Elongational flow techniques are applied to the examination of flow-induced chain scission of macromolecules in solution. An opposed-jets apparatus is used both to produce mechanical scission and to monitor the molecular weight distribution of the scission products. We have explored the combined effects of elongational flow and elevated temperatures upon degradation of almost monodisperse atactic polystyrene solutions. Between 25 and 150 °C degradation occurs as closely central scission of the molecules beyond a critical strain rate (ef). «f is found to be a decreasing function of temperature. At 150 °C we present also results for thermal degradation alone. These results correlate well with predictions based upon a thermally activated barrier to scission (TABS) model. We also present results on the strain-rate dependence of the scission rate beyond €f at room temperature. These results clearly indicate that in dilute solution only those molecules that are virtually fully stretched can undergo central scission. Degradation in real flow situations (for instance, flow through GPC columns) seems to parallel our idealized experiments. Our results have serious implications for the latest theories of polymer dynamics. Finally, we speculate that, contrary to common belief, simple laminar shear flows may be almost incapable of degrading polymer solutions and that degradation is only encountered when the flow contains an appreciable elongational component, commonly arising as a result of flow instabilities or turbulence.

A numerical simulation model that incorporates three phases, polymer matrix, interlayer, and clay platelet, was developed to predict the tensile modulus of nanoclay‐filled polymer composites. The interlayer was introduced to account for the fact that the mechanical properties of the polymer near the clay surface are different from those of the polymer matrix. The effects of the properties of interlayers, the structure of clay clusters, and platelet distributions upon the modulus of elasticity of the nanocomposites, were studied. The simulation results show that a decrease in the interlayer modulus, as well as an increase in the interlayer thickness, would decrease the modulus of the nanocomposites. Furthermore, it was found that the maximum strain, located in the interlayer near the end of the clay platelet, increases significantly with decreasing interlayer modulus. The effects of the distribution of clay platelets upon composite modulus were interpreted in terms of two parameters, platelet overlap length, and the lateral distance between platelets. Comparison of simulation results with experimental data from the literature has confirmed the reliability of the numerical simulation method used in the present study. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2391–2406, 2004

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Using an elongational flow technique, we have investigated the relationship between the molecular conformational relaxation time and the molecular weight for a solvent whose quality was altered thermally from near θ to a good solvent state. The materials used were closely monodisperse samples of atactic polystyrene. The results show that the relaxation time τ varies with the molecular weight M as τ ∝ M1.5, independent of the solvent quality, a result which apparently is at variance with the observed molecular weight dependence of intrinsic viscosity. Despite this invariance of the molecular weight exponent with solvent quality, our results also show that the coils do expand when the solvent quality was increased in agreement with the mean‐field theory of Flory.