The rheological characteristics of synthetic hectorite/water suspensions have been measured by a cone-plate rheometer as a function of additive NaCl concentration (C NaCl ). The hectorite particles, dialyzed preliminarily to remove electrolytic impurities involved, were utilized for preparing a 2.0 wt% aqueous suspension. The apparent viscosities of the suspensions decreased monotonically with increasing C NaCl ; these changes in the viscosities came from the primary electroviscous effect. In dynamic viscoelastic measurements of the suspensions, we found that the critical strain also decreased with increasing C NaCl . By the use of a Cryo-SEM, we observed that different types of the particle-coagulated structures in the various suspensions with respective NaCl concentrations. These findings can be explained by the different interaction modes originated from the electrostatic charge near the surface of hectorite particles, as in the following situations : (1) in the low C NaCl region, the electrostatic repulsion among the particles leads effectively to form an expanded network structure in the system; (2) in the high C NaCl region, the van der Waals attraction force among the particles governs the interaction mode in the system, thus resulting to form a dense-packed coagulation structures.

No abstract

Cellulose nanofibers (CNFs) produced by mechanical processing have a more uneven fiber shape, diameter, and length than those produced by chemical processing. Depending on the manufacturing conditions, CNFs containing insufficient fibrillated fibers may be produced. In order to find practical applications for CNFs containing unfibrillated fibers, it is important to understand how to control the rheological behavior of these systems. In this study, we investigated the relationship between the nanosized volume fraction and the rheological behaviors of CNF suspensions containing unfibrillated fibers prepared by a wet refining system (Water Jet System). The macroscopic structural changes in those suspensions under shear flow were also discussed based on rheo-optic measurements.According to the frequency sweeps of the CNF suspensions, it was found that they were elastic-dominated gels, and the elasticity was attributed to the nanofibers. The elastic moduli increased with the volume fraction of the nanofibers, suggesting that the entanglement of the nanofibers was enhanced. The pseudo-plateau modulus Gp' is proportional to the nanofiber volume fraction, with the constant  = 1.5, suggesting that the entropic elasticity is dominant.The viscosity curves of the CNF suspensions showed a shear thinning behavior, in which the viscosity linearly decreased with the increasing shear rate. From the Rheo-SALS measured at the same time, we found that the aggregates of the nanofibers elongated in the flow direction and deformed into an elliptical shape with the applied shearing. The shape change of the aggregates comprised of the nanofibers became more pronounced with the increased nanofiber volume fraction. However, the effect of the shape change of the aggregates was hardly observed on the viscosity curve. 3We speculate that this is due to the fact that the unnanosized fibers, which exhibit a Newtonian flow, play a significant role in the flow behavior of the CNF suspensions.

No abstract

No abstract