Methodology for imaging nano-to-microscale water condensation dynamics on complex nanostructures.

A better understanding of the role that nanoscale surface chemical heterogeneities and topographical features play in water droplet formation is necessary to improve design and robustness of nanostructured superhydrophobic surfaces as to make them fit for industrial applications. Lack of an imaging method capable of capturing the water condensation process on complex nanostructures with required magnification has thus far hindered experimental progress in this area. In this work, we demonstrate that by transferring a small part of a macroscale sample to a novel thermally insulated sample platform we are able to mitigate flooding and electron heating problems typically associated with environmental scanning electron microscopy of water condensation. We image condensation dynamics on individual complex particles and a superhydrophobic network of nanostructures fabricated from low thermal conductivity materials with an unobstructed 90° perspective of the surface-to-water interface with field of view as small as 1 μm(2). We clearly observe the three-stage drop growth process and demonstrate that even during late stages of the droplet growth the nearly spherical drop remains in a partially wetting Wenzel state.