Volume 28, Issue 1, February 1984
Index of content:
Linear and Nonlinear Rheological Properties of a Polystyrene Sample of Narrow Molecular Weight Distribution28(1984); http://dx.doi.org/10.1122/1.549737View Description Hide Description
We have measured and analyzed the rheological properties of a polystyrene sample of narrow molecular weight distribution in terms of the Doi‐Edwards theory from the linear to the nonlinear regimes in a consistent manner. First, the linear viscoelastic data of the polymer is correlated with the molecular weight distribution obtained by GPC. Then, a four‐component molecular weight distribution extracted from the linear viscoelasticity is used to calculate the steady‐state viscosities for comparison with experimental values. Independently we compare the experimental and theoretical values of the damping function. The good agreements between theory and experiment in both cases confirm each other, since they are directly related. The present study has also shed light on the role which the tension relaxation of the deformed chain plays at high strain rates. At deformation rates slower than the chain tension relaxation, the rheological properties are determined by the reptational process making it unnecessary to include the tension coefficient of the Curtis‐Bird theory into the calculations.
Response of Moderately Concentrated Xanthan Gum Solutions to Time‐Dependent Flows Using Two‐Color Flow Birefringence28(1984); http://dx.doi.org/10.1122/1.549767View Description Hide Description
A new optical arrangement for the flow birefringence experiment, based on a two‐color laser, is described. Using this system, flow birefringence measurements can be performed in transient flow conditions with the birefringence and orientation angle χ of the sample being obtained simultaneously in time. Unlike previous designs which have been devised to accomplish this capability, only a single experimental run is necessary. Measurements using a quarter‐wave retarder indicate that the experimental accuracy is 2.2% for the birefringence and 0.15 ° for the orientation angle. The minimum birefringence detectable by this system is estimated to be Using this technique. and χ of moderately concentrated xanthan solutions were measured following the inception and cessation of simple shear. The effects of increased ionic strength by adding NaCl to the xanthan solution were also examined. A qualitative comparison of measurements between the no salt and NaCl solutions indicates that the macromolecules might be somewhat stiffened in the presence of salt, which agrees with results reported previously in the literature.
28(1984); http://dx.doi.org/10.1122/1.549738View Description Hide Description
A kinetic network model is developed for the viscoelastic behavior of block copolymer melts with spherical microdomains. This model accounts for the variation in density of the matrix polymer segments from the domain boundary to the outer interphase boundary, with a non‐Gaussian segment distribution involving one new parameter. Rate terms consistent with this assumption are used to obtain expressions for the stress transients as well as steady‐state stress in uniaxial elongational flows. This model predicts an apparent yield stress at low strain rates, that is most sensitive to the new parameter a. Comparison of available data with model predictions indicates that increasing domain concentration is described by increasing values of a in the model.
28(1984); http://dx.doi.org/10.1122/1.549768View Description Hide Description
28(1984); http://dx.doi.org/10.1122/1.549778View Description Hide Description