An interfacial rheometer for both stress- and strain-controlled measurements of shear rheological properties at liquid/liquid and gas/liquid interfaces is presented. The device is based on a rotating or oscillating biconical bob design in combination with a low friction electronically commutated motor system. The interfacial shear stress, viscosity, and dynamic moduli are obtained by solving the Stokes equations (low Reynolds number) along with the Boussinesq–Scriven interfacial stress tensor, which is used for the boundary conditions at the interface. An improved and simple numerical method for the calculation of the velocity distribution in the measuring cell is presented. The scope and limitations of the rheometer are discussed. Results from steady shear and oscillatory experiments as well as creep recovery and stress relaxation tests at both oil/water and air/water interfaces with adsorbed films of a globular protein (ovalbumin) and spread films of a surfactant (sorbitan tristearate) are presented.

In a combined motor transducer (CMT) design, the torque is measured at the moving surface and the moment of inertia of the moving parts of the instrument and the fluid inertia might influence the measurement results, whereas in a separate motor transducer (SMT) setup only fluid inertia effects might come into play. In order to investigate inertia effects, oscillatory shear measurements have been performed on various Newtonian liquids with low viscosity with different measuring geometries and in a CMT and a SMT setup. For a CMT situation, it is shown that with an appropriate control mechanism, taking into account the instrument inertia reliable results can be achieved up to rather high ratio of acceleration to sample torque. Further, the measuring data on the Newtonian liquid agree well with the fluid inertia calculations following the approach from Schrag [Trans. Soc. Rheol. 21, 399–413 (1977)]. The results for a SMT setup show that for any given geometry, fluid inertia effects, when uncorrected, lead to a frequency dependent baseline in the elastic modulus G′. The larger the measuring gap the larger the G′. Combining the findings for both the CMT and the SMT situation, it can be concluded that for Newtonion liquids and fluids with low elasticity fluid inertia adds an elastictorque which in CMT points in opposite direction of the elastic part of the sample torque, whereas in SMT the additional elastictorque, while its absolute value is somewhat smaller, acts in the direction of the elastic part of the sample torque, respectively. To investigate weakly structured fluids, it is suggested to use geometries with rather small measuring gaps, and to determine the individual baseline for the geometry with Newtonian liquids.

The viscoelastic properties of a magneto-rheological fluid can be variably controlled using a magnetic field. A new measuring method is introduced which is based on oscillatory tests. In contrast to flow curves from experiments at steady shear rate, the new method allows an exact determination of a magneto-rheological fluid’s viscoelastic properties as a function of the preset magnetic field strength. The “Magneto Sweep” is an oscillatory test method, each with constant amplitude and constant frequency while logarithmically increasing the magnetic field strength (Magneto Sweep). For typical magneto-rheological fluids (MRF) three characteristic regions and two significant transition points can be determined. These transitions mark the corresponding change in material behavior resulting from an increasing magnetic field strength.

To investigate the influence of a simple shear flow on the late stage spinodal decomposition of a binary polymer blend, the shear viscosity and the domain growth have been studied by a combined rheo–small-angle-light-scattering technique. In a representation versus the applied strain, the viscosities as well as the structure deformation can be scaled on single curves for different shear rates. Both quantities show two characteristic crossovers at the same strain values. The behavior is compared with results of a recent computer simulation.