17 research outputs found
Letter to the Editor: Wall slip in dispersion rheometry
Whereas our understanding of the role and mechanism of wall slip has improved
substantially over the last decade or two, it is still common to see papers on
disperse systems appear wherein scant details of the measurement methods are
given and wherein no mention of the possibility (probability?) of slip is made.
It is argued that there is a need to raise awareness. It takes experience,
judgement and skill to make meaningful measurements on disperse systems and it
is suspected that the nature of the experimental challenge is under-estimated
grossly by too many workers even now.Comment: 10 pages, 2 figure
Wall Adhesion and Constitutive Modelling of Strong Colloidal Gels
Wall adhesion effects during batch sedimentation of strongly flocculated
colloidal gels are commonly assumed to be negligible. In this study in-situ
measurements of colloidal gel rheology and solids volume fraction distribution
suggest the contrary, where significant wall adhesion effects are observed in a
110mm diameter settling column. We develop and validate a mathematical model
for the equilibrium stress state in the presence of wall adhesion under both
viscoplastic and viscoelastic constitutive models. These formulations highlight
fundamental issues regarding the constitutive modeling of colloidal gels,
specifically the relative utility and validity of viscoplastic and viscoelastic
rheological models under arbitrary tensorial loadings. The developed model is
validated against experimental data, which points toward a novel method to
estimate the shear and compressive yield strength of strongly flocculated
colloidal gels from a series of equilibrium solids volume fraction profiles
over various column widths.Comment: 37 pages, 12 figures, submitted to Journal of Rheolog
Whither Compressional Rheology?
C1 - Journal Articles Referee