The rheology of water soluble polyelectrolytes
at intermediate and high concentrations is controlled by
entanglements, hydrophobic and electrostatic interac-
tions, whose influence is difficult to isolate. We investi-
gate the rheology of semidilute solutions of sodium car-
boxymethyl cellulose (NaCMC) with molecular weight
M
w
'
2
.
5
×
10
5
g/mol and varying degree of substi-
tution (D.S.) as a function of polymer concentration in
various solvent media: salt-free water (long ranged elec-
trostatic interactions), 0.5M aqueous NaCl (screened
electrostatics) and 0.5M aqueous NaOH (screened elec-
trostatics, diminished hydrophobic interactions) in or-
der to selectively probe the different interactions. De-
creasing D.S. is found to decrease solubility and induce
partial aggregation and eventual gelation. In salt-free
and 0.5M NaCl solution, NaCMC with D.S.
'
1.2 ex-
hibits hydrophilic polyelectrolyte and neutral polymer
in good solvent behaviour respectively. Decreasing D.S.
to
'
0.7-0.8 leads to hydrophobic behaviour in both
solvents, becoming weak gels at high concentrations. In
0.5M NaOH (pH = 13.5) the viscosities of samples with
different D.S. become identical when plotted against
the overlap parameter, which we interpret as result-
ing from the solubilisation of unsubstituted cellulose
blocks. Small angle neutron scattering (SANS) data in-
dicate that the polymer conformation is not strongly
affected by hydrophobic interactions. By varying D.S.,
ionic strength and pH, we demonstrate the tuning of
NaCMC-solvent interactions, controlling separately the electrostatic and hydrophobic effects on the solution
rheology.