Saturation of Shear-Induced Isothermal Crystallization of Polymers at the Steady State and the Entanglement-Disentanglement Transition

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• 作者：Jos&eacute ; A. Martins ; Weidong Zhang ; Antó ; nio M. Brito
• 刊名：Macromolecules
• 出版年：2006
• 出版时间：October 31, 2006
• 年：2006
• 卷：39
• 期：22
• 页码：7626 - 7634
• 全文大小：166K
• 年卷期：v.39,no.22(October 31, 2006)
• ISSN：1520-5835

文摘

To provide insight into the formation of shear-induced precursor structures, three apparently unrelatedsubjects are analyzed and discussed: the saturation of crystallization from sheared polymer melts, evaluated witha new shear DTA instrument, the steady state in steady shear, and the entanglement-disentanglement transition.It is shown that the same large strains that saturate crystallization also lead to a reversible steady state in steadyshear, where the viscosity of the sheared melt is constant in time, and their magnitude is only determined by thetemperature of the sheared melt. Features of the melt morphology at this state are discussed, and their importanceis highlighted to understand the possible mechanisms behind the formation of shear-induced precursors.Measurements of the reptation time for unsheared samples, and samples sheared up to the steady state, allowedthe quantification of the entanglements loss during the transition between these two states (around 2/3), which isinterpreted as an entanglement-disentanglement transition. The relevance of this result on assumptions of flowmodels, particularly the constant number of topological constraints, convective constraint release process, andchain stretch, is discussed.