Polymer motion as detected via dielectric spectra of 1,4-cis-polyisoprene under large amplitude oscillatory shear (LAOS)

In order to investigate the global polymer chain motion under large amplitude oscillatory shear (LAOS), the dielectric properties under LAOS are measured by a new rheo-dielectric combination. The design of the rheo-dielectric setup including a new fixture and modified oven is explained in detail. For 1,4-cis-polyisoprene, having type-A dipoles parallel to the backbone, the dielectric dipoles can detect the global polymer chain motion via the end-to-end vector. Thus rheological and dielectric (rheo-dielectric) properties reflect the dynamics of the polymer chain motion under LAOS. In this study, we investigate the rheo-dielectric properties under LAOS with 1,4-cis-polyisoprene as model component. As the strain amplitude was increased under LAOS, the relaxation strength from dielectric properties decreased for the whole spectra without changing the shape of the dielectric spectra. These results are analyzed on the basis of the molecular model of dynamic tube dilation (DTD) induced by the convective constraint release (CCR). It is found that the global chain motion under LAOS flow is affected by both rheological frequency and strain amplitude. It is also observed that segmental motion is affected via the oscillatory frequency under LAOS. This result differs from experiments under steady shear.