Measurement of fluid properties using an acoustically excited atomic force microscope micro-cantilever

Abstract

In this study, we develop a technique that can be used for extracting the properties of high viscosity Newtonian liquids at the microliter scale using an atomic force microscope. We obtained the responses of two different cantilevers in solutions of glycerin and water using thermal and acoustic frequency sweep excitations. The thermal excitation method cannot be used for liquids with viscosity substantially higher than 1 mPa s because of the existence of a noise floor which obscures the cantilever response. The acoustic frequency sweep excitation can overcome this limitation. The fluid properties were extracted by combining a theoretical model with the experimentally obtained results for the frequency sweep excitation. By using the cantilever phase response, errors of less than 14% in viscosity and density were achieved. This error can be explained by a local increase in fluid temperature of 3 °C due to the laser energy.