Viscosity and Scaling of Semiflexible Polyelectrolyte NaCMC in Aqueous Salt Solutions

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• 作者：Carlos G. LopezRalph H. Colby ; Peter GrahamJoao T. Cabral
• 刊名：Macromolecules
• 出版年：2017
• 出版时间：January 10, 2017
• 年：2017
• 卷：50
• 期：1
• 页码：332-338
• 全文大小：534K
• ISSN：1520-5835

文摘

We investigate the viscosity dependence on concentration and molecular weight of semiflexible polyelectrolyte sodium carboxymethylcellulose (NaCMC) in aqueous salt-free and NaCl solutions. Combining new measurements and extensive literature data, we establish relevant power laws and crossovers over a wide range of degree of polymerization (N) as well as polymer (c) and salt (c_s) concentrations. In salt-free solution, the overlap concentration shows the expected c* ∝ N^–2 dependence, and the entanglement crossover scales as c_e ∝ N^–0.6±0.3, in strong disagreement with scaling theory for which c_e ∝ c* is expected, but matching the behavior found for flexible polyelectrolytes. A second crossover, to a steep concentration dependence for specific viscosity (η_sp ∝ c^3.5±0.2), commonly assigned to the concentrated regime, is shown to follow c** ∝ N^–0.6±0.2 (with c**/c_e ≃ 6) which thus suggests instead a dynamic crossover, possibly related to entanglement. The scaling of c* and c_e in 0.01 and 0.1 M NaCl shows neutral polymer in good solvent behavior, characteristic of highly screened polyelectrolyte solutions. This unified scaling picture enables the estimation of viscosity of ubiquitous NaCMC solutions as a function of N, c, and c_s and establishes the behavior expected for a range of semiflexible polyelectrolyte solutions.