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 (cs) concentrations. In salt-free solution, the overlap concentration shows the expected c* ∝ N–2 dependence, and the entanglement crossover scales as ce ∝ N–0.6±0.3, in strong disagreement with scaling theory for which ce ∝ c* is expected, but matching the behavior found for flexible polyelectrolytes. A second crossover, to a steep concentration dependence for specific viscosity (ηsp ∝ c3.5±0.2), commonly assigned to the concentrated regime, is shown to follow c** ∝ N–0.6±0.2 (with c**/ce ≃ 6) which thus suggests instead a dynamic crossover, possibly related to entanglement. The scaling of c* and ce 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 cs and establishes the behavior expected for a range of semiflexible polyelectrolyte solutions.
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机译:我们研究了在无盐和NaCl水溶液中半柔性聚电解质羧甲基纤维素钠(NaCMC)的浓度和分子量对粘度的依赖性。结合新的测量结果和广泛的文献数据,我们建立了相关的功率定律和在广泛的聚合度(N)以及聚合物(c)和盐(cs)浓度范围内的转换。在无盐溶液中,重叠浓度显示出预期的c * ∝ N–2依赖性,并且缠结交换尺度为ce ∝ N–0.6±0.3,这与期望ce ∝ c *的标度理论有很大不同,但是匹配柔性聚电解质的行为。第二次交叉,通常取决于浓稠度,对比粘度(ηsp∝ c3.5±0.2)的浓度依赖性很强,显示遵循c ** ∝ N–0.6±0.2(c ** / ce with 6)因此建议动态交叉,可能与纠缠有关。 c *和ce在0.01 M和0.1 M NaCl中的结垢表明中性聚合物具有良好的溶剂性能,这是高度筛选的聚电解质溶液的特征。这种统一的缩放比例图片使得可以根据N,c和cs估算普遍存在的NaCMC溶液的粘度,并确定了一系列半柔性聚电解质溶液的预期行为。
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