MEASUREMENT OF INTERFACIAL SHEAR RHEOLOGICAL PROPERTIES - AN AUTOMATED APPARATUS

A new surface shear rheometer was designed on the basis of the princip le of a torsion pendulum. The torsion wire transfers the deformation, produced by a stepper motor, via a sharp edge onto the surface. The mo vement of the edge is registered by a position-sensitive photodiode wi th an accuracy to +/-0.01 degrees. After an impulsive torque is applie d by a rapid movement of the torsion head the pendulum performs damped oscillations with a damping factor a and a radian frequency beta. Thi s type of apparatus provides information on the surface shear coeffici ent of viscosity and the surface shear modulus of rigidity in one sing le experiment. Different instrumental parameters are discussed which i nfluence the range of application and the accuracy of the measurements . Different applications of the set-up to protein solutions (gelatine and human albumin) alone and mixed with a surfactant are discussed. Th e experimental data demonstrate the high reproducibility and accuracy of the apparatus.