Development of an elongational rheometer

Characterisation of viscoelastic fluids in process engineering and the chemical industry may require the measurement of the elongational viscosity in uniaxial flow. This ist he case where the fluids are exposed to elongational flows, as, e.g., in coating and atomization of the fluids. The presently developed device deforms a sample of the liquid such that a liquid filament of constant length is produced between two wettable surfaces. The filament thins in time under the influence of surface tension. The device measures the decrease of the filament diameter as a function of time. The measurement data are processed to extract the relaxation time of the fluid as a characteristic time of the (exponential) decrease of the filament diameter. The smallest measurable relaxation time is of the order of 5 ms. The device works both with aqueous and with organic liquids.