Measurement on the shear properties of liquid nanomeniscus bridge

The shear properties of liquid nanomeniscus bridge were measured by a nanorheometer which was developed recently. The meniscus bridges of PFPE (Perfluoropolyether) Z-dol were formed between two glass spheres. One was mounted on a piezo actuator and moved sinusoidally in the shear direction against the other which was mounted on a rectangular-type microcantilever. The diameters of the spheres were 90 μm and 20 μm, respectively. The induced oscillatory motions of the cantilever-sphere assembly were detected via a two phase lock-in amplifier with respect to the modulation frequency and the surface separation. The amplitude response was interpreted as elastic characteristics and phase shift as damping characteristics of the liquid meniscus bridge. The experimental results were qualitatively compared to those of the normal oscillatory experiments. teral meniscus force was much smaller than the normal case, which affected directly the amplitude ratio and phase shift of the system. In results, the system showed more viscous behavior compared to the normal case. However, the system still showed the excess stiffness and excess damping at low frequencies and large surface separations, which was originated from the existence of the liquid meniscus bridge. The excess stiffness was directly attributed to the lateral meniscus force and the excess damping to the moving contact line.