When you slide your finger across a surface, you perceive sensations such as "rough" or "smooth." These tactile feelings are determined by the friction and fine vibrations generated at the surface. To develop products with more realistic tactile experiences, we are investigating what happens between the finger and the surface at a fundamental level.

While there are several ways to modify surface texture, our research focuses on a chemical approach: coating surfaces with an ultrathin molecular film known as a Self-Assembled Monolayer (SAM). Despite being only a single molecule thick, SAMs can significantly alter the frictional properties of a surface. Our previous work has shown that simply changing the molecular structure of the SAM is enough to change the frictional force experienced by a sliding finger.

However, the underlying mechanism — why and how friction changes — remained poorly understood. In this study, we observe the contact area between the finger and the surface in real time as the finger slides, with the goal of visualizing the mechanisms of friction at the interface.