Rheology of dilute suspensions of charged fibers

Abstract

The rheology of a dilute suspension of charged fibers with a large ratio of length L to diameter d is examined. The fibers may possess both a net charge and a charge dipole and it is assumed that the Hartmann number is small. The double layer thickness is large compared with the rod diameter and may be comparable with the fiber length. Although the shear rate is sufficiently small so that the deformation of the double layer is small, no restriction is placed on the rotary Péclet number of the rods. The velocity disturbance caused by the rods is neglected when calculating the double layer deformation. This approximation is accurate when /LϭO(1) and L/d is very large, but leads to an overestimate of the ion cloud distortion for small values of /L or moderate values of L/d. The counterion cloud affects the stress both directly through a primary electroviscous stress and indirectly by exerting an electric torque that changes the fiber orientation distribution. The additional stress caused by electrostatics shear thins for a fiber with a net charge. However, when the fiber has a charge dipole, the electrical stress may increase with increasing shear rate at sufficiently high Péclet numbers. At very high Péclet numbers, the electrical torque can lead to a fixed orientation of the fibers near the flow direction of the simple shear flow.

Viscosity of a Dilute Suspension of Sodium Montmorillonite in a Electrostatically Stable Condition

“…possible explanation can be analogously given by the alignAs demonstrated in Fig. 1, the obtained data also clarified ment of sheets which is predicted for fiber suspension (25). the presence of the secondary electroviscous effect.…”

The Dilute Rheology of Swimming Suspensions: A Simple Kinetic Model

“…Neglecting particle-particle hydrodynamic interactions, we extend previous work on passive particle suspensions [20][21][22][23][24][25][26] to the case of active suspensions. Numerical solutions for the orientation distribution of a single rod in simple shear flow are obtained from first principles by solving a FokkerPlanck equation, and are used to calculate the particle extra stress as an average over orientations of the force dipoles on the particles, which include contributions from the external flow, Brownian rotations, and the permanent dipole arising from swimming.…”

Intrinsic viscosity of suspensions of electrosterically stabilized nanocrystals of cellulose

“…For charged rodlike colloidal particles, tumbling of particles due to Brownian motion creates an electrical stress that counteracts the particle rotation. When the particle rotates, the ion cloud is locally disturbed, which generates a concentration gradient of ions (higher concentration close to the particle wall and lower farther away), giving rise to an electrical field oriented in the opposite direction of the particle rotation (Chen and Koch 1996). This shows that the charges affect the primary electroviscous effect of rodlike particles in two ways.…”

“…Some investigations have been devoted to the primary electroviscous effects of rigid rods (Chen and Koch 1996;Sherwood 1981). In this case, the effect of the double layer is more difficult to take into account.…”