| Abstract
| - The rheology of rigid rod cellulose whisker suspensions has been investigated. The isotropic-at-rest suspension flow curves show two plateaus, one at low shear rates and another at high shearrates, that reflect the flow of isotropic (at low shear rates) or oriented (at high shear rates) suspensions.From the low shear rate viscosity plateau vs concentration, we see that the system is in the semidiluteregion above 0.02 wt %, in agreement with the theoretical predictions. From the same curve, we canestimate a maximum packing concentration of whiskers rods that corresponds to the experimentallymeasured isotropic-to-anisotropic transition. The high shear rate plateau viscosity data show that thesuspension is still in the dilute state above 0.6 wt %. The critical concentration at the dilute−semidilutetransition is thus strongly dependent on the state of order, which suggests that care has to be takenwhen measuring parameters extracted from flowing solutions or suspensions, as for example occurringwith Ubbelhode viscometry. Above a certain critical concentration, the suspensions become anisotropicat rest. The viscosity vs concentration curve has a maximum that vanishes at high shear rates as forliquid crystalline polymer solutions. Rheological and rheo-optical observations show fast inception andrelaxation of both the rheological functions and the texture, in complete contrast with liquid crystallinepolymer solutions.
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