Abstract
This paper gives a brief review of recent results of rheo-dielectricstudies for oligo-styrene (OS) and cis-polyisoprene (PI). OS has type-Bdipoles perpendicular to the backbone, and its dielectric αrelaxation (glassy mode relaxation) is accelerated under the shear flow evenat rates much smaller than the equilibrium relaxation frequency. Thisacceleration, resulting in the decrease of the viscosity (thinning) observed atthose rates, is related to flow-induced reduction of the cooperativity of thesegmental motion. For PI chains, having type-A dipoles parallel to thebackbone, the dielectric relaxation detects the global chain motion. For wellentangled PI chains, this relaxation is only moderately accelerated and itsintensity is only mildly reduced even under fast flow in the non-Newtonianthinning regime. This result is related to a flow-induced orientationalcross-correlation of entanglement segments. Within the context of thetube model for entangled chains, this cross-correlation can be related tothe dynamic tube dilation induced by the convective constraint release.
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