Shear-thinning of polydisperse suspensions

• Published in: Journal of physics. D, Applied physics Applied physics, 2008-06, Vol.41 (11), p.115408-115408 (7)
• Main Authors: Reardon, P T, Feng, S, Graham, A L, Chawla, V, Admuthe, R S, Abbott, J
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Heterogeneous liquids: suspensions, dispersions, emulsions, pastes, slurries, foams, block copolymers, etc; Material form; Physics; Rheology
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/41/11/115408

The effects of the polydispersivity of the particle phase on the rheology of suspensions are studied with falling-ball rheometry. The model suspensions consist of large, neutrally buoyant spheres in a viscous Newtonian suspending fluid. The experiments determine the average velocity of the settling particle along the centreline or axis of the containing cylinders. The objective of this study was to determine the effects of the dispersivity of the particulate phase on the relative viscosity of the suspensions. In dilute and moderately concentrated suspensions, there is no statistically significant difference in the relative viscosity, etar, between the model suspensions of spheres of uniform sizes and suspensions of spheres with polydisperse sizes for all settling sphere sizes examined. As increases to 0.5, suspensions made up of particles with very narrow size distributions have viscosities that are essentially shear-rate independent. As the standard deviation of the particle distribution normalized by the average particle size increases from 0.01 to 0.2, we find that etar exhibits significant shear thinning with a power-law exponent, n, decreasing to 0.50 from the roughly Newtonian behaviour (n = 1). Over the range of our data, etar increased as the degree of polydispersivity increased.