Correction of Wall Adhesion Effects in the Centrifugal Compression of Strong Colloidal Gels

TL;DR

This paper investigates the impact of wall adhesion on centrifuge measurements of colloidal gel strength, providing theoretical corrections and analyzing errors to improve accuracy near the gel point.

Contribution

It introduces correction factors for wall adhesion effects in centrifuge strength measurements and assesses errors from common approximations.

Findings

Adhesion causes significant errors near the gel point.

Dimensionless correction factors effectively mitigate adhesion effects.

Errors from assuming one-dimensional acceleration are minimal.

Abstract

Several methods for measuring the compressive strength of strong particulate gels are available, including the centrifuge method, whereby the strength as a function of volume-fraction is obtained parametrically from the dependence of equilibrium sediment height upon acceleration. The analysis used conventionally due to Buscall & White (1987) ignores the possibility that the particulate network might adhere to the walls of the centrifuge tube, even though many types of cohesive particulate gel can be expected to. The neglect of adhesion is justifiable when the ratio of the shear to compressive strength is small, which it can be for many systems away from the gel-point, but never very near it. The errors arising from neglect of adhesion are investigated theoretically and quantified by synthesising equilibrium sediment height versus acceleration data for various degrees of adhesion and then analysing them in the conventional manner. Approximate correction factors suggested by dimensionless analysis are then tested. The errors introduced by certain other approximations made routinely in order to render the data-inversion practicable are analysed too. For example, it shown that the error introduced by treating the acceleration vector as approximately one-dimensional is minuscule for typical centrifuge dimensions, whereas making this assumption renders the data inversion tractable.