Our overall goal is to obtain sub-10 nm spatially resolved electronic charge density at a liquid/solid interface using an atomic force microscope. In many cases of interest, this information is only measurable when the tip is within a few nanometers of the surface. In this region, the snap-to-contact event occurs which means the tip velocity becomes large and viscous forces can dominate the measurement. We have modeled these viscous forces with the intention of removing them from consideration so that electrostatic contributions can be focused on. A method is presented to obtain the viscosity and density of a fluid from the mechanical frequency response of a microcantilever beam immersed in fluids. A novel algorithm is described to measure the viscosity and density of an ambient fluid by comparing experimental results with the theory. The theoretical results are analytical with a closed form solution. The algorithm presented is easier to implement than the standard method currently used by most atomic force microscope practitioners. In addition, unlike the standard method, the new algorithm is applicable to high viscosity fluids that do not produce resonant peaks in the microcantilever power spectra. Experiments were carried out using standard cantilevers in a fluid cell filled with air, water, methanol and commercial oils. The result of comparing theory with experiment validates the algorithm. This makes it useful both for obtaining surface charges from force-separation curves and as a way to measure density and viscosity of uncharacterized fluids.

Viscosity of liquids from the transfer function of microcantilevers

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.