Microstructure of strongly sheared suspensions and its impact on rheology and diffusion
JOHN F. BRADY a1 and JEFFREY F. MORRIS a1
a1 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA; e-mail: [email protected]; [email protected]
The effects of Brownian motion alone and in combination with an interparticle force of hard-sphere type upon the particle configuration in a strongly sheared suspension are analysed. In the limit Pe[rightward arrow][infty infinity] under the influence of hydrodynamic interactions alone, the pair-distribution function of a dilute suspension of spheres has symmetry properties that yield a Newtonian constitutive behaviour and a zero self-diffusivity. Here, Pe=[gamma][ogonek]a2/2D is the Péclet number with [gamma][ogonek] the shear rate, a the particle radius, and D the diffusivity of an isolated particle. Brownian diffusion at large Pe gives rise to an O(aPe[minus sign]1) thin boundary layer at contact in which the effects of Brownian diffusion and advection balance, and the pair-distribution function is asymmetric within the boundary layer with a contact value of O(Pe0.78) in pure-straining motion; non-Newtonian effects, which scale as the product of the contact value and the O(a3Pe[minus sign]1) layer volume, vanish as Pe[minus sign]0.22 as Pe[rightward arrow][infty infinity].(Received August 7 1996)
(Revised February 19 1997)
Present address: School of Chemical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.