Understanding Constraint Release in Star/Linear Polymer Blends

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• 作者：M. E. Shivokhin ; E. van Ruymbeke ; C. Bailly ; D. Kouloumasis ; N. Hadjichristidis ; A. E. Likhtman
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：April 8, 2014
• 年：2014
• 卷：47
• 期：7
• 页码：2451-2463
• 全文大小：641K
• 年卷期：v.47,no.7(April 8, 2014)
• ISSN：1520-5835

文摘

In this paper, we exploit the stochastic slip-spring model to quantitatively predict the stress relaxation dynamics of star/linear blends with well-separated longest relaxation times and we analyze the results to assess the validity limits of the two main models describing the corresponding relaxation mechanisms within the framework of the tube picture (Doi鈥檚 tube dilation and Viovy鈥檚 constraint release by Rouse motions of the tube). Our main objective is to understand and model the stress relaxation function of the star component in the blend. To this end, we divide its relaxation function into three zones, each of them corresponding to a different dominating relaxation mechanism. After the initial fast Rouse motions, relaxation of the star is dominated at intermediate times by the 鈥渟kinny鈥?tube (made by all topological constraints) followed by exploration of the 鈥渇at鈥?tube (made by long-lived obstacles only). At longer times, the tube dilation picture provides the right shape for the relaxation of the stars. However, the effect of short linear chains results in time-shift factors that have never been described before. On the basis of the analysis of the different friction coefficients involved in the relaxation of the star chains, we propose an equation predicting these time-shift factors. This allows us to develop an analytical equation combining all relaxation zones, which is verified by comparison with simulation results.