Multimodal Sensing Transparent Droplet Probe for Characterization of Superhydrophobic Surfaces

Natural and artificial superhydrophobic surfaces are a rapidly growing topic in both academia and industry due to their unique properties and applications. Numerous techniques have been developed to characterize the wetting properties of such surfaces, such as the optical contact angle goniometer, force-based methods, and microscopic techniques for visualizing the wetting interface. However, a method that combines nN resolution force measurement with direct observation of the wetting interface on opaque superhydrophobic surfaces is missing. Here, we report a high-sensitivity multimodal force-sensing transparent droplet probe for the characterization of superhydrophobic surfaces that allows simultaneous visualization of the wetting interface and measurement of interaction forces. The probe is composed of a transparent glass cantilever with a droplet probe attached to its end. During the interaction with the sample, the wetting interface is directly imaged through the probe, illuminated with coaxial lighting. The interaction force is simultaneously measured as the deflection of the cantilever-shaped probe. By combining top view, side view, and high-resolution force sensing, the probe can reveal force contributions from both surface tension and Laplace pressure and measure super-repellent surfaces with contact angles near 180° with a low experimental uncertainty of 0.5°.