A novel resonance method for studying the viscoelasticity of very thin liquid films and elastic materials is developed using a shear force apparatus. The shear stress created by an oscillating piezo unit attached to leaf springs is recorded as the lateral displacement by capacitance probe. The oscillation frequency is varied around the resonance frequency of the mechanical system in order to trace the amplitude and the phase of the resonance peak. Two reference states are obtained: the resonance of free oscillations in air and one under constrain introduced by the cantilever spring in contact with the shear mechanical unit. The presence of a liquid film changes these resonance states depending on the film thickness and the cantilever load. A simple mechanical model is proposed entrapping the contribution of different parts in effective spring, mass, and damping constants. The model separates the effect of the liquid film from the background oscillation of the mechanical parts. The method is applied here to investigate the elastic contact between two solid surfaces.
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