Alignment-Assisted Networks of Polyelectrolyte-Grafted\nCellulose Nanocrystals

Abstract

This\nstudy aims to understand the role of polyelectrolyte grafting\non the dispersed cellulose nanocrystal (CNC) rods in water through\nmeasuring transport coefficients using depolarized and polarized dynamic\nlight scattering and by measuring the viscoelastic properties using\nrheometer. Rotational and translational diffusivities are found to\nslow down with poly(acrylic acid) (PAA)-grafted chains compared to\nbare CNCs. Translational diffusion is shown to remain constant between\npH 3 and 9, indicating the good dispersion and stability of PAA-grafted\nCNC suspensions. At the overlap solution concentration, chains play\na significant role in bridging the CNC and form a network, as measured\nwith the viscoelastic properties of neutral chains. When chains are\nionized by altering the pH, the higher viscosity is measured because\nof the hydrogen bonding between ionized and un-ionized carboxylic\ngroups, as previously demonstrated with PAA-grafted spherical nanoparticles.\nWe further measured the viscoelastic response of PAA-grafted CNC after\napplying large steady shear. The results show that CNCs with long\ngrafts presented enhanced viscoelastic moduli, and their critical\nstrain value decreased after large shear flow application. Short grafts,\nin contrast to the long grafts, did not show any changes in the viscoelastic\nresponse under shear. These results indicate that the alignment-assisted\nnetworks of PAA-grafted CNC enable better entanglements between long\ngrafted chains at the neutral state.