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. ±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.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry