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ORAL PRESENTATION
Session: 4 Complex fluid deformation and rheology: Theories and thermodynamic relationships
(scheduled: Tuesday, 14:50 )
Selected nonlinear physical properties of liquid crystalline elastomers
A.M. Menzel, H.R. Brand
Theoretical Physics III, University of Bayreuth, Germany
Side-chain liquid single crystal elastomers (SCLSCEs) are unique materials combining the properties of ordinary rubbers with those of a liquid crystalline phase. Furthermore the director describing the broken symmetry in the liquid crystalline phase is coupled to deformations of the elastomer, which allows for example the reorientation of the director by external mechanical forces. In a linearized continuum theory this coupling is determined by two terms in the free energy density, which were introduced by de Gennes and contain relative rotations between the director and the polymer network. A central goal of our studies, where we analyze the macroscopic behavior of SCLSCEs in external fields, is to generalize these two terms and the complete expression for the free energy into the nonlinear domain. Physical consequences of the nonlinear terms will be discussed. © IWNET 2006
ORAL PRESENTATION
Session: 4 Complex fluid deformation and rheology: Theories and thermodynamic relationships
(scheduled: Tuesday, 10:20 )
Polymer rheology and nonlinear transient elasticity
O. Müller1, M. Liu1, H. Pleiner2, H.R. Brand3
1 Theoretical Physics, University of Tübingen, Germany
2 Max Planck Institute for Polymer Research, Mainz, Germany
3 Theoretical Physics III, University of Bayreuth, Germany
We simplify our previously derived general macroscopic equations incorporating transient elasticity by assuming incompressibility as well as linear response for the dissipation. We take into account terms up to quartic order in the elasticity (3 independent coefficients) and have in addition only two dissipative constants: the shear viscosity and the relaxation time of transient elasticity. This simple model can account for many experimentally observed rheological effects qualitatively and sometimes even quantitatively. Flow phenomena discussed include the Weissenberg effect, overshoot, relaxation spectra and elongational flows. © IWNET 2006
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and Kleanthi for IWNET 2006