Fourier-transform resonance shear measurement for studying confined liquids

The resonance shear measurement we recently developed is an efficient tool for investigating the rheological and tribological properties of liquid nanofilms confined between solid surfaces with varying film thicknesses. However, the previously employed resonance shear measurement measured shear responses at various oscillation frequencies for one film thickness (the frequency scanning method), so it required at least several minutes to obtain a reliable resonance curve. The fast Fourier-transform resonance shear method was developed to rapidly acquire the resonance curves. The obtained curves were very similar to those obtained by the frequency scanning method. The time necessary for the FFT method was 2-10 s, much shorter than the time required for the scanning method. This technique is easy to use and extends the applicability of the method to volatile liquids and unstable samples.