A new tuning fork-based instrument for oscillatory shear rheology of nano-confined liquids

Abstract

We present a new method to measure rheological response of liquids confined to nano-scale which exhibit a considerable slow-down in dynamics compared to bulk liquids. The method relies on using a tuning fork force sensor that has stiffness of 5.5 × 104 N/m to avoid thermal noise. Off-resonance operation ensures application of a range of shear frequencies. This range is higher than the inverse of the system's mechanical relaxation time and allows the measurement of nonlinear effects emerging due to significant “slow down” in dynamics upon confinement. We develop necessary mathematical modelling to quantify our measurements. The instrument is a step forward towards resolving the controversies about the nature of nano-confined liquids.