Experimental studies on the relaxation behavior of commercial polymer melts

With a rotary rheometer, various methods were used to determine the characteristic relaxation times for a commercial polydimethylsiloxane (PDMS), and their consistency and relation to the linear relaxation spectrum were examined. The experimental damping functions of the step deformation of the PDMS, a polymethylvinylsiloxane, and a high‐density polyethylene were compared with predictions of the Doi–Edwards theory and Marrucci model; the effect of wall slip on the damping function data is discussed, and the appearance of stress peaks due to material instability as the strain increased above a critical value is detailed. Through the application of a previously proposed stress decomposition method to the data of large‐amplitude oscillatory shear for the PDMS sample, the relationship between the generalized elastic modulus G(ω,γ)] and the shear relaxation modulus G(γ,t)] was investigated. In the linear and initial nonlinear regimes, as the angular frequency (ω) increased, G(ω,γ) approached G(γ,t) on the timescale t = 1/ω, where t is the time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008