Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: Poster: Polymer Dynamics

CPP 31.3: Poster

Wednesday, March 24, 2010, 17:30–19:00, Poster C

Viscoelastic rheology of Polymer dispersed Liquid Crystals — •Marcel Roth¹, Chris Grigoriadis², Doris Vollmer¹, George Floudas², and Günter K. Auernhammer¹ — ¹Max Planck Institute for Polymer Research, Polymer Physics, 55128 Mainz, Germany — ²University of Ioannina, Department of Physics, 45110 Ioannina, Greece

Polymer dispersed liquid crystals consist of nematic liquid crystalline droplets embedded in a polymer matrix. Applications as optical diodes are manifold and also include curved modules.[1] A thorough understanding of the mechanical properties of theses devices is essential.

For composites of linear PMMA and 4 cyano-4'-biphenyl (5CB) phase separation is induced by cooling through the isotropic-nematic transition. This process is accompanied by a change from a viscous fluid into an elastic network. We employed rheometry and dielectric spectroscopy (DS) to follow the PMMA and 5CB dynamics, respectively. In rheology, all data could be reduced to a single master curve via time-temperature-superposition, irrespective of initial mixing ratios. This behavior relies on two facts: Firstly, 5CB acts as a plastifier for PMMA and thusly speed up the polymer segmental dynamics. Secondly, the phase separation strictly follows the equilibrium PMMA-5CB phase diagram. DS on the other hand, probes mainly the 5CB dynamics and revealed that a part of 5CB molecules does not crystallize in the presence of PMMA. The speed-up of the dynamics of these molecules is in accord with the restricted rotational diffusion model.

[1] D. Coates, J. Mater. Chem., 1995, 5, 2063 - 2072