LOW-SHEAR VISCOSITIES OF (SEMI-)DILUTE, AQUEOUS DISPERSIONS OF CHARGED BOEHMITE RODS - DYNAMIC SCALING OF DOUBLE-LAYER EFFECTS

Low-shear viscosities were measured of dilute aqueous dispersions of c harged boehmite rods with an average aspect ratio of 22.5 as a functio n of the Debye length kappa(-1) and the particle volume fraction Phi. It is found that the low-shear viscosity of the dispersions scales wit h the effective overlap concentration v/v(1), where v(1)* is the mini mum overlap concentration of rods with an effective length L = L + 5( kappa)(-1). This dynamic scaling is also valid for low-shear viscosity data of FD-virus solutions (Graf et al. J. Chen. Phys. 1993, 98, 4920 ). The rescaled relative viscosity curves can be described by the (Mar on-Pierce) equation eta(r) = (1 -(v/v(1))/(v/v(1)*)(max))(-2). The ef fective overlap concentration at which the low-shear viscosity diverge s, (v/v(1))max, is much lower for the boehmite rods than for the semi flexible FD-virus and hard rods without electric double layers. Extrap olation of the reduced viscosity to v/v(1) = 0 yields an unrealistic high intrinsic viscosity [eta]. Possibly the relative viscosity of dil ute dispersions at very low ionic strength shows a nonanalytical conce ntration dependence, which renders the definition of [eta] for colloid s with thick double layers questionable.