Droplet deformation under extensional flow in immiscible and partially miscible polymer blends based on poly(styrene-co-acrylonitrile)Results indicating the extent to which flow in a miscible polymer blend can displace the phase separation temperature are reported. Data were obtained on the system, polystyrene/poly (vinyl methyl ether), in the temperature ranges where it undergoes exsolution upon heating. The theoretical framework for the observed flow-induced miscibility is described.
We measure solvent uptake (and loss) taking place as toluene diffuses in and out of crosslinked polyisoprene spheres. We analyze our experimental data using a theoretical description of the swelling process recently put forward by two of us and use these data to test the physical assumptions at the basis of our description. We find that even though this system displays features which are commonly regarded as signature for anomalous or "non-Fickian" behavior (sigmoidal uptake), a correct use of Fick's law accounts for the evolution of the system within the limits of our experimental error. Our data analysis allows us to obtain information on the dependence of the diffusion coefficient on concentration.
We have examined the effect of thickness on the critical tearing energy of a simple gum vulcanizate of SBR in pure shear. Laboratory experiments and finite-element calculations agree that the tearing energy that is measured with a pure-shear specimen increases with the thickness of the specimen. Laboratory measurements indicate that the deformation for crack growth in a pure-shear specimen increases with the thickness of the specimen. Finite-element calculations show that the energy available for release at a given deformation also increases with thickness in the range from t=1.4 mm to t=14 mm. Experiments show that the crtical tearing energy varies linearly with thickness in the range t=0.7 mm to t=2.7 mm. The effect of thickness on the tearing energy was also studied by calculating the J-integral at various points of the crack through the thickness of the pure-shear specimen. In general, the J-integral calculated at the surface of the specimen can be higher than the J-integral calculated at the center of the specimen for specimens that are sufficiently thick. The thickness effect measured in this work suggests that the “critical tearing energy” obtained from standard laboratory specimens may not be a true material property. For this reason, critical tearing energy that is measured on standard specimens may not be generally applied to predict failure in arbitrary elastomeric components.
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