Cellulose Nanocrystals as a Model Substance for Rigid Rod Particle Suspension Rheology

Abstract

A cellulose nanocrystal (CNC) sample with an average particle length and width of 170 and 7.8 nm, respectively, that was prepared from chemical pulp via sulfuric acid hydrolysis procedures was used as the test sample for a basic rheological study on rigid rod particle suspensions. The dynamic viscoelastic (VE) behavior of the CNC suspensions dispersed into a highly viscous aqueous sucrose solution at 60 wt % was examined over a range of concentrations (ν) in a semidilute regime at several temperatures. The obtained VE spectra were smoothly superposed onto master curves at a standard temperature of 25 °C using shift factors identical to those of the medium aqueous sucrose solution. The fundamental VE parameters, such as the zero-shear viscosity, the high frequency limiting viscosity, the average relaxation time (τw), and the reciprocal of the steady-state compliance (Je–1), were precisely determined from the master curves as functions of ν. The average rotational diffusion constant of the CNC particles dispersed into suspensions at a dilute condition, Dr0, was also determined at 25 °C using depolarized dynamic light scattering techniques. The relationship τw0 = (6Dr0)−1 was confirmed in the dilute regime, and τw ∝ ν2(6Dr0)−1 was observed in the semidilute regime as predicted by the Doi–Edwards (D–E) theory. Another relationship Je–1 = (3/5)νkBT, where kBT is the product of the Boltzmann constant and the absolute temperature, was also reasonably confirmed in the semidilute regime until the concentration approached the liquid crystal phase transition boundary, as also predicted by the D–E theory. Consequently, the CNC sample behaves as ideal model particles for the detailed study of rigid rod particle suspensions.