Structure of sodium carboxymethyl cellulose aqueous solutions: A SANS and rheology study

Abstract

We report a small angle neutron scattering (SANS) and rheology study of cellulose derivative polyelectrolyte sodium carboxymethyl cellulose with a degree of substitution of 1.2. Using SANS, we establish that this polymer is molecularly dissolved in water with a locally stiff conformation with a stretching parameter. We determine the cross sectional radius of the chain ( 3.4 Å) and the scaling of the correlation length with concentration (ξ = 296 c−1/2Å for c in g/L) is found to remain unchanged from the semidilute to concentrated crossover as identified by rheology. Viscosity measurements are found to be in qualitative agreement with scaling theory predictions for flexible polyelectrolytes exhibiting semidilute unentangled and entangled regimes, followed by what appears to be a crossover to neutral polymer concentration dependence of viscosity at high concentrations. Yet those higher concentrations, in the concentrated regime defined by rheology, still exhibit a peak in the scattering function that indicates a correlation length that continues to scale as. © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 492–501

Effect of the degree of substitution on the rheology of sodium carboxymethylcellulose solutions in propylene glycol/water mixtures

“…As previously mentioned, in aqueous solutions of Na-CMC 1.04 a large number of COONa groups prevents the interchain hydrogen bond formation, which is evidenced by the lack of aggregates (Na-CMC 1.04 is molecularly dispersed in water) (Lopez et al 2015). The absence of cross-linking of Na-CMC 1.04 macromolecules in the aqueous solutions is most likely an effect of their solvation (Xiquan et al 1990).…”

“…As DS grows, there is a decrease in the number of O 6 H 6 groups and an increase in the number of COONa groups, the presence of which may lead to the destruction of interchain hydrogen bonds and the disappearance of aggregates. Consequently, at high DS values, sodium carboxymethylcellulose is molecularly dispersed in water (Lopez et al 2015), and the scaling exponent assumes values that are similar to those characteristic for liquid-like terminal behaviour (G 0 µ x 2 ; G 00 µ x). A deviation of the scaling exponent from the value of 2 for Na-CMC 1.04 may be a result of polymer polydispersity.…”

Viscosity and Scaling of Semiflexible Polyelectrolyte NaCMC in Aqueous Salt Solutions

“…in aqueous, salt-free solutions has been studied previously. 6,[17][18][19][20][21][22][23][24][25][26] A power law dependence of the specific viscosity (η sp = (η − η s )/η s where η is the solution viscosity and η s is the solvent viscosity) in the semidilute nonentangled regime close to the Fuoss law 27 (η sp ∼ c 1/2 ) is usually observed, where c is the polymer concentration. …”

“…However, the behaviour of their semiflexible counterparts, remains less well understood, despite their industrial importance, particularly in salt-free solution. [6][7][8][9] From a fundamental perspective, it is also of interest to establish whether the same scaling laws apply for flexible and semiflexible polyelectrolytes. 10,11 In this paper, we review experimental data for the viscosity and crossover concentrations of sodium carboxymethylcellulose (NaCMC) in aqueous solutions at different salt concentrations.…”

“…60,61 Further, the concentration dependence predicted by equation 3 for salt-free polyelectrolyte solutions η sp ∼ c 1/2 is not always observed. 6,60 Chains begin to entangle at c e , which is predicted to be proportional to c * :…”