Forced torsion pendulum for studies of interactions at solid–liquid interface

A forced torsion pendulum for measurement of friction forces between solid surfaces and flowing liquid environments was designed and assembled. The apparatus utilizes the axial Couette flow generated in removable cylinder specimen cell filled with a liquid. The cell is co-axial with the pendulum shaft and the liquid flow is excited within a thin layer adjacent to the inner wall of the cell, which is covered by the studied metal foil. The damping and the resonant frequency of the pendulum are calculated online. The construction allows control of the electrochemical potential of the studied metal foil immersed in an electrolytic environment. The high sensitivity of the apparatus was confirmed in measurements of the resonance parameters of the pendulum. The surface morphology of the metal wall exposed to distilled water has a measurable effect on damping and resonant frequency of the pendulum. A 3% reduction of damping was observed during illumination of a photoactive surface by an ultraviolet light.