Characterization of Concentration-Dependent Gelation Behavior of Aqueous 2,2,6,6-Tetramethylpiperidine-1-oxyl−Cellulose Nanocrystal Dispersions Using Dynamic Light Scattering

Abstract

Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) with high and low aspect ratios, respectively, were prepared from wood cellulose by catalytic oxidation with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and subsequent sonication in water. Aqueous dispersions of the TEMPO-CNFs and TEMPO-CNCs with different solid concentrations were prepared by dilution or condensation. Dynamic light scattering (DLS) was used to determine the solid concentrations at the transition points from the dilute to semi-dilute regions and from the semi-dilute to dense gel regions in the aqueous TEMPO-CNF and TEMPO-CNC dispersions. All the DLS data corresponded well to the fitting curves of the normalized time-correlation functions. The solid concentration at the gelation point increased from 0.40% w/v for the TEMPO-CNF dispersions to 1.71 % w/v for the TEMPO-CNC dispersions, and the aspect ratio decreased from 134 to 57, respectively. The solid concentrations of the TEMPO-CNF and TEMPO-CNC dispersions at the gelation point calculated using effective-medium theory based on their aspect ratios corresponded well with those experimentally determined by DLS.