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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Polymer and Molecular Dynamics, Friction and Rheology

CPP 8.3: Vortrag

Montag, 18. März 2024, 15:30–15:45, H 0107

Polymer dynamics and transport of energy and matter studied by rheological NMR — •Ulrich Scheler — Leibniz-Institut für Polymerforschung Dresden e.V

The effect of external shear on transport properties and polymer dynamics are studied by rheological NMR in a Searle cell. Nanoemulsions as phase-change materials are used for storage of thermal energy. A hysteresis of melting of the oil phase is observed following the fraction of the liquid signal from the oil. This is accompanied by a transition from Newtonian flow to shear banding determined by low NMR imaging. With the more flexible and deformable droplets a deviation from a linear flow profile is seen. That is accompanied by a variation of the concentration distribution as detected by spatially resolved NMR spectra in the gap. The chain dynamics in entangled polymer melts and solutions is effectively monitored by the spin-spin relaxation time T2 that is most sensitive to slow motions like chain segment motion. in polymer melt with a chain length above the entanglement length the dominating effect is the loss of entanglements. This effect sets in only at deformation rates in excess of 1000 s-1. The behavior of solutions of polyelectrolytes depends on concentration and ionic strength. Entanglement effects are observed above the entanglement concentration only. They are enhanced when the polyelectrolytes become more flexible by screening the electrostatic interaction by the addition of salt.

Keywords: Polymer chain dynamics; rheological NMR; phase-change materials; entanglements