Estimation of viscosity coefficients and rheological functions of nanocrystalline cellulose aqueous suspensions

Abstract

This paper presents a methodology to calculate different rheological functions and viscosity coefficients for lyotropic liquid crystals (LCs) using analytical calculations and experimental rheological data. By implementing Doi and Larson models for lyotropic nematic liquid crystals, the Leslie viscosity coefficients for nanocrystalline cellulose (NCC) aqueous suspensions have been calculated as a function of concentration of molecules per unit volume. The Landau viscosity coefficients from the symmetric viscous stress tensor have been calculated based on the mapping between Landau-de Gennes theory and the Leslie–Ericksen theory. Various parameters and dimensionless numbers from the Landau-de Gennes theory were calculated and related to experimental data. The validation was done using numerical simulations of the Landau-de Gennes equations for transient simple shear flow between parallel plates of 7 wt NCC aqueous suspensions and experimental rheological data. Apparent viscosity and shear stress from numerical simulations have been compared with the experimental results for the same concentration and found a good agreement. A cholesteric pattern was observed for low shear rates and flow-aligning regime for higher shear rates.

Keywords:

• lyotropic liquid crystals
• cholesteric
• flow-aligning
• the Leslie viscosity coefficients
• rheology
• rheological material functions

Acknowledgements

The authors are grateful to Dr Savvas G. Hatzikiriakos for his helpful discussions.