of relaxation parameters that are used to fit the individual molecules' dynamics. No spatial heterogeneity needs to be assumed, the system seems ergodic. The Synthesis of dual-labeled bola-polymers will enable the probing of this spatially homogeneous but dynamically heterogeneos system in more detail. First results from the synthesis are promising. An extension of the far-field two-point microrheology to near-field nano-rheology has been devised in theory and will give access to both the complex shear modulus as well as insight into hydrodynamics on nm length scales.