Self-Diffusion of Associating Star-Shaped Polymers

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• 作者：Shengchang Tang ; Axel Habicht ; Shuaili Li ; Sebastian Seiffert ; Bradley D. Olsen
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：August 9, 2016
• 年：2016
• 卷：49
• 期：15
• 页码：5599-5608
• 全文大小：500K
• 年卷期：0
• ISSN：1520-5835

文摘

The dynamics of associating bonds in transient polymer networks exerts a paramount influence on their relaxation and time-dependent mechanical properties. In particular, diffusive motion of polymers mediated by the dissociation and association equilibrium of reversible junctions can affect the materials’ structural stability, dynamic mechanical properties, and a broad spectrum of functionality that arises from the constant motion of polymer chains. In this work, forced Rayleigh scattering is used to measure the diffusion of terpyridine end-functionalized four-arm poly(ethylene glycol) polymers transiently interlinked by zinc ions in organic solvent across a wide range of length and time scales. Phenomenological superdiffusion, where the scaling of the squared length dimension vs time has a power-law exponent larger than one, is demonstrated as an intrinsic feature of these networks due to the interplay of chain dissociation and diffusion. Outside the superdiffusive regime, normal Fickian diffusion is recovered on both large and small length scales. The data are quantitatively described with a previously developed two-state model of one fast and one slow diffusing species that are allowed to interconvert. The extracted diffusivities show concentration-dependent scaling in good agreement with the sticky Rouse model. Diffusion of the same polymers but with only three associating arms through the same transient networks is also investigated, which exhibits faster chain diffusivities compared to the case of the polymers with four associating arms. These experimental results quantitatively show the effect of sticker density and valency on chain diffusion in transient polymer networks.