FM-AFM with a Hanging Fiber Probe for the Study of Liquid-Liquid Interfaces

This work describes how a frequency modulation atomic force microscope (AFM) using a hanging fiber force probe made from a quartz tuning fork provides local measurements on liquid-liquid interfaces. After detailing the manufacture and calibration of the force probe, we provide evidence that this AFM is suitable for quantitative measurements at the interface between two liquids. The repeatability of the measurements allows a poly-dimethylsiloxane-water moving interface to be monitored over several hours. The evaporation of a water droplet immersed in poly-dimethylsiloxane is observed, and its interfacial tension evolution over time is measured. Deformation of the interface is also observed. These capabilities, and preliminary results for the interface between two immiscible liquids, pave the way for interface manipulation and study of complex fluid-fluid interfaces.