The linear viscoelastic and shear thickening behavior in aqueous solutions of model hydrophobically end-capped poly(ethylene oxide) were examined. Comparisons are made between monodisperse samples, unimodal polydisperse samples, and bimodal polydisperse samples. While the linear viscoelastic behavior is qualitatively similar for both polydisperse and monodisperse systems, the steady shear response displayed a marked dependence on the type of polydispersity, especially in the shear thickening behavior. No significant shear thickening was observed in unimodal polydisperse samples, and one possible explanation for this lack of significant shear thickening could be due to a lack of cooperative non-Gaussian chain stretching. 1 Samples with bimodal molecular weight distribution exhibit similar shear thickening behavior as monodisperse samples. Furthermore, the characteristics of shear thickening of the bimodal system were found to be the same as in the monodisperse polymer with the lower molecular weight (10K), instead of that of the monodisperse polymer with the same average molecular weight (20K). The mechanism of shear thickening is due to the non-Gaussian chain stretching of the shorter polymer chain.
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Sharon et al. (2002) studied this question.
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