, Volume 47, Issue 1, pp 97-103
Date: 18 Aug 2007

Large amplitude oscillatory elongation flow

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A filament stretching rheometer (FSR) was used for measuring the elongation flow with a large amplitude oscillative elongation imposed upon the flow. The large amplitude oscillation imposed upon the elongational flow as a function of the time t was defined as \(\epsilon(t) = \dot{\epsilon}_0 t + \Lambda [1 - \cos( 2 \pi \Omega \dot{\epsilon}_0 t )]\) where ε is the Hencky strain, \(\dot{\epsilon}_0\) is a constant elongational rate for the base elongational flow, Λ the strain amplitude (Λ ≥ 0), and Ω the strain frequency. A narrow molecular mass distribution linear polystyrene with a molecular weight of 145 kg/mol was subjected to the oscillative flow. The onset of the steady periodic regime is reached at the same Hencky strain as the onset of the steady elongational viscosity ( Λ = 0). The integral molecular stress function formulation within the ‘interchain pressure’ concept agrees qualitatively with the experiments.