Extensional viscosity of silica dispersions

Abstract

The rheological behavior in extensional flow was investigated for silica dispersions in polymer solutions using the tubeless syphon technique. The flow field of tubeless syphon is unsteady in the Lagrangian sense; hence the data are taken under transient stress conditions. Due to the insensitive nature of the extensional rate to flow rate, the extensional viscosities at different flow rates lie very close to a single curve, once they are plotted against strain. Two important points are noted with regard to the behavior of the dispersions. First, the extensional viscosity decreases with increasing particle concentration. Second, the viscosity growth curves of the dispersions can be superimposed by a vertical shift, but the curve shape differs from that of the medium. This implies a change in the relaxation time.