A Rheological Investigation of the Crystallization Kinetics of Syndiotactic Polypropylene of Varying Degree of Tacticity

The crystallization behavior of five Syndiotactic Polypropylene (sPP) samples of varying degree of tacticity has been studied by means of rheological techniques and compared to the results of more standard DSC measurements. Small Amplitude Oscillatory Shear (SAOS) measurements have been performed on a controlled stress rotational rheometer equipped with a nitrogen-fed, forced convection oven, which allows for good temperature stability and relatively high heating/cooling rates. Both non-isothermal and isothermal crystallization tests have been carried out. The former proved useful to determine the melting and crystallization temperature of the polymers. The latter were exploited to determine the temperature dependence of the polymer crystallization rate. The results showed the strong influence of the degree of tacticity on the crystallization behaviour of sPP. In particular, it was confirmed that a decrease in the stereo-regularity of the polymer chain considerably shifts the crystallization process to lower temperatures. For the case of the lowest tacticity sample, rheology was crucial in determining the temperature where the maximum (but very small) crystallization rate is attained, a result that could not be achieved by standard calorimetry measurements.

Publisher's Note: Effect of the salt-induced micellar microstructure on the nonlinear shear flow behavior of ionic cetylpyridinium chloride surfactant solutions [Phys. Rev. E 95, 032603 (2017)]

This corrects the article DOI: 10.1103/PhysRevE.95.032603.

Effect of the salt-induced micellar microstructure on the nonlinear shear flow behavior of ionic cetylpyridinium chloride surfactant solutions

The shear flow dynamics of linear and branched wormlike micellar systems based on cetylpyridinium chloride and sodium salicylate in brine solution is investigated through rheometric and scattering techniques. In particular, the flow and the structural flow response are explored via velocimetry measurements and rheological and rheometric small-angle neutron scattering (SANS) experiments, respectively. Although all micellar solutions display a similar shear thinning behavior in the nonlinear regime, the experimental results show that shear banding sets in only when the micelle contour length L[over ¯] is sufficiently long, independent of the nature of the micellar connections (either linear or branched micelles). Using rheometric SANS, we observe that the shear banding systems both show very similar orientational ordering as a function of Weissenberg number, while the short branched micelles manifest an unexpected increase of ordering at very low Weissenberg numbers. This suggests the presence of an additional flow-induced relaxation process that is peculiar for branched systems.

The role of the binding salt sodium salicylate in semidilute ionic cetylpyridinium chloride micellar solutions: a rheological and scattering study

The viscosity varies as a consequence of binding, first, and screening, later, action of the penetrating salt.

Perspectives on the viscoelasticity and flow behavior of entangled linear and branched polymers

We briefly review the recent advances in the rheology of entangled polymers and identify emerging research trends and outstanding challenges, especially with respect to branched polymers. Emphasis is placed on the role of well-characterized model systems, as well as the synergy of synthesis-characterization, rheometry and modeling/simulations. The theoretical framework for understanding the observed linear and nonlinear rheological phenomena is the tube model, which is critically assessed in view of its successes and shortcomings, and alternative approaches are briefly discussed. Finally, intriguing experimental findings and controversial issues that merit consistent explanation, such as shear banding instabilities, multiple stress overshoots in transient simple shear and enhanced steady-state elongational viscosity in polymer solutions, are discussed, and future directions such as branch point dynamics and anisotropic monomeric friction are outlined.

Computer Aided Measurement, by a Stylus, of Surfaces with Double Contour

This paper deals with computer aided measurements by a “stylus” of doubly contoured surfaces. The main result consists in the proposal of suitable algorithms, to be implemented on a personal computer, to efficiently correct the measurement errors involved by the geometry of the stylus.