Structure and Rheology of Solutions and Gels of Stiff Polyelectrolyte at High Salt Concentration

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• 作者：Olga E. Philippova ; Andrey V. Shibaev ; Dmitry A. Muravlev ; Dmitry Yu. Mityuk
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：August 23, 2016
• 年：2016
• 卷：49
• 期：16
• 页码：6031-6040
• 全文大小：629K
• 年卷期：0
• ISSN：1520-5835

文摘

The rheology and the structural evolution of xanthan solutions and gels upon increasing polymer concentration were monitored in the absence and in the presence of cross-linker (chromium chloride). Direct visualization of the unperturbed structure of these systems by freeze-fracture transmission electron microscopy revealed the microphase-separated morphology with percolated polymer skeleton composed of aggregated chains. The thickness of the skeleton increases with increasing polymer concentration and at the addition of cross-linker, indicating enhancement of microphase separation. Upon cross-linking, the networks acquire higher plateau modulus G′, but it becomes less dependent on polymer concentration C than in the un-cross-linked state (G′ ∼ C^1.35 and G′ ∼ C^2.1, respectively). The molecular imaging also unraveled the presence of backfolded xanthan segments and many sharp kinks at distances smaller than the persistence length, suggesting the presence of flexible hinges between double-helical fragments of the polysaccharide, which is in agreement with small-angle X-ray scattering data.