This
study aims to understand the role of polyelectrolyte grafting
on the dispersed cellulose nanocrystal (CNC) rods in water through
measuring transport coefficients using depolarized and polarized dynamic
light scattering and by measuring the viscoelastic properties using
rheometer. Rotational and translational diffusivities are found to
slow down with poly(acrylic acid) (PAA)-grafted chains compared to
bare CNCs. Translational diffusion is shown to remain constant between
pH 3 and 9, indicating the good dispersion and stability of PAA-grafted
CNC suspensions. At the overlap solution concentration, chains play
a significant role in bridging the CNC and form a network, as measured
with the viscoelastic properties of neutral chains. When chains are
ionized by altering the pH, the higher viscosity is measured because
of the hydrogen bonding between ionized and un-ionized carboxylic
groups, as previously demonstrated with PAA-grafted spherical nanoparticles.
We further measured the viscoelastic response of PAA-grafted CNC after
applying large steady shear. The results show that CNCs with long
grafts presented enhanced viscoelastic moduli, and their critical
strain value decreased after large shear flow application. Short grafts,
in contrast to the long grafts, did not show any changes in the viscoelastic
response under shear. These results indicate that the alignment-assisted
networks of PAA-grafted CNC enable better entanglements between long
grafted chains at the neutral state.