Observing the chain stretch transition in a highly entangled polyisoprene melt using transient extensional rheometry
Measurements of and obtained from SAOS experiment. AR-G2 (TA Instruments) . The solid lines (——) are the MM prediction for , , and . The dotted lines (- - - -) are calculated from the Maxwell spectrum (Table I), with . The dash-dotted line is .
Measurements of (a) and (b) , for discrete values of the applied strain increasing from top to bottom. The dotted line is the predicted variation in from the Maxwell coefficients fitted to the SAOS measurements. AR-G2 (TA Instruments) .
Development of the normalized height of the PI film in the SER extensional rheometer as function of nominal Hencky strain for four nominal elongational rates and initial aspect ratio . Dotted lines are the predicted behavior from the nominal elongational rates assuming uniaxial extension. The elongational rates found from the initial linear slope (on this semilogarithmic scale for ) are, respectively, , , , and .
Normalized height of the PI film in the SER extensional rheometer as function of the nominal Hencky strain for different aspect ratios , , and at the same nominal elongational rate of . The data are taken from images obtained by high speed video microscopy. The ideal uniaxial kinematic response is shown by the dotted line. Ideal planar extension would correspond to a horizontal line. For , the deformation is seen to be a mixture of uniaxial and planar extension.
Black and white image frames from the video for and from the SER instrument. The nominal elongational rate is in both experiments. Close inspection of the frames show that the kinematics depend on the aspect ratio, as shown in Fig. 4.
Measurements of the engineering stress for , , and as a function of Hencky strain as determined by the EVF, SER, and FSR instruments . For the EVF and SER, is nominal Hencky strain [Eq. (8)], while for the FSR is computed from the instantaneous filament diameter. The Rouse Deborah numbers for the three experiments are , , and based on the Rouse time of . The solid line is the Doi–Edwards prediction [Eq. (3)] for , with .
Transient growth of the engineering stress for elongational rates: (), (▽), (▲), (△), (◇), (○), (▼), (◻), , (◼), and (●). (EVF instrument, ). The dotted lines are the prediction of the Doi–Edwards model for the seven lowest elongational rates, and the solid line is the rapid stretching limit of the Doi–Edwards model [Eq. (3)]. The bottom frames show the development of the PI sample at different times stretched at a rate of .
Transient elongational viscosity for 12 elongational rates from to . The solid line is the linear viscoelastic envelope (EVF instrument, ). Also included is the transient elongational viscosity measured during startup and stress relaxation for stretched to (◼) , (●) stretched to and (▲) stretched to a final strain . The dotted lines are the relaxation prediction during relaxation from the multimode linear Maxwell model.
Comparison between the transient extensional stress for elongational experiments performed with initial aspect ratio of and , respectively (EVF instrument, ). The imposed elongational rates range from to . The solid line is the Neo-Hookean prediction , and the dotted line is the rapid stretching limit from the Doi–Edwards equation from Eq. (3).
Measured values of Hencky strain at which the engineering stress goes through a maximum and Hencky strain at which the sample ruptures . Also shown is the Doi–Edwards prediction of .
Properties of the PI determined from small angle oscillatory shear.
Estimates of the maximum possible temperature increase for adiabatically elongated samples at high rates.
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