Viscoelastic Properties of Poly(vinyl alcohol) Hydrogels Having Permanent and Transient Cross-Links Studied by Microrheology, Classical Rheometry, and Dynamic Light Scattering

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• 作者：Tetsuharu Narita ; Koichi Mayumi ; Guylaine Ducouret ; Pascal H茅braud
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：May 28, 2013
• 年：2013
• 卷：46
• 期：10
• 页码：4174-4183
• 全文大小：435K
• 年卷期：v.46,no.10(May 28, 2013)
• ISSN：1520-5835

文摘

Dynamics of poly(vinyl alcohol) (PVA) hydrogels having chemical and physical transient cross-links simultaneously (dual cross-link PVA gels) were studied by microrheology based on diffusing-wave spectroscopy (DWS), classical rheology and single dynamic light scattering (DLS), and compared with those of corresponding chemical and physical PVA gels. Three different relaxation modes (fast, intermediate and slow modes) are observed for physical gels, while one mode (fast mode) is found for chemical gels, and two (fast and intermediate) for dual cross-link gels. The three modes are attributed respectively to Brownian diffusion of PVA polymer or collective diffusion of the network or gel mode (fast mode), macroscopic stress relaxation (intermediate mode whose characteristic time shows q⁰ dependence) and Brownian diffusion of aggregates (slow mode). Microrheological measurements are in good agreement with macrorheological showing segmental Rouse mode dynamics in the high frequency range. For physical gels, we found Maxwell type viscoelasticity characterized by a crossover frequency (maximum of G鈥? and G鈥? 蠅² and G鈥? 蠅¹ in the lower frequency range. The chemical gels displayed an elastic plateau with low G鈥?at low frequency. For the dual cross-link gel a maximum of G鈥?was observed, and its characteristic time agrees with that of the intermediate mode measured by DLS. We show that this relaxation mode corresponds to the associative Rouse mode characterized by G鈥?= G鈥? 蠅^0.5, depending on the dissociation rate of the reversible transient cross-links. We propose a stress relaxation mechanism of the PVA chains in the presence of elastically inactive but associative transient cross-links which induces incomplete stress relaxation.