Viscosity and rigidity in suspensions of fine particles. II.—Non-aqueous suspensions

In the first part of this investigation evidence was presented for the view that the shear-variable viscosity exhibited by aqueous suspensions containing suitable amounts of an electrolyte is due to the formation of loosely packed aggregates which enclose varying quantities of the dispersion medium. The progressive liberation of liquid as the aggregates are broken up by increasing shear gradients is equivalent to a gradual diminution of the volume concentration of solid, and accounts qualitatively for the variation of viscosity observed; whilst a complete linking up of the aggregates throughout the liquid gives rise to a structure possessing rigidity, a property which was demonstrated in suspensions containing a high enough proportion of solid. The conclusions reached were speculative in so far as the association of amicroscopic particles to form any but gross aggregates cannot be directly observed. The present communication describes evidence of a more complete character, provided by the microscopic examination of suspensions of visible particles in inert organic liquids, and the correlation of these observations with the results of parallel experiments on viscosity and rigidity.