The Creep Behavior of a High Molecular Weight Polystyrene
In 1932 Warren Busse noted that high molecular weight linear polymers at temperatures above their glass tempearature, Tg, responded for a time as if they were crosslinked: i.e. they exhibited1 a rubberlike molulus before viscous flow dominated the deformation. He proposed that entanglements involving neighboring threadlike molecules behaved as temporary crosslinks. The appearance of what is now referred to as the rubbery plateau in the creep compliance, J(t), and the stress relaxation modulus, G(t), curves plotted as a function of logarithmic time is the result of the diminution of viscous deformation by the entanglements. The enhanced molecular weight dependence of the viscosity at high molecular weights, M3.4 over the first power dependence observed at low molecular weights at constant monomeric friction coefficient2,3 is a related phenomenon attributed to the existence and influence of the molecular entanglements. The decrease of the entanglement concentration at high rates of shear is believed to be the principal mechanism responsible for the strong decrease in the shear viscosity with increasing shear rates. Graessley has developed a theory of non-Newtonian flow based on this concept4,5.
KeywordsCreep Compliance Entanglement Concentration Compliance Curve Viscous Deformation Rubbery Plateau
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