Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 2: DRG-DPG SYMPOSIUM Rheology II
CPP 2.4: Vortrag
Montag, 25. Februar 2008, 15:00–15:15, C 130
Non-equilibrium phenomena in sheared bottlebrush polymer solutions — •Silke Rathgeber1, Hyung-il Lee2, Krzysztof Matyjaszewski2, and Emanuela Di Cola3 — 1Max-Planck Institut für Polymerforschung, Polymer Physik, 55128 Mainz, Germany. — 2Carnegie Mellon University, Department of Chemistry, Pittsburgh, Pennsylvania 15213, USA. — 3European Synchrotron Radiation Facility, 38043 Grenoble Cedex, France.
Time-resolved small-angle x-ray scattering (SAXS) experiments were carried out on concentrated solutions of bottlebrush polymers exposed to an external shear flow.[1] The rheological response of the sample were recorded online. We followed the complex structural changes occurring in a, perpendicular to the flow direction pre-aligned sample during its reorientation into the flow direction. In the stress-controlled rheometer mode the reorientation is accompanied by a shear thinning process with a reduction in viscosity of two orders of magnitudes. In the strain controlled mode the rheological response of the bottlebrush polymer solution to the rotational shear shows oscillations with changes in viscosity of almost two orders of magnitude. The SAXS data reveal that this oscillatory response is due to a reentrant phase transition between a shear molten phase and a line hexatic phase. It is not due to shear induced phase separation leading to shear band formation. The insitu-rheological SAXS measurements allow a detailed description of the structural changes occurring in the sample during structural built-up and break-down. [1] S. Rathgeber et al., Macromolecules 40, 7680 (2007).