Atomic force microscopy shows behavior of nanoscale water capillary bridges

Understanding the behavior of water in nanoconfined spaces under dynamic conditions is a pressing issue in nanoscience, with implications in areas as diverse as the functioning of machinery to the exploration of geological features.

Cassin et al. conducted experiments to characterize the behavior of capillary bridges, or water menisci, between surfaces. Using an atomic force microscope (AFM), the group examined the nucleation and growth of water capillary bridges in the laterally moving interface between the AFM probe and a smooth silicon wafer, analyzing the behavior at different lateral speeds and separation gaps.

“An interesting aspect of our work is the repurposing of a technique used for something completely different to observe what I now jokingly call a nano-climate,” said author Felix Cassin. “We can create a dynamic setting and observe forces that are caused by just a few molecules of water.”

Even tiny quantities of water can cause adhesion and friction forces that can affect the performance or longevity of these systems.

To experimentally imitate this, the group measured forces between the AFM and wafer as the microscope’s probe hovered over the surface of the wafer at different speeds. After an initial period in which no force was measured, a chain of water condensed out of the air to connect the probe and the wafer, growing into a meniscus.

It had been initially believed that higher lateral speeds would impede the condensation of a chain of water molecules. In contrast, the group showed that a faster lateral speed leads to an enhanced water molecule entrainment, resulting in an increased nucleation rate.

The team hopes their work will act as a step toward predicting forces in these dynamic nanoconfined interfaces. They plan to expand their results by focusing on the friction of water bridges when stretched between two solid bodies.

Source: “The nucleation, growth, and adhesion of water bridges in sliding nano-contacts,” by Felix Cassin, Rachid Hahury, Thibault Lançon, Steve Franklin, and Bart Weber, Journal of Chemical Physics (2023). The article can be accessed at https://doi.org/10.1063/5.0150276 .

This paper is part of the Adhesion and Friction Collection, learn more here .