Shaocong Dai

Viscometric functions for noncolloidal sphere suspensions with Newtonian matrices

We present the results of measuring the three viscometric functions [the relative viscosity ηr, and the first (N1) and second (N2) normal stress differences] for nominally monosize sphere suspensions in a silicone fluid, which is nominally Newtonian. The measurements of ηr and N1−N2 were made with a parallel-plate rheometer, while we used the open semicircular trough method to give N2 directly. With the trough method measurements of N2 could be made down to a 10% concentration (φ=0.1); measurements were continued up to 45% concentration. The trough surface shows visually that N2 is directly proportional to the shear stress τ, and the measurements of N2 agree quite well with the results of Zarraga et al. [J. Rheol. 44, 185–220 (2000)] in the range where concentrations overlap (0.3–0.45) and with those of later investigators. The results for N1 show greater scatter. In the range 0.1≤φ≤0.45, our best estimate of N2/τ is −4.4φ3 and that of N1/τ is −0.8φ3. Hence, the magnitude of N2 is much greater than that o...

Viscometric functions of concentrated non-colloidal suspensions of spheres in a viscoelastic matrix

We have measured the viscometric functions (η, N1, and N2) for a suspension of noncolloidal spherical particles in a Boger fluid matrix. The polymethyl methacrylate particles were nominally 40 μm in size, and the matrix fluid was similar to that used by Zarraga et al. [J. Rheol. 45, 1065–1084 (2001)]. The volume concentrations (ϕ) ranged from 5% to 40%, and a combination of the open trough and parallel-plate methods was used. The viscosity did not shear-thin for higher concentrations, unlike the Newtonian matrix case; for the larger concentrations we saw a mild shear-thickening. This is in agreement with the work of Zarraga et al. [J. Rheol. 45, 1065–1084 (2001)] and Scirocco et al. [J. Rheol. 49, 551–567 (2005)]. N2 was always negative, and its magnitude increased with concentration. N1 was initially positive as in the matrix fluid, but for ϕ>0.3, it became negative, similar to the result of Aral and Kalyon [J. Rheol. 41, 599–620 (1997)]; also, we found, at a constant shear stress, that |N2/N1| was great...

Particle roughness and rheology in noncolloidal suspensions

We explore the effect of deliberately increased particle roughness on the rheology of noncolloidal suspensions of spheres, both in Newtonian (polydimethylsiloxane or silicone oil) and non-Newtonian (Boger fluid) matrices. The object of the experiment is to change only the roughness of the spheres, while leaving the density and the material of the particles unchanged, so as to isolate the effect of roughness on rheology. Two sphere materials, polystyrene (PS) and polymethylmethacrylate (PMMA) were used. The PS spheres were of 40 and 80 μm nominal diameters, and the PMMA spheres were 40 μm in diameter. Roughness ratios (average roughness/sphere radius) of 0.1%–5% were explored. With silicone matrices, there was up to 50% increase in viscosity with a 50% volume fraction suspension and an increase in the normal stress differences of a similar magnitude. Two polybutene-based Boger fluids were also used. The increases of viscosity with the polybutene matrices were somewhat larger than those with the Newtonian m...

Scaling the normal stresses in concentrated non-colloidal suspensions of spheres

We have collected six sets of results for the ratio of the second normal stress difference to the shear stress

A quest for a model of non-colloidal suspensions with Newtonian matrices

(N_{2}/\tau )

Relationships between traditional and fundamental dough-testing methods

in non-colloidal suspensions of spheres in Newtonian matrices. They all show a near-cubic dependence on the volume fraction

A bootstrap mechanism for non-colloidal suspension viscosity

\varphi

Bread dough rheology: Computing with a damage function model

in the range

Bread dough rheology and recoil: I. Rheology

0.1 < \varphi < 0.5

Bread dough rheology and recoil: 2. Recoil and relaxation

, in contrast to the square law predictions of Brady and Morris (J Fluid Mech 348:103–139, 1997) for dilute suspensions. We suggest that the difference can be resolved by using a dependence on the square of the effective volume fraction