Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 23: Poster: Semicrystalline Polymers, Polymer Crystallization and Self-Assembly

CPP 23.10: Poster

Dienstag, 15. März 2011, 18:00–20:00, P2

Direct estimation of spin diffusion constants by a cross-polarization based method — •Matthias Roos and Günter Hempel — Martin-Luther-Universität, Institut für Physik, Betty-Heimann-Straße 7, D-06120 Halle

Spin diffusion often influences the results of relaxation experiments in dependence of structural and dynamic heterogeneities of the sample. Therefore this phenomenon can be used for the estimation of such heterogeneities. Knowledge of the magnitude of the spin diffusion constant is a precondition for those investigations. Theoretical approaches for the estimation of this constant were used sometimes which however particularly in more mobile phases give rise to some uncertainty. Few experimental attempts for estimating this constant are known. Here we introduce a method which makes use of cross polarization between protons and 13C spins. This method produces holes in the proton magnetization at places where 13C spins are neighboured. During the following waiting time the holes are re-filled. This filling process is caused by spin diffusion; its speed contains information about the spin-diffusion constant. We follow the hole filling process by another cross polarization.

Applications to liquid crystals and polymers (amorphous and crystalline regions) are demonstrated. In a liquid crystal (7CB) the diffusion process could be proven as being one-dimensional.