Abstract
The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight Mw ≃ 2.5 × 105 g/mol and varying degree of substitution (DS) as a function of polymer concentration in various solvent media: salt-free water (long-ranged electrostatic interactions), 0.5 M aqueous NaCl (screened electrostatics), and 0.5 M aqueous NaOH (screened electrostatics, diminished hydrophobic interactions) in order to selectively examine the role played by these different interactions. Decreasing DS is found to decrease solubility and induce partial aggregation and eventual gelation. In salt-free and 0.5 M NaCl solution, NaCMC with DS ≃ 1.2 exhibits hydrophilic polyelectrolyte and neutral polymer in good solvent behavior, respectively. Decreasing DS to ≃0.7–0.8 leads to hydrophobic...
Highlights
Water-soluble polyelectrolytes play a crucial role as rheology modifiers, stabilizers, and functional ingredients in a range of formulations.[1]
We study the rheology of NaCMC solutions of varying degree of substitution (DS = 0.7, 0.8, and 1.2) as a function of polymer concentration, from approximately the overlap concentration (c*) to 100c*
We have examined the effect of the degree of substitution on the structure and rheology of NaCMC in aqueous solutions
Summary
Water-soluble polyelectrolytes play a crucial role as rheology modifiers, stabilizers, and functional ingredients in a range of formulations.[1]. Where b is the monomer length; B is the ratio of the chain’s end-to-end distance in dilute salt-free solution to the fully stretched chain length,[21,28] which is found to be B ≃ 1 for NaCMC and other semiflexible polyelectrolytes, consistent with the fact that the persistence length[27] for NaCMC with 0.75 < DS < 1.25 is far larger than b = 0.515 nm.[21,29,30] In salt solutions, c* can be estimated as the reciprocal of the intrinsic viscosity, obtained from the Huggins equation. C* chains overlap, and excluded volume (and hydrodynamic) interactions are screened for length scales larger than the correlation length:
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