Determination of dynamic surface tension and viscosity of non-Newtonian fluids from drop oscillations

The oscillations of free-falling drops with size range from pl to μl have been used to measure the transient shear viscosity and the dynamic surface tension of shear-thinning fluids on the timescale of 10-5-10-2 s. The method is first validated with Newtonian fluids. For a given surface tension, the lower and upper limits for accurate measurement of the viscosity are determined as a function of drop size. The dynamic properties of two types of shear-thinning fluids with varying viscoelasticity are reported: aqueous suspensions of the antifungal drug griseofulvin and of the organic light-emitting diode material poly(3,4-ethylenedioxythiophene): polystyrene-sulphonate. In both cases, the free-falling drop retains the high-shear viscosity.