The Double Mobility of Some Non-Newtonian Fluids with Particular Reference to Cellulose Nitrate Sols

The ratio of the mobility of nitrocellulose solutions at high shearing stresses to the mobility at low shearing stresses, where there exists in fact true fluidity, is called the ``mobility ratio.'' This mobility ratio may be very high for certain ``medium'' and ``high viscosity'' nitrocottons, but it does not necessarily prove to be a figure proportional to the usually accepted ``viscosity.'' Thus mixtures of ``high'' and ``low'' viscosity nitrocottons may be so blended that, although showing similar low shearing stress viscosities with the falling ball, one will show at high shearing stresses much higher viscosity than the other. Certain ``low'' viscosity nitrocottons appear to show a nearly constant true viscosity at all rates of shear. The two mobilities show significant differences in technical behavior. Thus under given conditions of use, such as spraying, brushing, roller coating, etc., the high stress mobility determines what may be called the solvent demand of the sol, whereas the viscosity at low stresses indicates the characteristics to be expected after application.