Extensional Viscosity of w/o Emulsions

The opposed nozzles configuration was used to measure the extensional viscosities of water-in-oil emulsions of dispersed volume fractions varying between 5% and 30%. The two Newtonian type mineral oils with dynamic viscosities about = 0.2182 and 0.0443 [Pa s] were used. All emulsions were prepared with sorbitan monooleate (Span 80) as emulsifier. The results obtained for extensional viscosity of w/o emulsions show that only at very low concentrations of dispersed phase values of the Trouton ratio (Tr = ηE/η) are approximately constant (in range of 7-11) while for pure oil are slightly lower (3-6). Additionally, the Trouton ratio is independent of oil phase viscosity in the range of water phase concentration from 5 to 10%. For 20% and higher concentration of disperse phase the extensional viscosity rises with increase of a nozzle diameter. Presented experimental results indicate that the opposing nozzles rheometer used in this work is not a suitable device for measuring the extensional viscosity of viscoplastic fluids.